Dystrophinopathy in a young boy with Klinefelter's syndrome.

We report the first case of a child with mild dystrophinopathy associated with Klinefelter's syndrome (karyotype 47, XXY). This 3.5-year-old boy was affected by some symptoms suggestive of Becker's muscular dystrophy. Dystrophin immunostaining and immunoblotting procedures confirmed the diagnosis, but polymerase chain reaction-directed gene analysis failed to reveal any macrodeletion. Methylation-based assay did not show preferential X-inactivation. This confirmed the coexistence of the two active X-chromosomes (one of which was of paternal origin), thus accounting for the mild form of dystrophinopathy in this child affected by Klinefelter's syndrome.