Severe mental retardation in a young boy with an in-frame deletion in the dystrophin gene.

We report here a mentally retarded 32-month-old boy whose initial diagnosis was Angelman syndrome based on his clinical features. Cytogenetic studies showed a normal karyotype. Due to an elevated level of serum creatine kinase activity, we performed analyses to rule out a myopathic process. Although the electromyogram was normal, a few scattered necrotic fibres were seen in the muscle biopsy. DNA and dystrophin studies revealed an in-frame deletion in the 5' region of the dystrophin gene and an abnormal form of the protein product, consistent with a diagnosis of dystrophinopathy. We cannot totally rule out the possibility that this boy has the two separate conditions.