 Normally these compounds are not present in the cerebrospinal fluid or urine because ASL acts on the majority of the substrate molecules before they can build up and be phosphorylated.In the past there has not been a good test for adenylosuccinate lyase deficiency, making the rare disease difficult to diagnose, but recently a test was developed to detect SAICA and S-Ado in the urine.The test is inexpensive and had no false positives or false negatives in the researchers’ small sample.