Crucially, since DUOX2 mutations may be associated with borderline bsTSH elevation but markedly subnormal venous free thyroxine (fT4) levels at confirmatory testing, higher bsTSH screening cutoffs may not detect these cases, resulting in overt hypothyroidism that remains untreated neonatally, although such dysfunction can resolve later in childhood (12). The gene discussed is DUOX2; the disease is hypothyroidism.