Partial trisomy 21.

This report presents and 18 1/2-year-old patient with clinical features of Down syndrome and severe mental retardation due to partial trisomy 21. Cytogenetic studies using Giemsa banding chromosomes revealed translocation of the 21q21 qter segment onto the short arms of chromosome #8 (46,XY,--8, + t(8qter 8p23::21q21 21 qter)). It is recommended that patients with features of Down syndrome whose chromosome analysis was done prior to introduction of banding studies undergo repeat karyotyping.