A high prevalence of consanguineous and severe congenital hypothyroidism in an Iranian population.

To determine the incidence of permanent congenital hypothyroidism (CH) in Tehran and Damavand, cord blood spots were collected from February 1998-August 2002 and infants with TSH > or =20 mU/l were recalled. CH was confirmed in neonates (aged > or =7 days) with serum TSH >10 mU/l and T4 <84 nmol/l. Cases were followed up until September 2003. Dysgenesis was detected by thyroid imaging. In eutopic cases, serum TSH and T4 measurements following levothyroxine discontinuation (2-3 years of age) confirmed dyshormonogenesis and transient CH. Of 35,067 neonates, 373 (1.06%) were recalled and 25 (1:1,403 births) had permanent CH (six had transient CH and four remain unknown). Dysgenesis was detected in 18 (1:1,948 births) and dyshormonogenesis in seven (1:5,010 births) infants. Parental consanguinity was present in 10 (55.6%) dysgenetic, three (42.9%) dyshormonogenetic, and overall 6,648 (28.6%) of 23,227 screened infants. Odds ratio (95%CI(OR)) of consanguinity in permanent CH and dysgenesis was 2.75 (1.17-6.47) and 3.74 (1.33-10.52), respectively. The high prevalence of parental consanguinity in infants with permanent CH warrants genetic assessment.