Fragile X syndrome in Japanese patients with infantile autism.

Forty-seven patients (39 boys and 8 girls) with infantile autism whose clinical symptoms had matched the diagnostic criteria of DSM III were studied cytogenetically for the occurrence of fragile X [fra(X)] syndrome. The existence of fra(X) chromosome in these patients was screened first by culturing peripheral blood lymphocytes in a medium in which folic acid was absent; the fra(X) chromosome then was confirmed by reculturing in another medium to which 5-fluoro-2'-deoxyuridine was added for the last 24 hours of culture. Fra(X) chromosome was found in 2 of 39 male patients, but in none of the female patients; the 2 patients are siblings. Thus, fra(X) syndrome occurs in 2.6% (1/38) in this study population of male autistic children. The frequencies of fra(X) expression in the older brother with mild mental retardation, in the more severely retarded younger brother, and in their mother were 3-5%, 17-20%, and 9-3%, respectively. Of the two methods used in the present study, the method employing 5-fluoro-2'-deoxyuridine tended to be more sensitive to fra(X) chromosome detection, especially for a suspected carrier.