Canavan disease, spongy degeneration of the brain, is an autosomal recessive disorder with increased prevalence among Ashkenazi Jews. The biochemical marker for this disease is increased levels of N-acetylaspartic acid, due to the defective enzyme, aspartoacylase. This discovery allowed for accurate diagnosis of the disease. The gene for aspartoacylase has been cloned and two mutations have been found to be responsible for Canavan disease among Ashkenazi Jewish patients in 98% of the cases. Molecular analysis of healthy Jewish individuals for these mutations has resulted in an unexpectedly high carrier frequency for Canavan disease among Jews. Therefore, carrier testing of the Jewish population is possible and indicated.