IDENTICAL DE-NOVO MUTATION AT THE D4F104S1 LOCUS IN MONOZYGOTIC MALE TWINS AFFECTED BY FACIOSCAPULOHUMERAL MUSCULAR-DYSTROPHY (FSHD) WITH DIFFERENT CLINICAL EXPRESSION

Facioscapulohumeral muscular dystrophy (FSHD) is a progressive heredit ary neuromuscular disorder, transmitted in an autosomal dominant fashi on. Its clinical expression is highly variable, ranging from almost as ymptomatic subjects to wheelchair dependent patients, The molecular de fect has been linked to chromosome 4q35 markers and has been related t o deletions of tandemly repeated sequences located in the subtelomeric region detected by probe p13E-11 (D4F104S1). We describe a pair of mo nozygotic male twins affected by FSHD, carrying an identical de novo p 13E-11 EcoRI fragment of paternal origin and showing great variability in the clinical expression of the disease,one being almost asymptomat ic and the other severely affected. Their medical history was the same , with the exception of an anti-rabies vaccination performed at the ag e of 5 in the more severely affected twin. We hypothesise that the vac cination might have triggered an inflammatory immune reaction contribu ting to the more severe phenotype.