Hereditary Ataxia with a Novel Mutation in the Senataxin Gene: A Case Report.

Hereditary ataxias (HA) are a group of inherited neurological disorders caused by changes in genes. At least 115 different mutations in the senataxin (SETX) gene causing ataxia have been identified. There are no reports of any SETX gene mutation among the Iranian population. Here we report on two cases with homozygous and heterozygous mutations in which one patient was affected by HA with oculomotor apraxia type 2, and the other was a carrier of the disorder. In 2016, the affected patient was referred to the Biogene Medical and Genetic Laboratory (Tehran, Iran) suffering from imbalance and tremor of both head and body. The coding regions of 18 genes, including the SETX gene, were screened. The target regions were captured using the NimbleGen chip followed by next-generation sequencing (NGS) technology on the Illumina Hiseq2500 platform. NGS, a DNA sequencing technology, has greatly increased the ability to identify new causes of ataxia; a useful tool for the prevention of primary manifestations and treatment of affected patients. In the present study, a novel mutation in the SETX gene has been identified.

[A case of sporadic amyotrophic lateral sclerosis (ALS) with Senataxin (SETX) gene variant].

A 67-year-old man presented slowly progressive weakness of the extremities visited our hospital. Nerve conduction study showed axonal neuropathy and needle electromyography showed neurogenic changes with denervation findings in multiple limb muscles. While he was diagnosed as Probable amyotrophic lateral sclerosis (ALS), which is defined by the Awaji criteria for diagnosis of ALS, he did not develop either respiratory muscle paralysis or bulbar palsy, which are characteristic symptoms of sporadic ALS. Genetic testing revealed a novel gene variant in senataxin (SETX), the causative gene of ALS4. We could not make a definite diagnosis of ALS4 because he had no relatives who could perform genetic testing (segregation study). However, we considered the variant can be pathogenic because it was not previously reported and absent in at least 1,000 healthy control individuals, the variant site was highly conserved in mammals, and it may impair the function of senataxin protein (in silico analysis).

Ataxia with oculomotor apraxia type 2 caused by a novel homozygous mutation in SETX gene, and literature review.

Objectives: Autosomal recessive inherited ataxia with oculomotor apraxia type 2 (AOA2), caused by SETX gene mutations, is characterized by early-onset, progressive cerebellar ataxia, peripheral neuropathy, oculomotor apraxia and elevated serum α-fetoprotein (AFP). This study aimed to expand and summarize the clinical and genetic characteristics of SETX variants related to AOA2. Methods: The biochemical parameters, electromyogram and radiological findings of the patient were evaluated. Whole-exome sequencing (WES) was performed on the patient using next-generation sequencing (NGS), the variants were confirmed by Sanger sequencing and the pathogenicity of the variants was classified according to the American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) guidelines. We reviewed 57 studies of AOA2 patients with SETX mutations and collected clinical and genetic information. Results: The patient was a 40-year-old Chinese woman who primarily presented with numbness and weakness of the lower limbs in her teenage years. She had elevated AFP, increased serum follicle-stimulating hormone (FSH) and luteinizing hormone (LH) and decreased anti-Müllerian hormone (AMH) levels. We identified a novel homozygous missense mutation of the SETX gene, c.7118 C>T (p. Thr2373Ile), in the patient via Whole-exome and Sanger sequencing. The variant was located in the DNA/RNA helicase domain and is highly conserved. The protein prediction analysis verified the SETX variant as a damaging alteration and ACMG/AMP guidelines classified it as likely pathogenic. Through a literature review, we identified 229 AOA2 cases with SETX variants, and among the variants, 156 SETX variants were exonic. We found that 107 (46.7%) patients were European, 50 (21.8%) were African and 48 (21.0%) were Asian. Among the Asian patients, five from two families were Mainland Chinese. The main clinical features were cerebellar ataxia (100%), peripheral neuropathy (94.6%), cerebellar atrophy (95.3%) and elevated AFP concentration (92.0%). Most reported SETX mutations in AOA2 patients were missense, frameshift and nonsense mutations. Conclusion: We discovered a novel homozygous variant of the SETX gene as a cause of AOA2 in the current patient and expanded the genotypic spectrum of AOA2. Moreover, the clinical features of AOA2 and genetic findings in SETX were assessed in reported cohorts and are summarized in the present study.

A novel SETX gene mutation associated with Juvenile amyotrophic lateral sclerosis.

OBJECTS: This study aimed to report a novel point mutation associated with juvenile amyotrophic lateral sclerosis (JALS) in a Chinese Han family. METHODS: Detailed clinical assessment was applied to two patients, including proband (II-2) and his mother (I-2). Next-generation sequencing (NGS), also known as high-throughput sequencing in whole exon sequence, was performed in the proband to reach the target region. Sanger sequencing was also used to detect DNA sequence variants of the proband and other three members of his family. RESULTS: The proband (II-2) and his mother (I-2) were successfully diagnosed according to the clinical manifestations and physical examination. A novel point mutation c.1157T > C in the exon 10 of the SETX gene was identified in II-2 and I-2, resulting in a substitution of methionine (ATG) to threonine (ACG). However, we ultimately did not find the same variant in the other two normal members of his family in addition to 100 unrelated normal subjects. CONCLUSION: We presented a novel probably pathogenic missense mutation in exon 10 of SETX gene in a Chinese Han family with JALS.

[A amyotrophic lateral sclerosis (ALS) 4 family misdiagnosed as hereditary spastic paraplegia-a case report].

We report a 44 years old man with slowly progressive muscular atrophy of the extremities for over 30 years. He experienced difficulty in walking in his 10's and was diagnosed as hereditary spastic paraplegia (HSP) in his 20's. And then, muscle atrophy of the extremities slowly progressed especially in his distal muscles. Sensory axonal neuropathy was detected with sural nerve biopsy. His father and uncle have been diagnosed as HSP in their early days. His father noticed weakness of his leg in his 20's. He lost motor function of the leg in his 60's. In addition, marked disturbance of thermal sensation, vibration, and sense of position were found by physical examination. Our genetic study detected senataxin (SETX) gene mutation (c.8C>T,p.T3I) in the blood of those two patients, and they had been identified as family cases of amyotrophic lateral sclerosis (ALS) 4. As clinical symptoms of ALS4 would be similar to those of HSP at the onset, we suggest considering ALS4 in seeing patients with HSP without gene diagnosis.

High-throughput sequencing revealed a novel SETX mutation in a Hungarian patient with amyotrophic lateral sclerosis.

BACKGROUND: Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the degeneration of the motor neurons. To date, 126 genes have been implicated in ALS. Therefore, the heterogenous genetic background of ALS requires comprehensive genetic investigative approaches. METHODS: In this study, DNA from 28 Hungarian ALS patients was subjected to targeted high-throughput sequencing of the coding regions of three Mendelian ALS genes: FUS, SETX, and C9ORF72. RESULTS: A novel heterozygous missense mutation (c.791A>G, p.N264S) of the SETX gene was identified in a female patient presenting an atypical ALS phenotype, including adult onset and lower motor neuron impairment. No further mutations were detected in the other Mendelian ALS genes investigated. CONCLUSION: Our study contributes to the understanding of the genetic and phenotypic diversity of motor neuron diseases (MNDs). Our results also suggest that the elucidation of the genetic background of MNDs requires a complex approach, including the screening of both Mendelian and non-Mendelian genes.

Senataxin protects the genome: Implications for neurodegeneration and other abnormalities.

Ataxia oculomotor apraxia type 2 (AOA2) is a rare autosomal recessive disorder characterized by cerebellar atrophy, peripheral neuropathy, loss of Purkinje cells and elevated α-fetoprotein. AOA2 is caused by mutations in the SETX gene that codes for the high molecular weight protein senataxin. Mutations in this gene also cause dominant neurodegenerative disorders. Similar to that observed for other autosomal recessive ataxias, this protein protects the integrity of the genome against oxidative and other forms of DNA damage to reduce the risk of neurodegeneration. Senataxin functions in transcription termination and RNA splicing and it has been shown to resolve RNA/DNA hybrids (R-loops) that arise at transcription pause sites or when transcription is blocked. Recent data suggest that this protein functions at the interface between transcription and DNA replication to minimise the risk of collision and maintain genome stability. Our recent data using SETX gene-disrupted mice revealed that male mice were defective in spermatogenesis and were infertile. DNA double strand-breaks persisted throughout meiosis and crossing-over failed in SETX mutant mice. These changes can be explained by the accumulation of R-loops, which interfere with Holiday junctions and crossing-over. We also showed that senataxin was localized to the XY body in pachytene cells and was involved in transcriptional silencing of these chromosomes. While the defect in meiotic recombination was striking in these animals, there was no evidence of neurodegeneration as observed in AOA2 patients. We discuss here potentially different roles for senataxin in proliferating and post-mitotic cells.