Four mutations of the spastin gene in Japanese families with spastic paraplegia

Hereditary spastic paraplegia (HSP) is a group of genetically heterogeneous neurodegenerative disorders characterized by slowly progressive spasticity and weakness of the lower limbs. HSP is caused by failure of development or selective degeneration of the corticospinal tracts, which contain the longest axons in humans. The most common form of HSP is caused by mutations of the spastin gene (SPAST), located on chromosome 2p21-p22, which encodes spastin, one of the ATPases associated with diverse cellular activities (AAA). In this study, we detected four causative mutations of SPAST among 14 unrelated patients with spastic paraplegia. Two missense mutations (1447A→G, 1207C→G) and two deletion mutations (1465delT, 1475-1476delAA) were located in the AAA cassette region. Three of these four mutations were novel. Previous reports and our results suggest that the frequency of SPAST mutations is higher among Japanese patients with autosomal dominant HSP, although SPAST mutations are also observed in patients with sporadic spastic paraplegia.Rehana Basri, Ichiro Yabe and Hiroyuki Soma have contributed equally to this work.     

Mutations in phospholipase DDHD2 cause autosomal recessive hereditary spastic paraplegia (SPG54)

Hereditary spastic paraplegias (HSP) are a genetically heterogeneous group of disorders characterized by a distal axonopathy of the corticospinal tract motor neurons leading to progressive lower limb spasticity and weakness. Intracellular membrane trafficking, mitochondrial dysfunction and myelin formation are key functions involved in HSP pathogenesis. Only recently defects in metabolism of complex lipids have been implicated in a number of HSP subtypes. Mutations in the 23 known autosomal recessive HSP genes explain less than half of autosomal recessive HSP cases. To identify novel autosomal recessive HSP disease genes, exome sequencing was performed in 79 index cases with autosomal recessive forms of HSP. Resulting variants were filtered and intersected between families to allow identification of new disease genes. We identified two deleterious mutations in the phospholipase DDHD2 gene in two families with complicated HSP. The phenotype is characterized by early onset of spastic paraplegia, mental retardation, short stature and dysgenesis of the corpus callosum. Phospholipase DDHD2 is involved in intracellular membrane trafficking at the golgi/ endoplasmic reticulum interface and has been shown to possess phospholipase A1 activity in vitro. Discovery of DDHD2 mutations in HSP might therefore provide a link between two key pathogenic themes in HSP: membrane trafficking and lipid metabolism.     

pEGFP-SPAST真核表达载体的构建及遗传性痉挛性截瘫的发病机制研究

目的 构建野生型和突变型SPAST真核表达载体,研究SPAST基因突变所致遗传性痉挛性截瘫的发病机制.方法 建立野生型pEGFP-SPAST基因表达载体,采用overlap PCR方法构建突变型pEGFP-SPAST真核表达载体.细胞转染野生型和突变型pEGFP SPAST真核表达载体,观察野生型和突变型spastin蛋白在COS-7细胞中的表达,采用免疫荧光染色技术观察spastin蛋白与微管、线粒体的定位关系.结果 野生型和突变型spastin蛋白均在细胞质中表达.免疫荧光检测发现野生型和突变型spastin蛋白均不与微管共定位,也均不与线粒体共定位.结论 成功构建了野生型和突变型pEGFP-SPAST真核表达载体.突变型spastin蛋白不改变其细胞质定位.功能研究提示spastin蛋白可能不直接调控微管功能和线粒体功能.     

遗传性痉挛性截瘫11型研究进展

遗传性痉挛性截瘫是一种遗传性、神经退行性变的疾病,具有明显的遗传异质性,遗传形式多样.遗传性痉挛性截瘫11型是隐形遗传尤其是合并有胼胝体发育不良患者中最常见的类型,现就近几年来该病的研究进展,从遗传性痉挛性截瘫11型的基因定位和克隆,基因突变情况及其临床表现,诊断与鉴别诊断、发病机制等方面进行全面的介绍.     

Novel and recurrent spastin mutations in a large series of SPG4 Italian families

Background

Hereditary spastic paraplegias (HSP) are heterogeneous neurodegenerative disorders, genetically classified according to the identified disease gene or locus. Clinically, HSP are distinguished in pure and complicated forms. Mutations in the spastin gene (SPAST) are responsible for SPG4 and account approximately for 50% of the dominantly inherited paraplegias with a pure HSP phenotype.

Methods

Molecular screening of the SPAST gene allowed the identification of 31 Italian mutation carriers, from 19 unrelated families. Genetic testing was performed by direct sequencing and multiplex ligation-dependent probe amplification. Subjects carrying SPAST mutations were retrospectively evaluated for clinical phenotype and disability score assessment.

Results

We found 12 recurrent mutations, and 7 novel SPAST mutations. Twenty-eight patients exhibited a pure spastic paraplegia phenotype, while 3 subjects were asymptomatic mutation carriers. Four patients were sporadic cases. Age at onset ranged from 10 to 61 years. Disability score increased with age at examination and disease duration. Patients with onset >38 years presented a faster disease progression, and a higher disability functional index, than the patients with earlier onset (p < 0.04).

Conclusions

Our study enlarges the number of pathogenic SPAST mutations, and confirms the association with a pure spastic paraplegia phenotype. Age at onset was highly variable and correlates with the rate of disease progression. Future longitudinal clinical studies are needed to confirm these observations.     

Expanding SPTAN1 monoallelic variant associated disorders: From epileptic encephalopathy to pure spastic paraplegia and ataxia

PurposeNonerythrocytic αII-spectrin (SPTAN1) variants have been previously associated with intellectual disability and epilepsy. We conducted this study to delineate the phenotypic spectrum of SPTAN1 variants.MethodsWe carried out SPTAN1 gene enrichment analysis in the rare disease component of the 100,000 Genomes Project and screened 100,000 Genomes Project, DECIPHER database, and GeneMatcher to identify individuals with SPTAN1 variants. Functional studies were performed on fibroblasts from 2 patients.ResultsStatistically significant enrichment of rare (minor allele frequency < 1 × 10^–5) probably damaging SPTAN1 variants was identified in families with hereditary ataxia (HA) or hereditary spastic paraplegia (HSP) (12/1142 cases vs 52/23,847 controls, p = 2.8 × 10^–5). We identified 31 individuals carrying SPTAN1 heterozygous variants or deletions. A total of 10 patients presented with pure or complex HSP/HA. The remaining 21 patients had developmental delay and seizures. Irregular αII-spectrin aggregation was noted in fibroblasts derived from 2 patients with p.(Arg19Trp) and p.(Glu2207del) variants.ConclusionWe found that SPTAN1 is a genetic cause of neurodevelopmental disorder, which we classified into 3 distinct subgroups. The first comprises developmental epileptic encephalopathy. The second group exhibits milder phenotypes of developmental delay with or without seizures. The final group accounts for patients with pure or complex HSP/HA.     

GPT2 mutations cause developmental encephalopathy with microcephaly and features of complicated hereditary spastic paraplegia

Various genetic defects can cause intellectual and developmental disabilities (IDDs). Often IDD is a symptom of a more complex neurodevelopmental or neurodegenerative syndrome. Identifying syndromic patterns is substantive for diagnostics and for understanding the pathomechanism of a disease. Recessive glutamate pyruvate transaminase (GPT2) mutations have recently been associated with IDD in 4 families. Here, we report a novel recessive GPT2 stop mutation p.Gln24* causing a complex IDD phenotype in a homozygous state in 5 patients from 2 consanguineous Arab families. By compiling clinical information of these individuals and previously described GPT2 patients a recognizable neurodevelopmental and potentially neurodegenerative phenotype can be assigned consisting of intellectual disability, pyramidal tract affection with spastic paraplegia, microcephaly and frequently epilepsy. Because of the consistent presence of pyramidal tract affection in GPT2 patients, we further suggest that GPT2 mutations should be considered in cases with complex hereditary spastic paraplegia.     

Complicated forms of autosomal dominant hereditary spastic paraplegia are frequent in SPG10

Hereditary spastic paraplegias (HSP) constitute a heterogeneous group of neurodegenerative disorders characterized by slowly progressive spasticity of the lower extremities. Only a few different mutations in the SPG10 gene, KIF5A, have been described in pure dominant forms of the disease. We sequenced the motor domain of KIF5A in a large panel of 205 European HSP patients with either pure or complicated forms of the disease. We identified eight different heterozygous missense mutations, seven novels, in eight different families of French origin. Residue R280 was a mutational hot spot. Interestingly, the patients in 7/8 families had a complex phenotype, with peripheral neuropathy, severe upper limb amyotrophy (Silver syndrome-like), mental impairment, parkinsonism, deafness and/or retinitis pigmentosa as variably associated features. We report the largest series of SPG10 families described so far, which extends both the mutational spectrum of the disease and its phenotype, which now includes complicated forms of HSP. SPG10 mutations were found in 10% of our complicated forms of HSP, suggesting that mutations in KIF5A represent the major cause of complicated AD-HSP in France.     

A novel missense mutation (I344K) in the SPG4gene in a Korean family with autosomal-dominant hereditary spastic paraplegia

 Hereditary spastic paraplegia (HSP) is a group of clinically and genetically heterogeneous neurodegenerative disorders characterized by slowly progressive spasticity and weakness of the lower extremities. Among eight loci linked with autosomal-dominant (AD)-HSP, the SPG4 locus on chromosome 2p22 accounts for about 40% of all patients. Recently, mutations in a new member of the AAA protein family, called spastin, have been identified as responsible for SPG4-linked AD-HSP. Here, we describe a novel missense mutation (c.1031T>A; I344K) in exon 7 of the SPG4 gene identified in a Korean family with typical clinical features of pure AD-HSP. The mutation affects the third amino acid of the highly conserved AAA cassette domain, which is the most fore part of the domain altered by a missense mutation reported so far. Clinical presentations of affected individuals carrying the I344K mutation were not different from those of pure AD-HSP with SPG4 mutations reported previously. However, it is noteworthy that neither urinary dysfunction nor involvement of upper extremities was noticed in this family. To our knowledge, this is the first report of genetically confirmed AD-HSP in Korea. Received: February 20, 2002 / Accepted: May 21, 2002     

Association of late onset spastic paraparesis and dementia: Probably an autosomal dominant form of complicated paraplegia

The hereditary paraplegias are a heterogeneous group of genetic disorders characterized mainly by spastic paraparesis, which may be found as an isolated “pure form” known as Strümpell-Lorrain syndrome, or associated with a wide group of other manifestations [Harding, 1990; McKusick, 1994]. We studied two unrelated families, one with five members and the other with 11 members (over four generations), affected by a syndrome of late onset spastic paraparesis and dementia. Both pedigrees suggest an autosomal dominant pattern of inheritance. However, this cannot be concluded definitely because male-to-male transmission was not seen. Since this disorder has a late age of onset, we still do not know who will become affected in the second, third, and fourth generations. The association of late onset spastic paraparesis and dementia, without other pathological findings, has not been reported and probably represents a distinct entity. Am. J. Med. Genet. 68:1–6, 1997 © 1997 Wiley-Liss, Inc.     

中国人遗传性痉挛性截瘫spastin基因突变研究

目的 探讨中国人遗传性痉挛性截瘫（hereditary spastic paraplegia,HSP)spastin基因的突变特点，为该病的基因诊断提供依据。方法 应用聚合酶链反应—单链构象多态性(PCR—single strand conformation polymorphism，PCR—SSCP)结合DNA序列分析方法，对22个常染色体显性遗传HSP家系的先证者和9例散发性HSP患者的spastin基因进行研究，对发现异常SSCP条带的家系内成员进行突变研究。结果 在22例常染色体显性遗传HSP家系的先证者和9例散发性HSP患者中发现异常SSCP条带6例，进行DNA序列分析，共发现3种spastin基因突变，为外显子8的T1258A和A1293G，外显子14的1667delACT或1668delCTA或1669delTAC，均未见报道，突变位点均位于spastin基因功能区域，其中两个家系存在同一种突变(T1258A)，各突变家系内患者存在同样的异常SSCP条带。结论 中国人遗传性痉挛性截瘫患者存在spastin基因突变，该基因在中国人常染色体显性遗传的遗传性痉挛性截瘫家系中的突变率较低(18．2％)，点突变是主要的突变形式，外显子8可能是中国人spastin基因的突变热点。     

Hereditary spastic paraplegia masqueraded by congenital melanocytic nevus syndrome: Dual pathogenesis of germline non-mosaicism and somatic mosaicism

Neurocutaneous disorders are caused by germline and/or somatic mutations and involve the integument and central nervous systems. Congenital melanocytic nevus syndrome is characterized by melanotic skin lesions caused by somatic mutations at codon 61 in NRAS. A large cutaneous lesion raises the risk of central nervous system involvement. We report an 8-year-old girl with a congenital giant pigmented nevus that covered almost her entire back. Despite the absence of any radiological evidence of intracranial melanosis, the patient exhibited progressive limb spasticity with preserved intellectual ability. An extensive genetic analysis identified a specific class of heterozygous germline mutation in SPAST, p.(Arg499His), which is responsible for hereditary spastic paraplegia with infantile onset. In addition, a known heterozygous somatic mutation in NRAS, p.(Gln61Lys) was detected in the cutaneous lesion. This observation recapitulates concomitant mosaicism and non-mosaicism within a single individual and suggests that the possibility of a dual genetic diagnosis should be considered when neurological decline is observed in a patient with a neurocutaneous disorder without any detectable intracranial lesions.     

Mutation of FA2H underlies a complicated form of hereditary spastic paraplegia (SPG35)

Hereditary spastic paraplegia (HSP) describes a heterogeneous group of inherited neurodegenerative disorders in which the cardinal pathological feature is upper motor neurone degeneration leading to progressive spasticity and weakness of the lower limbs. Using samples from a large Omani family we recently mapped a gene for a novel autosomal recessive form of HSP (SPG35) in which the spastic paraplegia was associated with intellectual disability and seizures. Magnetic resonance imaging of the brain of SPG35 patients showed white matter abnormalities suggestive of a leukodystrophy. Here we report homozygous mutations in the fatty acid 2‐hydroxylase gene (FA2H) in the original family used to define the SPG35 locus (p.Arg235Cys) as well as in a previously unreported Pakistani family with a similar phenotype (p.Arg53_Ile58del). Measurement of enzyme activity in vitro revealed significantly reduced enzymatic function of FA2H associated with these mutations. These results demonstrate that mutations in FA2H are associated with SPG35, and that abnormal hydroxylation of myelin galactocerebroside lipid components can lead to a severe progressive phenotype, with a clinical presentation of complicated HSP and radiological features of leukodystrophy. © 2010 Wiley‐Liss, Inc.     

Spastin gene mutations in Bulgarian patients with hereditary spastic paraplegia

Hereditary spastic paraplegia (HSP) is an extremely heterogeneous group of neurodegenerative disorders affecting the longest axons in the central nervous system. The most common genetic form accounting for about 40% of the autosomal-dominant HSP (ADHSP) cases is spastin gene, SPG4. We performed mutation screening of the spastin gene on 36 unrelated HSP patients from three different ethnic groups (Bulgarian, Turks and Gypsies) and found four new mutations and one already reported. The phenotype-genotype correlations in Bulgarian SPG4 patients showed a great difference in the age at disease onset between patients with missense mutations and those harboring deletions and splice-site mutations. Our study is the first to present corroborative clinical data in favor of the general hypothesis that the clinical course of the disease is related to the type of the spastin mutation. The clinical and genealogical findings in Bulgarian SPG4 patients suggest that a positive family history for inheritance as an autosomal-dominant trait is a strong indication for spastin mutation screening.     

A novel mutation in ALS2 associated with severe and progressive infantile onset of spastic paralysis

Infantile onset ascending spastic paralysis (IAHSP) is a type of recessively inherited spastic paraplegia. We investigated the clinical and genetic cause of a recessively inherited disorder in two siblings manifesting severe spasticity in the lower limbs which hindered their gait. A novel homozygous nonsense mutation c.1918 C?>?T (p.Arg640*) was identified after whole-exome sequencing within ALS2 in the DNA of both patients. The obligate carriers were heterozygous for the mutation and other unaffected members were homozygous for the wild type allele. The variant was absent from 100 control chromosomes and all public databases. This report extends the allelic heterogeneity of ALS2 mutations and emphasizes the importance of genetic testing for diagnosis of pediatric disorders.     

遗传性痉挛性截瘫伴胼胝体发育不良致病基因筛查

目的探讨微卫星标记D15S971-D15S1012区间内全部10个已知基因是否为所收集的遗传性痉挛性截瘫伴胼胝体发育不良(hereditary spastic paraplegia with thin corpus callosum,HSP-TCC)家系的致病基因。方法应用聚合酶链反应、DNA直接测序和疾病表型共分离研究,对收集的5个HSP-TCC家系患者进行染色体15q13-15微卫星标记D15S971和D15S1012区间内10个已知基因(AK128197、MGC14798、HH114、MEIS2、MGC35118、SPRED1、AK128458、FLJ38426、RASGRP1、AK093014)突变分析。结果5个HSP-TCC家系的10个基因突变分析未发现致病突变,仅发现13种多态,其中2个为新发现的多态。结论经突变分析基本排除微卫星标记D15S971-D15S1012区间内全部10个已知基因为所收集的5个HSP-TCC家系的致病基因。     

Mutation analysis of the spastin gene (SPG4) in patients in Germany with autosomal dominant hereditary spastic paraplegia

Hereditary spastic paraplegias (HSP) comprise a genetically and clinically heterogeneous group of neurodegenerative disorders characterized by progressive spasticity and hyperreflexia of the lower limbs. Autosomal dominant hereditary spastic paraplegia 4 linked to chromosome 2p (SPG4) is the most common form of autosomal dominant hereditary spastic paraplegia. It is caused by mutations in the SPG4 gene encoding spastin, a member of the AAA protein family of ATPases. In this study the spastin gene of HSP patients from 161 apparently unrelated families in Germany was analyzed. The authors identified mutations in 27 out of the 161 HSP families; 23 of these mutations have not been described before and only one mutation was found in two families. Among the detected mutations are 14 frameshift, four nonsense, and four missense mutations, one large deletion spanning several exons, as well as four mutations that affect splicing. Most of the novel mutations are located in the conserved AAA cassette-encoding region of the spastin gene. The relative frequency of spastin gene mutations in an unselected group of German HSP patients is approximately 17%. Frameshift mutations account for the majority of SPG4 mutations in this population. The proportion of splice mutations is considerably lower than reported elsewhere.     

Novel stop-gain RNF170 variation detected in a Chinese family with adolescent-onset hereditary spastic paraplegia

Hereditary spastic paraplegia (HSP) is a heterogeneous group of inherited neurodegenerative disease characterized by progressive lower limb spasticity. Recent studies revealed that biallelic variants in RNF170 gene cause autosomal recessive complicated HSP with infancy onset. Here, we report an adolescent-onset HSP patient from a consanguineous Chinese family, with lower extremity stiffness, spastic gait, and unstable straight-line walking as the main manifestations. Whole-exome sequencing identifies a novel RNF170 mutation c.190C>T (p.R64*), which co-segregates with the disease in this pedigree. Functional analysis, including quantitative real-time PCR (RT-qPCR) and Western blot, indicates that both the mRNA and protein levels of mutant RNF170 are significantly reduced, which confirms the loss-of-function mechanism. Our study expands the spectrum of RNF170-associated HSP, while the RNF170 protein-involved degradation of the inositol 1,4,5-trisphosphate receptor in neurodegenerative motor neuron disorders deserves further investigation.