Abstract
We report the case of a 2-year-old girl who had signs of Duchenne type muscular dystrophy on clinical, electromyographic, laboratory, and pathological examination. The parents of the child are first cousins. A brother and nephew of the mother also had Duchenne type muscular dystrophy. Karyotype analysis in the proband showed both X chromosomes to be morphologically normal. The mother had very high plasma CK levels, equivalent to those observed in carriers of the disease. We discuss different hypothetical mechanisms designed to account for the family pedigree.