Complex translocation t(9;21)(9;22)(q12p13)(q12q11) in the family of a child with 9p trisomy syndrome.

A case of partial trisomy 9 is described in a mentally retarded and dysmorphic child, confirming that this chromosome unbalance results in a characteristic clinical entity. This trisomy arose through aberrant segregation of translocation chromosome during meiosis in the patient's mother, who is a balanced heterozygote for a complex translocation involving chromosomes 9, 21 and 22. The phenotypically normal sister of the proposition is also carrier of the same complex translocation.