Adenylosuccinate lyase deficiency is a rare disorder; fewer than 100 cases have been reported. The condition is most common in the Netherlands and Belgium, but it has been found worldwide.

All forms of adenylosuccinate lyase deficiency are caused by mutations in the ADSL gene. This gene provides instructions for making an enzyme called adenylosuccinate lyase, which performs two steps in the process that produces purine nucleotides. These nucleotides are building blocks of DNA, its chemical cousin RNA, and molecules such as ATP that serve as energy sources in the cell. Adenylosuccinate lyase converts a molecule called succinylaminoimidazole carboxamide ribotide (SAICAR) to aminoimidazole carboxamide ribotide (AICAR) and converts succinyladenosine monophosphate (SAMP) to adenosine monophosphate (AMP).

Most of the mutations involved in adenylosuccinate lyase deficiency change single protein building blocks (amino acids) in the adenylosuccinate lyase enzyme, which impairs its function. Reduced function of this enzyme leads to buildup of SAICAR and SAMP, which are converted through a different reaction to succinylaminoimidazole carboxamide riboside (SAICAr) and succinyladenosine (S-Ado). Researchers believe that SAICAr and S-Ado are toxic; damage to brain tissue caused by one or both of these substances likely underlies the neurological problems that occur in adenylosuccinate lyase deficiency.

Studies suggest that the amount of SAICAr relative to S-Ado reflects the severity of adenylosuccinate lyase deficiency. Individuals with more SAICAr than S-Ado have more severe encephalopathy and psychomotor delay.