Type 1 Sialidosis Patient With a Novel Deletion Mutation in the NEU1 Gene: Case Report and Literature Review

Recent advances in next-generation sequencing technologies have uncovered the genetic backgrounds of various diseases. Type 1 sialidosis(OMIM#256550) is a rare autosomal recessive lysosomal storage diseasecaused by a mutation in the NEU1(OMIM * 608272) gene. In this study, we aimed to review the previous reports of type 1 sialidosisand compare those with the first case of type 1 sialidosisin Korea. A 36-year-old woman presented with progressive ataxia, myoclonus, and seizure since the age of 12. Whole- exome sequencingrevealed a pathogenic missense variant c.928G > A (p.D310N) and novel c.15_16del (p.P6Qfs*21) of the NEU1gene as final causal candidate as compound heterozygotes. We reviewed the literature and selected the clinical reports of genetically confirmed type 1 sialidosispatients. A total of 45 patients in 17 reports were identified. Cherry-red spot, myoclonus, ataxia, and seizure were reported in 51.2%, 100.0%, 87.8%, and 73.7% of patients, respectively. Abnormalities of cognitive function, EEG, and brain MRI and visual symptoms were reported in 22.2%, 40.7%, 66.7%, and 70.2% of patients, respectively. Overall, our patient showed similar clinical features to previous type 1 sialidosispatients, but she did not complain of visual symptoms despite having cherry-red spots. We summarize the clinical features of type 1 sialidosisand report the first case of type 1 sialidosiswith novel deletion variant in the NEU1gene in the Korean population. Our study suggests the importance of ophthalmologic examinations in patients with myoclonus, ataxia, and seizure who do not complain of visual symptoms.