ONLINE MUTATION REPORT Very low penetrance in 85 Japanese families with facioscapulohumeral muscular dystrophy 1A

acioscapulohumeral muscular dystrophy (FSHD) is the third most common form of muscular disorder with an autosomal dominant trait, and its frequency is about one in 20 000. It is characterised by weakness and atrophy of the facial, shoulder girdle, and upper limb muscles. The pelvic girdle and lower limbs subsequently also become involved, and, eventually, 20 % of patients have to use wheelchairs by the age of 40 years.1 Most patients develop clinical symptoms in late childhood or adolescence, although the onset of the disease and its clinical severity are heterogeneous. The FSHD locus was mapped to the subtelomeric region of the long arm of chromosome 4 by genetic linkage analysis.2–4 More than 95 % of patients with FSHD had a small (,35 kb) EcoRI fragment on chromosome 4q35 on southern blotting analysis with the probe p13E-11 (FSHD1A; MIM 158900).5–