A longitudinal study of Taiwanese Sialidosis type 1: an insight into the concept of cherry-red spot myoclonus syndrome

Background and purpose: Sialidosis type 1 (ST‐1) is a neurodegenerative disorder with limited long‐term follow‐up report. This study is to document the chronological profile of ST‐1. Methods: We perform serial analysis of 17 Taiwanese patients with ST‐1 focusing on evolution of clinical features, electrophysiological findings, genetic studies, and neuroimage examinations. Results: All patients had a mutation at 554A→G in exon 3 of the NEU1 gene causing Ser182Gly substitution. Fifteen patients were homozygous. Two patients were heterozygous with novel mutations, 956C→T causing Ala319Val in one and 163C→T causing Gln55stop codon in the other. The neuraminidase activity was markedly decreased in all 11 available patients. Only three patients (17.6%) manifested the macular cherry‐red spot. The majority of patients (82.3%) developed full‐blown manifestation of myoclonus, ataxia, and seizures within 5 years. Abnormal somatosensory evoked potentials with giant cortical waves were found in all patients. Prolonged P100 peak latency of the visual evoked potentials (VEPs) were found in 16 patients (94.1%) in the early stage even without visual symptoms. Conclusion: ST‐1 in Taiwanese population illustrates distinct characteristics of phenotype with infrequent cherry‐red spot. We suggest to screen the NEU1 mutations in patients presenting action myoclonus with abnormal VEPs, even without macular cherry‐red spots.