Therapeutic suppression of Tubb4a rescues H-ABC leukodystrophy

Hypomyelination and atrophy of basal ganglia and cerebellum (H-ABC) is a rare leukodystrophy associated with causal variants in β-tubulin 4A (TUBB4A). The recurring variant p.Asp249Asn (D249N) presents in infancy with dystonia, communication deficits, and loss of ambulation during the first decade of life. In this study, we characterized a genetic murine series (Tubb4a^KO/KO, Tubb4a^D249N/+, Tubb4a^D249N/KO, and Tubb4a^D249N/D249N) to demonstrate that disease severity correlates with the expression of mutant Tubb4a and relative preservation of wild-type tubulin. To further evaluate the translational potential of Tubb4a suppression as a therapy in H-ABC, we identified a well-tolerated Tubb4a-targeted antisense oligonucleotide (ASO) candidate that selectively reduces Tubb4a. Notably, single intracerebroventricular administration of ASO in postnatal Tubb4a^D249N/KO mice drastically extends its lifespan, improves motor phenotypes, and reduces seizures. Neuropathologically, treating ASO Tubb4a^D249N/KO mice prevents myelin and oligodendrocyte (OL) loss and recovers visual evoked potential latencies in vivo. Furthermore, the microtubule function of Mbp mRNA transport from the OL soma to the myelin sheath is retained. A major limitation we noted is that ASOs fail to target cerebellar granule neurons even with multiple routes of administration in the brain. This is the first preclinical proof-of-concept for Tubb4a suppression via ASO as a disease-modifying therapy for H-ABC.