Objective: The inactivating mutation of thyrotropin receptor (TSHR) gene results in partial or complete insensitivity of thyrotropin (TSH) and dysfunction of the TSH-TSHR-cAMP cascade. Therefore, it may cause congenital hypothyroidism (CH). Depending on the degree of impairment of TSHR function, patients can present with subclinical hypothyroidism at one extreme of the spectrum, or severe hypothyroidism at the other. This study aimed to understand the relation between inactivating mutations of TSHR gene and Chinese children with CH.
Methods: (1) Seventy-nine Chinese children with CH, including 14 subclinical hypothyroidism patients (8 boys and 6 girls, age 1 - 5.5 years) and 65 hypothyroidism patients (27 boys and 38 girls, age 1.5 - 6 years) were enrolled in this study. Meanwhile, 100 normal children were enrolled as control, 40 were male and 60 were female. The age of the normal children were at a range of 1 - 8 years. (2) Total genomic DNA was extracted from peripheral blood leukocytes of the 79 patients and 100 normal subjects. Exons 1 - 10 of TSHR gene were individually amplified by polymerase chain reaction (PCR) and mutations were detected by direct sequencing.
Results: (1) A compound heterozygous missense mutations (Pro52Thr/Val689Gly) and a heterozygous missense mutation (Gly245Ser) were detected in 79 patients. The mutations of Pro52Thr and Gly245Ser were located within the extracellular domain of TSHR, while Val689Gly was located within the intracellular domain of TSHR. In 30 patients the normal cytosine at position 2181 in exon 10 was replaced by a guanine (GAC-->GAG), resulting in the replacement of Glu(727) by Asp. In 47 patients, the normal thymidine at position 561 in exon 7 was replaced by a cytosine (AAT-->AAC). This substitution did not change the amino acid (Asn) at position 187. (2) In 33 normal children the normal cytosine at position 2181 in exon 10 was also replaced by a guanine (GAC-->GAG) and in 50 normal children the normal thymidine at position 561 in exon 7 was replaced by a cytosine (AAT-->AAC).
Conclusions: Three heterozygous missense mutations (Pro52Thr, Gly245Ser, Val689Gly) of TSHR gene were firstly detected in Chinese children with CH. There was a polymorphism in exon 10 at nucleotide 2181 (GAC-->GAG) and in exon 7 at nucleotide 561 (AAT-->AAC) in TSHR gene. The inactivating mutation of TSHR gene is an infrequent pathogeny for CH.