Search

Facioscapulohumeral muscular dystrophy type 1 (FSHD1) is one of the most prevalent hereditary myopathies caused by D4Z4 repeat contraction. Its etiology involves derepression of the DUX4 gene within the D4Z4 repeat in skeletal muscle, with disease severity inversely correlating with D4Z4 repeat size. The genetic mechanism of FSHD is mainly studied in patients with a European or Northeast (NE) Asian background. These studies showed a difference in the FSHD1 allele repeat size distribution, ranging from 1-10 units in European to 1-7 units in NE Asian patients, suggesting that the likelihood of developing FSHD may vary between ethnic populations. Despite this difference, the global threshold for FSHD1 for genetic counsellors is still 1-10 units and the patient's genetic background is generally not taken into account. Until now, the diagnosis of FSHD in India, with over 1.4 billion people one of the biggest populations in the world, is based predominantly on clinical diagnosis only. Here, we present the first genetically confirmed FSHD cohort of Indian ancestry collected via the International Centre for Genomic Medicine in neuromuscular diseases consortium. The ICGNMD aims to perform clinical and genetic testing for neuromuscular diseases patients in low and middle-income countries such as India. Our study revealed 54/91 (59%) probands with FSHD1 suggesting a pathogenic FSHD1 allele size distribution intermediate between European and NE Asian populations. We also identified five FSHD2 patients with mutations in SMCHD1. The possible reduced penetrance of FSHD1 in NE Asian individuals is strengthened by the substantial proportion of asymptomatic carriers with a rather short FSHD1 allele in India. Our data provides important evidence of differences relevant to clinical diagnostics and reconsideration of FSHD1 repeat size thresholds. It also underscores the need for global FSHD participation in research and the establishment of trial-ready Indian FSHD cohorts. [ABSTRACT FROM AUTHOR]

This paper describes an experiment to explore the effects of the TENCompetence infrastructure for supporting lifelong competence development which is now in development. This infrastructure provides structured, multi-leveled access to learning materials, based upon competences. People can follow their own learning path, supported by a listing of competences and their components, by competence development plans attached to competences and by the possibility to mark elements as complete. We expected the PCM to have an effect on (1) control of participants of their own learning, and (2) appreciation of their learning route, (3) of the learning resources, (4) of their competence development, and (5) of the possibilities of collaboration. In the experiment, 44 Bulgarian teachers followed a distance learning course on a specific teaching methodology for six weeks. Part of them used the TENCompetence infrastructure, part used an infrastructure which was similar, except for the characterizing elements mentioned above. The results showed that in the experimental condition, more people passed the final competence assessment, and people felt more in control of their own learning. No differences between the two groups were found on the amount and appreciation of collaboration and on further measures of competence development. [ABSTRACT FROM AUTHOR]

Facioscapulohumeral dystrophy (FSHD) is the third most prevalent inherited form of muscular dystrophy in individuals of European ancestry. FSHD is caused by derepression of the transcription factor DUX4 in skeletal muscle. For most cases of European ancestry, FSHD is caused by contraction of the D4Z4 repeat to a range of 1-10 units (U), known as FSHD1, whereas the typical size ranges between 8-100U. Alternatively, pathogenic variants in chromatin modifiers such as SMCHD1 underlie FSHD (FSHD2). Recent studies suggest that the northeast Asian population is less susceptible to FSHD1 as the common FSHD1 allele size ranges here between 1-7U. Only a few sub-Saharan African FSHD patients have been described, without genetic confirmation. Under-reporting of FSHD in individuals with African genetic ancestry may be attributed to limited access to diagnostic tools and scarcity of Neurology specialists in Africa. However, it is possible that epidemiological differences could arise from a different genomic background influencing susceptibility to FSHD between populations. We provide a clinical and genetic description of FSHD in eight unrelated individuals with African genetic ancestry from Senegal, Ivory Coast, Ethiopia, South Africa, Curaçao and the USA. Individuals were evaluated using the FSHD Evaluation Score and the FSHD Clinical Severity Score. Genetic analysis confirmed FSHD1 in seven individuals, where the FSHD1 allele ranged between 2-6U. One individual was genetically FSHD2, showing typical D4Z4 hypomethylation, a pathogenic SMCHD1 variant and an FSHD permissive haplotype with 11U repeat. More detailed analysis showed African-specific D4Z4 haplotypes in 6/7 patients. Genome wide SNP analysis confirmed the African genetic background in most of the patients. These findings underscore the importance of further investigation into factors contributing to the variability of FSHD presentation across diverse populations and highlight the need for tailored genetic diagnosis. [ABSTRACT FROM AUTHOR]

The International Centre for Genomic Medicine in Neuromuscular Diseases (ICGNMD) is an MRC funded study to define the international genetic spectrum of neuromuscular diseases (NMD), grow capacity in genomic medicine and develop "trial ready cohorts", with the ultimate aim of improving health outcomes for NMD patients globally. ICGNMD involves 14 Centres across Brazil, India, Turkey, South Africa, the UK and Zambia. We aimed to analyse the study outcomes to date of probands recruited to the ICGNMD partner site, the All India Institute of Medical Sciences (AIIMS), New Delhi. Participants attending AIIMS Neurology Clinics (including Teleneurology services) with clinically-suspected inherited NMD were invited to give informed consent to join the ICGNMD study. Participants underwent clinical assessment, nerve conduction studies (NCS), electromyography (EMG), and serum creatinine kinase (CK) measurement. Tailored genetic testing was applied. Single gene tests included Multiplex ligation-dependent probe amplification (MLPA) for Duchenne or Becker muscular dystrophy (DMD/BMD), or spinal muscular atrophy (SMA). Bespoke PCR-based approaches included tests for spinal and bulbar muscular atrophy (SBMA/Kennedy's), Friedrich's Ataxia, Charcot-Marie-Tooth 1A (CMT1A/HNPP), myotonic dystrophy type 1 (DM1), C9orf72 repeat expansion in amyotrophic lateral sclerosis (ALS), while Southern blot/optical genome mapping detected facioscapulohumeral dystrophy (FSHD). The majority of probands underwent singleton whole exome sequencing (WES), with subsequent Sanger sequencing of suspected variants in affected relatives. A bespoke informatics pipeline incorporating virtual diagnostic panels supported exome data analysis and ACMG criteria were used to classify suspected causative variants. To date, 789 probands have completed testing. Of 789 probands tested, 526 (67 %) were solved/likely solved. Single gene tests solved 268 (34%) probands: 124 DMD/BMD, 74 FSHD, 30 SMA, 24 myotonic dystrophy, 11 CMT1A/HNPP, 4 Friedrich's ataxia and 1 C9orf72-ALS. Singleton WES genetically solved/likely solved 135 limb girdle muscular dystrophy (LGMD), 45 distal myopathy, 22 hereditary neuropathy, 9 congenital myopathy/muscular dystrophy, 2 Emery-Dreyfuss muscular dystrophy, 13 channelopathy, 10 hereditary spastic paraplegia, 8 ALS, 3 congenital myasthenia and 3 mitochondrial participants. The 263 participants with no clear diagnosis after exome included 94 LGMD, 35 ALS 35, 57 Hirayama disease and 20 hereditary neuropathy participants. As ALS and Hirayama disease may occur without a monoallelic cause, removing these from metrics increased the genetic solved rate to 76% (of which 61% solved by WES). The AIIMS ICGNMD cohort is at an early stage in assessment, but is already enabling assessment of prevalence of inherited NMDs and their genetic spectrum in a Northern Indian population. It is delivering metrics on potential for genetic testing to provide a definitive diagnosis for specific clinical presentations. Our cohort's rich genetic and phenotypic data positions AIIMS to engage in inclusive therapeutic trials internationally. [ABSTRACT FROM AUTHOR]

Background and Objectives: Facioscapulohumeral muscular dystrophy (FSHD) represents the third most common muscular dystrophy in the general population and is characterized by progressive and often asymmetric muscle weakness of the face, upper extremities, arms, lower leg, and hip girdle. In FSHD type 1, contraction of the number of D4Z4 repeats to 1-10 on the chromosome 4-permissive allele (4qA) results in abnormal epigenetic derepression of the DUX4 gene in skeletal muscle. In FSHD type 2, epigenetic derepression of the DUX4 gene on the permissive allele (4qA) with normal-sized D4Z4 repeats (mostly 8-20) is caused by heterozygous pathogenic variants in chromatin modifier genes such as SMCHD1 , DNMT3B , or LRIF1 . We present validation of the optical genome mapping (OGM) platform for accurate mapping of the D4Z4 repeat size, followed by diagnostic testing of 547 cases with a suspected clinical diagnosis of FSHD and next-generation sequencing (NGS) of the SMCHD1 gene to identify cases with FSHD2., Methods: OGM with Bionano Genomics Saphyr and EnFocus FSHD analysis software was used to identify FSHD haplotypes and D4Z4 repeat number and compared with the gold standard of Southern blot-based diagnosis. A custom Agilent SureSelect enrichment kit was used to enrich SMCHD1 , followed by NGS on an Illumina system with 100-bp paired-end reads. Copy number variants were assessed using NxClinical software., Results: We performed OGM for the diagnosis of FSHD in 547 patients suspected of FSHD between December 2019 and December 2022, including 301 male (55%) and 246 female patients (45%). Overall, 308 of the referred patients were positive for D4Z4 contraction on a permissive haplotype, resulting in a diagnosis of FSHD1. A total of 252 of 547 patients were referred for concurrent testing for FSHD1 and FSHD2. This resulted in the identification of FSHD2 in 9/252 (3.6%) patients. In our FSHD2 cohort, the 4qA allele size ranged from 8 to 18 repeats. Among FSHD1-positive cases, 2 patients had biallelic contraction and 4 patients had homozygous contraction and showed early onset of clinical features. Nine of the 308 patients (3%) positive for 4qA contraction had mosaic 4q alleles with contraction on at least one 4qA allele. The overall diagnostic yield in our cohort was 58%., Discussion: A combination of OGM to identify the FSHD haplotype and D4Z4 repeat number and NGS to identify sequence and copy number variants in the SMCHD1 gene is a practical and cost-effective option with increased precision for accurate diagnosis of FSHD types 1 and 2., Competing Interests: The authors report no relevant disclosures. Go to Neurology.org/NG for full disclosures., (Copyright © 2023 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American Academy of Neurology.)

Background and Aims: High-density lipoproteins (HDL) of patients with type 2 diabetes mellitus (T2DM) have impaired anti-inflammatory activities. The anti-inflammatory activity of HDL has been determined ex vivo after isolation by different methods from blood mostly obtained after overnight fasting. We first determined the effect of the HDL isolation method, and subsequently the effect of food intake on the anti-inflammatory function of HDL from T2DM patients., Methods: Blood was collected from healthy controls and T2DM patients after an overnight fast, and from T2DM patients 3 h after breakfast ( n  = 17 each). HDL was isolated by a two-step density gradient ultracentrifugation in iodixanol (HDL DGUC2 ), by sequential salt density flotation (HDL SEQ ) or by PEG precipitation (HDL PEG ). The anti-inflammatory function of HDL was determined by the reduction of the TNFα-induced expression of VCAM-1 in human coronary artery endothelial cells (HCAEC) and retinal endothelial cells (REC)., Results: HDL isolated by the three different methods from healthy controls inhibited TNFα-induced VCAM-1 expression in HCAEC. With apoA-I at 0.7 μM, HDL DGUC2 and HDL SEQ were similarly effective (16% versus 14% reduction; n  = 3; p  > 0.05) but less effective than HDL PEG (28%, p  < 0.05). Since ultracentrifugation removes most of the unbound plasma proteins, we used HDL DGUC2 for further experiments. With apoA-I at 3.2 μM, HDL from fasting healthy controls and T2DM patients reduced TNFα-induced VCAM-1 expression in HCAEC by 58 ± 13% and 51 ± 20%, respectively ( p  = 0.35), and in REC by 42 ± 13% and 25 ± 18%, respectively ( p  < 0.05). Compared to preprandial HDL, postprandial HDL from T2DM patients reduced VCAM-1 expression by 56 ± 16% (paired test: p  < 0.001) in HCAEC and by 34 ± 13% (paired test: p  < 0.05) in REC., Conclusions: The ex vivo anti-inflammatory activity of HDL is affected by the HDL isolation method. Two-step ultracentrifugation in an iodixanol gradient is a suitable method for HDL isolation when testing HDL anti-inflammatory function. The anti-inflammatory activity of HDL from overnight fasted T2DM patients is significantly impaired in REC but not in HCAEC. The anti-inflammatory function of HDL is partly restored by food intake., Competing Interests: The authors declare that they have no conflict of interest., (© 2021 The Authors.)

Introduction: Electrical impedance myography (EIM) has been proposed as a noninvasive biomarker of muscle composition in facioscapulohumeral muscular dystrophy (FSHD). Here we determine the associations of EIM variables with muscle structure measured by MRI., Methods: We evaluated 20 patients with FSHD at two centers, comparing EIM measurements (resistance, reactance, and phase at 50, 100, and 211 kHZ) recorded from bilateral vastus lateralis, tibialis anterior, and medial gastrocnemius muscles to MRI skin and subcutaneous fat thickness, MRI T1-based muscle severity score (T1 muscle score), and MRI quantitative intramuscular Dixon fat fraction (FF)., Results: While reactance and phase both correlated with FF and T1 muscle score, 50 kHz reactance was most sensitive to muscle structure alterations measured by both T1 score (ρ = -0.71, P < .001) and FF (ρ = -0.74, P < .001)., Discussion: This study establishes the correlation of EIM with structural MRI features in FSHD and supports further evaluation of EIM as a potential biomarker in FSHD clinical trials., (© 2019 Wiley Periodicals, Inc.)

Background: Cardiac troponin T measured by a high-sensitivity assay (hs-cTnT) recently proved to be of prognostic value in several populations. The hs-cTnT assay may also improve risk stratification in acute dyspnea., Methods: We prospectively studied the prognostic value of hs-cTnT in 678 consecutive patients presenting to the emergency department with acute dyspnea. On the basis of conventional cardiac troponin T assay (cTnT) and hs-cTnT assay measurements, patients were divided into 3 categories: (1) neither assay increased (cTnT<0.03 μg/L, hs-cTnT<0.016 μg/L), (2) only hs-cTnT increased≥0.016 μg/L (cTnT<0.03 μg/L), and (3) both assays increased (cTnT≥0.03 μg/L, hs-cTnT≥0.016 μg/L). Moreover, the prognostic value of hs-cTnT was investigated if cTnT was not detectable (<0.01)., Results: One hundred seventy-two patients were in the lowest, 282 patients in the middle, and 223 patients in the highest troponin category. Patients in the second and third categories had significantly higher mortality compared to those in the first category (90-day mortality rate 2%, 10%, and 26% in groups 1, 2, and 3, respectively, P<0.001; 1-year mortality rate 9%, 21%, and 39%, P<0.001). Importantly, in patients with undetectable cTnT (n=347, 51%), increased hs-cTnT indicated worse outcome [90-day mortality, odds ratio 4.26 (95% CI 1.19-15.21); 1-year mortality, hazard ratio 2.27 (1.19-4.36), P=0.013], whereas N-terminal pro-brain-type natriuretic peptide (NT-proBNP) was not predictive of short-term outcome., Conclusions: hs-cTnT is associated with mortality in patients presenting with acute dyspnea. hs-cTnT concentrations provide additional prognostic information to cTnT and NT-proBNP testing in patients with cTnT concentrations below the detection limit. In particular, the hs-cTnT cutoff of 0.016 μg/L enables identification of low-risk patients.

Background: In the majority of facioscapulohumeral muscular dystrophy (FSHD) cases, the molecular basis of the disease is due to loss of subtelomeric D4Z4 repeat units at 4q35. Occasionally, an apparent absence of the contracted D4Z4 repeat is associated with FSHD. One explanation for this finding is a deletion in the region proximal to the D4Z4 repeat array that encompasses the p13E-11 (D4F104S1) probe-binding site used in the DNA diagnosis. The frequency of such proximally extended deletions is unknown, and to date, few patients have been described due to the difficulties in the molecular identification of such cases., Methods: We describe a family (DUK 2531) in which a contracted D4Z4 allele and a large proximal deletion of approximately 75 kb are segregating to 11 individuals. This is the largest deletion identified to date. Family DUK 2531 was initially thought to have normal D4Z4 fragment size and therefore unlinked to the 4q35 region (FSHD1B)., Results: Further molecular analysis of DUK 2531 reveals the presence of 10 repeat units (33 kb). The extended deletion includes the probe p13E-11 and B31 binding sites, the inverted repeat D4S2463, and genes FRG2 and TUBB4Q., Conclusion: Despite the length of the proximal deletion in this family, the range and severity of the clinical manifestations are typical for the disorder. Because such deletions can lead to misinterpretation in the diagnostic setting, this suggests the need for additional diagnostic tests in facioscapulohumeral muscular dystrophy.

Leukoencephalopathy with vanishing white matter (VWM) is an inherited brain disease that occurs mainly in children. The course is chronic-progressive with additional episodes of rapid deterioration following febrile infection or minor head trauma. We have identified mutations in EIF2B5 and EIF2B2, encoding the epsilon- and beta-subunits of the translation initiation factor eIF2B and located on chromosomes 3q27 and 14q24, respectively, as causing VWM. We found 16 different mutations in EIF2B5 in 29 patients from 23 families. We also found two distantly related individuals who were homozygous with respect to a missense mutation in EIF2B2, affecting a conserved amino acid. Three other patients also had mutations in EIF2B2. As eIF2B has an essential role in the regulation of translation under different conditions, including stress, this may explain the rapid deterioration of people with VWM under stress. Mutant translation initiation factors have not previously been implicated in disease.

Chromosomal rearrangements occur more frequently in subtelomeric domains than in other regions of the genome and are often associated with human pathology. To further elucidate the plasticity of subtelomeric domains, we examined the 3.3 kb D4Z4 repeat array on chromosome 4 and its homologue on chromosome 10 in 208 Dutch blood donors by pulsed field gel electrophoresis. These subtelomeric repeats are known to rearrange and partial deletions of this polymorphic array on chromosome 4 are associated with facioscapulohumeral muscular dystrophy (FSHD), an autosomal dominant myopathy. Our results show that mitotic rearrangements occur frequently as 3% of individuals display somatic mosaicism for a repeat expansion or contraction explaining the high variability of subtelomeric repeat array sizes. Translocated 4-type repeat arrays on chromosome 10 and the reverse configuration of 10-type repeat arrays on chromosome 4 are observed in 21% of individuals. The translocated repeat arrays on chromosome 4 tend to be more heterogeneous than 4-type repeats on chromosome 10. The repeat length on chromosome 4 is on average larger than on chromosome 10. But on both chromosomes we observe a multi-modal repeat length distribution with equidistant peaks at intervals of 65 kb, possibly reflecting a higher-order chromatin structure. Interestingly, in as many as six random blood donors (3%) we identified FSHD-sized 4-type repeat arrays. Assuming that these individuals are clinically unaffected, these results imply an incomplete penetrance in the upper range of FSHD alleles. Overall, the observed dynamic characteristics of these homologous domains may serve as a model for subtelomeric plasticity.

Autosomal dominant facioscapulohumeral muscular dystrophy (FSHD) is caused by deletion of most copies of the 3.3-kb subtelomeric D4Z4 repeat array on chromosome 4q. The molecular mechanisms behind the deletion and the high proportion of new mutations have remained elusive. We surveyed 35 de novo FSHD families and found somatic mosaicism in 40% of cases, in either the patient or an asymptomatic parent. Mosaic males were typically affected; mosaic females were more often the unaffected parent of a nonmosaic de novo patient. A genotypic-severity score, composed of the residual repeat size and the degree of somatic mosaicism, yields a consistent relationship with severity and age at onset of disease. Mosaic females had a higher proportion of somatic mosaicism than did mosaic males. The repeat deletion is significantly enhanced by supernumerary homologous repeat arrays. In 10% of normal chromosomes, 4-type repeat arrays are present on chromosome 10. In mosaic individuals, 4-type repeats on chromosome 10 are almost five times more frequent. The reverse configuration, also 10% in normal chromosomes, was not found, indicating that mutations may arise from transchromosomal interaction, to which the increase in 4-type repeat clusters is a predisposing factor. The somatic mosaicism suggests a mainly mitotic origin; mitotic interchromosomal gene conversion or translocation between fully homologous 4-type repeat arrays may be a major mechanism for FSHD mutations.

The human beta-tubulin supergene family consists of several isotypes with many associated pseudogenes. Here we report the identification of yet another beta-tubulin sequence designated TUBB4Q. This tubulin maps 80 kb proximal to the facioscapulohumeral muscular dystrophy (FSHD1) associated D4Z4 repeats on chromosome 4q35. The genomic structure contains four exons encoding a putative protein of 434 amino acids. The TUBB4Q nucleotide and protein sequence show 87% and 86% homology to beta2-tubulin, respectively. Although the genomic structure shows all functional aspects of a genuine gene, no transcript could be detected. TUBB4Q-related sequences were identified on multiple chromosomes. Since these sequences mutually exhibit a high nucleotide sequence homology, they presumably belong to a novel subfamily of beta-tubulin genes. Although the chromosome 4q35 tubulin-member probably represents a pseudogene, ectopic expression due to a postulated position effect variegation (PEV), makes TUBB4Q an ideal dominant-negative candidate gene for FSHD1., (Copyright 2000 S. Karger AG, Basel)

We report the cloning of a cDNA for the mouse unconventional myosin Myo9b, the orthologue of the rat myr5 and human MYOIXb genes. A full-length spleen cDNA of 7087bp encoding a protein of 1961 amino acids was isolated. By RT-PCR, we show that Myo9b is expressed in a wide range of tissues, including heart, brain, muscle and inner ear. In addition, we have identified two alternatively spliced exons. Equivalent exons have not been previously reported for either the human or rat homologues. These exons are located in the Myo9b specific actin-binding site insert of the head domain and in the tail region. A third splice form utilizing an alternative reading frame within the 3'UTR is also described. Several polymorphisms within the coding region were identified; of interest is an in-frame 33bp imperfect duplication within the tail region that was observed only in the C57Bl/6 strain. Myo9b has been previously mapped to mouse chromosome 8 and is a candidate for the mouse mutations myodystrophy and quinky.

Facioscapulohumeral muscular dystrophy (FSHD) is caused by the size reduction of a polymorphic repeat array on 4q35. Probe p13E-11 recognises this chromosomal rearrangement and is generally used for diagnosis. However, diagnosis of FSHD is complicated by three factors. First, the probe cross hybridises to a highly homologous repeat array locus on chromosome 10q26. Second, although a BlnI polymorphism allows discrimination between the repeat units on chromosomes 4 and 10 and greatly facilitates FSHD diagnosis, the occurrence of translocations between chromosomes 4 and 10 further complicates accurate FSHD diagnosis. Third, the recent identification of deletions of p13E-11 in both control and FSHD populations is an additional complicating factor. Although pulsed field gel electrophoresis is very useful and sometimes necessary to detect these rearrangements, this technique is not operational in most FSHD diagnostic laboratories. Moreover, repeat arrays >200 kb are often difficult to detect and can falsely suggest a deletion of p13E-11. Therefore, we have developed an easy and reliable Southern blotting method to identify exchanges between 4 type and 10 type repeat arrays and deletions of p13E-11. This BglII-BlnI dosage test addresses all the above mentioned complicating factors and can be carried out in addition to the standard Southern blot analysis for FSHD diagnosis as performed in most laboratories. It will enhance the specificity and sensitivity of conventional FSHD diagnosis to the values obtained by PFGE based diagnosis of FSHD. Moreover, this study delimits the FSHD candidate gene region by mapping the 4;10 translocation breakpoint proximal to the polymorphic BlnI site in the first repeat unit.

The autosomal dominant myopathy facioscapulohumeral muscular dystrophy (FSHD) is causally related to a short Eco RI fragment detected by probe p13E-11. This remnant fragment is the result of a deletion of an integral number of tandemly arrayed 3.3 kb repeat units (D4Z4) on 4q35. Despite intensive efforts, no transcribed sequences have been identified within this array. Previously, we have shown that these repeats on 4q35 have been exchanged for a similar highly homologous repeat locus on 10q26 in 20% of the population and that a short chromosome 10-like array on 4q35 also results in FSHD. Here, we describe the hybrid structure of some of these repeat arrays, reflecting additional sub-telomeric instability. In three healthy individuals carrying a 4-like repeat on chromosome 10 or vice versa, one repeat array was shown to consist of hybrid clusters of 4-derived and 10-derived repeat units. Moreover, employing pulsed field gel electrophoresis analysis, we identified two unrelated individuals carrying deletions of a chromosomal segment (p13E-11) proximal to the repeat locus. These deletions were not associated with FSHD. In one of these cases, however, an expansion of the deletion into the repeat array was observed in one of his children suffering from FSHD. These data provide additional evidence for instability of this sub-telomeric region and suggests that the length of the repeat, and not its intrinsic properties, is crucial to FSHD. Moreover, they are in agreement with the hypothesis that FSHD is caused by a position effect in which the repeat structure influences the expression of genes nearby. Therefore, the region deleted proximal to the repeat locus in healthy individuals can be instrumental to refine the critical region for FSHD1.

The human autosomal dominant neuromuscular disorder facioscapulohumeral muscular dystrophy (FSHD) is associated with deletions within a complex tandem DNA repeat (D4Z4) on Chromosome (Chr) 4q35. The molecular mechanism underlying this association of FSHD with DNA rearrangements is unknown, and, thus far, no gene has been identified within the repeat. We isolated a gene mapping 100 kb proximal to D4Z4 (FSHD Region Gene 1:FRG1), but were unable to detect any alterations in total or allele-specific mRNA levels of FRG1 in FSHD patients. Human Chr 4q35 exhibits synteny homology with the region of mouse Chr 8 containing the gene for the myodystrophy mutation (myd), a possible mouse homolog of FSHD. We report the cloning of the mouse gene (Frg1) and show that it maps to mouse Chr 8. Using a cross segregating the myd mutation and the European Collaborative Interspecific Backcross, we showed that Frg1 maps proximal to the myd locus and to the Clc3 and Ant1 genes.

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant myopathy, clinically characterized by asymmetric weakness of muscles in the face, shoulder girdle and upper arm. Deletion of an integral number of 3.3 kb repeated units within a highly polymorphic EcoRI fragment at chromosome 4q35, generating a relatively short EcoRI fragment (< 35 kb), has been shown to cause FSHD1. Probe p13E-11 detects these short fragments in FSHD1 patients, and has therefore been used for diagnostic DNA analysis. However, the reliability of this analysis has been hampered by cross-hybridization of p13E-11 to chromosome 10q26-linked EcoRI fragments of comparable size, which also contain a variable number of 3.3 kb repeated units. Recently, a BinI restriction site was identified within each of the repeated units derived from chromosome 10q26, which enables differentiation of the two polymorphic p13E-11 loci in most cases without haplotype analysis. Remarkably, applying the differential analysis to screen DNA of 160 Dutch cases referred to us for FSHD1 diagnosis, we obtained evidence for subtelomeric exchange of 3.3 kb repeated units between chromosomes 4q35 and 10q26 in affected and unaffected individuals. Subsequently, analysis of 50 unrelated control samples indicated such exchange between chromosomes 4q35 and 10q26 in at least 20% of the population. These subtelomeric rearrangements have generated a novel interchromosomal polymorphism, which has implications for the specificity and sensitivity of the differential restriction analysis for diagnostic purposes. Moreover, the high frequency of the interchromosomal exchanges of 3.3 kb repeated units suggests that they probably do not contain (part of) the FSHD1 gene, and supports position effect variegation as the most likely mechanism for FSHD1.

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant, neuromuscular disorder characterized by progressive weakness of muscles in the face, shoulder and upper arm. Deletion of integral copies of a 3.3 kb repeated unit from the subtelomeric region on chromosome 4q35 has been shown to be associated with FSHD. These repeated units which are apparently not transcribed, map very close to the 4q telomere and belong to a 3.3 kb repeat family dispersed over heterochromatic regions of the genome. Hence, position effect variegation (PEV), inducing allele-specific transcriptional repression of a gene located more centromeric, has been postulated as the underlying genetic mechanism of FSHD. This hypothesis has directed the search for the FSHD gene to the region centromeric to the repeated units. A CpG island was identified and found to be associated with the 5' untranslated region of a novel human gene, FRG1 (FSHD Region Gene 1). This evolutionary conserved gene is located about 100 kb proximal to the repeated units and belongs to a multigene family with FRG1 related sequences on multiple chromosomes. The mature chromosome 4 FRG1 transcript is 1042 bp in length and contains nine exons which encode a putative protein of 258 amino acid residues. Transcription of FRG1 was detected in several human tissues including placenta, lymphocytes, brain and muscle. To investigate a possible PEV mechanism, allele-specific FRG1 steady-state transcript levels were determined using RNA-based single-strand conformation polymorphism (SSCP) analysis. A polymorphic fragment contained within the first exon of FRG1 was amplified from reverse transcribed RNA from lymphocytes and muscle biopsies of patients and controls. No evidence for PEV mediated repression of allelic transcription was obtained in these tissues. However, detection of PEV in FSHD patients may require analysis of more specific cell types at particular developmental stages.

Infection of tobacco by tobacco mosaic virus (TMV) induces coordinate expression of genes encoding acidic and basic beta-1,3-glucanase isoforms. These genes are differentially expressed in response to other treatments. Salicylate treatment induces acidic glucanase mRNA to a higher level than basic glucanase mRNA. Ethylene treatment and wounding strongly induce the basic glucanase genes but have little effect on genes encoding the acidic isoforms. Furthermore, the basic glucanase genes are constitutively expressed in roots and lower leaves of healthy plants, whereas the acidic glucanase genes are not. In order to investigate how these expression patterns are established, we fused promoter regions of an acidic and a basic glucanase gene to the beta-glucuronidase (GUS) reporter gene and examined expression of these constructs in transgenic tobacco plants. A fragment of 1750 bp and two 5'-truncated fragments of 650 bp and 300 bp of the acidic glucanase promoter were tested for induction of GUS gene expression after salicylate treatment and TMV infection. Upstream sequences of 1750 bp and 650 bp were sufficient for induction of the reporter gene by salicylate treatment and TMV infection, but the activity of the 300 bp fragment was strongly reduced. The results suggest that the 1750 bp upstream sequence of the acidic glucanase gene contains multiple regulatory elements. For the basic glucanase promoter it is shown that 1476 bp of upstream sequences were able to drive expression in response to TMV infection and ethylene treatment, but no response was found to incision wounding. Furthermore, high GUS activity was found in lower leaves and roots of healthy transgenic plants, carrying the 1476 bp basic glucanase promoter/GUS construct. When the promoter was truncated up to position -446 all activity was lost, indicating that the region between -1476 and -446 of the basic glucanase promoter is necessary for organ-specific and developmentally regulated expression as well as for induced expression in response to infection and other stress treatments.