Clinical Consequences of Variable Results in the Measurement of Free Thyroid Hormones: Unusual Presentation of a Family with a Novel Variant in the THRB Gene Causing Resistance to Thyroid Hormone Syndrome.

Variable results of TFTs on some immunoassays can be a cause of RTHβ diagnostic delay, but the genotype-phenotype correlation in this family and functional studies support p.L428V as a novel variant expanding the spectrum of gene variants causing RTHβ. In vivo, rather than in vitro, functional assays may be required to demonstrate the dominant negative action of variants.