Clinical and Structural Characteristics of NEU1 Variants Causing Sialidosis Type 1

Sialidosis type 2 has variants that are both catalytically inactive (severe), while sialidosis type 1 has at least one catalytically active (mild) variant. This study aimed to discuss the structural changes associated with these variants in a newly reported family carrying N-acetyl-α-neuraminidase-1 (NEU1) variants and explore the clinical characteristics of different combinations of variants in sialidosis type 1.

First, whole-exome sequencing and detailed clinical examinations were performed on the family. Second, structural analyses, including assessments of energy, flexibility and polar contacts, were conducted for several NEU1 variants, and a sialidase activity assay was performed. Third, previous NEU1 variants were systematically reviewed, and the clinical characteristics of patients in the severe-mild and mild-mild groups with sialidosis type 1 were analyzed.

We report a novel family with sialidosis type 1 and the compound heterozygous variants S182G and V143E. The newly identified V143E variant was predicted to be a mild variant through structural analysis and was confirmed by a sialidase activity assay. Cherry-red spots were more prevalent in the severe-mild group, and ataxia was more common in the mild-mild group. Impaired cognition was found only in the severe-mild group. Moreover, patients with cherry-red spots and abnormal electroencephalographies and visual evoked potentials had a relatively early age of onset, whereas patients with myoclonus had a late onset.

Changes in flexibility and local polar contacts may be indicators of NEU1 pathogenicity. Sialidosis type 1 can be divided into two subgroups according to the variant combinations, and patients with these two subtypes have different clinical characteristics.