ADDITIONAL CASE OF FEMALE MONOZYGOTIC TWINS DISCORDANT FOR THE CLINICAL MANIFESTATIONS OF DUCHENNE MUSCULAR-DYSTROPHY DUE TO OPPOSITE X-CHROMOSOME INACTIVATION

A pair of female monozygotic (MZ) twins, heterozygous carriers for a deletion in the DMD gene and discordant for the clinical manifestations of Duchenne muscular dystrophy, were analyzed by molecular studies, in situ hybridization, and methylation pattern of X chromosomes to search for opposite X inactivation as an explanation of their clinical discordance. Results in lymphocytes and skin fibroblast cell lines suggest a partial mirror inactivation with the normal X chromosome preferentially active in the unaffected twin, and the maternal deleted X chromosome preferentially active in the affected twin. A review shows that MZ female twins discordant for X-linked diseases are not uncommon. ah inning and X inactivation may be interrelated and could explain the female twins discordant for X-linked traits. (C) 1994 Wiley-liss, Inc.