Types of UCDs

There are six different types of UCDs, one for each enzyme in the urea cycle:

  • NAGS (N-acetyl glutamate synthetase) deficiency
  • CPS 1 (carbamoyl phosphate synthe-tase) deficiency
  • OTC (ornithine transcarbamylase) deficiency
  • CTLN1 (Citrullinemia type 1, ASD or ASL) deficiency
  • ALD (Argininosuccinic Aciduria, ASA, ASL or AL) deficiency
  • ARG (hyperargininemia) deficiency

There are also two enzyme transporter deficiencies, which are often considered UCDs:

  • HHH Syndrome (ORNT deficiency)
  • CTLN2 (Citrullinemia Type II or Citrin deficiency)