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Although cystic fibrosis (CF) is recognized as a monogenic disease, due to variants within the CFTR (Cystic Fibrosis Transmembrane Regulator) gene, an extreme clinical heterogeneity is described among people with CF (pwCF). Apart from the exocrine pancreatic status, most studies agree that there is little association between CFTR variants and disease phenotypes. Environmental factors have been shown to contribute to this heterogeneity, accounting for almost 50% of the variability of the lung function of pwCF. Nevertheless, pwCF with similar CFTR variants and sharing the same environment (such as in siblings) may have highly variable clinical manifestations not explained by CFTR variants, and only partly explained by environmental factors. It is recognized that genetic variants located outside the CFTR locus, named “modifier genes”, influence the clinical expression of the disease. This short review discusses the latest studies that have described modifier factors associated with the various CF phenotypes as well as the response to the recent CFTR modulator therapies.

Leber’s hereditary optic neuropathy (LHON) is a maternally transmitted disease caused by mitochondria DNA (mtDNA) mutation. It is characterized by acute and subacute visual loss predominantly affecting young men. The mtDNA mutation is transmitted to all maternal lineages. However, only approximately 50% of men and 10% of women harboring a pathogenic mtDNA mutation develop optic neuropathy, reflecting both the incomplete penetrance and its unexplained male prevalence, where over 80% of patients are male. Nuclear modifier genes have been presumed to affect the penetrance of LHON. With conventional genetic methods, prior studies have failed to solve the underlying pathogenesis. Whole exome sequencing (WES) is a new molecular technique for sequencing the protein-coding region of all genes in a whole genome. We performed WES from five families with 17 members. These samples were divided into the proband group (probands with acute onset of LHON, n = 7) and control group (carriers including mother and relative carriers with mtDNSA 11778 mutation, without clinical manifestation of LHON, n = 10). Through whole exome analysis, we found that many mitochondria related (MT-related) nuclear genes have high percentage of variants in either the proband group or control group. The MT genes with a difference over 0.3 of mutation percentage between the proband and control groups include AK4, NSUN4, RDH13, COQ3, and FAHD1. In addition, the pathway analysis revealed that these genes were associated with cofactor metabolism pathways. Family-based analysis showed that several candidate MT genes including METAP1D (c.41G > T), ACACB (c.1029del), ME3 (c.972G > C), NIPSNAP3B (c.280G > C, c.476C > G), and NSUN4 (c.4A > G) were involved in the penetrance of LHON. A GWAS (genome wide association study) was performed, which found that ADGRG5 (Chr16:575620A:G), POLE4 (Chr2:7495872T:G), ERMAP (Chr1:4283044A:G), PIGR (Chr1:2069357C:T;2069358G:A), CDC42BPB (Chr14:102949A:G), PROK1 (Chr1:1104562A:G), BCAN (Chr 1:1566582C:T), and NES (Chr1:1566698A:G,1566705T:C, 1566707T:C) may be involved. The incomplete penetrance and male prevalence are still the major unexplained issues in LHON. Through whole exome analysis, we found several MT genes with a high percentage of variants were involved in a family-based analysis. Pathway analysis suggested a difference in the mutation burden of MT genes underlining the biosynthesis and metabolism pathways. In addition, the GWAS analysis also revealed several candidate nuclear modifier genes. The new technology of WES contributes to provide a highly efficient candidate gene screening function in molecular genetics.

Calpain-mediated proteolysis has been proposed to modulate the pathogenesis of spinocerebellar ataxia type 3, also known as Machado-Joseph disease (SCA3/MJD), a disorder due to a CAG repeat expansion (CAGexp) at ATXN3. We aimed to investigate if single-nucleotide polymorphisms (SNPs) at calpain gene CAPN2 and at calpastatin gene CAST modulate the age at onset (AO) and disease progression in SCA3/MJD. A total of 287 SCA3/MJD symptomatic subjects (151 families) were included. AO was analyzed and controlled by the CAG repeat length of expanded allele and family. Candidate polymorphisms were chosen based on the literature and on a priori criteria. The CAG repeat length and SNPs were genotyped according to standard methods. AO of carriers of AA and AG + GGrs1559085 genotypes in CAST and with the median value of 75 repeats at the expanded allele were 34.23 (33.07–35.38) and 36.42 years (34.50–38.34), respectively (p = 0.049, mixed model treating the expanded CAG repeat size as fixed effect and family as random effect). Carriers of haplotype Crs27852/Grs1559085 had mean AO of 37.23 (12.76) and 33.42 years (12.20) (p = 0.047, Student’s t test). Our data suggest an association between allele Grs1559085 and haplotype Crs27852/Grs1559085 at CAST and variations in the AO of SCA3/MJD subjects, independent from the effects of the CAGexp and family. The present results support the potential role of calpain cleavage pathway over modulation of SCA3/MJD phenotype.

Breast cancer is the most common tumor among women with inherited variants in the TP53 tumor suppressor, but onset varies widely suggesting interactions with genetic or environmental factors. Rodent models haploinsufficent for Trp53 also develop a wide variety of malignancies associated with Li-Fraumeni Syndrome, but BALB/c mice are uniquely susceptible to mammary tumors and is genetically linked to the Suprmam1 locus on chromosome 7. To define mechanisms that interact with deficiencies in p53 to alter susceptibility to mammary tumors, we fine-mapped the Suprmam1 locus in females from an N2 backcross of BALB/cMed and C57BL/6J mice. A major modifier was localized within a 10 cM interval on chromosome 7. The effect of the locus on DNA damage responses was examined in the parental strains and mice that are congenic for C57BL/6J alleles on the BALB/cMed background (SM1-Trp53+/−). The mammary epithelium of C57BL/6J-Trp53+/− females exhibited little radiation-induced apoptosis compared to BALB/cMed-Trp53+/− and SM1-Trp53+/− females indicating that the Suprmam1B6/B6 alleles could not rescue repair of radiation-induced DNA double-strand breaks mostly relying on non-homologous end joining. In contrast, the Suprmam1B6/B6 alleles in SM1-Trp53+/− mice were sufficient to confer the C57BL/6J-Trp53+/− phenotypes in homology-directed repair and replication fork progression. The Suprmam1B6/B6 alleles in SM1-Trp53+/− mice appear to act in trans to regulate a panel of DNA repair and replication genes which lie outside the locus. Significance: Genetic variation in replication-associated DNA repair can modify consequences of heterozygous mutations in Trp53 and contribute to susceptibility to mammary tumors in mouse models of Li-Fraumeni syndrome.

Modifier genes contribute significantly to our understanding of pathophysiology in human diseases; however, effective approaches to identify modifier genes are still lacking. Here, we aim to develop a rapid F0-based genetic assay in adult zebrafish using the bag3 gene knockout (bag3e2/e2) cardiomyopathy model as a paradigm. First, by utilizing a classic genetic breeding approach, we identified dnajb6b as a deleterious modifier gene for bag3 cardiomyopathy. Next, we established an F0-based genetic assay in adult zebrafish through injection of predicted microhomology-mediated end joining (MMEJ)-inducing single guide RNA/Cas9 protein complex. We showed that effective gene knockdown is maintained in F0 adult fish, enabling recapitulation of both salutary modifying effects of the mtor haploinsufficiency and deleterious modifying effects of the dnajb6b gene on bag3 cardiomyopathy. We finally deployed the F0-based genetic assay to screen differentially expressed genes in the bag3 cardiomyopathy model. As a result, myh9b was identified as a novel modifier gene for bag3 cardiomyopathy. Together, these data prove the feasibility of an F0 adult zebrafish-based genetic assay that can be effectively used to discover modifier genes for inherited cardiomyopathy.

FAN1 encodes a DNA repair nuclease. Genetic deficiencies, copy number variants, and single nucleotide variants of FAN1 have been linked to karyomegalic interstitial nephritis, 15q13.3 microdeletion/microduplication syndrome (autism, schizophrenia, and epilepsy), cancer, and most recently repeat expansion diseases. For seven CAG repeat expansion diseases (Huntington’s disease (HD) and certain spinocerebellar ataxias), modification of age of onset is linked to variants of specific DNA repair proteins. FAN1 variants are the strongest modifiers. Non-coding disease-delaying FAN1 variants and coding disease-hastening variants (p.R507H and p.R377W) are known, where the former may lead to increased FAN1 levels and the latter have unknown effects upon FAN1 functions. Current thoughts are that ongoing repeat expansions in disease-vulnerable tissues, as individuals age, promote disease onset. Fan1 is required to suppress against high levels of ongoing somatic CAG and CGG repeat expansions in tissues of HD and FMR1 transgenic mice respectively, in addition to participating in DNA interstrand crosslink repair. FAN1 is also a modifier of autism, schizophrenia, and epilepsy. Coupled with the association of these diseases with repeat expansions, this suggests a common mechanism, by which FAN1 modifies repeat diseases. Yet how any of the FAN1 variants modify disease is unknown. Here, we review FAN1 variants, associated clinical effects, protein structure, and the enzyme’s attributed functional roles. We highlight how variants may alter its activities in DNA damage response and/or repeat instability. A thorough awareness of the FAN1 gene and FAN1 protein functions will reveal if and how it may be targeted for clinical benefit.

Historically, Huntington’s disease (HD; OMIM #143100) has played an important role in the enormous advances in human genetics seen over the past four decades. This familial neurodegenerative disorder involves variable onset followed by consistent worsening of characteristic abnormal movements along with cognitive decline and psychiatric disturbances. HD was the first autosomal disease for which the genetic defect was assigned to a position on the human chromosomes using only genetic linkage analysis with common DNA polymorphisms. This discovery set off a multitude of similar studies in other diseases, while the HD gene, later renamed HTT, and its vicinity in chromosome 4p16.3 then acted as a proving ground for development of technologies to clone and sequence genes based upon their genomic location, with the growing momentum of such advances fueling the Human Genome Project. The identification of the HD gene has not yet led to an effective treatment, but continued human genetic analysis of genotype-phenotype relationships in large HD subject populations, first at the HTT locus and subsequently genome-wide, has provided insights into pathogenesis that divide the course of the disease into two sequential, mechanistically distinct components.

Huntington’s disease (HD) is one of a large group of human disorders that are caused by expanded DNA repeats. These repeat expansion disorders can have repeat units of different size and sequence that can be located in any part of the gene and, while the pathological consequences of the expansion can differ widely, there is evidence to suggest that the underlying mutational mechanism may be similar. In the case of HD, the expanded repeat unit is a CAG trinucleotide located in exon 1 of the huntingtin (HTT) gene, resulting in an expanded polyglutamine tract in the huntingtin protein. Expansion results in neuronal cell death, particularly in the striatum. Emerging evidence suggests that somatic CAG expansion, specifically expansion occurring in the brain during the lifetime of an individual, contributes to an earlier disease onset and increased severity. In this review we will discuss mouse models of two non-CAG repeat expansion diseases, specifically the Fragile X-related disorders (FXDs) and Friedreich ataxia (FRDA). We will compare and contrast these models with mouse and patient-derived cell models of various other repeat expansion disorders and the relevance of these findings for somatic expansion in HD. We will also describe additional genetic factors and pathways that modify somatic expansion in the FXD mouse model for which no comparable data yet exists in HD mice or humans. These additional factors expand the potential druggable space for diseases like HD where somatic expansion is a significant contributor to disease impact.

At fifteen different genomic locations, the expansion of a CAG/CTG repeat causes a neurodegenerative or neuromuscular disease, the most common being Huntington’s disease and myotonic dystrophy type 1. These disorders are characterized by germline and somatic instability of the causative CAG/CTG repeat mutations. Repeat lengthening, or expansion, in the germline leads to an earlier age of onset or more severe symptoms in the next generation. In somatic cells, repeat expansion is thought to precipitate the rate of disease. The mechanisms underlying repeat instability are not well understood. Here we review the mammalian model systems that have been used to study CAG/CTG repeat instability, and the modifiers identified in these systems. Mouse models have demonstrated prominent roles for proteins in the mismatch repair pathway as critical drivers of CAG/CTG instability, which is also suggested by recent genome-wide association studies in humans. We draw attention to a network of connections between modifiers identified across several systems that might indicate pathway crosstalk in the context of repeat instability, and which could provide hypotheses for further validation or discovery. Overall, the data indicate that repeat dynamics might be modulated by altering the levels of DNA metabolic proteins, their regulation, their interaction with chromatin, or by direct perturbation of the repeat tract. Applying novel methodologies and technologies to this exciting area of research will be needed to gain deeper mechanistic insight that can be harnessed for therapies aimed at preventing repeat expansion or promoting repeat contraction.

SCNN1B encodes the beta subunit of the epithelial sodium channel ENaC. Previously, we reported an association between SNP markers of SCNN1B gene and disease severity in cystic fibrosis-affected sibling pairs. We hypothesized that factors interacting with the SCNN1B genomic sequence are responsible for intrapair discordance. Concordant and discordant pairs differed at six SCNN1B markers (Praw = 0.0075, Pcorr = 0.0397 corrected for multiple testing). To identify the factors binding to these six SCNN1B SNPs, we performed an electrophoretic mobility shift assay and captured the DNA–protein complexes. Based on protein mass spectrometry data, the epithelial splicing regulatory protein ESRP2 was identified when using SCNN1B-derived probes and the ESRP2-SCNN1B interaction was independently confirmed by coimmunoprecipitation assays. We observed an alternative SCNN1B transcript and demonstrated in 16HBE14o− cells that levels of this transcript are decreased upon ESRP2 silencing by siRNA. Furthermore, we confirmed that mildly and severely affected siblings have different ESPR2 genetic backgrounds and that ESRP2 markers are linked to the response of CF patients’ nasal epithelium to amiloride, indicating ENaC involvement (Pbest = 0.0131, Pcorr = 0.068 for multiple testing). Our findings demonstrate that sibling pairs clinically discordant for CF can be used to identify meaningful DNA regulatory elements and interacting factors.

To nominate novel disease genes for obesity and type 2 diabetes (T2D), we recently generated two mouse backcross populations of the T2D-susceptible New Zealand Obese (NZO/HI) mouse strain and two genetically different, lean and T2D-resistant strains, 129P2/OlaHsd and C3HeB/FeJ. Comparative linkage analysis of our two female backcross populations identified seven novel body fat-associated quantitative trait loci (QTL). Only the locus Nbw14 (NZO body weight on chromosome 14) showed linkage to obesity-related traits in both backcross populations, indicating that the causal gene variant is likely specific for the NZO strain as NZO allele carriers in both crosses displayed elevated body weight and fat mass. To identify candidate genes for Nbw14, we used a combined approach of gene expression and haplotype analysis to filter for NZO-specific gene variants in gonadal white adipose tissue, defined as the main QTL-target tissue. Only two genes, Arl11 and Sgcg, fulfilled our candidate criteria. In addition, expression QTL analysis revealed cis-signals for both genes within the Nbw14 locus. Moreover, retroviral overexpression of Sgcg in 3T3-L1 adipocytes resulted in increased insulin-stimulated glucose uptake. In humans, mRNA levels of SGCG correlated with body mass index and body fat mass exclusively in diabetic subjects, suggesting that SGCG may present a novel marker for metabolically unhealthy obesity. In conclusion, our comparative-cross analysis could substantially improve the mapping resolution of the obesity locus Nbw14. Future studies will throw light on the mechanism by which Sgcg may protect from the development of obesity.

Refereed/Peer-reviewed

In both Drosophila melanogaster and mammalian systems, epithelial structure and underlying cell polarity are essential for proper tissue morphogenesis and organ growth. Cell polarity interfaces with multiple cellular processes that are regulated by the phosphorylation status of large protein networks. To gain insight into the molecular mechanisms that coordinate cell polarity with tissue growth, we screened a boutique collection of RNAi stocks targeting the kinome for their capacity to modify Drosophila “cell polarity” eye and wing phenotypes. Initially, we identified kinase or phosphatase genes whose depletion modified adult eye phenotypes associated with the manipulation of cell polarity complexes (via overexpression of Crb or aPKC). We next conducted a secondary screen to test whether these cell polarity modifiers altered tissue overgrowth associated with depletion of Lgl in the wing. These screens identified Hippo, Jun kinase (JNK), and Notch signaling pathways, previously linked to cell polarity regulation of tissue growth. Furthermore, novel pathways not previously connected to cell polarity regulation of tissue growth were identified, including Wingless (Wg/Wnt), Ras, and lipid/Phospho-inositol-3-kinase (PI3K) signaling pathways. Additionally, we demonstrated that the “nutrient sensing” kinases Salt Inducible Kinase 2 and 3 (SIK2 and 3) are potent modifiers of cell polarity phenotypes and regulators of tissue growth. Overall, our screen has revealed novel cell polarity-interacting kinases and phosphatases that affect tissue growth, providing a platform for investigating molecular mechanisms coordinating cell polarity and tissue growth during development.

Recent genome-wide association studies of age-at-onset in Huntington’s disease (HD) point to distinct modes of potential disease modification: altering the rate of somatic expansion of the HTT CAG repeat or altering the resulting CAG threshold length-triggered toxicity process. Here, we evaluated the mouse orthologs of two HD age-at-onset modifier genes, FAN1 and RRM2B, for an influence on somatic instability of the expanded CAG repeat in Htt CAG knock-in mice. Fan1 knock-out increased somatic expansion of Htt CAG repeats, in the juvenile- and the adult-onset HD ranges, whereas knock-out of Rrm2b did not greatly alter somatic Htt CAG repeat instability. Simultaneous knock-out of Mlh1, the ortholog of a third HD age-at-onset modifier gene (MLH1), which suppresses somatic expansion of the Htt knock-in CAG repeat, blocked the Fan1 knock-out-induced acceleration of somatic CAG expansion. This genetic interaction indicates that functional MLH1 is required for the CAG repeat destabilizing effect of FAN1 loss. Thus, in HD, it is uncertain whether the RRM2B modifier effect on timing of onset may be due to a DNA instability mechanism. In contrast, the FAN1 modifier effects reveal that functional FAN1 acts to suppress somatic CAG repeat expansion, likely in genetic interaction with other DNA instability modifiers whose combined effects can hasten or delay onset and other CAG repeat length-driven phenotypes.

Alzheimer's disease (AD) is a major cause of dementia. The molecular basis of disease progression is unknown. We hypothesized that the identified AD genome‐wide association study (GWAS) genes would regulate this process. We used CRISPR‐mediated knockout of these genes to test their effects in the cell model systems of tau propagation. GWAS gene knockouts had no effect in these models of tau pathology., Alzheimer's disease (AD) afflicts millions of people worldwide and is caused by accumulated amyloid beta and tau pathology. Progression of tau pathology in AD may utilize prion mechanisms of propagation in which pathological tau aggregates released from one cell are taken up by neighboring or connected cells and act as templates for their own replication, a process termed ‘seeding’. We have used HEK293T cells to model various aspects of pathological tau propagation, including uptake of tau aggregates, induced seeding by exogenous aggregates, seeding caused by Lipofectamine‐mediated delivery to the cell interior, and stable maintenance of aggregates in dividing cells. The factors that regulate these processes are not well understood, and we hypothesized that AD risk modifier genes might play a role. We identified 22 genes strongly linked to AD via meta‐analysis of genome‐wide association study (GWAS). We used CRISPR/Cas9 to individually knock out each gene in HEK293T cells and verified disruption using genomic sequencing. We then tested the effect of gene knockout in tau aggregate uptake, naked and Lipofectamine‐mediated seeding, and aggregate maintenance in these cultured cell lines. GWAS gene knockouts had no effect in these models of tau pathology. With obvious caveats due to the model systems used, these results imply that the 22 AD risk modifier genes are unlikely to directly modulate tau uptake, seeding, or aggregate maintenance in a cell‐autonomous fashion.

Background GBA mutations are numerically the most significant genetic risk factor for Parkinson's disease (PD), yet these mutations have low penetrance, suggesting additional mechanisms. Objectives The objective of this study was to determine if the penetrance of GBA in PD can be explained by regulatory effects on GBA and modifier genes. Methods Genetic variants associated with the regulation of GBA were identified by screening 128 common single nucleotide polymorphisms (SNPs) in the GBA locus for spatial cis‐expression quantitative trail locus (supported by chromatin interactions). Results We identified common noncoding SNPs within GBA that (1) regulate GBA expression in peripheral tissues, some of which display α‐synuclein pathology and (2) coregulate potential modifier genes in the central nervous system and/or peripheral tissues. Haplotypes based on 3 of these SNPs delay disease onset by 5 years. In addition, SNPs on 6 separate chromosomes coregulate GBA expression specifically in either the substantia nigra or cortex, and their combined effect potentially modulates motor and cognitive symptoms, respectively. Conclusions This work provides a new perspective on the haplotype‐specific effects of GBA and the genetic etiology of PD, expanding the role of GBA from the gene encoding the β‐glucocerebrosidase (GCase) to that of a central regulator and modifier of PD onset, with GBA expression itself subject to distant regulation. Some idiopathic patients might possess insufficient GBA‐encoded GCase activity in the substantia nigra as the result of distant regulatory variants and therefore might benefit from GBA‐targeting therapeutics. The SNPs’ regulatory impacts provide a plausible explanation for the variable phenotypes also observed in GBA‐centric Gaucher's disease and dementia with Lewy bodies. © 2020 The Authors. Movement Disorders published by Wiley Periodicals, LLC on behalf of International Parkinson and Movement Disorder Society.

Aims In long QT syndrome (LQTS) patients, modifier genes modulate the arrhythmic risk associated with a disease-causing mutation. Their recognition can improve risk stratification and clinical management, but their discovery represents a challenge. We tested whether a cellular-driven approach could help to identify new modifier genes and especially their mechanism of action. Methods and results We generated human-induced pluripotent stem cell-derived cardiomyocytes (iPSC-CM) from two patients carrying the same KCNQ1-Y111C mutation, but presenting opposite clinical phenotypes. We showed that the phenotype of the iPSC-CMs derived from the symptomatic patient is due to impaired trafficking and increased degradation of the mutant KCNQ1 and wild-type human ether-a-go-go-related gene. In the iPSC-CMs of the asymptomatic (AS) patient, the activity of an E3 ubiquitin-protein ligase (Nedd4L) involved in channel protein degradation was reduced and resulted in a decreased arrhythmogenic substrate. Two single-nucleotide variants (SNVs) on the Myotubularin-related protein 4 (MTMR4) gene, an interactor of Nedd4L, were identified by whole-exome sequencing as potential contributors to decreased Nedd4L activity. Correction of these SNVs by CRISPR/Cas9 unmasked the LQTS phenotype in AS cells. Importantly, the same MTMR4 variants were present in 77% of AS Y111C mutation carriers of a separate cohort. Thus, genetically mediated interference with Nedd4L activation seems associated with protective effects. Conclusion Our finding represents the first demonstration of the cellular mechanism of action of a protective modifier gene in LQTS. It provides new clues for advanced risk stratification and paves the way for the design of new therapies targeting this specific molecular pathway.

Background The ABCG2 rs2231142 single nucleotide polymorphism (SNP) is one of the most significant genetic variants associated with hyperuricemia (HUA) in Asian populations. However, the risk of ABCG2 rs2231142 variants for HUA could interact with other important HUA risk variants and cardiovascular factors. This study investigated the effects of the combined association among ABCG2 rs2231142 and multiple HUA genetic variants or cardiovascular risk factors on HUA risk and serum uric acid (sUA) levels in an elderly Chinese population. Methods A total of 1206 participants over 65 years old were enrolled in this study. Physical and laboratory examinations were performed for all participants. The ABCG2 rs2231142, SLC2A9 rs3733591, and SLC22A12 rs893006 SNPs were assayed using a standardized protocol. Logistic regression analysis and liner regression were adjusted respectively to account for the association between ABCG2 rs2231142 and other genetic variants, as well as between cardiovascular risk factors and HUA risk and sUA levels. Results The prevalence of HUA was 14.71% in the elderly community-dwelling population. The ABCG2 rs2231142 risk T allele was associated with HUA risk (odds ratio (OR) = 1.63, 95% confidence interval (CI): 1.27–2.11; p = 1.65 × 10− 4) and with increased sUA levels (Beta = 0.16, p = 6.75 × 10− 9) in the whole study population. Linear regression analysis showed that the mean sUA level increased linearly with the number of risk alleles of the three candidate genetic variants (Beta = 0.18, p = 1.94 × 10− 12) The joint effect of the ABCG2 rs2231142 T allele and cardiovascular risk factors (obesity, hypertension and dyslipidemia) was also associated with increased HUA risk and sUA levels. Each copy of the risk T allele was significantly associated with enhanced HUA risk in patients with hypertriglyceridemia (OR = 2.52, 95% CI: 1.33–4.60; p = 0.003) compared to controls. Conclusion Our findings reinforce the importance of the ABCG2 rs2231143 variant as a crucial genetic locus for HUA in Chinese populations and demonstrated the combined effects of multiple genetic risk variants and cardiovascular risk exposures on HUA risk and increased sUA level.

PRDM16 (positive regulatory domain 16) is localized in the critical region for cardiomyopathy in patients with deletions of chromosome 1p36, as defined by Gajecka et al., American Journal of Medical Genetics, 2010, 152A, 3074-3083, and encodes a zinc finger transcription factor. We present the first fetal case of left ventricular non-compaction (LVNC) with a PRDM16 variant. The third-trimester obstetric ultrasound revealed a hydropic fetus with hydramnios and expanded hypokinetic heart. After termination of pregnancy, foetopathology showed a eutrophic fetus with isolated cardiomegaly. Endocardial fibroelastosis was associated with non-compaction of the myocardium of the left ventricle. Exome sequencing (ES) identified a de novo unreported p.(Gln353*) heterozygous nonsense variant in PRDM16. ES also identified two rare variants of unknown significance, according to the American College of Medical Genetics and Genomics guidelines, in the titin gene (TTN): a de novo missense p.(Lys14773Asn) variant and a c.33043+5A>G variant inherited from the mother. Along with the PRDM16 de novo probably pathogenic variant, TTN VOUS variants could possibly contribute to the severity and early onset of the cardiac phenotype. Because of the genetic heterogeneity of cardiomyopathies, large panels or even ES could be considered as the main approaches for the molecular diagnosis, particularly in fetal presentations, where multiple hits seem to be common.

Context Individuals with cystic fibrosis (CF) develop a distinct form of diabetes characterized by β-cell dysfunction and islet amyloid accumulation similar to type 2 diabetes (T2D), but generally have normal insulin sensitivity. CF-related diabetes (CFRD) risk is determined by both CFTR, the gene responsible for CF, and other genetic variants. Objective To identify genetic modifiers of CFRD and determine the genetic overlap with other types of diabetes. Design and Patients A genome-wide association study was conducted for CFRD onset on 5740 individuals with CF. Weighted polygenic risk scores (PRSs) for type 1 diabetes (T1D), T2D, and diabetes endophenotypes were tested for association with CFRD. Results Genome-wide significance was obtained for variants at a novel locus (PTMA) and 2 known CFRD genetic modifiers (TCF7L2 and SLC26A9). PTMA and SLC26A9 variants were CF-specific; TCF7L2 variants also associated with T2D. CFRD was strongly associated with PRSs for T2D, insulin secretion, postchallenge glucose concentration, and fasting plasma glucose, and less strongly with T1D PRSs. CFRD was inconsistently associated with PRSs for insulin sensitivity and was not associated with a PRS for islet autoimmunity. A CFRD PRS comprising variants selected from these PRSs (with a false discovery rate < 0.1) and the genome-wide significant variants was associated with CFRD in a replication population. Conclusions CFRD and T2D have more etiologic and mechanistic overlap than previously known, aligning along pathways involving β-cell function rather than insulin sensitivity. Two CFRD risk loci are unrelated to T2D and may affect multiple aspects of CF. An 18-variant PRS stratifies risk of CFRD in an independent population.

Atrial fibrillation (AF) is the most frequent sustained arrhythmia and can lead to structural cardiac changes, known as tachycardia-induced cardiomyopathy (TIC). HCN4 is implicated in spontaneous excitation of the sinoatrial node, while channel dysfunction has been associated with sinus bradycardia, AF and structural heart disease. We here asked whether HCN4 mutations may contribute to the development of TIC, as well. Mutation scanning of HCN4 in 60 independent patients with AF and suspected TIC followed by panel sequencing in carriers of HCN4 variants identified the HCN4 variant P883R [minor allele frequency (MAF): 0,88%], together with the KCNE1 variant S38G (MAF: 65%) in three unrelated patients. Family histories revealed additional cases of AF, sudden cardiac death and cardiomyopathy. Patch-clamp recordings of HCN4-P883R channels expressed in HEK293 cells showed remarkable alterations of channel properties shifting the half-maximal activation voltage to more depolarized potentials, while channel deactivation was faster compared to wild-type (WT). Co-transfection of WT and mutant subunits, resembling the heterozygous cellular situation of our patients, revealed significantly higher current densities compared to WT. In conclusion HCN4-P883R may increase ectopic trigger and maintenance of AF by shifting the activation voltage of If to more positive potentials and producing higher current density. Together with the common KCNE1 variant S38G, previously proposed as a genetic modifier of AF, HCN4-P883R may provide a substrate for the development of AF and TIC.

A mouse strain intercross between Apoe−/− AKR/J and DBA/2J mice identified three replicated atherosclerosis quantitative trait loci (QTLs). Our objective was to fine map mouse atherosclerosis modifier genes within a genomic region known to affect lesion development in apoE-deficient (Apoe−/−) mice. We dissected the Ath28 QTL on the distal end of chromosome 2 by breeding a panel of congenic strains and measuring aortic root lesion area in 16-week-old male and female mice fed regular laboratory diets. The parental congenic strain contained ~9.65 Mb of AKR/J DNA from chromosome 2 on the DBA/2J genetic background, which had lesions 55% and 47% smaller than female and male DBA/2J mice, respectively (p < 0.001). Seven additional congenic lines identified three separate regions associated with the lesion area, named Ath28.1, Ath28.2, and Ath28.3, where the AKR/J alleles were atherosclerosis-protective for two regions and atherosclerosis-promoting for the other region. These results were replicated in both sexes, and in combined analysis after adjusting for sex. The congenic lines did not greatly impact total and HDL cholesterol levels or body weight. Bioinformatic analyses identified all coding and non-coding genes in the Ath28.1 sub-region, as well as strain sequence differences that may be impactful. Even within a

The mutations in modifier genes may contribute to some inherited diseases including Wilson disease (WD). This study was designed to identify potential modifier genes that contribute to WD. A total of 10 WD patients with single or no heterozygous ATP7B mutations were recruited for whole-exome sequencing (WES). Five hundred and thirteen candidate genes, of which the genetic variants present in at least two patients, were identified. In order to clarify which proteins might be involved in copper transfer or metabolism processes, the isobaric tags for relative and absolute quantitation (iTRAQ) was performed to identify the differentially expressed proteins between normal and CuSO4-treated cell lines. Thirteen genes/proteins were identified by both WES and iTRAQ, indicating that disease-causing variants of these genes may actually contribute to the aberrant copper ion accumulation. Additionally, the c.86C > T (p.S29L) mutation in the SLC31A2 gene (coding CTR2) has a relative higher frequency in our cohort of WD patients (6/191) than reported (0.0024 in gnomAD database) in our healthy donors (0/109), and CTR2S29L leads to increased intracellular Cu concentration and Cu-induced apoptosis in cultured cell lines. In conclusion, the WES and iTRAQ approaches successfully identified several disease-causing variants in potential modifier genes that may be involved in the WD phenotype.

Hemoglobinopathies though a monogenic disorder, show phenotypic variability. Hence, understanding the genetics underlying the heritable sub-phenotypes of hemoglobinopathies, specific to each population, would be prognostically useful and could inform personalized therapeutics. This study aimed to evaluate the role of genetic modifiers leading to higher HbF production with cumulative impact of the modifiers on disease severity. 200 patients (100 β-thalassemia homozygotes, 100 Sickle Cell Anemia), and 50 healthy controls were recruited. Primary screening followed with molecular analysis for confirming the β-hemoglobinopathy was performed. Co-existing α-thalassemia and the polymorphisms located in 3 genetic loci linked to HbF regulation were screened. The most remarkable result was the association of SNPs with clinically relevant phenotypic groups. The γ-globin gene promoter polymorphisms [− 158 C → T, + 25 G → A],BCL11A rs1427407 G → T, − 3 bp HBS1L-MYB rs66650371 and rs9399137 T → C polymorphisms were correlated with higher HbF, in group that has lower disease severity score (P

Cone-rod dystrophies (CORDs) are a heterogeneous group of inherited retinopathies (IRDs) with more than 30 already known disease-causing genes. Uncertain phenotypes and extended range of intra- and interfamilial heterogenicity make still difficult to determine a precise genotype-phenotype correlation. Here, we used a next-generation sequencing approach to study a Sicilian family with a suspected form of CORD. Affected family members underwent ophthalmological examinations and a proband, blind from 50 years, underwent whole genome and exome sequencing. Variant analysis was enriched by pathway analysis and relevant variants were, then, investigated in other family members and in 100 healthy controls from Messina. CORD diagnosis with an intricate pattern of symptoms was confirmed by ophthalmological examinations. A total of about 50,000 variants were identified in both proband’s genome and exome. All affected family members presented specific genotypes mainly determined by mutated GUCY2D gene, and different phenotypical traits, mainly related to focus and color perception. Thus, we looked for possible modifier genes. According to relationship with GUCY2D, predicted functional effects, eye localization, and ocular disease affinity, only 9 variants, carried by 6 genes (CACNG8, PAX2, RXRG, CCDC175, PDE4DIP and LTF), survived the filtering. These genes encode key proteins involved in cone development and survival, and retina neurotransmission. Among analyzed variants, CACNG8c.*6819A>T and the new CCDC175 c.76C>T showed extremely low frequency in the control group, suggesting a key role on disease phenotypes. Such discovery could enforce the role of modifier genes into CORD onset/progression, contributing to improve diagnostic test towards a better personalized medicine.

CFTR encodes for a chloride and bicarbonate channel expressed at the apical membrane of polarized epithelial cells. Transepithelial sodium transport mediated by the amiloride-sensitive sodium channel ENaC is thought to contribute to the manifestation of CF disease. Thus, ENaC is a therapeutic target in CF and a valid cystic fibrosis modifier gene. We have characterized SCNN1B as a genetic modifier in the three independent patient cohorts of F508del-CFTR homozygotes. We could identify a regulatory element at SCNN1B to the genomic segment rs168748-rs2303153-rs4968000 by fine-mapping (Pbest = 0.0177), consistently observing the risk allele rs2303153-C and the contrasting benign allele rs2303153-G in all three patient cohorts. Furthermore, our results show that expression levels of SCNN1B are associated with rs2303153 genotype in intestinal epithelia (p = 0.003). Our data confirm that the well-established biological role of SCNN1B can be recognized by an association study on informative endophenotypes in the rare disease cystic fibrosis and calls attention to reproducible results in association studies obtained from small, albeit carefully characterized patient populations.

Variation in respiratory response to cystic fibrosis (CF) small molecule therapies is due in part to the contribution of CF lung disease modifier genes. Cultured human bronchial epithelia (HBE) is the gold standard respiratory model for assessing CF therapeutic efficacy but it is hard to access. Cultured human nasal epithelia (HNE) is proposed as a more accessible surrogate model but it is unknown whether the expression profile of the modifier genes are comparable between HNE and HBE which we assess here.RNA-sequencing was conducted on paired cultured and fresh HNE and HBE (n = 71 samples) collected from 21 individuals with CF. Genome-wide gene expression was first compared between cultured and fresh cells and then between cultured HNE and HBE based on an equivalence testing procedure we implemented. The co-expression relationships of CFTR and CF lung disease modifier genes were compared between cultured HNE and HBE to determine equivalent interactions.The culturing process had little impact on the expression level of CF lung disease modifier genes. Over 90% of expressed genes showed significant equivalent expression level across cultured HNE and HBE (expression fold-change2, FDR0.1), including CFTR and CF lung disease modifier genes. The difference in co-expression relationships among these genes was not significant (p-value=0.99), suggesting their functional interactions are likely to be consistent in the two models.Cultured HNE recapitulates the expression profile of CF lung disease modifier genes in cultured HBE, suggesting the biological processes involving these genes are likely to be consistent across the two models.

Retinitis pigmentosa 11 (RP11) is caused by dominant mutations in PRPF31, however a significant proportion of mutation carriers do not develop retinopathy. Here, we investigated the relationship between CNOT3 polymorphism, MSR1 repeat copy number and disease penetrance in RP11 patients and non-penetrant carriers (NPCs). We further characterized PRPF31 and CNOT3 expression in fibroblasts from eight RP11 patients and one NPC from a family carrying the c.1205C&gt, T variant. Retinal organoids (ROs) and retinal pigment epithelium (RPE) were differentiated from induced pluripotent stem cells derived from RP11 patients, an NPC and a control subject. All RP11 patients were homozygous for the 3-copy MSR1 repeat in the PRPF31 promoter, while 3/5 NPCs carried a 4-copy MSR1 repeat. The CNOT3 rs4806718 genotype did not correlate with disease penetrance. PRFP31 expression declined with age in adult cadaveric retina. PRPF31 and CNOT3 expression was reduced in RP11 fibroblasts, RO and RPE compared with controls. Both RP11 and NPC RPE displayed shortened primary cilia compared with controls, however a subpopulation of cells with normal cilia lengths was present in NPC RPE monolayers. Our results indicate that RP11 non-penetrance is associated with the inheritance of a 4-copy MSR1 repeat, but not with CNOT3 polymorphisms.

The Nakano cataract mouse (NCT) manifests a wavy coat for their first hair as a genetic trait. In this study, we explored the molecular genetic basis of the wavy coat. We revealed by crossing experiments that the wavy coat is controlled by a major gene on chromosome 7 of NCT, homozygosity of which is a prerequisite for developing the wavy coat, and by a gene on chromosome 9 with a minor effect to reinforce the manifestation of the trait. In humans, a polymorphism of the protease, serine 53 (PRSS53) gene on the homologous chromosome is known to be associated with curly scalp hair. We then investigated the Prss53 gene and discovered that NCT has an insertion of an intracisternal A particle element in the first intron of the gene. Nevertheless, the expression of the Prss53 is not altered in the NCT skin both in transcript and protein levels. Subsequently, we created C57BL/6J-Prss53

Introduction Patients with a homozygous β0‐thalassemia mutation usually have a transfusion‐dependent β‐thalassemia major phenotype. However, some β‐thalassemia patients present with a relatively mild and even normal phenotype and always have a high level of Hb F induced by genetic modifiers. Methods In this study, we identified a homozygous β0‐thalassemia mutation (HBB: c.126_129delCTTT) in a 36‐year‐old pregnant woman. She had not presented any clinical symptoms of β‐thalassemia since birth. To investigate her unexpected mild phenotype, known genetic modifiers that ameliorate the severity of β‐thalassemia were analysed. Besides, we described the haematological changes during pregnancy. Results Two genetic modifiers (a heterozygous KLF1: c.519_525dup mutation; and two homozygous HBS1L‐MYB locus SNP variants: rs7776054 and rs9399137) were identified. However, she showed a gradually decreased level of Hb during pregnancy, and serious transfusion complication of hyperhaemolysis was induced and complicated the pregnancy. Conclusion This report is in accordance with previous findings that genetic modifiers can ameliorate the clinical severity of β‐thalassemia, even without obvious clinical symptoms in a prolonged steady state. However, the steady state can be disrupted during pregnancy. In addition, raising awareness of hyperhaemolysis among clinicians treating patients with thalassemia is necessary., We identified a homozygous β0‐thalassemia mutation (HBB: c.126_129delCTTT) and two genetic modifiers in a 36‐year‐old pregnant woman, who had not presented any clinical symptoms of β‐thalassemia since birth. However, she showed a gradually decreased level of Hb during pregnancy, and serious transfusion complication of hyperhaemolysis was induced and complicated the pregnancy. ​

Congenital microcephaly is the clinical presentation of significantly reduced head circumference at birth. It manifests as both non-syndromic—microcephaly primary hereditary (MCPH)—and syndromic forms and shows considerable inter- and intrafamilial variability. It has been hypothesized that additional genetic variants may be responsible for this variability, but data are sparse. We have conducted deep phenotyping and genotyping of five Pakistani multiplex families with either MCPH (n = 3) or Seckel syndrome (n = 2). In addition to homozygous causal variants in ASPM or CENPJ, we discovered additional heterozygous modifier variants in WDR62, CEP63, RAD50 and PCNT—genes already known to be associated with neurological disorders. MCPH patients carrying an additional heterozygous modifier variant showed more severe phenotypic features. Likewise, the phenotype of Seckel syndrome caused by a novel CENPJ variant was aggravated to microcephalic osteodysplastic primordial dwarfism type II (MOPDII) in conjunction with an additional PCNT variant. We show that the CENPJ missense variant impairs splicing and decreases protein expression. We also observed centrosome amplification errors in patient cells, which were twofold higher in MOPDII as compared to Seckel cells. Taken together, these observations advocate for consideration of additional variants in related genes for their role in modifying the expressivity of the phenotype and need to be considered in genetic counseling and risk assessment.

Collagen type IV alpha 1 and alpha 2 (COL4A1 and COL4A2) are major components of almost all basement membranes. COL4A1 and COL4A2 mutations cause a multisystem disorder that can affect any organ but typically involves the cerebral vasculature, eyes, kidneys and skeletal muscles. In recent years, patient advocacy and family support groups have united under the name of Gould syndrome. The manifestations of Gould syndrome are highly variable, and animal studies suggest that allelic heterogeneity and genetic context contribute to the clinical variability. We previously characterized a mouse model of Gould syndrome caused by a Col4a1 mutation in which the severities of ocular anterior segment dysgenesis (ASD), myopathy and intracerebral hemorrhage (ICH) were dependent on genetic background. Here, we performed a genetic modifier screen to provide insight into the mechanisms contributing to Gould syndrome pathogenesis and identified a single locus [modifier of Gould syndrome 1 (MoGS1)] on Chromosome 1 that suppressed ASD. A separate screen showed that the same locus ameliorated myopathy. Interestingly, MoGS1 had no effect on ICH, suggesting that this phenotype could be mechanistically distinct. We refined the MoGS1 locus to a 4.3 Mb interval containing 18 protein-coding genes, including Fn1, which encodes the extracellular matrix component fibronectin 1. Molecular analysis showed that the MoGS1 locus increased Fn1 expression, raising the possibility that suppression is achieved through a compensatory extracellular mechanism. Furthermore, we found evidence of increased integrin-linked kinase levels and focal adhesion kinase phosphorylation in Col4a1 mutant mice that is partially restored by the MoGS1 locus, implicating the involvement of integrin signaling. Taken together, our results suggest that tissue-specific mechanistic heterogeneity contributes to the variable expressivity of Gould syndrome and that perturbations in integrin signaling may play a role in ocular and muscular manifestations., Summary: We performed a genetic screen in Col4a1 mutant mice to elucidate the mechanisms contributing to Gould syndrome. Our results implicate FN1 as a genetic modifier of some, but not all, aspects of Gould syndrome.