Japanese patients with infantile autism were studied cytogenetically for the occurrence of fragile X (fra(x)) syndrome at the Universities of Kurume and Nagasaki. Fra(X) chromosome was detected in 2 (siblings) of 39 boys and in none of 8 girls; a frequency of 2.6% (1/38) in the study population of male autistic children. 
COMMENT. The fragile X syndrome is the most common familial form of mental retardation known, with an incidence of 1 in 1000 in the general population. The classical physical features in males are a long narrow face, large ears, and large testes. The pediatric neurologist may encounter cases referred because of large head circumference, hyperactive behavior and short attention span (ADD), and hand-flapping movement disorders. Poor eye contact and stereotyped movement have led to confusion with autism, reported in 5-53% of males with fragile X syndrome, and the classical manifestations have matched the DSM III diagnostic criteria for autism in some, as in the above study. For a comprehensive current overview of fragile C syndrome.