The common feature of urea cycle diseases (UCD) is a defect in ammonium elimination in
liver, leading to hyperammonemia. This excess of circulating ammonium eventually reaches
the central nervous system, where the main toxic effects of ammonium occur. These are
reversible or irreversible, depending on the age of onset as well as the duration and the
level of ammonium exposure. The brain is much more susceptible to the deleterious effects
of ammonium during development than in adulthood, and surviving UCD patients may …