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Contains fulltext : 229735.pdf (Publisher’s version ) (Closed access) BACKGROUND AND PURPOSE: The aim was to define the radiological picture of facioscapulohumeral muscular dystrophy 2 (FSHD2) in comparison with FSHD1 and to explore correlations between imaging and clinical/molecular data. METHODS: Upper girdle and/or lower limb muscle magnetic resonance imaging scans of 34 molecularly confirmed FSHD2 patients from nine European neuromuscular centres were analysed. T1-weighted and short-tau inversion recovery (STIR) sequences were used to evaluate the global pattern and to assess the extent of fatty replacement and muscle oedema. RESULTS: The most frequently affected muscles were obliquus and transversus abdominis, semimembranosus, soleus and gluteus minimus in the lower limbs; trapezius, serratus anterior, latissimus dorsi and pectoralis major in the upper girdle. Iliopsoas, popliteus, obturator internus and tibialis posterior in the lower limbs and subscapularis, spinati, sternocleidomastoid and levator scapulae in the upper girdle were the most spared. Asymmetry and STIR hyperintensities were consistent features. The pattern of muscle involvement was similar to that of FSHD1, and the combined involvement of trapezius, abdominal and hamstring muscles, together with complete sparing of iliopsoas and subscapularis, was detected in 91% of patients. Peculiar differences were identified in a rostro-caudal gradient, a predominant involvement of lower limb muscles compared to the upper girdle, and in the higher percentage of STIR hyperintensities in FSHD2. CONCLUSION: This multicentre study defines the pattern of muscle involvement in FSHD2, providing useful information for diagnostics and clinical trial design. Both similarities and differences between FSHD1 and FSHD2 were detected, which is also relevant to better understand the pathogenic mechanisms underlying the FSHD-related disease spectrum.

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant neuromuscular disorder that is characterized by extreme variability in symptoms, with females being less severely affected than males and presenting a higher proportion of asymptomatic carriers. The sex-related factors involved in the disease are not known. Here, we have utilized myoblasts isolated from FSHD patients (FSHD myoblasts) to investigate the effect of estrogens on muscle properties. Our results demonstrated that estrogens counteract the differentiation impairment of FSHD myoblasts without affecting cell proliferation or survival. Estrogen effects are mediated by estrogen receptor beta (ERbeta), which reduces chromatin occupancy and transcriptional activity of double homeobox 4 (DUX4), a protein whose aberrant expression has been implicated in FSHD pathogenesis. During myoblast differentiation, we observed that the levels and activity of DUX4 increased progressively and were associated with its enhanced recruitment in the nucleus. ERbeta interfered with this recruitment by relocalizing DUX4 in the cytoplasm. This work identifies estrogens as a potential disease modifier that underlie sex-related differences in FSHD by protecting against myoblast differentiation impairments in this disease.

Background Facioscapulohumeral muscular dystrophy is associated with an epigenetic defect on 4q subtelomere. This dystrophy is caused by contraction of the D4Z4 macrosatellite array on chromosome 4qter in FSHD1, or by functional impairment of SMCHD1, a chromatin modifier binding to D4Z4, in FSHD2. Both genetic defects lead to D4Z4 DNA hypomethylation associated with inappropriate expression in skeletal muscle of the D4Z4-encoded DUX4 transcription factor in the presence of a polymorphic polyadenylation signal (PAS) distal to the last D4Z4 unit (4qA). Currently, hypomethylation is not diagnostic per se because of the interference of non-pathogenic arrays and because it does not interrogate the presence of DUX4-PAS. Importantly, the methylation status of the DUX4-PAS critical region has not been thoroughly investigated. Methods We investigated, by bisulfite sequencing, the DNA methylation levels of the region distal to the D4Z4 array critical to FSHD development in PAS-positive alleles. Results Comparison of FSHD1, FSHD2 and control subjects showed highly significant differences of methylation levels in all CpGs tested. Noteworthy, one of these CpGs (CpG6) is able to discriminate the affected individuals with a sensitivity of 0.95 in a fully characterized samples, supporting the potential usefulness of this assay for FSHD diagnosis. Moreover, our study evidenced a relationship between PAS-specific methylation and severity of the disease. Conclusions These data point to CpGs distal to the D4Z4 array as a critical region that summarizes multiple factors affecting epigenetics of FSHD. Additionally, methylation analysis of this region allows the establishment of a rapid and sensitive tool for FSHD diagnosis

Contains fulltext : 58455.pdf (Publisher’s version ) (Closed access) BACKGROUND: Autosomal dominant facioscapulohumeral muscular dystrophy (FSHD) is associated with partial deletion of the subtelomeric D4Z4 repeat array on chromosome 4qter. This chromosomal rearrangement may result in regional chromatin relaxation and transcriptional deregulation of genes nearby. METHODS AND RESULTS: Here we describe the isolation and characterisation of FRG2, a member of a chromosomally dispersed gene family, mapping only 37 kb proximal to the D4Z4 repeat array. Homology and motif searches yielded no clues to the function of the predicted protein. FRG2 expression is undetectable in all tissues tested except for differentiating myoblasts of FSHD patients, which display low, yet distinct levels of FRG2 expression, partly from chromosome 4 but predominantly originating from its homologue on chromosome 10. However, in non-FSHD myopathy patients only distantly related FRG2 homologues are transcribed, while differentiating myoblasts from healthy controls fail to express any member of this gene family. Moreover, fibroblasts of FSHD patients and control individuals undergoing forced Ad5-MyoD mediated myogenesis show expression of FRG2 mainly originating from chromosome 10. Luciferase reporter assays show that the FRG2 promoter region can direct high levels of expression but is inhibited by increasing numbers of D4Z4 repeat units. Transient transfection experiments with FRG2 fusion-protein constructs reveal nuclear localisation and apparently FRG2 overexpression causes a wide range of morphological changes. CONCLUSION: The localisation of FRG2 genes close to the D4Z4 repeats on chromosome 4 and 10, their transcriptional upregulation specifically in FSHD myoblast cultures, potential involvement in myogenesis, and promoter properties qualify FRG2 as an attractive candidate for FSHD pathogenesis.

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.

Genotype analysis by using the p13E-11 probe and other 4q35 polymorphic markers was performed in 122 Italian facioscapulohumeral muscular dystrophy families and 230 normal controls. EcoRI-BlnI double digestion was routinely used to avoid the interference of small EcoRI fragments of 10qter origin that were found in 15% of the controls. An EcoRI fragment ranging between 10 and 28 kb that was resistant to BlnI digestion was detected in 114 of 122 families (93%) comprising 76 familial and 38 isolated cases. Among the unaffected individuals, 3 were somatic mosaics and 7, carrying an EcoRI fragment larger than 20 kb, could be rated as nonpenetrant gene carriers. In a cohort of 165 patients with facioscapulohumeral muscular dystrophy we found an inverse correlation between fragment size and clinical severity. A severe lower limb involvement was observed in 100% of patients with an EcoRI fragment size of 10 to 13 kb (1-2 KpnI repeats left), in 53% of patients with a fragment size of 16 to 20 kb (3-4 KpnI repeats left), and in 19% of patients with a fragment size larger than 21 kb (>4 KpnI repeats left). Our results confirm that the size of the fragment is a major factor in determining the facioscapulohumeral muscular dystrophy phenotype and that it has an impact on clinical prognosis and genetic counseling of the disease.

In the majority of facioscapulohumeral muscular dystrophy (FSHD) families (about 95%) the genetic defect has been identified as a deletion of a variable number of KpnI repeats in the 4q35 region, although no specific transcripts from this locus have been isolated so far. Molecular diagnosis is based on the detection by probe p13E–11 of EcoRI small fragments, in the range 10–28 kb, that are resistant to BlnI digestion. In family studies this probe is used with other 4q35 polymorphic markers to assign the haplotype associated with the disease. So far, we performed DNA analysis in 145 FSHD families and identified the 4q35 DNA rearrangement not only in affected individuals, but also in healthy subjects at risk of transmitting the disease, such as non-penetrant gene carriers and somatic mosaics. In addition we applied prenatal tests to 19 fetuses, using DNA extracted from chorionic villi samples (CVS) at 10–11 weeks of gestation. The FSHD status, as determined by the presence of BlnI-resistant small fragments associated with the at risk haplotype, was assessed in nine fetuses; in the remaining 10 cases the disease was excluded. Our results show that molecular analysis of 4q35 rearrangements is a reliable indirect method to perform diagnostic, predictive and prenatal tests in FSHD.

p13E-11, a probe (D4F104S1 locus) derived from chromosome 4q35, detects EcoRI-rearranged fragments less than 28 kb in both sporadic and familial cases of facioscapulohumeral muscular dystrophy (FSHD). These fragments are smaller than those observed in healthy individuals. The interpretation of Southern blots is complicated by the fact that p13E-11 reveals two pairs of polymorphic alleles, one 4q35-specific and the other unlinked to 4q35, that sometimes overlap each other. We cloned a non-4q35 13-kb fragment not related to the disease from a sporadic FSHD patient of Italian origin. Haplotype analysis and in situ hybridization experiments showed that this fragment was located on the 10qter region. Restriction mapping of the 10qter clone, when compared with the 4q35 fragment, indicates a similar arrangement of KpnI tandemly repeated units and flanking sequences. However 4q35 and 10q26 EcoRI clones can be distinguished by restriction analysis with SfiI and StyI. This observation could be exploited for future applications in the field of molecular diagnosis and genetic counseling. In addition the isolation of two 10q26 cosmid clones (D10S1484 and D10S1485) from a human genomic library and the construction of a detailed physical map, spanning about 40 kb, showed that the structural homology extended upstream of the EcoRI sites, suggesting that a duplicated FSHD locus resided in the subtelomeric region of the long arm of chromosome 10. We cannot exclude the involvement of the duplicated locus in the molecular mechanism of the disease and in the genetic heterogeneity of FSHD syndromes.

The highly conserved facioscapulohumeral muscular dystrophy (FSHD) region gene 1 (FRG1) was initially cloned as candidate gene of unknown function for FSHD. To explore the biological function of the FRG1 protein (FRG1P), we studied its cellular localisation in untransfected and FRG1 transfected cell lines. In interphase cells, FRG1P is localised in the dense structures of the nucleolus, in Cajal bodies, and in 60–80% of cells in nuclear speckles. A time course study revealed that FRG1P accumulates in nuclear speckles before its appearance in nucleoli, whereas the localisation in Cajal bodies remains unchanged, as does the localisation of NHPX protein. In accordance with the presence of FRG1P in these nuclear structures, transcription inhibition experiments showed an effect of RNA polymerases I and II on the localisation of FRG1P. Finally, by deletion of the predicted nuclear localisation signals of FRG1P, we demonstrated that both signals are necessary for this subnuclear localisation. FRG1P is an attractive candidate for the pathogenesis of FSHD because of its high evolutionary conservation; its transcriptional deregulation in FSHD; and its colocalisation with proteins that are defective in the neuromuscular disorders oculopharyngeal muscular dystrophy (OPMD) and spinal muscular atrophy (SMA). FRG1 (FSHD Region Gene 1, accession number L76159) was isolated as the first candidate gene for the autosomal dominant myopathy, facioscapulohumeral muscular dystrophy, in 1996.1 FSHD is primarily characterised by progressive weakness and atrophy of the facial, upper arm, and shoulder muscles.2 The FSHD locus on 4q35 contains a polymorphic repeat array consisting of 3.3 kb repeated elements (D4Z4). In control individuals, this array may vary between 11–100 units, whereas FSHD patients carry 1–10 units on one of their chromosomes 4, owing to the deletion of an integral number of D4Z4 units.3 It is becoming increasingly evident that FSHD is caused by a local chromatin alteration, …

SummaryPhysical mapping and in situ hybridization experiments have shown that a duplicated locus with a structural organization similar to that of the 4q35 locus implicated in facioscapulohumeral muscular dystrophy is present in the subtelomeric portion of 10q. We performed sequence analysis of the p13E-11 probe and of the adjacent KpnI tandem-repeat unit derived from a 10qter cosmid clone and compared our results with those published, by other laboratories, for the 4q35 region. We found that the sequence homology range is 98%–100% and confirmed that the only difference that can be exploited for differentiation of the 10qter from the 4q35 alleles is the presence of an additional BlnI site within the 10qter KpnI repeat unit. In addition, we observed that the high degree of sequence homology does facilitate interchromosomal exchanges resulting in displacement of the whole set of BlnI-resistant or BlnI-sensitive KpnI repeats from one chromosome to the other. However, partial translocations escape detection if the latter simply relies on the hybridization pattern from double digestion with EcoRI/BlnI and with p13E-11 as a probe. We discovered that the restriction enzyme Tru9I cuts at both ends of the array of KpnI repeats of different chromosomal origins and allows the use of cloned KpnI sequences as a probe by eliminating other spurious fragments. This approach coupled with BlnI digestion permitted us to investigate the structural organization of BlnI-resistant and BlnI-sensitive units within translocated chromosomes of 4q35 and 10q26 origin. A priori, the possibility that partial translocations could play a role in the molecular mechanism of the disease cannot be excluded.

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 p13E-11 probe has been shown to detect DNA rearrangements in sporadic and familial cases of FSHD. Its use, however, has been hampered by the fact that it detects at least two pairs of EcoRI alleles, one derived from the 4q35 region (D4F104S1), the other from 10q26 (D10F104S2). We have cloned p13E-11 EcoRI fragments from the 4q35 and 10q26 subtelomeric regions and shown the presence of several restriction site differences within the KpnI tandem repeat units. The two loci present a different distribution of restriction sites for the enzyme BlnI which allows differential cleavage of the KpnI units derived from 10q26, leaving intact the 4q35 pair of alleles. This method of differential restriction greatly facilitates the interpretation of Southern blots obtained from affected and unaffected subjects, with an important improvement in reliability for diagnosis and genetic counselling. In addition, this method can be used to investigate the molecular mechanism of the 4q35 rearrangement implicated in the disease and to ascertain whether the rearrangement is because of interchromosomal exchange between 4qter and 10qter KpnI repeats.