Identifying SYNE1 ataxia and extending the mutational spectrum in Korea

Genetic origin of patients having spastic paraplegia with or without other neurologic manifestations

Background

Hereditary spastic paraplegia (HSP) is a group of neurodegenerative diseases characterized by lower-limb spastic paraplegia with highly genetic and clinical heterogeneity. However, the clinical sign of spastic paraplegia can also be seen in a variety of hereditary neurologic diseases with bilateral corticospinal tract impairment. The purpose of this study is to identify the disease spectrum of spastic paraplegia, and to broaden the coverage of genetic testing and recognize clinical, laboratorial, electrophysiological and radiological characteristics to increase the positive rate of diagnosis.

Methods

Twenty-seven cases were screened out to have definite or suspected pathogenic variants from clinically suspected HSP pedigrees through HSP-associated sequencing and/or expanded genetic testing. One case was performed for enzyme detection of leukodystrophy without next-generation sequencing. In addition, detailed clinical, laboratorial, electrophysiological and radiological characteristics of the 28 patients were presented.

Results

A total of five types of hereditary neurological disorders were identified in 28 patients, including HSP (15/28), leukodystrophy (5/28), hereditary ataxia (2/28), methylmalonic acidemia/methylenetetrahydrofolate reductase deficiency (5/28), and Charcot-Marie-tooth atrophy (1/28). Patients in the HSP group had chronic courses, most of whom were lower limbs spasticity, mainly with axonal neuropathy, and thinning corpus callosum, white matter lesions and cerebellar atrophy in brain MRI. In the non-HSP groups, upper and lower limbs both involvement was more common. Patients with homocysteine remethylation disorders or Krabbe’s disease or autosomal recessive spastic ataxia of Charlevoix-Saguenay had diagnostic results in laboratory or imaging examination. A total of 12 new variants were obtained.

Conclusions

HSP had widespread clinical and genetic heterogeneity, and leukodystrophy, hereditary ataxia, Charcot-Marie-Tooth atrophy and homocysteine remethylation disorders accounted for a significant proportion of the proposed HSP. These diseases had different characteristics in clinical, laboratorial, electrophysiological, and radiological aspects, which could help differential diagnosis. Genetic analysis could ultimately provide a clear diagnosis, and broadening the scope of genetic testing could improve the positive rate of diagnosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-022-02708-z.

Eye-tracking-aided characterization of saccades and antisaccades in SYNE1 ataxia patients: a pilot study

Background

SYNE1 ataxia is an autosomal recessive hereditary condition, the main characteristic features of which are gait and limb ataxia and cerebellar dysarthria. Reports have revealed that the clinical phenotype of SYNE1 ataxia is more complex than the first published cases with pure cerebellar signs indicated. The aim of this study was to characterize eye movement alterations in the first diagnosed Hungarian SYNE1 ataxia patients.

Results

Saccades and antisaccades were examined with an eye tracker device in 3 SYNE1 (one patient has two frameshift mutations [c.8515_8516insA, p.Met2839Asnfs*53 and c.11594_11595insG, p.Glu3866*] in a compound heterozygous state, whereas two subjects have a splicing variant [c.23146-2A > G] in a homozygous state), 6 Friedreich ataxia (FA) patients and 12 healthy controls. Besides that, detailed clinical phenotyping and comprehensive neuropsychological assessment were carried out in all patients with ataxia.

In addition to the characteristic cerebellar alterations, pyramidal signs and polyneuropathy were observed at least in 2 SYNE1 ataxia patients, for which no other underlying reason was found. The eye tracking assessment revealed hypometric saccades in the longer amplitude (18.4°) saccadic paradigm in all SYNE1 patients, whereas 2 out of 3 SYNE1 subjects performed slow saccades as well. In the antisaccade task, higher incorrect ratios of antisaccades were demonstrated in SYNE1 patients compared to healthy controls, showing inverse correlation with working memory test results. The corresponding data of FA patients was dispersed over a wide range, partially overlapping with control data.

Conclusions

The current study draws attention to the presence of eye movement disorders in patients with SYNE1 ataxia and demonstrates that alterations in the antisaccade paradigm may be related to working memory deficits.

Clinical characteristics of ataxia-telangiectasia presenting dystonia as a main manifestation

INTRODUCTION

Besides cerebellar ataxia, various other movement disorders, including dystonia, could manifest as main clinical symptoms in ataxia-telangiectasia (A-T). However, the clinical characteristics of dystonic A-T patients are not clearly elucidated.

METHODS

To investigate the characteristics of dystonic A-T, we screened previous reports with A-T patients presenting dystonia as a main manifestation, and included 38 dystonic A-T patients from 16 previous studies and our 2 cases. We reviewed clinical and demographic data of dystonic A-T patients. Additionally, to figure out clinical meaning of cerebellar involvement in dystonic A-T, we divided them into two groups based on the presence of cerebellar involvement, and compared clinical features between two groups.

RESULTS

In the patients with dystonic A-T, dystonia tended to appear during childhood or adolescence and became generalized over time. Choreoathetosis and myoclonus accompanied more frequently than the typical clinical features, including cerebellar ataxia or atrophy, telangiectasia, or oculomotor apraxia. Additionally, alpha-fetoprotein level was also elevated in the patients with dystonic A-T. When we compared dystonic A-T with and without cerebellar involvement, the former was related with more chance for telangiectasia and oculomotor apraxia, while the latter with that for choreoathetosis and malignancy.

CONCLUSION

Even without ataxia, telangiectasia, or oculomotor apraxia, A-T should be considered in undiagnosed dystonia, especially generalized dystonia which started from childhood or adolescence period, and alpha-fetoprotein level can be a useful screening tool. In addition, cerebellar involvement is important considering different phenotype in dystonic A-T patients with and without cerebellar sign.

Autosomal Recessive Cerebellar Ataxia Type 1: Phenotypic and Genetic Correlation in a Cohort of Chinese Patients with SYNE1 Variants

Mutations in the synaptic nuclear envelope protein 1 (SYNE1) gene have been reported to cause autosomal recessive cerebellar ataxia (ARCA) type 1 with highly variable clinical phenotypes. The aim of this study was to describe the phenotypic-genetic spectrum of SYNE1-related ARCA1 patients in the Chinese population. We screened 158 unrelated patients with autosomal recessive or sporadic ataxia for variants in SYNE1 using next-generation sequencing. Pathogenicity assessment of SYNE1 variants was interpreted according to the American College of Medical Genetics standards and guidelines. We identified eight truncating variants and two missense variants spreading throughout the SYNE1 gene from six unrelated families, including nine novel variants and one reported variant. Of the six index patients, two patients showed the classical pure cerebellar ataxia, while four patients exhibited non-cerebellar phenotypes, including motor neuron symptoms, cognitive impairment, or mental retardation. The variants associated with motor neuron or cognition involvement tend to be located in the C-terminal region of SYNE1 protein, compared with the variants related to pure cerebellar ataxia. Our data indicating SYNE1 mutation is one of the more common causes of recessive ataxia in the Chinese population. The use of next-generation sequencing has enabled the rapid analysis of recessive ataxia and further expanded our understanding of genotype-phenotype correlation.

Identifying SYNE1 Ataxia With Novel Mutations in a Chinese Population

Objective: Variants in SYNE1 have been widely reported in ataxia patients in Europe, with highly variable clinical phenotype. Until now, no mutation of SYNE1 ataxia has been reported among the Chinese population. Our aim was to screen for SYNE1 ataxia patients in China and extend the clinicogenetic spectrum.

Methods: Variants in SYNE1 were detected by high-throughput sequencing on a cohort of 126 unrelated index patients with unexplained autosomal recessive or sporadic ataxia. Pathogenicity assessments of SYNE1 variants were interpreted according to the ACMG guidelines. Potential pathogenic variants were confirmed by Sanger sequencing. Clinical assessments were conducted by two experienced neurologists.

Results: Two Chinese families with variable ataxia syndrome were identified (accounting for 1.6%; 2/126), separately caused by the novel homozygous SYNE1 mutation (NM_033071.3: c.21568C>T, p.Arg7190Ter), and compound heterozygous SYNE1 mutation (NM_033071.3: c.18684G>A, p.Trp6228Ter; c.17944C>T, p.Arg5982Ter), characterized by motor neuron impairment, mental retardation and arthrogryposis.

Conclusions:SYNE1 ataxia exists in the Chinese population, as a rare form of autosomal recessive ataxia, with a complex phenotype. Our findings expanded the ethnic, phenotypic and genetic diversity of SYNE1 ataxia.