Clinical, neuroimaging and genetic findings in the Japanese case series of CLCN2-related leukoencephalopathy

Biallelic loss-of-function variants in CLCN2 lead to CLCN2-related leukoencephalopathy (CC2L), also called leukoencephalopathy with ataxia (LKPAT). CC2L is characterized clinically by a spectrum of clinical presentations including childhood- to adult-onset mild ataxia, spasticity, cognitive decline, and vision loss as well as typical MRI findings of symmetrical high signal intensities on the DWIs/T2WIs of the middle cerebellar peduncles (MCPs). We searched for pathogenic variants of CLCN2 in a case series of undiagnosed leukoencephalopathy accompanied by MCP signs, which led to the identification of four Japanese patients with CC2L. All the patients carried at least one allele of c.61dupC (p.Leu21Profs*27) in CLCN2, including compound heterozygosity with either the novel pathogenic variant c.983 + 2 T > A or the previously reported pathogenic variant c.1828C > T (p.Arg610*). Of note, all the four previously reported cases from Japan also harbored c.61dupC, and no reports of this variant have been documented from outside Japan. The allele frequency of c.61dupC in the Japanese population is 0.002152, raising the possibility of a relatively high prevalence of CC2L in Japan. Patients in this study developed symptoms after the age of 30, and demonstrated neurological signs including cerebellar ataxia, pyramidal signs, and mild cognitive impairment, consistent with previous reports. One male patient had two children, supporting preserved fertility, and another patient had calcifications in the cerebral and cerebellar surfaces. These findings provide valuable insights into the broader clinical and genetic spectra of CC2L in the Japanese population, and emphasize the importance of considering this disease in the differential diagnoses of leukoencephalopathy with MCP signs.