Resistance to thyrotropin (TSH) (RTSH; defined by elevated TSH and a normal or hypoplastic thyroid gland) can be caused by mutations in genes encoding the TSH receptor and PAX8, and it has been linked to a locus on chromosome 15.
Analyses of the TSHR gene revealed two novel variants in a 2-year-old boy with thyroid hypoplasia: a missense mutation c.1582C>T (p.R528C) and a splice-site deletion c.392+4del4.
Complete TSH resistance due to biallelic LOF TSHR mutations must be suspected in all patients with severe not syndromic CH and severe thyroid hypoplasia diagnosed at birth by neonatal screening.
Although commonly regarded as sporadic disease, nonsyndromic thyroid hypoplasia has, in rare cases, been attributed to inherited defects in PAX8 and the TSHR gene.
Our observations also suggest that heterozygosity for an inactivating TSHR mutation may be associated with compensated hypothyroidism and thyroid hypoplasia.
Congenital hypothyroidism associated with thyroid hypoplasia can be caused by several genetic defects, including mutations in the TSHbeta-subunit, the TSH receptor, the G(s)alpha-subunit, and the transcription factor PAX8.
Inactivating germline mutations of both TSH receptor alleles lead to variable degrees of resistance to TSH, encompassing a spectrum ranging from euthyroid hyperthyrotropinemia to overt hypothyroidism with thyroid hypoplasia.
The autosomal recessive inheritance of mutations of the thyroid-stimulating hormone receptor gene was recognized in patients with CH and thyroid hypoplasia, while autosomal dominant mutations of the Pax-8 gene were described in patients with thyroid dysgenesis.
Autosomal recessive inheritance of mutations of the thyrotrophin (TSH) receptor gene has also been reported in patients with CH and thyroid hypoplasia, and autosomal dominant mutations of the PAX8 gene have been described in patients with different forms of thyroid dysgenesis.