Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is an ultrarare, infantile-onset leukodystrophy characterized by white matter edema for which there is no treatment. More than 75% of diagnosed cases result from biallelic loss-of-function mutations in the astrocyte-specific gene MLC1, leading to early-onset macrocephaly, cerebellar ataxia, epilepsy, and mild cognitive decline. To develop a gene therapy for MLC, we administered an adeno-associated viral vector capable of crossing the murine blood-brain barrier, delivering the human MLC1 cDNA under the control of a human astrocyte-specific promoter, to 10-month-old Mlc1-/- mice. We observed long-term astrocyte-driven expression of MLC1 up to 1 year after viral vector administration in all brain areas analyzed. Despite the late-stage intervention, in vivo magnetic resonance imaging revealed normalization of water accumulation. Notably, our therapy successfully reversed locomotor deficits in Mlc1-/- mice, as evidenced by improved performance in motor tests assessing cerebellar ataxia-like behaviors. Collectively, these findings not only demonstrate the sustained efficacy of our gene therapy but also highlight the reversibility of vacuolation and motor impairments in Mlc1-/- mice, suggesting that MLC patients could benefit from treatment even after symptom onset.

Loss-of-function mutations in the CLCN2 gene were recently discovered to be a cause of a type of leukodystrophy named CLCN2-related leukoencephalopathy (CC2L), which is characterized by intramyelinic edema. Herein, we report a novel mutation in CLCN2 in an individual with leukodystrophy. A 38-year-old woman presented with mild hand tremor, scanning speech, nystagmus, cerebellar ataxia in the upper limbs, memory decline, tinnitus, and dizziness. An ophthalmologic examination indicated macular atrophy, pigment epithelium atrophy and choroidal capillary atrophy. Brain magnetic resonance imaging (MRI) showed the diffuse white matter involvement of specific white matter tracts. Decreased diffusion anisotropy was detected in various brain regions of the patient. Diffusion tensor tractography (DTT) showed obviously thinner tracts of interest than in the controls, with a decreased fiber number (FN), increased radial diffusivity (RD) and unchanged axial diffusivity (AD). A novel homozygous c.2257C > T (p.Arg753Ter) mutation in exon 20 of the CLCN2 gene was identified. CC2L is a rare condition characterized by diffuse edema involving specific fiber tracts that pass through the brainstem. The distinct MRI patterns could be a strong indication for CLCN2 gene analysis. The findings of our study may facilitate the understanding of the pathophysiology and clinical symptoms of this disease.