Metabolic acidosis stimulates renal ammoniagenesis with proportionate urinary excretion where it combines with H+ ions to promote acid excretion.[6] Ammonia is eventually taken up from the portal and systemic venous circulation by hepatocytes and incorporated into urea cycle to produce urea, which is excreted by kidneys.[7] The brain also metabolizes small amounts of circulating ammonia, which crosses the blood–brain barrier utilizing glutamine synthetase (GS), which is exclusive to glia in central nervous system. The gene discussed is GLUL; the disease is metabolic acidosis.