GERMINAL MOSAICISM IN FACIOSCAPULOHUMERAL MUSCULAR-DYSTROPHY (FSHD)

Facioscapulohumeral dystrophy (FSHD) is an autosomal-dominant neuromus cular disorder with a prevalence of 1 in 20,000. The DNA marker p13E-1 1 (D4F104S1) detects a de novo DNA rearrangement in the majority of sp oradic and FSHD cases. These rearrangements consist of deletions of mu ltiple copies of tandem repeat (D4Z4). We have studied 34 new mutation FSHD families of which 26 showed a de novo fragment with p13E-11. In three of the remaining eight families without a de novo fragment, germ inal mosaicism was noted. In each case, the proband had inherited a sm all EcoR1 fragment from the clinically unaffected mother; however, the hybridization signal intensity of this fragment in the mother's DNA w as significantly reduced in all three families. This is the first stud y to describe such mosaicism in FSHD families using DNA analysis and t herefore has a considerable significance for genetic counseling and pr enatal diagnosis. (C) 1995 John Wiley and Sons, Inc.