Manifesting carrier of Becker muscular dystrophy (BMD): clinical and recombinant DNA studies.

We studied a Becker muscular dystrophy (BMD) family with a manifesting carrier. Proximal muscle weakness, pseudohypertrophy of the calves, significantly elevated serum creatine kinase and dystrophic alterations in the muscle biopsy were the characteristic phenotypical features of this manifesting carrier. The recombinant DNA study showed a recombinant chromosome with a crossover between pERT 87-8 and pERT J-Bir in the manifesting carrier. However, the proximal part of the short arm of her X chromosome was identical to a non-manifesting carrier (her sister) and to her affected brother. For this reason, we assumed the BMD mutation was proximal to the crossover. The dystrophin cDNA probes showed no deletion of DMD/BMD gene.