DNA rearrangements in Japanese facioscapulohumeral muscular dystrophy patients: clinical correlations

Type 1 FSHD with 6-10 Repeated Units: Factors Underlying Severity in Index Cases and Disease Penetrance in Their Relatives Attention

Molecular defects in type 1 facioscapulohumeral muscular dystrophy (FSHD) are caused by a heterozygous contraction of the D4Z4 repeat array from 1 to 10 repeat units (RUs) on 4q35. This study compared (1) the phenotype and severity of FSHD1 between patients carrying 6-8 vs. 9-10 RUs, (2) the amount of methylation in different D4Z4 regions between patients with FSHD1 with different clinical severity scores (CSS). This cross-sectional multicenter study was conducted to measure functional scales and for genetic analysis. Patients were classified into two categories according to RUs: Group 1, 6-8; Group 2, 9-10. Methylation analysis was performed in 27 patients. A total of 99 carriers of a contracted D4Z4 array were examined. No significant correlations between RUs and CSS (r = 0.04, p = 0.73) and any of the clinical outcome scales were observed between the two groups. Hypomethylation was significantly more pronounced in patients with high CSS (>3.5) than those with low CSS (<1.5) (in DR1 and 5P), indicating that the extent of hypomethylation might modulate disease severity. In Group 1, the disease severity is not strongly correlated with the allele size and is mostly correlated with the methylation of D4Z4 regions.

The Genetics and Epigenetics of Facioscapulohumeral Muscular Dystrophy

Facioscapulohumeral muscular dystrophy (FSHD), a progressive myopathy that afflicts individuals of all ages, provides a powerful model of the complex interplay between genetic and epigenetic mechanisms of chromatin regulation. FSHD is caused by dysregulation of a macrosatellite repeat, either by contraction of the repeat or by mutations in silencing proteins. Both cases lead to chromatin relaxation and, in the context of a permissive allele, aberrant expression of the DUX4 gene in skeletal muscle. DUX4 is a pioneer transcription factor that activates a program of gene expression during early human development, after which its expression is silenced in most somatic cells. When misexpressed in FSHD skeletal muscle, the DUX4 program leads to accumulated muscle pathology. Epigenetic regulators of the disease locus represent particularly attractive therapeutic targets for FSHD, as many are not global modifiers of the genome, and altering their expression or activity should allow correction of the underlying defect.

Genotype-phenotype correlations in FSHD

BACKGROUND

Facial-scapular-humeral myodystrophy Landouzy-Dejerine (FSHD) is an autosomal dominant disease, the basis of its pathogenesis is ectopic expression of the transcription factor DUX4 in skeletal muscle. There are two types of the disease: FSHD1 (MIM:158900) and FSHD2 (MIM: 158901), which have different genetic causes but are phenotypically indistinguishable. In FSHD1, partial deletion of the D4Z4 repeats on the 4th chromosome affects the expression of DUX4, whereas FSHD2 is caused by the mutations in the protein regulating the methylation status of chromatin - SMCHD1. High variability of clinical picture, both intra - and inter-family indicates a large number of factors influencing clinical picture. There are key genetic, epigenetic and gender factors that influence the expressivity and penetrance of the disease. Using only one of these factors allows just a rough prediction of the course of the disease, which indicates the combined effect of all of the factors on the DUX4 expression and on the clinical picture.

RESULTS

In this paper, we analyzed the impact of genetic, epigenetic and gender differences on phenotype and the possibility of using them for disease prognosis and family counselling.

CONCLUSIONS

Key pathogenesis factors have been identified for FSHD. However, the pronounced intra - and inter-family polymorphism of manifestations indicates a large number of modifiers of the pathological process, many of which remain unknown.

Facioscapulohumeral Muscular Dystrophy

Facioscapulohumeral Muscular Dystrophy is a common form of muscular dystrophy that presents clinically with progressive weakness of the facial, scapular, and humeral muscles, with later involvement of the trunk and lower extremities. While typically inherited as autosomal dominant, facioscapulohumeral muscular dystrophy (FSHD) has a complex genetic and epigenetic etiology that has only recently been well described. The most prevalent form of the disease, FSHD1, is associated with the contraction of the D4Z4 microsatellite repeat array located on a permissive 4qA chromosome. D4Z4 contraction allows epigenetic derepression of the array, and possibly the surrounding 4q35 region, allowing misexpression of the toxic DUX4 transcription factor encoded within the terminal D4Z4 repeat in skeletal muscles. The less common form of the disease, FSHD2, results from haploinsufficiency of the SMCHD1 gene in individuals carrying a permissive 4qA allele, also leading to the derepression of DUX4, further supporting a central role for DUX4. How DUX4 misexpression contributes to FSHD muscle pathology is a major focus of current investigation. Misexpression of other genes at the 4q35 locus, including FRG1 and FAT1, and unlinked genes, such as SMCHD1, has also been implicated as disease modifiers, leading to several competing disease models. In this review, we describe recent advances in understanding the pathophysiology of FSHD, including the application of MRI as a research and diagnostic tool, the genetic and epigenetic disruptions associated with the disease, and the molecular basis of FSHD. We discuss how these advances are leading to the emergence of new approaches to enable development of FSHD therapeutics. © 2017 American Physiological Society. Compr Physiol 7:1229-1279, 2017.

Polycomb repressive complex 1 provides a molecular explanation for repeat copy number dependency in FSHD muscular dystrophy

Repression of repetitive elements is crucial to preserve genome integrity and has been traditionally ascribed to constitutive heterochromatin pathways. FacioScapuloHumeral Muscular Dystrophy (FSHD), one of the most common myopathies, is characterized by a complex interplay of genetic and epigenetic events. The main FSHD form is linked to a reduced copy number of the D4Z4 macrosatellite repeat on 4q35, causing loss of silencing and aberrant expression of the D4Z4-embedded DUX4 gene leading to disease. By an unknown mechanism, D4Z4 copy-number correlates with FSHD phenotype. Here we show that the DUX4 proximal promoter (DUX4p) is sufficient to nucleate the enrichment of both constitutive and facultative heterochromatin components and to mediate a copy-number dependent gene silencing. We found that both the CpG/GC dense DNA content and the repetitive nature of DUX4p arrays are important for their repressive ability. We showed that DUX4p mediates a copy number-dependent Polycomb Repressive Complex 1 (PRC1) recruitment, which is responsible for the copy-number dependent gene repression. Overall, we directly link genetic and epigenetic defects in FSHD by proposing a novel molecular explanation for the copy number-dependency in FSHD pathogenesis, and offer insight into the molecular functions of repeats in chromatin regulation.

Bimaxillary Osteotomy for Jaw Deformity With Facioscapulohumeral Muscular Dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is a subtype of muscular dystrophies which reduces the muscle strength, especially the regions of scapular, shoulder, and upper arms, progressively. According to progressive muscle weakness in FSHD, postoperative stability of patient with FSHD after orthognathic surgery is not reliably acquired same as healthy subjects. A 32-year-old woman with FSHD underwent orthodontic and orthognathic surgical treatment due to jaw deformity. She has been followed up more than 3 years after surgery and acquired skeletal stability. This patient is the first report that showed long-term skeletal stability after orthognathic surgery in patient with FSHD. This patient report suggests that it is possible to apply orthognathic surgical treatment to patients with FSHD.

Genetic and epigenetic contributors to FSHD

Facioscapulohumeral dystrophy (FSHD) is an autosomal dominant muscle disorder characterized by distinct chromatin changes including DNA hypomethylation of the D4Z4 macrosatellite repeat array on a disease-permissive 4qA allele and aberrant expression of the D4Z4-embedded DUX4 retrogene in skeletal muscle. Insufficient epigenetic repression of the D4Z4 repeat is the result of at least two different genetic mechanisms leading to two forms of disease, FSHD1 and FSHD2. In the case of FSHD1, a contraction of the D4Z4 repeat array is disease causing whereas FSHD2 is most often caused by mutations in the structural maintenance of chromosomes hinge domain 1 (SMCHD1) gene. Recent studies indicate that a combination of genetic and epigenetic factors that act on the D4Z4 repeat array determine the probability of DUX4 expression in skeletal muscle and disease penetrance and progression.

Evidence-based guideline summary: Evaluation, diagnosis, and management of facioscapulohumeral muscular dystrophy: Report of the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology and the Practice Issues Review Panel of the American Association of Neuromuscular & Electrodiagnostic Medicine

OBJECTIVE

To develop recommendations for the evaluation, diagnosis, prognostication, and treatment of facioscapulohumeral muscular dystrophy (FSHD) from a systematic review and analysis of the evidence.

METHODS

Relevant articles were analyzed in accordance with the American Academy of Neurology classification of evidence schemes for diagnostic, prognostic, and treatment studies. Recommendations were linked to the strength of the evidence and other factors.

RESULTS AND RECOMMENDATIONS

Available genetic testing for FSHD type 1 is highly sensitive and specific. Although respiratory insufficiency occurs rarely in FSHD, patients with severe FSHD should have routine pulmonary function testing. Routine cardiac screening is not necessary in patients with FSHD without cardiac symptoms. Symptomatic retinal vascular disease is very rare in FSHD. Exudative retinopathy, however, is potentially preventable, and patients with large deletions should be screened through dilated indirect ophthalmoscopy. The prevalence of clinically relevant hearing loss is not clear. In clinical practice, patients with childhood-onset FSHD may have significant hearing loss. Because undetected hearing loss may impair language development, screening through audiometry is recommended for such patients. Musculoskeletal pain is common in FSHD and treating physicians should routinely inquire about pain. There is at present no effective pharmacologic intervention in FSHD. Available studies suggest that scapular fixation is safe and effective. Surgical scapular fixation might be cautiously offered to selected patients. Aerobic exercise in FSHD appears to be safe and potentially beneficial. On the basis of the evidence, patients with FSHD might be encouraged to engage in low-intensity aerobic exercises.

Facioscapulohumeral muscular dystrophy as a model for epigenetic regulation and disease

SIGNIFICANCE

Aberrant epigenetic regulation is an integral aspect of many diseases and complex disorders. Facioscapulohumeral muscular dystrophy (FSHD), a progressive myopathy that afflicts individuals of all ages, is caused by disrupted genetic and epigenetic regulation of a macrosatellite repeat. FSHD provides a powerful model to investigate disease-relevant epigenetic modifiers and general mechanisms of epigenetic regulation that govern gene expression.

RECENT ADVANCES

In the context of a genetically permissive allele, the one aspect of FSHD that is consistent across all known cases is the aberrant epigenetic state of the disease locus. In addition, certain mutations in the chromatin regulator SMCHD1 (structural maintenance of chromosomes hinge-domain protein 1) are sufficient to cause FSHD2 and enhance disease severity in FSHD1. Thus, there are multiple pathways to generate the epigenetic dysregulation required for FSHD.

CRITICAL ISSUES

Why do some individuals with the genetic requirements for FSHD develop disease pathology, while others remain asymptomatic? Similarly, disease progression is highly variable among individuals. What are the relative contributions of genetic background and environmental factors in determining disease manifestation, progression, and severity in FSHD? What is the interplay between epigenetic factors regulating the disease locus and which, if any, are viable therapeutic targets?

FUTURE DIRECTIONS

Epigenetic regulation represents a potentially powerful therapeutic target for FSHD. Determining the epigenetic signatures that are predictive of disease severity and identifying the spectrum of disease modifiers in FSHD are vital to the development of effective therapies.

The FSHD2 gene SMCHD1 is a modifier of disease severity in families affected by FSHD1

Facioscapulohumeral muscular dystrophy type 1 (FSHD1) is caused by contraction of the D4Z4 repeat array on chromosome 4 to a size of 1-10 units. The residual number of D4Z4 units inversely correlates with clinical severity, but significant clinical variability exists. Each unit contains a copy of the DUX4 retrogene. Repeat contractions are associated with changes in D4Z4 chromatin structure that increase the likelihood of DUX4 expression in skeletal muscle, but only when the repeat resides in a genetic background that contains a DUX4 polyadenylation signal. Mutations in the structural maintenance of chromosomes flexible hinge domain containing 1 (SMCHD1) gene, encoding a chromatin modifier of D4Z4, also result in the increased likelihood of DUX4 expression in individuals with a rare form of FSHD (FSHD2). Because SMCHD1 directly binds to D4Z4 and suppresses somatic expression of DUX4, we hypothesized that SMCHD1 may act as a genetic modifier in FSHD1. We describe three unrelated individuals with FSHD1 presenting an unusual high clinical severity based on their upper-sized FSHD1 repeat array of nine units. Each of these individuals also carries a mutation in the SMCHD1 gene. Familial carriers of the FSHD1 allele without the SMCHD1 mutation were only mildly affected, suggesting a modifier effect of the SMCHD1 mutation. Knocking down SMCHD1 in FSHD1 myotubes increased DUX4 expression, lending molecular support to a modifier role for SMCHD1 in FSHD1. We conclude that FSHD1 and FSHD2 share a common pathophysiological pathway in which the FSHD2 gene can act as modifier for disease severity in families affected by FSHD1.

Expression of DUX4 in zebrafish development recapitulates facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is a common form of muscular dystrophy characterized by an asymmetric progressive weakness and wasting of the facial, shoulder and upper arm muscles, frequently accompanied by hearing loss and retinal vasculopathy. FSHD is an autosomal dominant disease linked to chromosome 4q35, but the causative gene remains controversial. DUX4 is a leading candidate gene as causative of FSHD. However, DUX4 expression is extremely low in FSHD muscle, and there is no DUX4 animal model that mirrors the pathology in human FSHD. Here, we show that the misexpression of very low levels of human DUX4 in zebrafish development recapitulates the phenotypes seen in human FSHD patients. Microinjection of small amounts of human full-length DUX4 (DUX4-fl) mRNA into fertilized zebrafish eggs caused asymmetric abnormalities such as less pigmentation of the eyes, altered morphology of ears, developmental abnormality of fin muscle, disorganization of facial musculature and/or degeneration of trunk muscle later in development. Moreover, DUX4-fl expression caused aberrant localization of myogenic cells marked with α-actin promoter-driven enhanced green fluorescent protein outside somite boundary, especially in head region. These abnormalities were rescued by coinjection of the short form of DUX4 (DUX4-s). Our results suggest that the misexpression of DUX4-fl, even at extremely low level, can recapitulate the phenotype observed in FSHD patients in a vertebrate model. These results strongly support the current hypothesis for a role of DUX4 in FSHD pathogenesis. We also propose that DUX4 expression during development is important for the pathogenesis of FSHD.

[Recent advances in facioscapulohumeral muscular dystrophy]

Facioscapulohumeral muscular dystrophy (FSHD) is a common autosomal dominant muscular dystrophy caused by truncation of D4Z4 repeat array on chromosome 4q35. Facial and shoulder-girdle muscles are preferentially affected but clinical symptoms are quite variable even within the same family. Asymmetrical muscle involvement is also characteristic in this disease. There are no disease specific changes on muscle pathology, and genetic diagnosis is performed by the southern blotting analysis. Recent advances provide us several ideas on possible pathomechanisms of this complicated disease. There are several genes on chromosome 4q35 region including DUX4 within D4Z4 repeats. Transcription of these genes is usually repressed by epigenetic modifications of this chromosomal region and also accumulation of transcriptional repressors to the repeat array. Shortening of the D4Z4 repeats observed in FSHD can cause structural changes of this chromosomal region, reduced recruitment of repressors, and expression of noncoding RNA which can enhance transcription of the genes on chromosome 4q35 region. Actually, increased mRNA expression levels of 4q35 genes was reported in FSHD cells, together with their undesirable roles on muscles by overexpression models. Further analysis is required to elucidate the precise pathomechanisms of FSHD.

Deciphering transcription dysregulation in FSH muscular dystrophy

DUX4, a homeobox-containing gene present in a tandem array, is implicated in facioscapulohumeral muscular dystrophy (FSHD), a dominant autosomal disease. New findings about DUX4 have raised as many fundamental questions about the molecular pathology of this unique disease as they have answered. This review discusses recent studies addressing the question of whether there is extensive FSHD-related transcription dysregulation in adult-derived myoblasts and myotubes, the precursors for muscle repair. Two models for the role of DUX4 in FSHD are presented. One involves transient pathogenic expression of DUX4 in many cells in the muscle lineage before the myoblast stage resulting in a persistent, disease-related transcription profile ('Majority Rules'), which might be enhanced by subsequent oscillatory expression of DUX4. The other model emphasizes the toxic effects of inappropriate expression of DUX4 in only an extremely small percentage of FSHD myoblasts or myotube nuclei ('Minority Rules'). The currently favored Minority Rules model is not supported by recent studies of transcription dysregulation in FSHD myoblasts and myotubes. It also presents other difficulties, for example, explaining the expression of full-length DUX4 transcripts in FSHD fibroblasts. The Majority Rules model is the simpler explanation of findings about FSHD-associated gene expression and the DUX4-encoded homeodomain-type protein.

The cell biology of disease: FSHD: copy number variations on the theme of muscular dystrophy

In humans, copy number variations (CNVs) are a common source of phenotypic diversity and disease susceptibility. Facioscapulohumeral muscular dystrophy (FSHD) is an important genetic disease caused by CNVs. It is an autosomal-dominant myopathy caused by a reduction in the copy number of the D4Z4 macrosatellite repeat located at chromosome 4q35. Interestingly, the reduction of D4Z4 copy number is not sufficient by itself to cause FSHD. A number of epigenetic events appear to affect the severity of the disease, its rate of progression, and the distribution of muscle weakness. Indeed, recent findings suggest that virtually all levels of epigenetic regulation, from DNA methylation to higher order chromosomal architecture, are altered at the disease locus, causing the de-regulation of 4q35 gene expression and ultimately FSHD.

The Facioscapulohumeral muscular dystrophy region on 4qter and the homologous locus on 10qter evolved independently under different evolutionary pressure

Background

The homologous 4q and 10q subtelomeric regions include two distinctive polymorphic arrays of 3.3 kb repeats, named D4Z4. An additional BlnI restriction site on the 10q-type sequence allows to distinguish the chromosomal origin of the repeats. Reduction in the number of D4Z4 repeats below a threshold of 10 at the 4q locus is tightly linked to Facioscapulohumeral Muscular Dystrophy (FSHD), while similar contractions at 10q locus, are not pathogenic. Sequence variations due to the presence of BlnI-sensitive repeats (10q-type) on chromosome 4 or viceversa of BlnI-resistant repeats (4q-type) on chromosome 10 are observed in both alleles.

Results

We analysed DNA samples from 116 healthy subiects and 114 FSHD patients and determined the size distributions of polymorphic 4q and 10q alleles, the frequency and the D4Z4 repeat assortment of variant alleles, and finally the telomeric sequences both in standard and variant alleles.

We observed the same frequency and types of variant alleles in FSHD patients and controls, but we found marked differences between the repeat arrays of the 4q and 10q chromosomes. In particular we detected 10q alleles completely replaced by the 4q subtelomeric region, consisting in the whole set of 4q-type repeats and the distal telomeric markers. However the reciprocal event, 10q-type subtelomeric region on chromosome 4, was never observed. At 4q locus we always identified hybrid alleles containing a mixture of 4q and 10q-type repeats.

Conclusion

The different size distribution and different structure of 10q variant alleles as compared with 4q suggests that these loci evolved in a different manner, since the 4q locus is linked to FSHD, while no inheritable disease is associated with mutations in 10qter genomic region. Hybrid alleles on chromosome 4 always retain a minimum number of 4q type repeats, as they are probably essential for maintaining the structural and functional properties of this subtelomeric region.

In addition we found: i) several instances of variant alleles that could be misinterpreted and interfere with a correct diagnosis of FSHD; ii) the presence of borderline alleles in the range of 30–40 kb that carried a qA type telomere and were not associated with the disease.

FSHD-like patients without 4q35 deletion

Facioscapulohumeral muscular dystrophy (FSHD) is characterized by progressive weakness and wasting of facial, shoulder-girdle and upper arm muscles. Despite of the characteristic clinical features, the diagnosis of FSHD is sometimes difficult because clinical symptoms are extremely variable including facial sparing type, limb-girdle type, and distal myopathy type. Most of the FSHD patients have a deletion in the subtelomeric region of chromosome 4q35 (FSHMD1A), however the linkage analysis in some families suggested genetic heterogeneity. In the present study, we identified 40 patients without a deletion in the 4q35 region (non-4q35del) among 200 Japanese patients who were clinically suspected to have FHSD. All non-4q35del patients had shoulder-girdle weakness and 75% also had facial weakness. Eight patients showed clinical features that were indistinguishable from FSHD, but two of them had Becker muscular dystrophy. FSHD is clinically, and most likely genetically, as well, variable. Other forms of muscular dystrophy can also mimic FSHD.

Chromosome 4q;10q translocations; comparison with different ethnic populations and FSHD patients

BACKGROUND

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant disorder characterized by the weakness of facial, shoulder-girdle and upper arm muscles. Most patients with FSHD have fewer numbers of tandem repeated 3.3-kb KpnI units on chromosome 4q35. Chromosome 10q26 contains highly homologous KpnI repeats, and inter-chromosomal translocation has been reported.

METHODS

To clarify the influence on the deletion of the repeats, we surveyed three different ethnic populations and FSHD patients using the BglII/BlnI dosage test.

RESULTS

The frequency of translocation in 153 Japanese, 124 Korean, 114 Chinese healthy individuals and 56 Japanese 4q35-FSHD patients were 27.5%, 29.8%, 19.3%, and 32.1%, respectively. The ratio of '4 on 10' (trisomy and quatrosomy of chromosome 4) was higher than that of '10 on 4' (nullsomy and monosomy of chromosome 4) in all populations.

CONCLUSIONS

The inter-chromosomal exchange was frequently observed in all four populations we examined, and no significant difference was observed between healthy and diseased groups.

Inappropriate gene activation in FSHD: a repressor complex binds a chromosomal repeat deleted in dystrophic muscle

Facioscapulohumeral muscular dystrophy (FSHD), a common myopathy, is an autosomal dominant disease of unknown molecular mechanism. Almost all FSHD patients carry deletions of an integral number of tandem 3.3 kilobase repeats, termed D4Z4, located on chromosome 4q35. Here, we find that in FSHD muscle, 4q35 genes located upstream of D4Z4 are inappropriately overexpressed. We show that an element within D4Z4 specifically binds a multiprotein complex consisting of YY1, a known transcriptional repressor, HMGB2, an architectural protein, and nucleolin. We demonstrate that this multiprotein complex binds D4Z4 in vitro and in vivo and mediates transcriptional repression of 4q35 genes. Based upon these results, we propose that deletion of D4Z4 leads to the inappropriate transcriptional derepression of 4q35 genes resulting in disease.

Molecular diagnosis of facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is the third most common inherited neuromuscular disorder after Duchenne muscular dystrophy and myotonic dystrophy. The gene underlying FSHD was mapped to chromosome 4q35 in 1990 and was shown to be closely linked to locus D4F104S1. Although D4F104S1-associated deletions are closely associated with FSHD, the identity and location of the FSHD gene (or genes) still remain elusive, as does the mechanistic basis of the disease. In addition, although approximately 5% of FSHD families fail to exhibit linkage to 4q35, a putative second locus remains unidentified. The search for the FSHD gene has been hampered both by sequence homologies between the 4q35 candidate region and other chromosomal regions and by the presence of many highly repetitive sequences. Molecular diagnosis for FSHD is usually offered with 98% accuracy but because of its complexity, a much more simple test would be preferable. Indeed, the identification of the FSHD gene itself should potentiate major improvements in diagnostic testing.

Muscular dystrophy

Muscular dystrophy is a group of genetically determined muscular disorders marked by progressive wasting and weakness of the skeletal muscle, but which often affect cardiac and smooth muscles or other tissues. The patterns of inheritance are either dominant or recessive although the gene may be defective because of a new mutation. Growing evidence revealed the marked heterogeneity of the muscle disorders, and considerable numbers of Japanese scientists and physicians have contributed to the research progress in muscular dystrophy. Among these the discovery of an increased serum creatine kinase activity in muscular dystrophy opened the way for the most reliable laboratory test for muscular dystrophy in 1959, and subsequently accelerated progress in a broad range of research areas in medicine. Progress in modern genetics and molecular pathology provided another breakthrough in muscular dystrophy research and, in 1987, dystrophin was identified, a deficiency of which causes DMD. The present review article highlights contributions of Japanese scientists to muscular dystrophy research.

Progress in the molecular diagnosis of facioscapulohumeral muscular dystrophy and correlation between the number of KpnI repeats at the 4q35 locus and clinical phenotype

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.

Early-onset facioscapulohumeral muscular dystrophy: two case reports

This report concerns two patients with facioscapulohumeral muscular dystrophy (FSHD) whose facial weakness began in infancy. In both patients, biopsied muscle histology showed mild myogenic changes accompanied by some regenerating and some small angular fibers, while endomysial inflammatory cellular infiltration was observed in Patient 1. The finding that our very young patients had muscle histopathological findings compatible with classical FSHD supports the previously expressed view that muscle histopathology is not related to either age or duration of the disease. Although Patient 2 was a sporadic case, both patients had the abnormal EcoRI DNA fragment detected by Southern blot analysis with probes p13E-11 and pFR-1, a finding compatible with FSHD. This indicates that gene analysis of sporadic cases must be as significant as that of familial cases. This report on patients with very early-onset and with common muscle histopathological and molecular genetic findings should contribute to widening the clinical spectrum of FSHD.

Application of chromosome 4q35-qter marker (pFR-1) for DNA rearrangement of facioscapulohumeral muscular dystrophy patients in Taiwan

Facioscapulohumeral muscular dystrophy (FSHD) has been found to be linked to chromosome 4qter. A chromosome 4q35-ter marker, pFR-1 (subclone of the cosmid c51), has been recently isolated and used as a probe for mapping near, or within, the FSHD gene. To examine FSHD-associated DNA rearrangements in the Taiwan population, we used the pFR-1 probe to perform Southern blot analysis on 142 individuals, including 32 FSHD patients within 9 autosomal dominant families, five sporadic FSHD patients from 4 families (include one pair of twins), three sporadic scapuloperoneal syndrome (SPS) patients and two sporadic polymyositis patients with their unaffected parents, and 29 healthy controls. In 29 healthy individuals, 3 SPS and 2 polymyositis patients with their families, probe pFR-1 analysis revealed that all had polymorphic restriction fragments that were larger than 28 kb in length. All but 1 FSHD-affected individual had specific smaller EcoRI fragments (ranging in size from 10.5 to 27 kb). Two point linkage analysis between pFR-1 and the FSHD locus provided significant evidence for FSHD linkage (Z(max)=6.84). A similar smaller fragment was also present in 5 sporadic patients, while this smaller fragment could not be found in one of their parents. Identical EcoRI restriction fragment length polymorphism (RFLP) patterns linked to FSHD were shown in the monozygotic twins, even though they showed extreme variability in the expression of FSHD. We conclude that the pFR-1 probe is a tightly linked marker of FSHD and can be used to detect most DNA rearrangements associated with this disease in the Taiwan population. However, the same RFLP patterns may represent extreme variability in the expression of the FSHD gene.

Detection of the mutation in facioscapulohumeral muscular dystrophy patients

The gene responsible for facioscapulohumeral muscular dystrophy (FSHD) was mapped to chromosome 4q35 by linkage analyses. Recently, the probe p13E-11 derived from the cosmid clone 13E, which has been mapped to 4qter, detected a polymorphic EcoRI fragment, usually greater than 28 kb in normal individuals. In sporadic and familial FSHD patients, a specific shorter fragment, usually smaller than 28 kb, was found to cosegregate with FSHD. Two FSHD patients are presented here. Patient 1 is a sporadic case of FSHD with healthy parents. He had a de novo mutation identified by Southern blot analysis using the above-mentioned probe. Patient 2 is a typical familial FSHD patient clinically and histologically. A rearranged and shortened EcoRI fragment was identified by molecular analysis. Southern blot analysis using the probe p13E-11 also indicated a rearranged EcoRI fragment in both patients.

Evidence for anticipation and association of deletion size with severity in facioscapulohumeral muscular dystrophy. The FSH-DY Group

Facioscapulohumeral muscular dystrophy (FSHD) is characterized by marked inter- and intrafamilial heterogeneity in its clinical expression. The contribution of genetic factors to this variability is not well characterized. We examined the relationship of phenotype to genotype in a clinically and genetically well-defined FSHD population. Quantitative isometric myometry (QMT) scores, normalized for age, gender, and height, were used to quantify disease severity. We found a significant (r = 0.92, p < 0.004) correlation between disease severity and the size of the 4q35-associated deletion. In addition, when relative disease severity of parent-offspring pairs was compared, the offspring were found to be significantly more severely affected (p = 0.011). This generational effect suggests the presence of anticipation in FSHD and raises the possibility of an underlying dynamic mutation.