Type II citrullinaemia (CTLN2) is an adult- or late childhood-onset liver disease characterized by a liver-specific defect in argininosuccinate synthetase protein.
Adult-onset type II citrullinemia (CTLN2), characterized by a liver-specific deficiency of urea cycle enzyme, argininosuccinate synthetase, is caused by mutations in SLC25A13 that encodes a calcium binding mitochondrial solute carrier protein, citrin.
CTLN2 differs from classical citrullinaemia (CTLN1, OMIM 215700) in that CTLN1 is neonatal or infantile in onset, with ASS enzyme defects (in all tissues) arising due to mutations in ASS on chromosome 9q34 (refs 18-21).
Adult-onset type II citrullinemia (CTLN2) is a form of the disease that is defined by a quantitative decrease in ASS protein, but with normal kinetic properties.