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

Sialidosis type 1 in a Turkish family: a case report and review of literatures

OBJECTIVES

Sialidosis type 1 is a rare autosomal recessive lysosomal storage disorder caused by pathogenic variants in the NEU1 gene, which encodes the sialic acid-degrading enzyme α-neuraminidase. Sialidosis type 1 is a milder form with a late-onset phenotype, characterized by progressive myoclonic epilepsy and ataxia with cherry-red spots. Sialidosis type 2 is an early-onset and more severe form presenting with dysmorphic features, hepatosplenomegaly and cognitive delay. Clinical diagnosis is usually supported by increased urinary bound sialic acid excretion and confirmed by genetic analysis or demonstration of α-neuraminidase enzyme deficiency in cultured fibroblasts. The aim of this study was to present a case of type 1 sialidosis, review the literature, and investigate genotype-phenotype correlations, symptom frequencies, and race-specific mutations in patients diagnosed with type 1 sialidosis.

CASE PRESENTATION

We report herein a family of four Turkish siblings affected with sialidosis type 1 associated with a homozygous variant, c.403G>A p. (Asp135Asn), in the NEU1 gene. A systematic literature review on sialidosis type 1 was carried out, by the PubMed database was searched using keywords included sialidosis and/or NEU1 gene. We selected case reports or series that included genetically confirmed type 1 sialidosis from 1996 to 2023. So far, nearly genetically confirmed 80 patients from unrelated 65 families, more than 40 NEU1 disease causing mutations, have been identified in patients with sialidosis type 1. Among the reported mutations, missense variants are the most common, and few nonsense, frameshift, exonic duplications or small deletions have been reported. c.239C>T p. (Pro80Leu) variant in Chinese and Japanese patients, c.649G>A p. (Val217Met) variant in Japanese patients, c.880C>T p. (Arg294Cys) variant in Indian patients, c.629C>T p. (Pro210Leu) variant in Ecuadorian patients, c.982G>A p. (Gly328Ser) variant in Italian patients, and c.403G>A p (Asp135Asn) and c.625del p. (Glu209Serfs*94) variants in Turkish patients were found higher.

CONCLUSIONS

Race-specific variants were found with higher percentages in certain populations.

Progressive myoclonic ataxia as an initial symptom of typical type I sialidosis with NEU1 mutation

OBJECTIVE

Expand genetic screening for atypical Type I sialidosis (ST-1) could address its underdiagnosed in both progressive myoclonic ataxia (PMA) and ataxia patients. To evaluate the potential founder effect of mutation in the population.

METHODS

We enrolled 231 patients with PMA or ataxia from the First Affiliated Hospital of Fujian Medical University. Through Whole Exome Sequencing and Sanger sequencing, we identified the causative gene in patients. Haplotype analysis was employed to explore a potential founder effect of the NEU1 c.544A>G mutation.

RESULTS

A total of 31 patients from 23 unrelated families were genetically diagnosed with ST-1. A significant 80.6% of these patients were homozygous for the c.544A>G mutation. We discovered six different NEU1 variants, including two novel mutations: c.951_968del and c.517T>G. The mean age of onset was 18.0 ± 7.1 years. The clinical spectrum of ST-1 featured ataxia and myoclonus as the most common initial symptoms. Over 40% suffered from controlled generalized tonic-clonic seizures. Mobility and independence varied greatly across the cohort. Cherry-red spots were rare, occurring in just 9.5% (2/21) of patients. Brain MRIs were typically unremarkable, except for two patients with unusual findings. EEGs showed diffuse paroxysmal activity in 17 patients. The c.544A>G mutation in NEU1 is a founder variant in Fujian, with a unique haplotype prevalent in East Asians.

INTERPRETATION

ST-1 should be suspected in patients with PMA or ataxia in Southeast China, even without macular cherry-red spots and seizures, and the premier test could be a variant screening of the founder variant NEU1 c.544A>G.

Genotype-phenotype correlation and founder effect analysis in southeast Chinese patients with sialidosis type I

BACKGROUND

Sialidosis type 1 (ST-1) is a rare autosomal recessive disorder caused by mutation in the NEU1 gene. However, limited reports on ST-1 patients in the Chinese mainland are available.

METHODS

This study reported the genetic and clinical characteristics of 10 ST-1 patients from southeastern China. A haplotype analysis was performed using 21 single nucleotide polymorphism (SNP) markers of 500 kb flanking the recurrent c.544 A > G in 8 families harboring the mutation. Furthermore, this study summarized and compared previously reported ST-1 patients from Taiwan and mainland China.

RESULTS

Five mutations within NEU1 were found, including two novel ones c.557 A > G and c.799 C > T. The c.544 A > G mutation was most frequent and identified in 9 patients, 6 patients were homozygous for c.544 A > G. Haplotype analysis revealed a shared haplotype surrounding c.544 A > G was identified, suggesting a founder effect presenting in southeast Chinese population. Through detailed assessment, 52 ST-1 patients from 45 families from Taiwan and mainland China were included. Homozygous c.544 A > G was the most common genotype and found in 42.2% of the families, followed by the c.544 A > G/c.239 C > T compound genotype, which was observed in 22.2% of the families. ST-1 patients with the homozygous c.544 A > G mutation developed the disease at a later age and had a lower incidence of cherry-red spots significantly.

CONCLUSION

The results contribute to gaps in the clinical and genetic features of ST-1 patients in southeastern mainland China and provide a deeper understanding of this disease to reduce misdiagnosis.

Clinical and Structural Characteristics of NEU1 Variants Causing Sialidosis Type 1

OBJECTIVE

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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.

Unique clinical and electrophysiological features in the peripheral nerve system in patients with sialidosis - a case series study

BACKGROUND

To investigate the peripheral nervous system involvement in S sialidosis with typical features of myoclonus, seizure, and giant waves in somatosensory evoked potentials suggesting hyperexcitability in the central nervous system.

METHODS

The clinical presentation of patients with genetically confirmed sialidosis was recorded. Neurophysiological studies, including nerve conduction studies (NCSs), F-wave studies, and needle electromyography (EMG), were performed on these patients.

RESULTS

Six patients (M/F: 2:4) were recruited. In addition to the classical presentation, intermittent painful paresthesia was noted in four patients, and three of whom reported it as the earliest symptom. In the NCSs, one patient had reduced compound muscle action potential amplitudes in the right ulnar nerve, while another patient had prolonged distal motor latency in the bilateral tibial and peroneal nerves. Prolonged F-wave latency (83.3%), repeater F-waves (50%), and neurogenic polyphasic waves in EMG (in 2 out of 3 examined patients) were also noted. Interestingly, a very late response was noted in the F-wave study of all patients, probably indicating lesions involving the proximal peripheral nerve or spinal cord.

CONCLUSION

In addition to the central nervous system, the peripheral nervous system is also involved in sialidosis, with corresponding clinical symptoms. Further study on these phenomena is indicated.

Lysosomal storage disorders identified in adult population from India: Experience of a tertiary genetic centre and review of literature

Lysosomal storage disorders (LSDs) in adults have milder phenotype and variable age at presentation. Several studies have described the phenotype, genotype and treatment outcomes for adult-onset LSDs like Gaucher, Fabry, Pompe disease and others. We describe the first systematic study on the occurrence of LSDs in an adult population from India. It describes, the key clinical signs seen in these patients and those from literature review that can aid in early detection. Of 2102 biochemically diagnosed LSDs cases, 32 adult patients were identified with LSDs. Based on the clinical suspicion, screening test and enzyme study was carried out. Twenty-two patients were subjected to a genetic study to identify the causative variant in a respective gene. Of the 32 adult patients, we observed a maximum percentage of 37.5% (n = 12) cases with Gaucher disease, followed by 13% (n = 4) with Fabry disease. We found 10% of cases with MPS IVA and MPS I, and 9% cases with Pompe. Single case of adult mucolipidosis III and two cases each of Type 1 Sialidosis, Niemann-Pick disease B and metachromatic leukodystrophy were identified. We observed two common variants p.Leu483Pro and p.Ala487Thr in the GBA1 gene in 23% of Indian patients with adult Gaucher disease. No common variants were observed in other aforementioned LSDs. Study identified 50% of Fabry patients and 4% of Gaucher patients diagnosed at our centre to be adults. The prevalence of adult Pompe patients was low (3.4%) as compared to 80% reported in the Caucasian population. Adult LSDs such as, MPS III, GM1/GM2 gangliosidosis and Krabbe disease were not identified in our cohort.

Sialidosis type 1 without cherry-red spots: a case report and literature review

Background

Sialidosis is a rare disorder caused by mutations in the NEU1 gene located on chromosome 6p21.3, constituting a group of autosomal recessive diseases. Enzyme activity analysis, electron microscopy examination and genetic testing are reliable methods for diagnosis. Despite previous reports on the disease, its rarity means that its clinical manifestations and prognosis still warrant attention due to the limited amount of information available.

Methods

We report a case of a 40-year-old woman who was admitted to our hospital for worsening dysarthria of 16 years duration and facial and limb twitching that had been present for 2 years. Genetic testing was undertaken.

Results

Genetic testing confirmed type I sialidosis, the first reported instance of this disease in the Hainan Free Trade Port in China. The patient did not have the typical cherry-red spot in the fundus. Despite aggressive treatment, she died of status epilepticus 2 months later. This result indicates that the disease has a poor prognosis.

Discussion

Cherry-red spots in the fundus are characteristic features of type I sialidosis and it has been referred to as the cherry-red spot myoclonus syndrome. We hypothesise that environmental factors may also play a significant role. Overemphasis on the presence of cherry-red spots may mislead clinicians and delay diagnosis. Furthermore, patients presenting with isolated myoclonus should undergo visual evoked potential and somatosensory evoked potential tests, as well as genetic testing to confirm or rule out sialidosis.