SELENOS and hyperinsulinemic hypoglycemia, familial, 4: Diminished activity of deiodinase enzymes and low circulating selenoproteins cause a distinctive biochemical signature of raised FT4, normal or low FT3, normal or raised TSH, elevated reverse T3 and low circulating selenium concentrations in all patients (Table 4); this biochemical pattern has also been documented in 2 patients with selenoprotein deficiency due to a homozygous nucleotide substitution in TRU-TCA1-1 (46).