A cytogenetic study of children with clinically unclassifiable multiple congenital malformations and mental retardation.

A cytogenetic study was performed on 74 children with at least three major or minor congenital malformations and mental retardation, and whose phenotypes did not fit any well-defined syndrome. The chromosomes were examined routinely using banding techniques. A total of 11 patients (14.9%) was found to have a major chromosome abnormality: one patient had a sex chromosome structural abnormality and 10 patients had an autosomal structural abnormality, including 4 patients with partial trisomies, 4 patients with partial monosomies, and 2 patients with tertiary trisomies. Two of them had probable intrachromosomal duplication which would not have been identified by conventional staining alone. Familial transmission was ascertained in 5 of 10 cases in which both parents were studied. In addition, 5 patients (6.8%) were noted to have the following chromosome heteromorphisms: partial inv 1qh, inv 9qh, 9qh+, and Yqh+. These results show that chromosome abnormalities contribute much to the etiology of unclassifiable multiple malformations associated with mental retardation. Furthermore, the demonstration of subtle chromosome rearrangements by means of banding techniques provides important implications in medical practice for the diagnosis of affected patients as well as for the genetic counseling of the families.