Facioscapulohumeral dystrophy type 1 (FSHD-1) is the most common autosomal dominant form of muscular dystrophy with a prevalence of ∼1 in 8000 individuals.
SMCHD1 c.1040+1G>A, a pathogenic splice-site variant, was identified in a FSHD1 family with a borderline number of D4Z4 repeats (10) and a variable phenotype (in which a LMNA1 sequence variant was previously described), and SMCHD1 c.2606 G>T, a putative missense variant (p.Gly869Val) with strong in vitro indications of pathogenicity, was identified in a family with an unusual muscular dystrophy with some FSHD-like features.
While much is known about the clinical course of adult FSHD, the third most common inherited muscular dystrophy, data on the "infantile phenotype" and especially on the progression of the disease in children are limited.