Hypothyroidism in siblings due to a homozygous mutation of the TSH-beta subunit gene

We report two American sisters of Scottish-Irish ancestry with isolated thyrotropin (TSH) deficiency. The diagnosis of central congenital hypothyroidism was based on low levels of TSH and free thyroxine. Sequencing of the TSH-beta subunit gene revealed a homozygous single nucleotide deletion in codon 105, producing a frame shift and resulting in inactive TSH. This mutation has previously been reported in a Brazilian family, two German families, and a Belgian family. Our case, along with a review of the other reports, supports the theory that this mutation may be a common cause of isolated TSH deficiency.