Genetic analysis of SPG4 and SPG3A genes in a cohort of Chinese patients with hereditary spastic paraplegia

Copy Number Variations in Hereditary Spastic Paraplegia-Related Genes: Evaluation of an Iranian Hereditary Spastic Paraplegia Cohort and Literature Review

Introduction

In human genetic disorders, copy number variations (CNVs) are considered a considerable underlying cause. CNVs are generally detected by array-based methods but can also be discovered by read-depth analysis of whole-exome sequencing (WES) data. We performed WES-based CNV identification in a cohort of 35 Iranian families with hereditary spastic paraplegia (HSP) patients.

Methods

Thirty-five patients whose routine single-nucleotide variants (SNVs) and insertion/deletion analyses from exome data were unrevealing underwent a pipeline of CNV analysis using the read-depth detection method. Subsequently, a comprehensive search about the existence of CNVs in all 84 known HSP-causing genes was carried out in all reported HSP cases, so far.

Results and Discussion

CNV analysis of exome data indicated that 1 patient harbored a heterozygous deletion in exon 17 of the SPAST gene. Multiplex ligation-dependent probe amplification analysis confirmed this deletion in the proband and his affected father. Literature review demonstrated that, to date, pathogenic CNVs have been identified in 30 out of 84 HSP-causing genes (∼36%). However, CNVs in only 17 of these genes were specifically associated with the HSP phenotype. Among them, CNVs were more common in L1CAM, PLP1, SPAST, SPG7, SPG11, and REEP1 genes. The identification of the CNV in 1 of our patients suggests that WES allows the detection of both SNVs and CNVs from a single method without additional costs and execution time. However, because of intrinsic issues of WES in the detection of large rearrangements, it may not yet be exploited to replace the CNV detection methods in standard clinical practice.

Elucidating miRNA Function in Cancer Biology via the Molecular Genetics' Toolbox

Micro-RNA (miRNAs) are short non-coding RNAs of about 18-20 nucleotides in length and are implicated in many cellular processes including proliferation, development, differentiation, apoptosis and cell signaling. Furthermore, it is well known that miRNA expression is frequently dysregulated in many cancers. Therefore, this review will highlight the various mechanisms by which microRNAs are dysregulated in cancer. Further highlights include the abundance of molecular genetics tools that are currently available to study miRNA function as well as their advantages and disadvantages with a special focus on various CRISPR/Cas systems This review provides general workflows and some practical considerations when studying miRNA function thus enabling researchers to make informed decisions in regards to the appropriate molecular genetics tool to be utilized for their experiments.

A novel insertion mutation in atlastin 1 is associated with spastic quadriplegia, increased membrane tethering, and aberrant conformational switching

Hereditary spastic paraplegia (HSP) comprises a heterogeneous group of neuropathies affecting upper motor neurons and causing progressive gait disorder. Mutations in the gene SPG3A/atlastin-1 (ATL1), encoding a dynamin superfamily member, which utilizes the energy from GTP hydrolysis for membrane tethering and fusion to promote the formation of a highly branched, smooth endoplasmic reticulum (ER), account for approximately 10% of all HSP cases. The continued discovery and characterization of novel disease mutations are crucial for our understanding of HSP pathogenesis and potential treatments. Here, we report a novel disease-causing, in-frame insertion in the ATL1 gene, leading to inclusion of an additional asparagine residue at position 417 (N417ins). This mutation correlates with complex, early-onset spastic quadriplegia affecting all four extremities, generalized dystonia, and a thinning of the corpus callosum. We show using limited proteolysis and FRET-based studies that this novel insertion affects a region in the protein central to intramolecular interactions and GTPase-driven conformational change, and that this insertion mutation is associated with an aberrant prehydrolysis state. While GTPase activity remains unaffected by the insertion, membrane tethering is increased, indicative of a gain-of-function disease mechanism uncommon for ATL1-associated pathologies. In conclusion, our results identify a novel insertion mutation with altered membrane tethering activity that is associated with spastic quadriplegia, potentially uncovering a broad spectrum of molecular mechanisms that may affect neuronal function.

Genetic, clinical and neuroimaging profiles of sporadic and autosomal recessive hereditary spastic paraplegia cases in Chinese

Spastic paraplegias (SPGs) are a group of clinically and genetically heterogeneous neurodegenerative diseases. Mutations in 78 genes have been identified in autosomal dominant hereditary SPG (AD-HSP) and autosomal recessive hereditary SPG (AR-HSP). Compared to familial HSP, much less is known about the genetic and clinical profiles of sporadic SPGs. In this study, we have screened mutations for 18 sporadic SPGs or AR-HSP patients (mainly Northern Chinese) by whole-exome sequencing. We identified 12 mutations in five genes in 9 (50%) patients, including 9 novel ones: SPG5A/CYP7B1 (c.851C > A; c.122 + 2 T > G), SPG11/KIAA1840 (c.1735 + 3_ 1735 + 6del AAGT); SPG7/SPG7 (c.1454G > A; c.1892_ 1906dup GAGGACGGGCCTCGG); SPG39/PNPLA6 (c.1591G > A; c. 2990C > T); SPG15/ ZFYVE26 (c. 4804C > T; c. 4278 G > A). Among all the mutations, 7 were detected in the SPG5A and SPG11. Age at onset was significantly younger in cases with mutations (15.45 ± 6.78 years) than those without mutations (25.56 ± 10.90 years) (P = 0.03). Except for two cases with the SPG5A mutations, all cases presented with complicated SPGs. Three cases carrying mutations in SPG7, SPG15, SPG39 showed symptoms and signs of ataxia. One case carrying the homozygous c.259 + 2 T > C mutation in CYP7B1 showed serum parameters indicating liver impairment. Magnetic resonance imaging showed significantly thinned corpus callosum in cases with SPG11 and SPG15, but not in those with SPG5A, SPG7 or SPG39. In contrast, cerebellar atrophy was prominent in the SPG7 and SPG39 cases. These findings expand the spectrum of genetic, clinical and imaging features of sporadic SPG and AR-HSP, and have important implications in genetic counselling, molecular mechanisms and precise diagnosis of the disease.

Extensive In Silico Analysis of ATL1 Gene : Discovered Five Mutations That May Cause Hereditary Spastic Paraplegia Type 3A

BACKGROUND

Hereditary spastic paraplegia type 3A (SPG3A) is a neurodegenerative disease inherited type of Hereditary spastic paraplegia (HSP). It is the second most frequent type of HSP which is characterized by progressive bilateral and mostly symmetric spasticity and weakness of the legs. SPG3A gene mutations and the phenotype-genotype correlations have not yet been recognized. The aim of this work was to categorize the most damaging SNPs in ATL1 gene and to predict their impact on the functional and structural levels by several computational analysis tools.

METHODS

The raw data of ATL1 gene were retrieved from dbSNP database and then run into numerous computational analysis tools. Additionally; we submitted the common six deleterious outcomes from the previous functional analysis tools to I-mutant 3.0 and MUPro, respectively, to investigate their effect on the structural level. The 3D structure of ATL1 was predicted by RaptorX and modeled using UCSF Chimera to compare the differences between the native and the mutant amino acids.

RESULTS

Five nsSNPs out of 249 were classified as the most deleterious (rs746927118, rs979765709, rs119476049, rs864622269, and rs1242753115).

CONCLUSIONS

In this study, the impact of nsSNPs in the ATL1 gene was investigated by various in silico tools that revealed five nsSNPs (V67F, T120I, R217Q, R495W, and G504E) are deleterious SNPs, which have a functional impact on ATL1 protein and, therefore, can be used as genomic biomarkers specifically before 4 years of age; also, it may play a key role in pharmacogenomics by evaluating drug response for this disabling disease.

Genotype-phenotype associations in hereditary spastic paraplegia: a systematic review and meta-analysis on 13,570 patients

AIMS

The hereditary spastic paraplegias (HSPs) are a heterogeneous group of inherited neurodegenerative disorders. Although, several genotype-phenotype studies have carried out on HSPs, the association between genotypes and clinical phenotypes remain incomplete since most studies are small in size or restricted to a few genes. Accordingly, this study provides the systematic meta-analysis of genotype-phenotype associations in HSP.

METHODS AND RESULTS

We retrieved literature on genotype-phenotype associations in patients with HSP and mutated SPAST, REEP1, ATL1, SPG11, SPG15, SPG7, SPG35, SPG54, SPG5. In total, 147 studies with 13,570 HSP patients were included in our meta-analysis. The frequency of mutations in SPAST (25%) was higher than REEP1 (3%), as well as ATL1 (5%) in AD-HSP patients. As for AR-HSP patients, the rates of mutations in SPG11 (18%), SPG15 (7%) and SPG7 (13%) were higher than SPG5 (5%), as well as SPG35 (8%) and SPG54 (7%). The mean age of AD-HSP onset for ATL1 mutation-positive patients was earlier than patients with SPAST, REEP1 mutations. Also, the tendency toward younger age at AR-HSP onset for SPG35 was higher than other mutated genes. It is noteworthy that the mean age at HSP onset ranged from infancy to adulthood. As for the gender distribution, the male proportion in SPG7-HSP (90%) and REEP1-HSP (78%) was markedly high. The frequency of symptoms was varied among patients with different mutated genes. The rates of LL weakness, superficial sensory abnormalities, neuropathy, and deep sensory impairment were noticeably high in REEP1 mutations carriers. Also, in AR-HSP patients with SPG11 mutations, the presentation of symptoms including pes cavus, Neuropathy, and UL spasticity was higher.

CONCLUSION

Our comprehensive genotype-phenotype assessment of available data displays that the mean age at disease onset and particular sub-phenotypes are associated with specific mutated genes which might be beneficial for a diagnostic procedure and differentiation of the specific mutated genes phenotype among diverse forms of HSP.

An allosteric network in spastin couples multiple activities required for microtubule severing

The AAA+ ATPase spastin remodels microtubule arrays through severing and its mutation is the most common cause of hereditary spastic paraplegias (HSP). Polyglutamylation of the tubulin C-terminal tail recruits spastin to microtubules and modulates severing activity. Here, we present a ~3.2 Å resolution cryo-EM structure of the Drosophila melanogaster spastin hexamer with a polyglutamate peptide bound in its central pore. Two electropositive loops arranged in a double-helical staircase coordinate the substrate sidechains. The structure reveals how concurrent nucleotide and substrate binding organizes the conserved spastin pore loops into an ordered network that is allosterically coupled to oligomerization, and suggests how tubulin tail engagement activates spastin for microtubule disassembly. This allosteric coupling may apply generally in organizing AAA+ protein translocases into their active conformations. We show that this allosteric network is essential for severing and is a hotspot for HSP mutations.

Novel ATL1 mutation in a Chinese family with hereditary spastic paraplegia: A case report and review of literature

BACKGROUND

Hereditary spastic paraplegias (HSPs) refer to a group of heterogeneous neurodegenerative diseases characterized by lower limbs spasticity and weakness. So far, over 72 genes have been found to cause HSP (SPG1-SPG72). Among autosomal dominant HSP patients, spastic paraplegia 4 (SPG4/SPAST) gene is the most common pathogenic gene, and atlastin-1 (ATL1) is the second most common one. Here we reported a novel ATL1 mutation in a Chinese spastic paraplegia 3A (SPG3A) family, which expands the clinical and genetic spectrum of ATL1 mutations.

CASE SUMMARY

A 9-year-old boy with progressive spastic paraplegia accompanied by right hearing loss and mental retardation for five years was admitted to our hospital. Past history was unremarkable. The family history was positive, and his grandfather and mother had similar symptoms. Neurological examinations revealed hypermyotonia in his lower limbs, hyperreflexia in knee reflex, bilateral positive Babinski signs and scissors gait. The results of blood routine test, liver function test, blood glucose test, ceruloplasmin test and vitamin test were all normal. The serum lactic acid level was significantly increased. The testing for brainstem auditory evoked potential demonstrated that the right side hearing was impaired while the left was normal. Magnetic resonance imaging showed mild atrophy of the spinal cord. The gene panel test revealed that the proband carried an ATL1 c.752A>G p.Gln251Arg (p.Q251R) mutation, and Sanger sequencing confirmed the existence of family co-segregation.

CONCLUSION

We reported a novel ATL1 Q251R mutation and a novel clinical phenotype of hearing loss in a Chinese SPG3A family.

Disease-Causing Variants in the ATL1 Gene Are a Rare Cause of Hereditary Spastic Paraplegia among Czech Patients

Variants in the ATL1 gene have been repeatedly described as the second most frequent cause of hereditary spastic paraplegia (HSP), a motor neuron disease manifested by progressive lower limb spasticity and weakness. Variants in ATL1 have been described mainly in patients with early onset HSP. We performed Sanger sequencing of all coding exons and adjacent intron regions of the ALT1 gene in 111 Czech patients with pure form of HSP and additional Multiplex-Ligation Probe Analysis (MLPA) testing targeting the ATL1 gene in 56 of them. All patients except seven were previously tested by Sanger sequencing of the SPAST gene with negative results. ATL1 diagnostic testing revealed only five missense variants in the ATL1 gene. Four of them are novel, but we suppose only two of them to be pathogenic and causal. The remaining variants are assumed to be benign. MLPA testing in 56 of sequence variant negative patients revealed no gross deletion in the ATL1 gene. Variants in the ATL1 gene are more frequent in patients with early onset HSP, but in general the occurrence of pathogenic variants in the ATL1 gene is low in our cohort, less than 4.5% and less than 11.1% in patients with onset before the age of ten. Variants in the ATL1 gene are a less frequent cause of HSP among Czech patients than has been previously reported among other populations.

Clinical features and genotype-phenotype correlation analysis in patients with ATL1 mutations: A literature reanalysis

Background

The hereditary spastic paraplegias (HSPs) are a group of clinically and genetically heterogeneous disorders. Approximately 10% of the autosomal dominant (AD) HSPs (ADHSPs) have the spastic paraplegia 3A (SPG3A) genotype which is caused by ATL1 gene mutations. Currently there are more than 60 reported ATL1 gene mutations and the genotype-phenotype correlation remains unclear. The study aims to investigate the genotype-phenotype correlation in SPG3A patients.

Methods

We performed a reanalysis of the clinical features and genotype-phenotype correlations in 51 reported studies exhibiting an ATL1 gene mutation.

Results

Most HSPs-SPG3A patients exhibited an early age at onset (AAO) of <10 years old, and showed an autosomal dominant pure spastic paraplegia. We found that 14% of the HSPs-SPG3A patients presented complicated phenotypes, with distal atrophy being the most common complicated symptom. The AAO of each mutation group was not statistically significant (P > 0.05). The mutational spectrum associated with ATL1 gene mutation is wide, and most mutations are missense mutations, but do not involve the functional motif of ATL1 gene encoded atlastin-1 protein.

Conclusions

Our findings indicate that there is no clear genotype-phenotype correlation in HSPs-SPG3A patients. We also find that exons 4, 7, 8 and 12 are mutation hotspots in ATL1 gene.

Electronic supplementary material

The online version of this article (doi:10.1186/s40035-017-0079-3) contains supplementary material, which is available to authorized users.

Exon 8-17 deletions of SPAST in a Chinese family with hereditary spastic paraplegia: a case report and literature review

Hereditary spastic paraplegia (HSP) is a group of clinically and genetically heterogeneous neurodegenerative disorders. SPG4 is the most common autosomal dominant form of HSP subtypes and is caused by mutations of the SPAST gene. Here we reported a Chinese family with HSP caused by deletion of exons 8-17 of the SPAST gene and reviewed the clinical phenotypes of patients with exon deletion that were reported in literatures. The patients with deletions of exons in the SPAST gene showed pure HSP, and the age at onset showed interfamily and intrafamily variations. This study suggests that exon deletion should be examined routinely in patients who are clinically diagnosed with HSP.