Novel Gene Therapy Strategies for Canavan Disease

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ABSTRACT Canavan disease (CD) is a rare childhood leukodystrophy caused by autosomal recessive mutations in the aspartoacylase (ASPA) gene. Deficiency of ASPA in Canavan patients leads to the accumulation of N- Acetyl-Aspartic Acid (NAA), resulting in swelling and spongy degeneration of white matter in the brain. The clinical manifestations of this fatal disease include psychomotor retardation, muscular hypotonia, macrocephaly, head lag, seizures, and early death. Synthesis of NAA is carried out in the mitochondria of neurons by N-acetyltransferase-8-like (NAT8L) and hydrolyzed in oligodendrocytes by ASPA. Gene replacement therapy for ASPA deficiency is currently the most promising strategy for treating CD. Notably, we have recently achieved full therapeutic correction of the Canavan phenotype in the Aspa knockout (CD-KO) mouse model. A single intravenous injection of recombinant adeno-associated virus packaged with the human ASPA transgene (rAAV-hASPA) at early ages completely resolves neuropathology, resulting in treated animals that outperform wild-types in motor function tests. However, based on strong preliminary evidence, we now hypothesize that the CD phenotype presents a secondary etiology related to metabolism dysfunction. In addition, we recently revealed that overexpression of ASPA in wild type cells in vitro resulted in abnormal mitochondrial shape and function. These findings necessitate further preclinical investigations that focus on: 1) characterizing the possible toxicity of ASPA overexpression in cell types of the CNS and peripheral organs, 2) developing ASPA regulatory cassette(s) that can mimic endogenous physiological levels of ASPA to circumvent adverse effects that may exist due to treatment, and 3) determining the physiological and behavioral effects of ASPA overexpression using a clinically relevant non-human primate model. Our new research strategy now builds on our current promising progress and advances our goals for a safe and effective gene therapy for CD.