[Epidemiology of congenital hypothyroidism in France: recent data].

Congenital hypothyroidism (CH) is the leading cause of preventable mental retardation. It is mainly due to thyroid dysgenesis or dyshormonogenesis with normally located gland, and detected at birth in developed countries, by mass biochemical screening of newborns. An increase in the incidence of congenital hypothyroidism with a normally located gland has been reported worldwide over the last three decades. The etiology of CH with a normally located gland remains elusive and the factors driving its clinical diversity are largely unknown. A role for known dyshormonogenesis-associated genetic variants or TSH receptor gene variants is well-known, but the possible effects of environmental agents toxic to the fetal and neonatal thyroid gland are currently being investigated.