Fragile X syndrome: associated neurological abnormalities and developmental disabilities.

The fragile X syndrome is a frequent cause of developmental disabilities. It is associated primarily with nonprogressive X-linked mental retardation. The neurodevelopmental abnormalities of 25 males and 3 females are described. Mental retardation was mild in 4, moderate in 11, severe in 6, and profound in 2 patients, while 4 patients had only learning disabilities. The presence or absence of a developmental disability could not be determined in the youngest (8 months). Seven patients had had infantile autism and 7 had epilepsy. Generally no major focal neurological abnormalities were observed but most of the patients exhibited minor signs. The severity of developmental disabilities in our patients varied between and within families and between genders. All adult males had macroorchidism. Unusual facial features were present in 13 males but none were seen in the females. Familial occurrences were found in 18 cases (64%); 10 cases (36%) were sporadic. Overall, males were more severely affected than females. Diagnostic tests including computed tomographic scans, electroencephalograms, and evoked potentials did not disclose any specific abnormalities.