The leukodystrophy
Canavan disease is a fatal white matter disorder caused by loss-of-function mutations of the
aspartoacylase-encoding ASPA gene. There are no effective treatments available and experimental gene therapy trials have failed to provide sufficient amelioration from
Canavan disease symptoms. Preclinical studies suggest that
Canavan disease-like pathology can be addressed by either ASPA gene replacement
therapy or by lowering the expression of the
N-acetyl-L-aspartate synthesizing
enzyme NAT8L. Both approaches individually prevent or even reverse pathological aspects in
Canavan disease mice. Here, we combined both strategies and assessed whether intracranial adeno-associated virus-mediated gene delivery to a
Canavan disease mouse model at 12 weeks allows for reversal of existing pathology. This was enabled by a single vector dual-function approach. In vitro and in vivo biopotency assessment revealed significant knockdown of neuronal Nat8l paired with robust ectopic
aspartoacylase expression. Following nomination of the most efficient cassette designs, we performed proof-of-concept studies in post-symptomatic Aspa-null mice. Late-stage gene therapy resulted in a decrease of brain vacuoles and long-term reversal of all pathological hallmarks, including loss of
body weight, locomotor impairments, elevated
N-acetyl-L-aspartate levels,
astrogliosis, and
demyelination. These data suggest feasibility of a dual-function vector combination
therapy, directed at replacing
aspartoacylase with concomitantly suppressing
N-acetyl-L-aspartate production, which holds potential to permanently alleviate
Canavan disease symptoms and expands the therapeutic window towards a treatment option for adult subjects.