Administration of PB has been used as an ammonia‐lowering drug for patients with UCD (Brusilow, 1991), but depletion of circulating BCAA has been observed in these patients (Scaglia et al., 2004), and PB has directly been shown to activate the BCKA dehydrogenase complex (Brunetti‐Pierri et al., 2011). The gene discussed is ARID4B; the disease is urea cycle disorder.