Patients with a phenotype consistent with facioscapulohumeral muscular dystrophy display genetic and epigenetic heterogeneity

Abstract

Objective To identify the genetic and epigenetic defects in patients presenting with a facioscapulohumeral (FSHD) clinical phenotype without D4Z4 contractions on chromosome 4q35 tested by linear gel electrophoresis (LGE) and Southern blot analysis. Design and patients We studied 16 patients displaying an FSHD-like phenotype, with normal cardiovascular and respiratory function, a myopathic pattern on EMG, and a muscle biopsy being normal or displaying only mild and a specific dystrophic changes. We sequenced the genes calpain 3 (CAPN3), valosin containing protein (VCP) and four and a half LIM domains protein 1 (FHL1) and we analyzed the D4Z4 repeat arrays by extensive genotyping and DNA methylation analysis. Results We identified one patient carrying a complex rearrangement in the FSHD locus that masked the D4Z4 contraction associated with FSHD1 in standard genetic testing, one patient with somatic mosaicism for the D4Z4 4q35 contraction, six patients that were diagnosed with FSHD2, four patients with CAPN3 mutations, two patients with a VCP mutation, No mutations were detected in FHL1, and in two patients we could not identify the genetic defect. Conclusions In patients presenting an FSHD-like clinical phenotype with a negative molecular testing for FSHD consider: 1) detailed genetic testing including D4Z4 contraction of permissive hybrid D4Z4 repeat arrays, p13E-11 probe deletions, D4Z4 hypomethylation in absence of repeat contraction as observed in FSHD2, 2) mutations in CAPN3 even in the absence of protein deficiency on western blot analysis 3) VCP mutations even in the absence cognitive impairment, Paget disease and typical inclusion in muscle biopsy.

Allele-specific DNA hypomethylation characterises FSHD1 and FSHD2

“…However, since these assays show the methylation status of 4q and 10q arrays, they are not diagnostic per se due to lack of information about the presence of DUX4 PAS-positive alleles and their methylation status. For this reason, the FSHD diagnostic flow chart considers hypomethylation analysis as a secondary step to distinguish FSHD1 from FSHD2, the latter being characterised by hypomethylation in all 4q and 10q D4Z4 units 4 24…”

Magnetic resonance imaging in a large cohort of facioscapulohumeral muscular dystrophy patients: Pattern refinement and implications for clinical trials

“…These molecular discoveries paved the way to the development of therapies, and the possibility to recruit patients into forthcoming clinical trials makes it essential to establish a correct clinical diagnosis. Because FSHD can show phenotypic overlap with other myopathies, or might even coexist with other diseases, additional instrumental criteria may be useful in the diagnostic workup to support or exclude the diagnosis in selected patients harboring the permissive genetic background without straightforward phenotypic features or positive family history. Also important in the present context, there is an urge to define parameters to enroll and stratify patients in clinical trials as well as to define useful outcome measures and biomarkers of disease progression …”

Diagnosis by sequencing: correction of misdiagnosis from FSHD2 to LGMD2A by whole-exome analysis

“…This agrees with the results of a recent candidate gene screen of patients who had been initially diagnosed with FSHD, but lacked D4Z4 deletions. 21 Furthermore, we assigned the genetic diagnosis in an isolated case using exome sequencing. This was possible without a family pedigree or direct access to the patient.…”