Fragile X testing in a diagnostic cytogenetics laboratory.

Chromosome results obtained from 1012 patients referred with developmental delay without known cause within the three years 1985 to 1987 are reported. G banding analysis and assessment of 70 cells for fragile X gave abnormal results in 84 cases: fragile X in 31 patients and other abnormalities in 53 patients. A further 16 sibs expressing the fragile X were detected in family studies originating from the 31 index cases. This yield justifies continuation of procedures which detect both fragile X and subtle chromosomal abnormalities in these patients.