Review Article
Metabolic Causes of Epileptic Encephalopathy
Table 7
Urea cycle defects and biochemical characteristics.
| Defective enzyme
or component | Citrulline | Arginine | Ammonia | Additional biochemical characteristics |
| | Ornithine transcarbamylase | ↓ | ↓ | ↑ | ↑ Glutamine
Normal orotic acid | |
Carbamoylphosphate synthetase I (CPS1) | ↓ | ↓ | ↑ | ↑ Glutamine
↑ Orotic acid | | N-acetyl glutamate synthase (NAGS) | | | | Reduced CPS1 activity
(NAGS is a vital cofactor) | | Argininosuccinate synthase (ASS) | ↑++
(10–100x normal) | ↓ | ↑ | | | Argininosuccinate lyase (ASL) | ↑ | ↓ | ↑ | ↑ Argininosuccinic acid (unique to ASL deficiency) | | Arginase (ARG1) | | | Normal in absence of metabolic stress | | | Ornithine transporter mitochondrial I (ornithine translocase deficiency) | | | ↑ | ↑ Homocitrulline
↑ Ornithine | | Citrin (solute carrier family 5) deficiency | ↑ | | | |
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Adapted from Pearl [2].
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