Congenital primary hypothyroidism can be caused by reduced or absent responsiveness of the thyroid gland to thyrotropin (TSH), which normally binds to the thyrotropin receptor (TSHR) and exerts its effects mainly by stimulating intracellular cyclic adenosine monophosphate (cAMP). So far 22 causative loss-of-function mutations in the
TSHR
gene have been reported as occurring in families from different ethnic and geographical origins. We here report a family of Turkish origin in which all four children were diagnosed as having congenital primary hypothyroidism. A homozygous nonsense mutation in codon 609 (R609X) of the
TSHR
gene was identified in all affected individuals as the underlying molecular defect. The mutation leads to a truncated
TSHR
, which is likely to be biologically inactive. This mutation has been identified before to cause resistance to TSH in a large Bedouin kindred where two affected hypothyroid individuals were also resistant to adrenocorticotrophic hormone (ATCH). Interestingly none of the affected individuals in our family had symptoms consistent with hypocortisolism, which excludes a direct impact of this
TSHR
mutation on the hypothalamicpituitary-adrenal axis.
