Multimodality evoked potentials and EEG in a case of cherry red spot-myoclonus syndrome and alpha-neuraminidase deficiency (sialidosis type 1)

Clinical and genetic characteristics of type I sialidosis patients in mainland China

Objective

Type I sialidosis (ST‐1) is a rare autosomal recessive inherited disorder. To date, there has been no study on ST‐1 patients in mainland China.

Methods

We reported in detail the cases of five Chinese ST‐1 patients from two centers, and summarized all worldwide cases. Then, we compared the differences between Chinese and foreign patients.

Results

A total of 77 genetically confirmed ST‐1 patients were identified: 12 from mainland China, 23 from Taiwan, 10 from other Asian regions, and 32 from European and American regions. The mean age of onset was 16.0 ± 6.7 years; the most common symptoms were myoclonus seizures (96.0%), followed by ataxia (94.3%), and blurred vision (67.2%). Compared to other groups, the onset age of patients from mainland China was much younger (10.8 ± 2.7 years). The incidence of visual impairment was lower in patients from other Asian regions than in patients from mainland China and Taiwan (28.6% vs. 81.8%–100%). Cherry‐red spots were less frequent in the Taiwanese patients than in patients from other regions (27.3% vs. 55.2%–90.0%). Furthermore, 48 different mutation types were identified. Chinese mainland and Taiwanese patients were more likely to carry the c.544A > G mutation (75% and 100%, respectively) than the patients from other regions (only 0%–10.0%). Approximately 50% of Chinese mainland patients carried the c.239C > T mutation, a much higher proportion than that found in the other populations. In addition, although the brain MRI of most patients was normal, ¹⁸F‐FDG‐PET analysis could reveal cerebellar and occipital lobe hypometabolism.

Interpretation

ST‐1 patients in different regions are likely to have different mutation types; environmental factors may influence clinical manifestations. Larger studies enrolling more patients are required.

Type I sialidosis, a normosomatic lysosomal disease, in the differential diagnosis of late-onset ataxia and myoclonus: An overview

Lysosomal storage diseases (LSDs) are rare to extremely rare monogenic disorders. Their incidence, however, has probably been underestimated owing to their complex clinical manifestations. Sialidosis is a prototypical LSD inherited as an autosomal recessive trait and caused by mutations in the NEU1 gene that result in a deficiency of alpha-N-acetyl neuraminidase 1 (NEU1). Two basic forms of this disease, type I and type II, are known. The dysmorphic type II form features LSD symptoms including congenital hydrops, dysmorphogenetic traits, hepato-splenomegaly and severe intellectual disability. The diagnosis is more challenging in the normosomatic type I forms, whose clinical findings at onset include ocular defects, ataxia and generalized myoclonus. Here we report the clinical, biochemical and molecular analysis of five patients with sialidosis type I. Two patients presented novel NEU1 mutations. One of these patients was compound heterozygous for two novel NEU1 missense mutations: c.530A>T (p.Asp177Val) and c.1010A>G (p.His337Arg), whereas a second patient was compound heterozygous for a known mutation and a novel c.839G>A (p.Arg280Gln) mutation. We discuss the impact of these new mutations on the structural properties of NEU1. We also review available clinical reports of patients with sialidosis type I, with the aim of identifying the most frequent initial clinical manifestations and achieving more focused diagnoses.

First report of two Taiwanese siblings with sialidosis type I: A 10-year follow-up study

We report the clinical features, electrophysiological findings and genetic characteristics of the first two Taiwanese siblings ever reported with sialidosis type I. We also provide a 10-year follow-up result. Enzymological analysis revealed a primary sialidase deficit. The back-averaged electroencephalography demonstrated myoclonic jerk-related cortical activities and the somatosensory evoked potential studies revealed giant cortical components. During the 10-year follow-up, the brain magnetic resonance images of the younger brother remained normal, whereas they showed mild cerebellar atrophy in the older sister. Macular cherry red spots were absent in both siblings. However, visual evoked potential revealed progressively prolonged latencies of P100 bilaterally, which was consistent with progressive deterioration of the siblings' visions. DNA analysis showed that the siblings had a homozygous missense point mutation c.544A-->G (Ser182Gly) in the exon 3 of the alpha-N-acetyl-neuraminidase (NEU1) gene. The mutation is predicted to cause a decreased sialidase activity but the mutant sialidase can still be targeted to the lysosomes, which may correlate with the mild clinical phenotypes and absent cherry red spots in the siblings.