RESUMO
Fundamento y objetivo: La resistencia a la acción de las hormonas tiroideas (SRHT) es un síndrome causado mayoritariamente por mutaciones en el gen receptor beta de las hormonas tiroideas (THRB). Se estudian cinco familias con fenotipo de SRHT. Pacientes y método: Se realizó secuenciación de THRB. Se evaluó la respuesta a triyodotironina (T3) y efecto dominante negativo de los mutantes in vitro y se estudiaron los mecanismos de resistencia en sujetos sin mutación THRB cuantificando en cultivos de fibroblastos cambios de expresión en los genes regulator of calcineurin 2 (ZAKI4) y Kruppel-like factor 9 (BTEB). Resultados: Tres casos presentaron mutaciones en THRB: R243Q, R320C, R429Q, dando lugar a receptores TRβ con menor respuesta a T3. R243Q y R320C ejercen efecto dominante negativo. Un sujeto sin mutación THRB presentó cambios de expresión en ZAKI4 y BTEB similar a R230C, mientras que el otro mostró niveles de expresión superiores a los controles. Conclusiones: Mutaciones heterocigotas en THRB causaron tres de los casos de SRHT estudiados. Uno de los casos con SRHT sin mutación se comporta a nivel molecular como los portadores de mutación, mientras que en el otro la resistencia no está mediada por TRβ (AU)
Background and objective: Resistance to thyroid hormone (RTH) is a syndrome mostly caused by mutations in thyroid hormone receptor beta gen (THRB). We present five families with RTH phenotype. Patients and methods:THRB gene sequencing. In vitro studies to evaluate the mutants response to thyroid hormones and their dominant negative effect. Mechanism of resistance in patients with RTH without THRB mutations quantifying expression of regulator of calcineurin 2 (ZAKI4) and Kruppel-like factor 9 (BTEB) genes in patients fibroblast cultures.Results: THRB mutations were found in three cases: R243Q, R320C, R429Q. Mutants showed a decreased response to T3. R243Q and R320C had a strong dominant negative effect. One subject without THRB mutation showed changes in ZAKI4 and BTEB expression similar to R320C and the other showed expression levels higher than normal controls. Conclusions:Three cases of RTH were caused by THRB heterozygous mutations but in two cases mutations were not found. THRB mutation carriers and one of the patients without mutations share a similar mechanism of resistance and in the other subject RTH is TRβ independent (AU)
Assuntos
Humanos , /genética , Mutação/genética , Testes de Função Tireóidea/métodos , Receptores beta dos Hormônios Tireóideos/genéticaRESUMO
BACKGROUND AND OBJECTIVE: Resistance to thyroid hormone (RTH) is a syndrome mostly caused by mutations in thyroid hormone receptor beta gen (THRB). We present five families with RTH phenotype. PATIENTS AND METHODS: THRB gene sequencing. In vitro studies to evaluate the mutants response to thyroid hormones and their dominant negative effect. Mechanism of resistance in patients with RTH without THRB mutations quantifying expression of regulator of calcineurin 2 (ZAKI4) and Kruppel-like factor 9 (BTEB) genes in patients fibroblast cultures. RESULTS: THRB mutations were found in three cases: R243Q, R320C, R429Q. Mutants showed a decreased response to T3. R243Q and R320C had a strong dominant negative effect. One subject without THRB mutation showed changes in ZAKI4 and BTEB expression similar to R320C and the other showed expression levels higher than normal controls. CONCLUSIONS: Three cases of RTH were caused by THRB heterozygous mutations but in two cases mutations were not found. THRB mutation carriers and one of the patients without mutations share a similar mechanism of resistance and in the other subject RTH is TRß independent.
