Epidemiology of thyroid dysgenesis: the familial component.

The pathophysiology of thyroid dysgenesis remains unclear and, until recently, this disorder was generally regarded as sporadic. However, a small but significant proportion of familial cases have been identified (2%) through the study of subjects with congenital hypothyroidism, and more recent work has revealed an even higher proportion of familial thyroid dysgenesis in both symptomatic and asymptomatic individuals. These studies strongly suggest the existence of a familial component of this disorder involving dominant genetic predisposition factors with a low penetrance.