Higher prevalence of permanent congenital hypothyroidism in the Southwest of Iran mostly caused by dyshormonogenesis: a five-year follow-up study

OBJECTIVE: The incidence of congenital hypothyroidism (CH) varies globally. This 5-year study aimed to determine the prevalence of permanent CH in the southwest of Iran. MATERIALS AND METHODS: Between January 2007 and December 2009, all newborns in Ahvaz, the biggest city in the southwest of Iran, were screened for CH using a heel-prick sample for thyrotropin (TSH) levels. Subjects with TSH ≥ 5 mU/L were evaluated for T4-TSH. Infants with T4 < 6.5 µg/dL, TSH > 10 mU/L, and normal T4 but persistent (> 60 days) high TSH were considered to have CH. After the third birthday, treatment was discontinued, and T4-TSH was reevaluated; subjects with TSH ≥ 10 mU/L were investigated using thyroid Tc99 scintigraphy (TS). Based on TS, they were classified as normal, dysgenetic, or athyretic (agenesis). RESULTS: Screening was performed for 86,567 neonates, and 194 were confirmed to have CH (100 males; F/M = 0.94; overall incidence 1:446). After the third birthday, reevaluation was performed in all (except 18 that were not accessible). From 176 patients, 81 (46%) were diagnosed with permanent CH, and 95 were discharged as transient. Considering the same percentage in the lost cases, the prevalence of permanent CH was found to be 1:970. TS performed for 53 of the permanent subjects found agenesis/dysgenesis in 25 (F:M = 15:10) and a normal result in 28 (F:M = 11:17), indicating dyshormonogenesis as the cause in more than 50% of subjects. CONCLUSIONS: The incidence of CH in this area was found to be higher than that in other countries but less than the incidence rate reported in central Iran. The large number of transient cases of CH suggests environmental or maternal causes for the incidence rather than a genetic basis.