No abstract

In facioscapulohumeral muscular dystrophy (FSHD) the majority of patients carry a D4Z4 macrosatellite repeat contraction in the subtelomere of chromosome 4q. Several disease mechanisms have been proposed to explain how repeat contraction causes muscular dystrophy. All proposed mechanisms foresee a change from a closed to a more open chromatin structure followed by loss of control over expression of genes in or proximal to D4Z4. Initially, a distance and residual repeat size-dependent upregulation of the candidate genes FRG2, FRG1 and ANT1 was observed, but most successive expression studies failed to support transcriptional upregulation of 4qter genes. Moreover, chromatin studies do not provide evidence for a cis-spreading mechanism operating at 4qter in FSHD. In part, this inconsistency may be explained by differences in the techniques used, and the use of RNA samples obtained from different muscle groups. The aim of this study is to comprehensively and uniformly study the expression of the FSHD candidate genes FRG1, FRG2, CRYM, ANT1, ALP, PITX1 and LRP2BP at the RNA and protein level in identically processed primary myoblasts, myotubes and quadriceps muscle. Expression was compared between samples obtained from FSHD patients and normal controls with samples from myotonic dystrophy type 1 patients as disease controls. No consistent changes in RNA or protein expression levels were observed between the samples. The one exception was a selective increase in FRG2 mRNA expression in FSHD myotubes. This study provides further evidence that there is no demonstrable consistent, large magnitude, overexpression of any of the FSHD candidate genes.

Muscle concentrations of mRNAs encoded by mitochondrial DNA (mtDNA) decline with aging. To determine whether this can be explained by diminished mtDNA levels, we measured the relative concentrations of mtDNA and a representative mtDNA transcript [encoding cytochrome-c oxidase, subunit 2 (COX-2)] in muscle of young (21-27 yr) and older subjects (65-75 yr). The amount of COX-2 mRNA (relative to 28S rRNA) was 22% lower (P = 0.04) in older muscle, and the amount of mtDNA (relative to nuclear DNA) was 38% lower (P = 0.0002). The average level of mitochondrial transcription factor A (Tfam), a protein essential for mtDNA replication, was similar in younger and older muscle. Tfam mRNA, nuclear respiratory factor-1 mRNA, and several mRNAs encoding proteins required for mtDNA replication were expressed at similar levels in younger and older muscle. The mtDNA concentrations were only weakly related to age-adjusted aerobic fitness (maximal oxygen consumption) and self-reported physical activity levels. We conclude that the lower concentration of mitochondrial mRNAs in older muscle can be explained by a reduced concentration of mtDNA.

Silvère M. van der Maarel (2012) Correlation analysis of clinical parameters with epigenetic modifications in the DUX4 promoter in FSHD, Epigenetics, 7:6, 579-584,

Background As we move towards planning for clinical trials in Facioscapulohumeral Muscular Dystrophy (FSHD), a better understanding of the clinical relationship with morphological changes in FSHD muscle biopsies will be important for stratifying patients and understanding post-therapeutic changes in muscle. Methods We performed a prospective cross-sectional study of quadriceps muscle biopsies in 74 genetically confirmed FSHD participants (64 FSHD1, 10 FSHD2). We compared a 12-point muscle pathology grade to genetic mutation, disease severity score, and quantitative myometry. Results Pathology grade had moderate correlations with genetic mutation (rho=−0.45, P<0.001), clinical severity score (rho=0.53, P<0.001), disease duration (rho=0.31, P=0.03), and quantitative myometry (rho=−0.47, P<0.001). We found no difference in the frequency of inflammation between FSHD types 1 and 2. Conclusions The pathology grade of quadriceps muscle may be a useful marker of disease activity in FSHD, and it may have a role in stratification for future clinical trials.