Study On TSH Receptor Gene Inactivating Mutations In The Syndrome Of Resistance To TSH

IntroductionResistance to thyrotropin (TSH) is a syndrome of reduced sensitivity to a biologically active TSH molecule, which is caused by the defect of TSH receptor (TSHR) itself or disfunction of postreceptor signal transfer in cell. Subjects have elevated TSH levels but no goiter. However, thyroid hormone concentration may vary from normal to very low, depending on the severity of the resistance. So it manifests such two types as subclinical hypothyroidism and congenital hypothyroidism (CH). The syndrome of resistance to TSH caused by inactivating mutations in TSHR gene has been recognized in recent years, and the TSHR gene is considered to be one of the candidate genes involved in the syndrome. The TSHR gene is located on human chromosome 14q31, it spans 188kbp and is composed of 10 exons and 9 introns. The mRNA is 4.4kb long. Mutations in the TSHR gene have been reported in 22 families with homozygous or compound heterozygous or heterozygous inheritance. The mutant TSHRs show reduced or no function due to either altered ligand binding or defect inmembrane expression. However, these inactivating mutations in TSHR gene have only been detected in foreign population, nothing has been reported in Chinese population. In the present study, we evaluated 60 Chinese children in Zhejiang province with the syndrome of resistance to TSH and performed the genetic analysis of TSHR, in order to study the TSHR genetic mutation types, and the correlation between genetype and clinical manifestations which is of great help to early diagnosis, prevention and treatment in children with subclinical hypothyroidism or CH.Materials and MethodsSubjectsA total of 60 children, born between October 1999 and December 2004, diagnosed with the syndrome of resistance to TSH at the Zhejiang Neonatal Screening Center, were enrolled, including 10 subclinical hypothyroidism and 50 CH. Meanwhile, the genomic DNA from 100 normal children was collected for genetic analysis, which served as controls.MethodsThe 60 children with the syndrome of resistance to TSH and 100 normal children were evaluated. The coding region of the TSHR gene was amplified by polymerase chain reaction (PCR) and sequenced.Results(1) We detected a compound heterozygous missense mutations in one patient (Pro52Thr/Val689Gly).(2) We detected a heterozygous missense mutation in one patient (Gly245Ser).(3) In 56 patients the normal guanine at position 2181 in exon 10 was replaced by a cytosine, resulting in the placement of Glu727 by Asp. The same placement wasobserved in 96 normal children.(4) In 37 patients and 62 normal children, there was a single nucleotide polymorphism in exon 7 at nucleotide 561 (AAT—>AAC). This substitution did not change the amino acid in position 187.Conclusions(1) Three heterozygous missense mutations (Pro52Thr, Val689Gly, Gly245Ser) were firstly detected in Chinese children with the syndrome of resistance to TSH.(2) The normal nucleotide at position 2181 in exon 10 was cytosine in Chinese population, while the guanine was a polymorphism.(3) There was a single nucleotide polymorphism in exon 7 at nucleotide 561 (AAT—>AAC). This substitution did not change the amino acid in position 187.