Abstract
Sialidosis type 1 is a rare lysosomal storage disorder caused by mutations of the neuraminidase gene. Specific features suggesting this condition include myoclonus, ataxia and macular cherry-red spots. However, phenotypic variability exists. Here, we present detailed clinical and video description of three patients with this rare condition. We also provide an in-depth characterization of eye movement abnormalities, as an additional tool to investigate pathophysiological mechanisms and to facilitate diagnosis. In our patients, despite phenotypic differences, eye movement deficits largely localized to the cerebellum.
Highlights
Sialidosis, known as mucolipidosis type 1, is a rare autosomal recessive lysosomal storage disorder caused by mutations in the neuraminidase (NEU1) gene
Patients affected with sialidosis type 1 can manifest with resting or action myoclonus, which can be sensitive to tactile and auditory stimuli; light sensitivity is usually more indicative of other forms of progressive myoclonic epilepsy, such as Gaucher’s disease, Lafora disease, or ceroid-lipofuscinosis [3]
Sialidosis type 1 was genetically confirmed by the findings of two variants in the NEU1 gene: c.649G>A (p.V217M), a previously reported pathogenic variant, and c.644T>C (p.L215P), a variant never previously reported in patients with sialidosis type 1 and not found in large databases of unaffected subjects (ExAC/gnomAD, dbSNP)
Summary
Sialidosis, known as mucolipidosis type 1, is a rare autosomal recessive lysosomal storage disorder caused by mutations in the neuraminidase (NEU1) gene. Different mutations induce variable degrees of residual neuraminidase function, which affect the age of disease onset and symptom severity. Patients affected with sialidosis type 1 can manifest with resting or action myoclonus, which can be sensitive to tactile and auditory stimuli; light sensitivity is usually more indicative of other forms of progressive myoclonic epilepsy, such as Gaucher’s disease, Lafora disease, or ceroid-lipofuscinosis [3]. Because of great variability in disease symptoms and signs, of the myoclonus, patients affected with sialidosis type 1 can appear very phenotypically different from one another. In this case series, we present three patients with sialidosis type 1, all differing in their disease severity and patterns of myoclonus (Table 1). To our knowledge, detailed eye movement assessments have not been previously reported in patients with sialidosis type 1
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