Argininosuccinate Lyase (ASL) Deficiency Workup

Updated: Jan 07, 2019
  • Author: Karl S Roth, MD; Chief Editor: Maria Descartes, MD  more...
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Laboratory Studies

No routine laboratory data assist diagnosis of argininosuccinate (ASA) lyase deficiency.

BUN testing is subject to numerous factors aside from the rate of production via the urea cycle. Among the most obvious is the state of hydration, which frequently causes an artifactual increase to a normal concentration in a very sick infant. A very low BUN level is suggestive but must never be relied on as a diagnostic indicator.

As with all other urea cycle disorders, clinical suspicion is essential and should prompt the clinician to obtain blood ammonia levels, which are significantly elevated in symptomatic patients. This finding should lead to an immediate blood and urine amino acid quantitation, which confirms the presence of argininosuccinic acid in both fluids. In addition, levels of blood citrulline, glutamine, alanine, and lysine may be increased. Argininosuccinic acid lyase may be assayed in cultured fibroblasts, providing the definitive biochemical diagnosis. Urine orotic acid levels are elevated.

All 50 states in the United States include argininosuccinate (ASA) lyase deficiency in their newborn screening programs.


Other Tests

Molecular diagnosis is available for diagnostic confirmation. Prenatal diagnosis is possible, but the nature of the mutation must be known, given the wide variety of private mutations reported.