About 20% of boys with DMD have an IQ of less than 70, with more intellectual impairment observed in those with mutations in the brain-specific dystrophin isoform.8 This form of dystrophin is initiated between exons 62 and 63, contains only the cysteine-rich and carboxyl-terminus domains, and is only 71 kD compared to the 427 kD form expressed in muscle.9 Intellectual impairment is greater in patients with deletion break-points distal to exon 30. This evidence concerns the gene DMD and Cognitive impairment.