Clustering of Juvenile Canavan disease in an Indian community due to population bottleneck and isolation: genomic signatures of a founder event

Urine N-Acetylaspartate Distinguishes Phenotypes in Canavan Disease

Canavan disease (CD) is an ultra-rare autosomal recessive leukodystrophy caused by loss-of-function mutations in ASPA, which encodes aspartoacylase (ASPA), leading to accumulation of N-acetylaspartate (NAA). Patients with CD typically present with profound psychomotor deficits within the first 6 months of life and meet few motor milestones. Within CD a subset of patients exhibits a milder phenotype with more milestone acquisition, possibly related to greater residual ASPA activity. An ongoing CD natural history study and a literature search were leveraged to compare urine NAA levels and associated genotypes in patients classified with mild or typical CD, with the hypothesis that urine NAA levels reflect ASPA activity and therefore can distinguish between the two phenotypes. Urine NAA levels were lower, on average (p < 0.0001), in individuals with mild (mean 525.3, range 25.2-1,335 mmol/mol creatinine [Cr]) compared with typical CD (mean 1,369, range 391.7-2,420 mmol/mol Cr). Mutations R71H and Y288C, variants that may harbor residual ASPA activity, were unique to the mild phenotype population (56%, 14/25) and not found in individuals with a typical phenotype (0%, 0/39). In aggregate, urine NAA levels can distinguish between mild and typical CD phenotypes, suggesting the ability to reflect ASPA activity.

Cellular and molecular mechanisms of aspartoacylase and its role in Canavan disease

Canavan disease is an autosomal recessive and lethal neurological disorder, characterized by the spongy degeneration of the white matter in the brain. The disease is caused by a deficiency of the cytosolic aspartoacylase (ASPA) enzyme, which catalyzes the hydrolysis of N-acetyl-aspartate (NAA), an abundant brain metabolite, into aspartate and acetate. On the physiological level, the mechanism of pathogenicity remains somewhat obscure, with multiple, not mutually exclusive, suggested hypotheses. At the molecular level, recent studies have shown that most disease linked ASPA gene variants lead to a structural destabilization and subsequent proteasomal degradation of the ASPA protein variants, and accordingly Canavan disease should in general be considered a protein misfolding disorder. Here, we comprehensively summarize the molecular and cell biology of ASPA, with a particular focus on disease-linked gene variants and the pathophysiology of Canavan disease. We highlight the importance of high-throughput technologies and computational prediction tools for making genotype-phenotype predictions as we await the results of ongoing trials with gene therapy for Canavan disease.