Biochemical Differentiation of Trisomic Down's Syndrome (Mongolism) from That Due to Translocation

IN 1959 Lejeune, Gautier and Turpin1 observed that patients with Down's syndrome had 47 chromosomes instead of the usual 46. An extra small acrocentric chromosome, belonging to the No. 21 group, was present, producing "trisomy 21." Since then, other patients with mongolism have been described with only 46 chromosomes but with "translocation" of chromatin material from 1 chromosome to another. If an entire chromosome is translocated an equivalent trisomy is produced. (In translocations of human acrocentric chromosomes part of the short arms may be deleted in the process of translocation.) Thus, there are at least 2 very distinct types of . . .