Partial trisomy of chromosome no. 1 in two adult brothers due to maternal translocation (1q--;6p+).

Extra chromosome material on the short arm of chromosome no. 6 (46,XY,6p+) was found in two mentally retarded adult half-brothers with mildly dysmorphic features. The phenotypically normal mother had a balanced translocation between the long arm of chromosome no. 1 and the short arm of chromosome no. 6:46,XX,t(1;6)(q32;p25). Thus the two affected brothers were trisomic for the long arm segment of chromosome no. 1, distal to q 32. These patients, with mildly dysmorphic features and mental retardation, represent the first cases of partial trisomy 1q surviving to adult-hood. The clinical and cytogenetic data obtained from eight individuals with partial trisomies for different long arm segments of chromosome no. 1 suggest that partial trisomy of the distal two-thirds of the long arm in characterized by severe malformations, growth retardation, and early death. Conversely, partial trisomy for the distal one-third of the long arm is associated with milder malformations and longer survival time as well as growth and mental retardation.