General overgrowth in the fragile X syndrome: variability in the phenotypic expression of the FMR1 gene mutation

The fragile X syndrome, which often presents in childhood with overgrowth, may in some cases show some diagnostic overlap with classical Sotos syndrome. We describe four fragile X patients with general overgrowth, all of whom are from families with other affected relatives who show the classic Martin-Bell phenotype. Molecular studies of the FMR1 gene in all cases showed the typical full mutation as seen in males affected by the fragile X syndrome. Endocrine studies were unremarkable, except in one case where there were raised levels of insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding protein-3 (IGFBP-3) These cases illustrate the clinical variability of the fragile X syndrome and the necessity of performing analysis of the FMR1 gene in mentally retarded patients presenting with general overgrowth.