Prevalence of mental retardation related to fragile X syndrome and other chromosomal abnormalities in the Republic of San Marino.

The prevalence of mental retardation related to chromosomal abnormalities, including fragile X syndrome, was studied among 2735 males aged between five and 20 years living in the Republic of San Marino. Five cases of chromosomal abnormalities were found, including one case with fragile X syndrome, with partial epilepsy and a CT scan showing a large arachnoid cyst in the posterior fossa. The prevalence of mental retardation due to chromosomal abnormality was 1.83 per 1000, and that due to fragile X syndrome was 0.37 per 1000. Although these findings relate to only a small population, they are the first from a Mediterranean area.