Endocrine Abstracts

Loss-of-function mutations in the TSH receptor (TSHR) gene are one of the most common known causes of congenital hypothyroidism (CH). While heterozygous mutations result in nonautoimmune isolated hyperthyrotropinemia, homozygous and compound heterozygous mutations may cause overt CH of various severity depending on the localization and type of the mutations.

In our study we performed the systematic genetic analysis of the TSHR gene of a cohort of 85 Hungarian patients diagnosed postnatally with CH in Szeged, one of the two Hungarian centres involved in the neonatal TSH screening program. Patients’ detailed clinical data were collected and DNA was isolated from peripheral blood. Genetic analysis was implemented at the Division of Endocrinology and Metabolic Disease, Laboratory of Endocrine and Metabolic Research, Italian Auxological Institute, as follows. Exons and their immediate flanking intronic sequences were PCR amplified. Examination of the resulting PCR fragments were performed either with denaturing HPLC (DHPLC), or with direct sequencing, where it was appropriate. In those cases, where DHPLC result indicated genetic alteration, sequencing was also performed.

As a result, beside polymorphic variants, we identified six missense mutations in four patients, among which two mutations are new, so far unidentified naturally occurring mutations (N432D and P449L). Patients 24 and 79 harboured heterozygous mutations (N432D and P162A respectively), whereas Patients 52 and 58 were compound heterozygotes (P162A–P449L and C41S–P162A respectively).

As all four patients had overt CH, genetic examination of the post-transcriptional regulatory elements of the TSHR gene in the heterozygous patients may be also considered. These results along with future genetic examination of the patients’ families, as well as the in vitro functional studies of the new mutations may help us deciphering further details of the complex signalling mechanism through TSHR.