Low TSH congenital hypothyroidism: Identification of a novel mutation of the TSH β-subunit gene in one sporadic case (C85R) and of mutation Q49stop in two siblings with congenital hypothyroidism
Isolated congenital hypothyroidism resulting from mutation of the TSH β-subunit gene, has rarely been reported. In the present article, we report a new mutation (C85R) in exon 3 of the TSH β-subunit gene in one sporadic case and the mutation Q49stop in two siblings with congenital hypothyroidism. The novel mutation is a T to C transition at codon 85, resulting in a change of cysteine to arginine (C85R) of the β-subunit. Because the cysteine residues of all glycoproteins are highly conserved, this mutation is expected to result in conformational changes of the β-subunit, rendering it incapable to form a functional heterodimer with the α-subunit. The second mutation described is a C to T transition resulting in a premature stop at codon 49 (Q49stop), leading to the formation of a truncated protein. Although the two siblings reported herein carried the same mutation, they had slightly modified clinical and biochemical phenotype. The mutation C85R and the previously described E11 stop have, thus far, exclusively been detected in Greek patients. The Q49stop mutation initially detected in Greek patients was subsequently identified in an Egyptian girl and most recently in two Turkish siblings. These three reports possibly indicate the presence of a mutational hot spot on the TSH β-subunit gene. Hence, with the novel mutation herein reported, a total of five mutations of the TSH β-subunit gene are recognized as a cause of low-TSH congenital hypothyroidism worldwide
