Neonatal thyrotoxicosis and maternal infertility in thyroid hormone resistance due to a mutation in the TRbeta gene (M313T).

We report two unusual cases of resistance to thyroid hormone (RTH) in one family. The first case, a male infant, had clinical features of thyrotoxicosis in the neonatal period. In the fourth week of life weight gain was poor despite a daily intake of standard infant formula almost double the infant's estimated requirements.