Skeletal anomalies in trisomy 21 as an example of amplified developmental instability in chromosome disorders: a histological study of the feet of 21 mid-trimester fetuses with trisomy 21.

In a previous radiographic study on the feet of 71 adults with trisomy 21 we found, in comparison to control individuals, an increased prevalence of biphalangeal toes and metatarsophalangeal sesamoid bones. The present histological study on the feet of 21 mid-trimester fetuses with prenatally diagnosed trisomy 21 confirms results of the earlier study. At both stages of development these minor bone anomalies have about the same frequency, thus suggesting 1) that they are selectively neutral, and 2) that they reflect a basic (innate) failure of ordered morphogenesis. Our observation that the normal spatial pattern of skeletal variants is reproduced in trisomy 21 simply on a quantitatively higher level lends sound support to the hypothesis of amplified developmental instability in chromosome trisomies.