Extrapolating the figures from a previous study on FSHD in a province of The 
Netherlands to the entire Dutch population suggests that at present a nearly 
complete overview is obtained of all symptomatic kindred. In 139 families, 
dominant inheritance was observed in 97, a pattern compatible with germline 
mosaicism in 6, while sporadic cases were found in 36 families. A mutation 
frequency of 9.6% was calculated. Mental retardation and severe retinal 
vasculopathy were reported in low frequencies (1%). Early onset was seen more 
frequently in sporadic cases. Chromosome 4 linkage appeared excluded in 3 of 22 
autosomal-dominant families. The clinical pictures in the linked and nonlinked 
families were identical.