Male with typical fragile X phenotype is deleted for part of the FMR1 gene and for about 100 kb of upstream region.

We report on a patient with moderate mental retardation and a typical fragile X phenotype, with no family history and no fragile X site on cytogenetic analysis. The patient was found to have a deletion encompassing part of the FMR1 gene and a 70-100 kb region upstream of the FMR1 promotor region. This deletion is smaller than those previously reported and confirms that FMR1 is the major and probably the only gene implicated in the phenotype of the fragile X syndrome.