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

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Abstract
Two brothers (Nos. 1 and 3), with physical and mental retardation and many other clinical characteristics in common, were both trisomic for 12p(ter .fwdarw. 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 rcp (12;21) (p12.1;p11). Another cousin (No. 10) had Down syndrome: he had 2 normal 21 chromosomes in addition to both translocation chromosomes. A sister (No. 2), who died at the age of 1 yr without being karyotyped, had several phenotypical features in common with her brothers. The 2 cases of trisomy 12p (ter .fwdarw. 12.1) were compared with 8 cases of trisomy 12p, 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 5th being short; bilateral genu valgum; bilateral pes planus and talus valgus; increased space between the 1st and 2nd toes; generalized hypotonia; and certain dermatoglyphic characteristics. An elevated serum lactate dehydrogenase (LDH) was measured in 4 cases.