The frequency of trisomy and translocation in Down's syndrome.

Abstract

Data are now available to provide guidelines for determining which patients with Down's syndrome, and their families, should be studied by chromosomal analysis to determine if the disorder is genetically transmitted. Tables are presented to indicate the approximate incidence or frequency of the trisomy and translocation syndromes at different maternal ages, as well as the probability of a transmittable translocation. Available data indicate that if the maternal age is less than 30 years at the time of the birth of an infant with Down's syndrome, there is a 1 in 50 probability that the affected child has an inherited translocation; if the maternal age is 30 years or over, the chances are abou..