Multigene panel next generation sequencing in a patient with cherry red macular spot: Identification of two novel mutations in NEU1 gene causing sialidosis type I associated with mild to unspecific biochemical and enzymatic findings

Detection Strategies for Sialic Acid and Sialoglycoconjugates

Glycoconjugates are a vast class of biomolecules implicated in biological processes important for human health and disease. The structural complexity of glycoconjugates remains a challenge to deciphering their precise biological roles and for their development as biomarkers and therapeutics. Human glycoconjugates on the outside of the cell are modified with sialic (neuraminic) acid residues at their termini. The enzymes that install sialic acids are sialyltransferases (SiaTs), a family of 20 different isoenzymes. The removal and degradation of sialic acids is mediated by neuraminidase (NEU; sialidase) enzymes, of which there are four isoenzymes. In this review, we discuss chemical and biochemical approaches for the detection and analysis of sialoglycoconjugate (SGC) structures and their enzymatic products. The most common methods include affinity probes and synthetic substrates. Fluorogenic and radiolabelled substrates are also important tools for many applications, including screening for enzyme inhibitors. Strategies that give insight into the native substrate-specificity of enzymes that regulate SGCs (SiaT & NEU) are necessary to improve our understanding of the role of sialic acid metabolism in health and disease.

Looking "Cherry Red Spot Myoclonus" in the Eyes: Clinical Phenotype, Treatment Response, and Eye Movements in Sialidosis Type 1

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.

Compound heterozygous mutations in the neuraminidase 1 gene in type 1 sialidosis: A case report and review of literature

BACKGROUND

Type 1 sialidosis, also known as cherry-red spot-myoclonus syndrome, is a rare autosomal recessive lysosomal storage disorder presenting in the second decade of life. The most common symptoms are myoclonus, ataxia and seizure. It is rarely encountered in the Chinese mainland.

CASE SUMMARY

A 22-year-old male presented with complaints of progressive myoclonus, ataxia and slurred speech, without visual symptoms; the presenting symptoms began at the age of 15-year-old. Whole exome sequencing revealed two pathogenic heterozygous missense variants [c.239C>T (p.P80L) and c.544A>G (p.S182G) in the neuraminidase 1 (NEU1) gene], both of which have been identified previously in Asian patients with type 1 sialidosis. All three patients identified in Mainland China come from three unrelated families, but all three show the NEU1 mutations p.S182G and p.P80L pathogenic variants. Increasing sialidase activity through chaperones is a promising therapeutic target in sialidosis.

CONCLUSION

Through retrospective analysis and summarizing the clinical and genetic characteristics of type 1 sialidosis, we hope to raise awareness of lysosomal storage disorders among clinicians and minimize the delay in diagnosis.

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.

Genetic and clinical characterization of mainland Chinese patients with sialidosis type 1

Background

Sialidosis type 1 is a rare inherited disorder with a high disability. No genetically confirmed mainland Chinese patient with sialidosis type 1 has been reported. This study evaluated the phenotypes and genotypes of mainland Chinese patients with sialidosis type 1.

Methods

It was a retrospective case series study. Four unrelated patients were enrolled. Comprehensive clinical evaluations and molecular genetic analysis of the NEU1 gene were performed.

Results

Three out of four patients presented progressive myoclonus epilepsy. The best‐corrected visual acuity ranged from 20/2000 to 20/25. Punctate cataracts were found in all of the patients. Distinct macular cherry red spots were observed in three patients by fundoscopy, and a relatively normal fundus was revealed in one patient. Optical coherence tomography (OCT) showed increased reflectivity of the nerve fiber and ganglion cell layers, and fundus autofluorescence (FAF) revealed hyperautofluorescent areas surrounding the fovea in all of the patients. Only superficial retinal vessels can be observed using OCT angiography; the deeper capillary plexus could not be observed. Visual evoked potential revealed varying degrees of decreased amplitude and/or prolonged latency of P100 or P2 waves. The most frequent sequence variant identified was c.544A>G (p.S182G) (NM_000434.3).

Conclusions

Our study first described the ophthalmic and neurologic characteristics of a small cohort of unrelated mainland Chinese patients with sialidosis type 1. We found that c.544A>G (p. S182G) might be a hotspot variant in Chinese patients. The accumulation of metabolic products in the nerve fiber and ganglion cell layers is a characteristic ocular finding that could be sensitively detected by OCT and FAF imaging.

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.

Type 1 Sialidosis Patient With a Novel Deletion Mutation in the NEU1 Gene: Case Report and Literature Review

Recent advances in next-generation sequencing technologies have uncovered the genetic backgrounds of various diseases. Type 1 sialidosis (OMIM#256550) is a rare autosomal recessive lysosomal storage disease caused by a mutation in the NEU1 (OMIM * 608272) gene. In this study, we aimed to review the previous reports of type 1 sialidosis and compare those with the first case of type 1 sialidosis in Korea. A 36-year-old woman presented with progressive ataxia, myoclonus, and seizure since the age of 12. Whole-exome sequencing revealed a pathogenic missense variant c.928G > A (p.D310N) and novel c.15_16del (p.P6Qfs*21) of the NEU1 gene as final causal candidate as compound heterozygotes. We reviewed the literature and selected the clinical reports of genetically confirmed type 1 sialidosis patients. A total of 45 patients in 17 reports were identified. Cherry-red spot, myoclonus, ataxia, and seizure were reported in 51.2%, 100.0%, 87.8%, and 73.7% of patients, respectively. Abnormalities of cognitive function, EEG, and brain MRI and visual symptoms were reported in 22.2%, 40.7%, 66.7%, and 70.2% of patients, respectively. Overall, our patient showed similar clinical features to previous type 1 sialidosis patients, but she did not complain of visual symptoms despite having cherry-red spots. We summarize the clinical features of type 1 sialidosis and report the first case of type 1 sialidosis with novel deletion variant in the NEU1 gene in the Korean population. Our study suggests the importance of ophthalmologic examinations in patients with myoclonus, ataxia, and seizure who do not complain of visual symptoms.

Clinical and electrophysiological characteristics of a type 1 sialidosis patient with a novel deletion mutation in NEU1 gene

BACKGROUND/PURPOSE

Type 1 sialidosis is a rare autosomal recessive lysosomal storage disease caused by Neuraminidase 1 (NEU1) gene mutations. We report a type 1 sialidosis patient with a novel deletion mutation in NEU1 and compared the phenotypes within different ethnicities.

METHODS

Targeted next generation sequencing and segregation analysis were performed to identify the causative gene mutation of the index patient. The clinical and electrophysiological characteristics of the patient were compared to those reported in previous studies of type 1 sialidosis from 1996 to 2019.

RESULTS

A 16-year-old boy presented with progressive onset of seizure, myoclonus, and ataxia since 5 years of age. Targeted next generation sequencing revealed the pathogenic missense variant c.544A>G (p.Ser182Gly) and the novel c.314_352del (p.A106_G118del) deletion in NEU1 in a compound heterozygote state. The leukocyte neuraminidase activity was significantly decreased (0.0323 nmol/mg protein/hour, normal reference: 0.326 ± 0.095 nmol/mg protein/hour). A total of 46 patients were identified in 18 reports from the literature. The most common symptoms were myoclonus (100%), followed by ataxia (88.3%) and seizure (72.5%). Notably, impaired cognition (50.0% vs. 21.7%, P = 0.04) and cherry-red spots (61.1% vs. 40.7%, P = 0.02) were less frequently reported in Asian patients than in Caucasian patients. Abnormal somatosensory evoked potentials with giant cortical waves and prolonged visual evoked potential latency were found consistently in Asian and Caucasian patients, and could be a surrogate marker of early diagnosis.

CONCLUSION

Our findings suggest a distinct phenotype of infrequent cherry-red spots and abnormal evoked potentials in Asian patients with type 1 sialidosis.