Given the familial and therapeutic implications for accurate diagnosis of DMD mutations, this case raises the possible need for screening boys with global developmental delay/intellectual disability even in the absence of any overt muscle weakness and further shows the utility of comparative genomic hybridization (CGH) analysis in the evaluation of patients with nonsyndromic mental retardation.
Mental retardation in our patient and absence of the b-wave in his electroretinogram indicate that central nervous functions of dystrophin isoforms also depend on the presence of cysteine 3340.
A number of data raised the possibility that the C-terminal region of dystrophin might be involved in some cases of mental retardation associated with DMD.
Our observations in the group of patients who had detected DNA deletions suggest that exon 52 of the dystrophin gene may be functionally significant in the manifestation of MR: 70% (19/27) of patients with a deletion of this exon were mentally retarded, whereas only 38% (15/39) of MR patients had deletions not involving exon 52.