Absence of the fragile X CGG trinucleotide repeat expansion in girls diagnosed with a pervasive developmental disorder

The purpose of this study was to determine the prevalence of the fragile X (FRAX) CGG trinucleotide expansion in a population of young girls (n = 45) diagnosed with pervasive developmental disorder (PDD). Their mean age was 43.7 months (range, 25 to 132 months). Diagnoses included autistic disorder (n = 20), PDD (n = 23), and Asperger’s syndrome (n = 2). Molecular FRAX testing was performed on all patients by using the Southern gene blot technique. Genomic DNA was digested with both Eco RI and Eag I, fractionated on agarose gel, and blotted and probed with the radiolabeled StB12.3 FMR-1 probe. None of the subjects were found to have an expansion of CGG in either the 2.8 kb or 5.2 kb fragments. A 95% CI, for the prevalence of the FRAX mutation in female subjects with PDD, has an upper bound of 2.9%. We conclude that the prevalence of FRAX positivity in girls with PDD is lower than previously reported. This raises the question of whether any association between FRAX and PDD in female subjects is specific to PDD or is related rather to the presence of mental retardation. (J Pediatr 1998;133:363-5)