Weakened sarcomeric contractility distinguishes Facio Scapulo Humeral Dystrophy muscle fibers

To gain further insights into the specificity of the muscle alteration in this disease, we derived induced pluripotent stem cells from patients affected with type 1 and 2 FSHD, differentiated these cells into contractile innervated muscle fibers and analyzed their transcriptome by RNA Seq. Overall design: In order to identify pathways involved in FSHD which are specific to the muscle, we took advantage of our collection of induced pluripotent stem cells and our recently developed procedure for production of innervated and contractile skeletal Muscle Fibers (MFs) to analyze gene expression in cells from FSHD1 or FSHD2 patients compared to healthy donors at day 30 post-differentiation. Given the implication of SMCHD1 in both FSHD2 and bosma arhinia microphthalmia syndrome (BAMS), but the absence of muscle symptoms in BAMS, RNA Seq was also carried in BAMS MFs to identify pathways that are specific to FSHD. For FSHD1, RNA seq was performed on cells from one patient affected with FSHD carrying a short D4Z4 allele (FQMR19, FQMR20; 7 RU) and cells from a mosaic patient (FQMR17, 18, 27, 28; 25% of mosaicism, clinically affected). For this patient, we compared two isogenic clones, one with a short allele (2 RU, 4qA haplotype, diseased clone: FQMR17, 18) and one with a long healthy allele (15 RU; 4qA haplotype: healthy clone: FQMR27, 28). For patients with SMCHD1 variants, we compared FSHD2 cells with a missense mutation in the ATPase domain, never reported in BAMS that abrogates SMCHD1 enzymatic activity (FQMR21, 22; Q194P) to BAMS cells with a variant in the ATPase domain (FQMR23, 24; E136G) that causes a gain of the enzymatic activity.