Congenital hypothyroidism, seasonality and consanguinity in the West Midlands, England.

Seasonal variation in the incidence of congenital hypothyroidism (CHT) is reported by some centres. Also, the incidence of CHT varies with ethnic origin. We report our experience in the West Midlands, England. The overall incidence of CHT among 1128 632 neonates screened over 16 years in the West Midlands was 1:2924 live births, but was increased (1:2323; p<0.05) between October and December. In the city of Birmingham between 1981 and 1991, the incidence of CHT was 1:781, 1:5540 and 1:2257 in Pakistani, Indian and North-West European children, respectively; no cases were seen in those from other ethnic groups. Consanguinity among those of Pakistani descent could account for the increased incidence within this population. Identification of the cause of seasonal variation may aid development of preventative strategies.