The Six Urea Cycle Disorders
There are six disorders of the urea cycle. Each is referred to by the initials of the missing enzyme.
| Location | Abb. | Enzyme | Disorder | Measurements |
| Mitochondria | NAGS | N-Acetylglutamate synthetase | N-Acetylglutamate synthase deficiency | +Ammonia |
| Mitochondria | CPS1 | Carbamoyl phosphate synthetase I | Carbamoyl phosphate synthetase I deficiency | +Ammonia |
| Mitochondria | OTC | Ornithine transcarbamylase | Ornithine transcarbamylase deficiency | +Ornithine, +Uracil, +Orotic acid |
| Cytosol | ASS | Argininosuccinic acid synthetase | "AS deficiency" or citrullinemia | +Citrulline |
| Cytosol | ASL | Argininosuccinase acid lyase | "AL deficiency" or argininosuccinic aciduria (ASA) | +Citrulline, +Argininosuccinic acid |
| Cytosol | ARG | Arginase | "Arginase deficiency" or argininemia | +Arginine |
Individuals with childhood or adult onset disease may have a partial enzyme deficiency. All of these disorders are transmitted genetically as autosomal recessive genes - each parent contributes a defective gene to the child, except for one of the defects, Ornithine Transcarbamylase Deficiency. This urea cycle disorder is acquired in one of three ways: as an X-linked trait from the mother, who may be an undiagnosed carrier; in some cases of female children, the disorder can also be inherited from the father's X-chromosome; and finally, OTC deficiency may be acquired as a "new" mutation occurring in the fetus uniquely. Recent research has shown that some female carriers of the disease may become symptomatic with the disorder later in life, suffering high ammonia levels. Several undiagnosed women have died during childbirth as a result of high ammonia levels and on autopsy were determined to have been unknown carriers of the disorder.
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