Prenatal diagnosis of a large heteromorphic region in a chromosome 5: implications for genetic counseling.

We performed an amniotic fluid chromosome study at 16 weeks of gestation because of advanced maternal age. G-band chromosome analysis demonstrated that one 5q was significantly longer than its homologue. The region subjacent to the centromere appeared similar to a 9qh region. Subsequent Giemsa-11 and C-band staining results of this area were positive. Cytogenetic studies in this family demonstrated several other individuals who have the same chromosome 5qh+ as the proposita. All are asymptomatic. The clinical insignificance of the chromosome heteromorphism in this family readily demonstrates the need for special cytogenetic and family chromosome studies before performing genetic counseling.