EFFECTS OF IMMIGRATION ON THE INCIDENCE OF CONGENITAL HYPOTHYROIDISM

Objective: The incidence of congenital hypothyroidism (CH) has been sh own to vary among different parts of the world. This could result from environmental or hereditary factors. Studies of other congenital dise ases have shown that immigrants tend to retain the incidence of their country of origin while their children acquire the incidence of their new homeland, suggesting an environmental influence. This study aimed to assess the differences in the incidence of CH among immigrants from different parts of the world and to study the effects of immigration on its occurrence. Methods: During the 9-year period between 1979 and 1987, 196 Jewish infants with primary CH were born in Israel; this con stitutes an incidence of 1:3354 live births. We collected data from ho spitals, endocrine pediatric clinics and the children's parents regard ing the birth place of the parents and grandparents of those infants. These data were compared with the birth place of the parents and grand parents of all infants born in Israel during that period in order to l earn about the incidence of CH among infants of different origins and to compare the incidence between children of parents born in Israel an d those of immigrants of the same grandparental origin. Results: CH in cidence was lower among offspring of mothers and fathers of Israeli or igin (1:4717 and 1:4255 live births respectively) and higher among tho se of African mothers (1:2950) and Asian fathers (1:2941). Parents of Asian or African origin, born in Israel have a lower incidence of CH-a ffected children compared with parents of the same origin born in thei r own continent. This trend is reversed for European and American pare nts, for whom being born in Israel is related to an increase in the CH incidence in their children. The difference in CH incidence between o ffspring of parents born in Israel and those of parents born in their original country was statistically significant (P<0.05). In the differ ent origin groups the gender of the parent did not influence significa ntly the incidence of CH. Conclusions: Environmental changes resulting from immigration can influence the incidence of congenital hypothyroi dism.