Fragile 22q13 segregating in a family.

During the course of a population study of non-specific mental retardation in school-age males, a 13-year-old boy was ascertained. Cytogenetic studies revealed the presence of a fragile site at chromosome 22. The site was found to be both folate-dependent and heritable. The possibility that the presence of this fragile site is linked to mental retardation is discussed.