Testing the hypothesis of amplified developmental instability in autosomal trisomies as proposed by Shapiro we predicted and found an increased frequency of symphalangies in the toes of patients with Down syndrome. In our X-ray study of the feet of 71 adults with trisomy 21 we also detected a greater than normal number of sesamoid bones.
A corollary to Shapiro's hypothesis is a dependence on ethnic origin of the frequency of symptoms in Down syndrome. Compared to data from Europe, toe symphalangies are more prevalent in Japan. We predict this anomaly to occur even more often in Japanese patients with trisomy 21.