Genetic counselling in facioscapulohumeral muscular dystrophy.

Clinical data are presented from a survey of 41 families with dominantly inherited facioscapulohumeral muscular dystrophy (FSHD) in which over 500 family members were examined, including 168 affected subjects. New mutation could account for six isolated cases. Results suggest that 33% of heterozygotes over 40 years are mildly affected and a majority develop significant lower limb weakness; 19% over 40 years require wheelchairs. Presymptomatic testing of serum creatine kinase level (CK) is limited as a raised level occurs in only 80% of affected males under 40 years and 48% of affected women. Distribution of weakness, severity, age at onset, and CK varied between subjects, but provided no clinical evidence for genetic heterogeneity in a comparison between the 11 largest families. The conclusion of genetic homogeneity in FSHD, including subjects previously diagnosed as FSH type spinal muscular atrophy, is strongly supported by recent genetic linkage data.