Trisomy 12p syndrome. Evaluation of a family with a t(12;21) (p12.1;p11) translocation with unbalanced offspring.

Two brothers (Nos. 1 and 3), with physical and mental retardation and many other clinical characteristics in common, were both trisomic for 12p(ter leads to 12.1) and monosomic for 21p. Their mother (No. 5), the maternal grandmother (No. 7), aunt (No. 8), and a first-cousin (No. 9) were balanced translocation carriers, 46 rep (12;21) (p12.1;p11). Another cousin (No. 10) had Down syndrome: he had two normal 21 chromosomes in addition to both translocation chromosomes. A sister (No. 2), who died at the age of 1 year without being karyotyped, had several phenotypical features in common with her brothers. Our two cases of trisomy 12p (ter leads to 12.1) were compared with eight cases of trisomy 12p described earlier, and the following common characteristics were found: severe mental and physical retardation; flat and round, broad face with prominent cheeks; flat and broad nasal bridge with short nose; anteverted nostrils and large philtrum; broad and prominent lower lip; low-set or slanting ears, poorly formed with folded helix, prominent antihelix and deep concha; short neck; short sternum; "spade"-shaped fingers, the fifth being short; bilateral genu valgum; bilateral pes planus and talus valgus; increased space between the first and second toes; generalized hypotonia; and certain dermatoglyphic characteristics. An elevated serum lactate dehydrogenase (LDH) was measured in four cases.