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Biallelic loss-of-function variants in the SMG9 gene, encoding a regulatory subunit of the mRNA nonsense-mediated decay (NMD) machinery, are reported to cause heart and brain malformation syndrome. Here we report five patients from three unrelated families with intellectual disability (ID) and a novel pathogenic SMG9 c.551 T > C p.(Val184Ala) homozygous missense variant, identified using exome sequencing. Sanger sequencing confirmed recessive segregation in each family. SMG9 c.551T > C p.(Val184Ala) is most likely an autozygous variant identical by descent. Characteristic clinical findings in patients were mild to moderate ID, intention tremor, pyramidal signs, dyspraxia, and ocular manifestations. We used RNA sequencing of patients and age- and sex-matched healthy controls to assess the effect of the variant. RNA sequencing revealed that the SMG9 c.551T > C variant did not affect the splicing or expression level of SMG9 gene products, and allele-specific expression analysis did not provide evidence that the nonsense mRNA-induced NMD was affected. Differential gene expression analysis identified prevalent upregulation of genes in patients, including the genes SMOX, OSBP2, GPX3, and ZNF155. These findings suggest that normal SMG9 function may be involved in transcriptional regulation without affecting nonsense mRNA-induced NMD. In conclusion, we demonstrate that the SMG9 c.551T > C missense variant causes a neurodevelopmental disorder and impacts gene expression. NMD components have roles beyond aberrant mRNA degradation that are crucial for neurocognitive development.

Protein truncating variants (PTVs) are likely to modify gene function and have been linked to hundreds of Mendelian disorders. However, the impact of PTVs on complex traits has been limited by the available sample size of whole-exome sequencing studies (WES). Here we assemble WES data from 100,304 individuals to quantify the impact of rare PTVs on 13 quantitative traits and 10 diseases. We focus on those PTVs that occur in PTV-intolerant (PI) genes, as these are more likely to be pathogenic. Carriers of at least one PI-PTV were found to have an increased risk of autism, schizophrenia, bipolar disorder, intellectual disability and ADHD (P-value (p) range: 5x10-3-9x10-12). In controls, without these disorders, we found that this burden associated with increased risk of mental, behavioral and neurodevelopmental disorders as captured by electronic health record information. Furthermore, carriers of PI-PTVs tended to be shorter (p=2x10-5), have fewer years of education (p=2x10-4) and be younger (p=2x10-7); the latter observation possibly reflecting reduced survival or study participation. While other gene-sets derived from in vivo experiments did not show any associations with PTV-burden, gene sets implicated in GWAS of cardiovascular-related traits and inflammatory bowel disease showed a significant PTV-burden with corresponding traits, mainly driven by established genes involved in familial forms of these disorders. We leveraged population health registries from 14,117 individuals to study the phenome-wide impact of PI-PTVs and identified an increase in the number of hospital visits among PI-PTV carriers. In conclusion, we provide the most thorough investigation to date of the impact of rare deleterious coding variants on complex traits, suggesting widespread pleiotropic risk.

Intellectual disability (ID), megalencephaly, frontal predominant pachygyria, and seizures, previously called “thin” lissencephaly, are reported to be caused by recessive variants in CRADD. Among five families of different ethnicities identified, one homozygous missense variant, c.509G>A p.(Arg170His), was of Finnish ancestry. Here we report on the phenotypic variability associated for this potential CRADD founder variant in 22 Finnish individuals. Exome sequencing was used to identify candidate genes in Finnish patients presenting with ID. Targeted Sanger sequencing and restriction enzyme analysis were applied to screen for the c.509G>A CRADD variant in cohorts from Finland. Detailed phenotyping and genealogical studies were performed. Twenty two patients were identified with the c.509G>A p.(Arg170His) homozygous variant in CRADD. The majority of the ancestors originated from Northeastern Finland indicating a founder effect. The hallmark of the disease is frontotemporal predominant pachygyria with mild cortical thickening. All patients show ID of variable severity. Aggressive behavior was found in nearly half of the patients, EEG abnormalities in five patients and megalencephaly in three patients. This study provides detailed data about the phenotypic spectrum of patients with lissencephaly due to a CRADD variant that affects function. High inter- and intrafamilial phenotypic heterogeneity was identified in patients with pachygyria caused by the homozygous CRADD founder variant. The phenotype variability suggests that additional genetic and/or environmental factors play a role in the clinical presentation. Since frontotemporal pachygyria is the hallmark of the disease, brain imaging studies are essential to support the molecular diagnosis for individuals with ID and a CRADD variant., SCOPUS: ar.j, info:eu-repo/semantics/published

Objective To define the clinical, radiologic, and molecular genetic characteristics of a family with early progressive osteoarthritis mimicking childhood rheumatoid arthritis, Scheuermann-like changes of the spine, tall stature, short 3 and 4 metatarsals, and moderate sensorineural hearing loss. Methods We describe a 22-year-old woman and her 54-year-old mother with early progressive osteoarthritis mimicking childhood rheumatoid arthritis. The index case, her mother, and 3 other family members underwent a physical examination, anthropometric measurements, and radiologic studies. Their DNA was sequenced for the procollagen type II (COL2A1) gene. Results Mild scoliosis was noticed in the proband at the age of 6 years, and at the age of 7 years large Schmorl's nodes were found in the vertebrae L1-2. At the age of 11 years, changes resembling Scheuermann's disease were seen, mostly in the thoracic vertebrae. At the same age, she began to have arthralgia in the weight-bearing joints and osteoarthritis progressed fast, necessitating a hip prosthesis at the age of 18 years. The proband and her mother had bilateral sensorineural hearing loss of moderate degree. Both mother and daughter had an Arg75-Cys mutation in the COL2A1 gene. Conclusion This family is the fourth example of the Arg75-Cys mutation in the COL2A1 gene, which appears to lead to a clearly recognizable phenotype. The finding suggests that sensorineural hearing loss may be a part of this syndrome.

Osteogenesis imperfecta (OI) is caused by mutations in COL1A1 and COL1A2 that code for the alpha1 and alpha2 chains of type I collagen. Phenotypes correlate with the mutation types in that COL1A1 null mutations lead to OI type I, and structural mutations in alpha1(I) or alpha2(I) lead to more severe OI types (II-IV). However, correlative analysis between mutation types and OI associated hearing loss has not been previously performed. A total of 54 Finnish OI patients with previously diagnosed hearing loss or age 35 or more years were analyzed here for mutations in COL1A1 or COL1A2. Altogether 49 mutations were identified, of which 41 were novel. The 49 mutations represented the molecular genetic background of 41.1% of the Finnish OI population. A total of 38 mutations were in COL1A1 and 11 were in COL1A2. Of these, 16 were glycine substitutions and 16 were splicing mutations in alpha1(I) or alpha2(I). In addition, 17 null allele mutations were detected in COL1A1. A total of 32 patients (65.3%) with a mutation had hearing loss. That is slightly more than in our previous population study on Finnish adults with OI (57.9%). The association between the mutation types and OI type was statistically evident. Patients with COL1A1 mutations more frequently had blue scleras than those with COL1A2 mutations. In addition, patients with COL1A2 mutations tended to be shorter than those with COL1A1 mutations. However, no correlation was found between the mutated gene or mutation type and hearing pattern. These results suggest that the basis of hearing loss in OI is complex, and it is a result of multifactorial, still unknown genetic effects.

Purpose To report posterior chorioretinal atrophy (PCRA) and correlate the vitreous phenotype with inheritance of the disease mutation in a family with vitreoretinal dystrophy. Design Prospective observational case series. Methods Twenty-four members of a family with 14 affected individuals were examined, and genetic linkage analysis was performed at the COL2A1, COL11A1, and Wagner disease loci. The vitreous phenotype was prospectively graded as optically empty with retrolenticular membrane, fibrillar, or normal. Ocular ultrasonography and optical coherence tomography (OCT) were performed on selected individuals to study the vitreous structure and vitreoretinal interface. Results The 6-year-old proband had PCRA and optically empty vitreous without systemic features, suggestive of Wagner disease. The family history was negative for systemic disease, except for one cousin with cleft palate. However, when examined, clinical features of the 14 affected subjects included 5 with small chin, 4 with at least submucosal cleft palate, and 9 with a myopic refractive error greater than 5 diopters. Lens opacity or previous cataract extraction was found in 13 family members. All affected individuals in whom the vitreous could be examined had an optically empty vitreous with retrolental membrane. Posterior chorioretinal atrophy was found in eight of the affected subjects. The finding was not limited to highly myopic subjects, nor did all the high myopes have PCRA. Ultrasonography and OCT revealed vitreous adherent to the retina, but without apparent retinal distortion or edema of the macula. Significant linkage was established to the COL2A1 locus; the other loci were excluded. A single nucleotide insertion mutation (c.2012^2013insC) was identified in exon 34, leading to a downstream premature stop codon in the COL2A1 gene. Conclusions Although posterior chorioretinal atrophy and vitreoretinal degeneration have been classically associated with Wagner disease, we demonstrate its presence in a family with typical Stickler syndrome. On the basis of clinical, ultrasonographic, and OCT studies, the etiology of PCRA in this family does not seem to be attributable to vitreomacular traction or myopia. The vitreous findings in this large family confirm reports that mutations in the COL2A1 gene lead to the optically empty vitreous with retrolenticular membrane phenotype.

PURPOSE: To identify the genetic defect and present the ocular and extraocular findings in a large pedigree of predominantly ocular Stickler syndrome. DESIGN: Observational case series. METHODS: An eight-generation pedigree with hereditary retinal detachments was retrospectively and prospectively studied. Clinical information was obtained by medical records, telephone interviews, medical questionnaires, detailed ophthalmologic examinations, physical examinations, and personal observations. Linkage analysis of the COL2A1 gene was performed on 21 family members, and mutation analysis was performed on three family members. RESULTS: The pedigree consisted of 100 affected individuals. The ocular findings, frequently bilateral, consisted of radial perivascular retinal degeneration (RPRD) (100%), vitreous syneresis (100%), high myopia (76%), retinal detachment (65%), presenile cataract development (occurring before 50 years of age; 78%), and glaucoma (18%). Most (70%) of the retinal detachments occurred between 4 and 18 years of age. Extraocular manifestations, characteristic for Stickler syndrome, were detected in only four of 100 (4%) affected individuals. Linkage analysis with COL2A1 flanking markers showed evidence for linkage to the COL2A1 locus. The COL2A1 gene analysis identified a mutation converting a codon TGC for cysteine 86 to a premature termination codon in the alternatively spliced exon 2. CONCLUSIONS: A variant of Stickler syndrome, caused by mutations in exon 2 of COL2A1, may present in families with all of the ocular findings and no clinically identifiable extraocular findings associated with Stickler syndrome. The predominant ocular findings are a congenitally abnormal vitreous and an acquired radial perivascular retinal degeneration that may lead to complicated childhood and adult retinal detachment.

Previous in vitro data on type I collagen self-assembly into fibrils suggested that the amino acid 776-796 region of the alpha1(I) chain is crucial for fibril formation because it serves as the recognition site for the telopeptide of a docking collagen monomer. We used a natural collagen mutation with a deletion of amino acids 766-801 to confirm the importance of this region for collagen fibril formation. The proband has type III osteogenesis imperfecta and is heterozygous for a COL1A1 IVS 41 A(+4) --C substitution. The intronic mutation causes splicing of exon 41, confirmed by sequencing of normal and shorter reverse transcriptase-PCR products. Reverse transcriptase-PCR using RNA from proband dermal fibroblasts and clonal cell lines showed the mutant cDNA was about 15% of total alpha1(I) cDNA. The mutant transcript is translated; structurally abnormal alpha chains are demonstrated in the cell layer of proband fibroblasts by SDS-urea-PAGE. The proportion of mutant chains in the secreted procollagen was determined to be 10% by resistance to digestion with MMP-1, since chains lacking exon 41 are missing the vertebral collagenase cleavage site. Secreted proband collagen was used for analysis of kinetics of binding of alpha1(I) C-telopeptide using an optical biosensor. Telopeptide had slower association and faster dissociation from proband than from normal collagen. Purified proband pC-collagen was used to study fibril formation. The presence of the mutant molecules decreases the rate of fibril formation. The fibrils formed in the presence of 10-15% mutant molecules have strikingly increased length compared with normal collagen, but are well organized, as demonstrated by D-periodicity. These results suggest that some collagen molecules containing the mutant chain are incorporated into fibrils and that the absence of the telopeptide binding region from even a small portion of the monomers interferes with fibril growth. Both abnormal fibrils and slower remodeling may contribute to the severe phenotype.in

Type I collagen is the most abundant protein in humans, and it helps to maintain the integrity of many tissues via its interactions with cell surfaces, other extracellular matrix molecules, and growth and differentiation factors. Nearly 50 molecules have been found to interact with type I collagen, and for about half of them, binding sites on this collagen have been elucidated. In addition, over 300 mutations in type I collagen associated with human connective tissue disorders have been described. However, the spatial relationships between the known ligand-binding sites and mutation positions have not been examined. To this end, here we have created a map of type I collagen that includes all of its ligand-binding sites and mutations. The map reveals the existence of several hot spots for ligand interactions on type I collagen and that most of the binding sites locate to its C-terminal half. Moreover, on the collagen fibril some potentially relevant relationships between binding sites were observed including the following: fibronectin- and certain integrin-binding regions are near neighbors, which may mechanistically relate to fibronectin-dependent cell-collagen attachment; proteoglycan binding may potentially impact upon collagen fibrillogenesis, cell-collagen attachment, and collagen glycation seen in diabetes and aging; and mutations associated with osteogenesis imperfecta and other disorders show apparently nonrandom distribution patterns within both the monomer and fibril, implying that mutation positions correlate with disease phenotype. These and other observations presented here may provide novel insights into evaluating type I collagen functions and the relationships between its binding partners and mutations.

Mesenchymal stem cells (MSCs) isolated from the bone marrow of adult organisms are capable of differentiating into adipocytes, chondrocytes, myoblasts, osteoblasts, and hematopoiesis-supporting stroma. We recently demonstrated that MSCs also adopt glial cell fates when transplanted into the developing central nervous system and hence can produce tissue elements derived from a separate embryonic layer. Despite these remarkable properties, it has been difficult to establish specific criteria to characterize MSCs. Using a modified protocol for micro-serial analysis of gene expression, we cataloged 2,353 unique genes expressed by a single cell-derived colony of undifferentiated human MSCs. This analysis revealed that the MSC colony simultaneously expressed transcripts characteristic of various mesenchymal cell lineages including chondrocytes, myoblasts, osteoblasts, and hematopoiesis-supporting stroma. Therefore, the profile of expressed transcripts reflects the developmental potential of the cells. Additionally, the MSC colony expressed mRNAs characteristic of endothelial, epithelial and neuronal cell lineages, a combination that provides a unique molecular signature for the cells. Other expressed transcripts included various products involved in wound repair as well as several neurotrophic factors. A total of 268 novel transcripts were also identified, one of which is the most abundantly expressed mRNA in MSCs. This study represents the first extensive gene expression analysis of MSCs and as such reveals new insight into the biology, ontogeny, and in vivo function of the cells.

Because of the clinical and histopathologic similarities between otosclerosis and type I osteogenesis imperfecta and prior evidence that some cases of clinical otosclerosis have reduced expression of one COL1A1 allele, we analyzed the COL1A1 and COL1A2 genes in 10 patients with clinical otosclerosis, including 2 patients with reduced or null expression of one COL1A1 allele. Conformation-sensitive gel electrophoresis of all exons and flanking sequences and the promoter sequences for each gene were performed. There were no mutations found in the coding or promoter sequence of either gene in any of the cases examined. One case with reduced allelic expression revealed evidence of a possible splicing mutation at intervening sequence intron 44+4. The second case of reduced allelic expression failed to demonstrate evidence for mutations in the coding or splice site regions of the COL1A1 gene, suggesting a different mechanism for reduced allelic expression than that which has been observed thus far in type I osteogenesis imperfecta.

Pseudoachondroplasia (PSACH) and spondyloepiphyseal dysplasia congenita (SEDC) are autosomal dominant forms of short-limb short stature caused by mutations in genes that encode structural components of the cartilage extracellular matrix. PSACH results from mutations in the cartilage oligomeric matrix protein (COMP) gene, while SEDC is caused by mutations in the gene for type II procollagen (COL2A1). We report a child with a distinct skeletal dysplasia due to the combined phenotypes of PSACH and SEDC. The proband's mother had PSACH and his father had SEDC. The child was suspected of having both phenotypes on the basis of the severity of his clinical and radiographic findings, and this was confirmed by molecular analysis. The COMP gene mutation (C348R), while not previously published, is typical of those in PSACH patients, whereas the COL2A1 mutation (T1370M) is somewhat atypical, as it predicts an amino acid change within the carboxyl-terminal region of the protein. Both mutations segregated with their respective phenotypes within this family. The description and natural history of the double heterozygote phenotype may be useful in counseling families regarding risk and prognosis.

The COL2A1 gene was assayed for mutations in genomic DNA from 12 patients with achondrogenesis type II/hypochondrogenesis. The exons and flanking sequences of the 54 exons in the COL2A1 gene were amplified by a series of specific primers using PCR. The PCR products were scanned for mutations by conformation sensitive gel electrophoresis, and PCR products that generated heteroduplex bands were then sequenced. Mutations in the COL2A1 gene were found in all 12 patients. Ten of the mutations were single base substitutions that converted a codon for an obligate glycine to a codon for an amino acid with a bulkier side chain. One of the mutations was a change in a consensus RNA splice site. Another was an 18-base pair deletion of coding sequences. The results confirmed previous indications that conformation sensitive gel electrophoresis is highly sensitive for detection of mutations in large and complex genes. They also demonstrate that most, if not all, patients with achondrogenesis type II/hypochondrogenesis have mutations in the COL2A1 gene.

SummaryAlthough >90% of patients with osteogenesis imperfecta (OI) have been estimated to have mutations in the COL1A1 and COL1A2 genes for type I procollagen, mutations have been difficult to detect in all patients with the mildest forms of the disease (i.e., type I). In this study, we first searched for mutations in type I procollagen by analyses of protein and mRNA in fibroblasts from 10 patients with mild OI; no evidence of a mutation was found in 2 of the patients by the protein analyses, and no evidence of a mutation was found in 5 of the patients by the RNA analyses. We then searched for mutations in the original 10 patients and in 5 additional patients with mild OI, by analysis of genomic DNA. To assay the genomic DNA, we established a consensus sequence for the first 12 kb of the COL1A1 gene and for 30 kb of new sequences of the 38-kb COL1A2 gene. The sequences were then used to develop primers for PCR for the 103 exons and exon boundaries of the two genes. The PCR products were first scanned for heteroduplexes by conformation-sensitive gel electrophoresis, and then products containing heteroduplexes were sequenced. The results detected disease-causing mutations in 13 of the 15 patients and detected two additional probable disease-causing mutations in the remaining 2 patients. Analysis of the data developed in this study and elsewhere revealed common sequences for mutations causing null alleles.

Previous observations on mutations causing osteogenesis imperfecta (OI) suggested that unrelated patients had private mutations. Here preliminary studies on two patients with type I OI indicated that some mutations in the COL1A1 gene for type I procollagen cannot be detected by analyses of cDNAs. Therefore, we developed a protocol whereby 43 exon and exon flanking sequences of the COL1A1 gene can be amplified by PCR and scanned for mutations by denaturing gradient gel electrophoresis. Two new recurrent nucleotide mutations in the gene were found in four apparently unrelated patients with OI. Analysis of previous publications indicated that up to one-fifth of the mutations causing OI are recurrent in the sense that they were identical in apparently unrelated probands. About 80% of these identical mutations were in CpG dinucleotide sequences.

Osteogenesis imperfecta (OI) is a generalized disorder of connective tissue characterized by fragile bones and easy susceptibility to fracture. Most cases of OI are caused by mutations in type I collagen. We have identified and assembled structural mutations in type I collagen genes (COL1A1 and COL1A2, encoding the proalpha1(I) and proalpha2(I) chains, respectively) that result in OI. Quantitative defects causing type I OI were not included. Of these 832 independent mutations, 682 result in substitution for glycine residues in the triple helical domain of the encoded protein and 150 alter splice sites. Distinct genotype-phenotype relationships emerge for each chain. One-third of the mutations that result in glycine substitutions in alpha1(I) are lethal, especially when the substituting residues are charged or have a branched side chain. Substitutions in the first 200 residues are nonlethal and have variable outcome thereafter, unrelated to folding or helix stability domains. Two exclusively lethal regions (helix positions 691-823 and 910-964) align with major ligand binding regions (MLBRs), suggesting crucial interactions of collagen monomers or fibrils with integrins, matrix metalloproteinases (MMPs), fibronectin, and cartilage oligomeric matrix protein (COMP). Mutations in COL1A2 are predominantly nonlethal (80%). Lethal substitutions are located in eight regularly spaced clusters along the chain, supporting a regional model. The lethal regions align with proteoglycan binding sites along the fibril, suggesting a role in fibril-matrix interactions. Recurrences at the same site in alpha2(I) are generally concordant for outcome, unlike alpha1(I). Splice site mutations comprise 20% of helical mutations identified in OI patients, and may lead to exon skipping, intron inclusion, or the activation of cryptic splice sites. Splice site mutations in COL1A1 are rarely lethal; they often lead to frameshifts and the mild type I phenotype. In alpha2(I), lethal exon skipping events are located in the carboxyl half of the chain. Our data on genotype-phenotype relationships indicate that the two collagen chains play very different roles in matrix integrity and that phenotype depends on intracellular and extracellular events.

To define the clinical, radiologic, and molecular genetic characteristics of a family with early progressive osteoarthritis mimicking childhood rheumatoid arthritis, Scheuermann-like changes of the spine, tall stature, short 3 and 4 metatarsals, and moderate sensorineural hearing loss.We describe a 22-year-old woman and her 54-year-old mother with early progressive osteoarthritis mimicking childhood rheumatoid arthritis. The index case, her mother, and 3 other family members underwent a physical examination, anthropometric measurements, and radiologic studies. Their DNA was sequenced for the procollagen type II (COL2A1) gene.Mild scoliosis was noticed in the proband at the age of 6 years, and at the age of 7 years large Schmorl's nodes were found in the vertebrae L1-2. At the age of 11 years, changes resembling Scheuermann's disease were seen, mostly in the thoracic vertebrae. At the same age, she began to have arthralgia in the weight-bearing joints and osteoarthritis progressed fast, necessitating a hip prosthesis at the age of 18 years. The proband and her mother had bilateral sensorineural hearing loss of moderate degree. Both mother and daughter had an Arg75-Cys mutation in the COL2A1 gene.This family is the fourth example of the Arg75-Cys mutation in the COL2A1 gene, which appears to lead to a clearly recognizable phenotype. The finding suggests that sensorineural hearing loss may be a part of this syndrome.

Patients with pseudohypoparathyroidism type Ib (PHP-Ib) have hypocalcemia and hyperphosphatemia due to renal parathyroid hormone (PTH) resistance, but lack physical features of Albright hereditary osteodystrophy. PHP-Ib is thus distinct from PHP-Ia, which is caused by mutations in the GNAS exons encoding the G protein alpha subunit. However, an imprinted autosomal dominant form of PHP-Ib (AD-PHP-Ib) has been mapped to a region of chromosome 20q13.3 containing GNAS. Furthermore, loss of methylation at a differentially methylated region (DMR) of this locus, exon A/B, has been observed thus far in all investigated sporadic PHP-Ib cases and the affected members of multiple AD-PHP-Ib kindreds. We now report that affected members and obligate gene carriers of 12 unrelated AD-PHP-Ib kindreds and four apparently sporadic PHP-Ib patients, but not healthy controls, have a heterozygous approximately 3-kb microdeletion located approximately 220 kb centromeric of GNAS exon A/B. The deleted region, which is flanked by two direct repeats, includes three exons of STX16, the gene encoding syntaxin-16, for which no evidence of imprinting could be found. Affected individuals carrying the microdeletion show loss of exon A/B methylation but no epigenetic abnormalities at other GNAS DMRs. We therefore postulate that this microdeletion disrupts a putative cis-acting element required for methylation at exon A/B, and that this genetic defect underlies the renal PTH resistance in AD-PHP-Ib.

To report posterior chorioretinal atrophy (PCRA) and correlate the vitreous phenotype with inheritance of the disease mutation in a family with vitreoretinal dystrophy.Prospective observational case series.Twenty-four members of a family with 14 affected individuals were examined, and genetic linkage analysis was performed at the COL2A1, COL11A1, and Wagner disease loci. The vitreous phenotype was prospectively graded as optically empty with retrolenticular membrane, fibrillar, or normal. Ocular ultrasonography and optical coherence tomography (OCT) were performed on selected individuals to study the vitreous structure and vitreoretinal interface.The 6-year-old proband had PCRA and optically empty vitreous without systemic features, suggestive of Wagner disease. The family history was negative for systemic disease, except for one cousin with cleft palate. However, when examined, clinical features of the 14 affected subjects included 5 with small chin, 4 with at least submucosal cleft palate, and 9 with a myopic refractive error greater than 5 diopters. Lens opacity or previous cataract extraction was found in 13 family members. All affected individuals in whom the vitreous could be examined had an optically empty vitreous with retrolental membrane. Posterior chorioretinal atrophy was found in eight of the affected subjects. The finding was not limited to highly myopic subjects, nor did all the high myopes have PCRA. Ultrasonography and OCT revealed vitreous adherent to the retina, but without apparent retinal distortion or edema of the macula. Significant linkage was established to the COL2A1 locus; the other loci were excluded. A single nucleotide insertion mutation (c.2012 2013insC) was identified in exon 34, leading to a downstream premature stop codon in the COL2A1 gene.Although posterior chorioretinal atrophy and vitreoretinal degeneration have been classically associated with Wagner disease, we demonstrate its presence in a family with typical Stickler syndrome. On the basis of clinical, ultrasonographic, and OCT studies, the etiology of PCRA in this family does not seem to be attributable to vitreomacular traction or myopia. The vitreous findings in this large family confirm reports that mutations in the COL2A1 gene lead to the optically empty vitreous with retrolenticular membrane phenotype.

SummaryStickler and Marshall syndromes are dominantly inherited chondrodysplasias characterized by midfacial hypoplasia, high myopia, and sensorineural-hearing deficit. Since the characteristics of these syndromes overlap, it has been argued whether they are distinct entities or different manifestations of a single syndrome. Several mutations causing Stickler syndrome have been found in the COL2A1 gene, and one mutation causing Stickler syndrome and one causing Marshall syndrome have been detected in the COL11A1 gene. We characterize here the genomic structure of the COL11A1 gene. Screening of patients with Stickler, Stickler-like, or Marshall syndrome pointed to 23 novel mutations. Genotypic-phenotypic comparison revealed an association between the Marshall syndrome phenotype and splicing mutations of 54-bp exons in the C-terminal region of the COL11A1 gene. Null-allele mutations in the COL2A1 gene led to a typical phenotype of Stickler syndrome. Some patients, however, presented with phenotypes of both Marshall and Stickler syndromes.

Previously, an assay called conformation sensitive gel electrophoresis (CSGE) was developed for scanning PCR products for the presence of single-base and larger base mismatches in DNA. The assay was based on the assumption that mildly denaturing solvents in an appropriate buffer can accentuate the conformational changes produced by single-base mismatches in double-stranded DNA and thereby increase the differential migration in electrophoretic gels of heteroduplexes and homoduplexes. Here the sensitivity of assays by CSGE was improved by limiting the maximal size of the PCR products to 450 bp and making several changes in the conditions for PAGE. With the improved conditions, CSGE detected all 76 previously identified single-base changes in a large series of PCR products from collagen genes that contain multiple exons with highly repetitive and GC-rich sequences. In a survey of 736 alleles of collagen genes, CSGE detected 223 unique single-base mismatches that were confirmed by nucleotide sequencing. CSGE has the advantage over other methods for scanning PCR products in that it is simple, requires no special preparation of PCR products, has a large capacity, and does not use radioactivity.

Previous observations on mutations causing osteogenesis imperfecta (OI) suggested that unrelated patients had private mutations. Here preliminary studies on two patients with type I OI indicated that some mutations in the COL1A1 gene for type I procollagen cannot be detected by analyses of cDNAs. Therefore, we developed a protocol whereby 43 exon and exon flanking sequences of the COL1A1 gene can be amplified by PCR and scanned for mutations by denaturing gradient gel electrophoresis. Two new recurrent nucleotide mutations in the gene were found in four apparently unrelated patients with OI. Analysis of previous publications indicated that up to one-fifth of the mutations causing OI are recurrent in the sense that they were identical in apparently unrelated probands. About 80% of these identical mutations were in CpG dinucleotide sequences.

To use a recently developed procedure for analysis of blood leukocyte DNA to detect mutations in the gene for type II procollagen (COL2A1) in patients with cartilage diseases ranging from early-onset familial osteoarthritis (OA) to lethal chondrodysplasias.The technique of denaturing gradient gel electrophoresis was used to scan polymerase chain reaction (PCR) products from 45 exons and exon-flanking sequences of the COL2A1 gene in more than 70 patients with cartilage diseases whose severity ranged from mild to lethal. PCR products with abnormal migrations were then sequenced.Among the 3 patients with lethal hypochondrogenesis who were analyzed, all 3 were found to have a mutation in the COL2A1 gene. Among 17 patients with spondyloepiphyseal or spondyloepimetaphyseal dysplasia, 2 well-defined and 2 probable mutations were found. Among 15 patients with the Wagner-Stickler syndrome, 2 well-defined and 2 probable mutations were found. Among 45 patients with early-onset familial OA, 1 probable mutation was found.Using the procedure developed for analysis of the COL2A1 gene, mutations were detected in20% of patients with chondrodysplasias and up to 2% of patients with early-onset familial OA. However, these percentages are only minimal estimates because all possible mutations in the gene cannot be detected with this procedure.