Partial trisomy 12q: a clinically recognisable syndrome. Genetic risks associated with translocations of chromosome 12q.

A newborn child with an unusual facial appearance and multiple abnormalities was found to be trisomic for a large part of 12q as a result of adjacent 1 segregation of a familial translocation, t(9;12) (p24;q21.2). A combination of cytogenetic analysis, clinical features, and enzyme marker studies allows an accurate assessment of the breakpoints. Although trisomic for a considerably larger area of 12q than other reported cases, there are many similar features suggesting that trisomy 12q is a clinically recognisable syndrome. The frequency and mode of segregation of 12q translocations and their implications for genetic counselling are discussed.