THRA and hypothyroidism: RTHα, a dominantly-inherited or sporadic disorder, due to heterozygous THRA mutations affecting TRα1 alone or in combination with variant α2 protein, is characterised by clinical, biochemical and physiological features of hypothyroidism in specific tissues, together with subtle abnormalities (low T4/T3 ratio, variably reduced rT3) of thyroid function.