Trisomy-12p syndrome: Family study and prenatal diagnosis.

A young unrelated Indian couple produced a baby who had an unusual facies, marked abdominal distension and muscular hypotonia. At 8 weeks cytogenetic investigation revealed what appeared to be trisomy-21. Because this did not agree with the clinical signs the parents were tested and the mother was found to have a balanced translocation between chromosomes 12 and 14; her karyotype was 46,XX,rcp(12; 14)(p11; q11) and it was realized that her son had inherited her translocation chromosome involving the short arms of chromosomes 12 and 14. He thus had trisomy-12p. The present case and 10 others reported in the literature confirm that trisomy-12p produces a recognizable syndrome. Parents carrying a balanced translocation have a 50:50 risk of producing an abnormal infant at every pregnancy because both the trisomic and monosomic conditions may be viable. Amniocentesis for fetal karyotyping must be recommended to the couples concerned.