SECISBP2 and Allan-Herndon-Dudley syndrome: Abnormally high or low FT3/FT4 ratios are seen in several congenital disorders that may affect peripheral thyroid hormone economy, such as Allan-Herndon-Dudley syndrome (MCT8 deficiency) [4], selenocysteine insertion sequence binding protein 2 deficiency [5], and thyroid hormone resistance [6, 7].