RESUMO
Iodine deficiency is the most important etiological factor for euthyroid endemic goiter. However, family and twin pair studies also indicate a genetic predisposition for euthyroid simple goiter. In hypothyroid goiters several molecular defects in the thyroglobulin (TG), thyroperoxidase (TPO), and Na+/I- symporter (NIS) genes have been identified. The TSH receptor with its central role for thyroid function and growth is also a strong candidate gene. Therefore, we investigated a proposita with a relapsing euthyroid goiter and her family, in which several members underwent thyroidectomy for euthyroid goiter. Sequence analysis of the complementary DNA (cDNA) of the TPO and TSH receptor genes revealed several previously reported polymorphisms. As it is not possible to exclude a functional relevance for all polymorphisms, we opted for linkage analysis with microsatellite markers to investigate whether the candidate genes are involved in the pathogenesis of euthyroid goiter. The markers for the genes TG, TPO, and NIS gave two-point and multipoint logarithm of odds score analysis scores that were negative or below 1 for all assumed recombination fractions. As no significant evidence of linkage was found, we conclude that these candidate genes can be excluded as a major cause of the euthyroid goiters in this family. In contrast, we have found evidence for linkage of familial euthyroid goiter to the recently identified locus for familial multinodular nontoxic goiter (MNG-1) on chromosome 14q. The haplotype cosegregates clearly with familial euthyroid goiter. Our results provide the first confirmation for MNG-1 as a locus for nontoxic goiter.
Assuntos
Proteínas de Transporte/genética , Mapeamento Cromossômico , Ligação Genética , Bócio Nodular/genética , Bócio/genética , Iodeto Peroxidase/genética , Proteínas de Membrana/genética , Simportadores , Tireoglobulina/genética , Adolescente , Adulto , Idoso , Northern Blotting , Cromossomos Humanos Par 14/genética , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Hibridização de Ácido Nucleico , Linhagem , Receptores da Tireotropina/genética , RibonucleasesRESUMO
Autosomal dominant nonautoimmune hyperthyroidism is a hereditary form of hyperthyroidism caused by constitutively activating germline mutations in the TSH-receptor gene. Clinical features comprise familial prevalence of thyroid autonomy in more than 2 generations and conditions of persisting neonatal hyperthyroidism or nonautoimmune hyperthyroidism of childhood onset with frequent relapses of hyperthyroidism under thyrostatic therapy and after thyroid surgery. Once clinically suspected the diagnosis can be confirmed by mutation analysis of genomic DNA extracted from a routinely obtainable EDTA blood sample. In patients with hereditary nonautoimmune hyperthyroidism a near total thyroidectomy is recommended as the first line treatment to avoid relapses from residual thyroid tissue with the activating TSHR mutation. Furthermore, genetic counselling of the affected patients is advised.