Despite the favorable results from neurodevelopmental outcome studies, especially children with severe CH - defined as a serum FT4 < 5 pmol/L - may have subtle cognitive (e.g., memory problems) and motor deficits (clumsiness) that may result from TH deficiency in utero, not completely reversed by LT4 treatment started shortly after birth.2 The gene discussed is TH; the disease is cyclic hematopoiesis.