First U.S. case of adenylosuccinate lyase deficiency with severe hypotonia

Adenylosuccinate lyase (ASL) deficiency is a defect in purine de novo synthesis pathway. The disease has variable clinical presentation involving psychomotor retardation, seizures, hypotonia, and autism. The presence of succinyladenosine and succinylaminoimidazole carboxamide riboside (SAICA riboside) in body fluids characterizes the biochemical phenotype. All cases of ASL deficiency described to date have been diagnosed in Europe. Using a high-resolution thin-layer chromatography (TLC) technique combining screening for ASL deficiency and disorders of saccharide metabolism, we found the first case of this disease in the US. The patient presented with delayed motor development and profound hypotonia. The family history and routine laboratory tests were negative. Screening for metabolic disorders detected the presence of succinyladenosine and SAICA riboside in urine. The activity of ASL in the patient's skin fibroblasts was 43% of controls (patient, mean = 1.20 nmol/min/mg of protein, s = 0.21, n = 3; controls, mean = 2.78 nmol/min/mig of protein, s = 0.61, n = 7). In a 15-month-old girl with profound hypotonia, we established the diagnosis of ASL deficiency by demonstrating succinyladenosine and SAICA riboside in urine and decreased residual activity of ASL in skin fibroblasts.