Linking axonal degeneration to microtubule remodeling by spastin mediated microtubule severing. (2005 Feb)
linking axonal degeneration to microtubule remodeling by spastin mediated microtubule severing . mutations in the AAA adenosine triphosphatase ( atpase ) spastin ( SPG4 ) cause an autosomal dominant form of hereditary spastic paraplegia , which is a retrograde axonopathy primarily characterized pathologically by the degeneration of long spinal neurons in the corticospinal tracts and the dorsal columns . using recombinant spastin , we find that six mutant forms of spastin , including three disease associated forms , are severely impaired in atpase activity . In contrast to a mutation designed to prevent adenosine triphosphate ( ATP ) binding , an ATP hydrolysis deficient spastin mutant predicted to remain kinetically trapped on target proteins decorates microtubules in transfected cells . analysis of disease associated missense mutations shows that some more closely resemble the canonical hydrolysis mutant , whereas others resemble the ATP binding mutant . using real time imaging , we show that spastin severs microtubules when added to permeabilized , cytosol depleted cells stably expressing GFP tubulin . using purified components , we also show that spastin interacts directly with microtubules and is sufficient for severing . these studies suggest that defects in microtubule severing are a cause of axonal degeneration in human disease .

Spastin , the protein mutated in autosomal dominant hereditary spastic paraplegia , is involved in microtubule dynamics. (2002 Jan)
spastin , the protein mutated in autosomal dominant hereditary spastic paraplegia , is involved in microtubule dynamics . hereditary spastic paraplegia ( HSP ) is characterized by progressive weakness and spasticity of the lower limbs , caused by the specific degeneration of the corticospinal tracts , the longest axons in humans . Most cases of the autosomal dominant form of the disease are due to mutations in the SPG4 gene , which encodes spastin , an atpase belonging to the AAA family . The cellular pathways in which spastin operates and its role in causing degeneration of motor axons are currently unknown . By expressing wild type or atpase defective spastin in several cell types , we now show that spastin interacts dynamically with microtubules . spastin association with the microtubule cytoskeleton is mediated by the N terminal region of the protein , and is regulated through the atpase activity of the AAA domain . expression of all the missense mutations into the AAA domain , which were previously identified in patients , leads to constitutive binding to microtubules in transfected cells and induces the disappearance of the aster and the formation of thick perinuclear bundles , suggesting a role of spastin in microtubule dynamics . consistently , wild type spastin promotes microtubule disassembly in transfected cells . these data suggest that spastin may be involved in microtubule dynamics similarly to the highly homologous microtubule severing protein , katanin . impairment of fine regulation of the microtubule cytoskeleton in long …

The drosophila homologue of the hereditary spastic paraplegia protein , spastin , severs and disassembles microtubules. (2005 Apr)
The drosophila homologue of the hereditary spastic paraplegia protein , spastin , severs and disassembles microtubules . hereditary spastic paraplegias ( HSPs ) , a group of neurodegenerative disorders characterized by lower extremity spasticity and weakness , are most commonly caused by mutations in the spastin gene , which encodes a AAA atpase related to the microtubule severing protein katanin . A drosophila homolog of spastin ( D spastin ) was identified recently , and D spastin RNAi treated or genetic null flies show neurological defects , and protein overexpression decreases the density of cellular microtubules . elucidating spastin s function and disease mechanism will require a more detailed understanding of its structure and biochemical mechanism . Here , we have investigated the effects of D spastin , individual D spastin domains , and D spastin proteins bearing disease mutations on microtubules in cellular and in vitro assays . We show that D spastin , like katanin , displays atpase activity and uses energy from ATP hydrolysis to sever and disassemble microtubules ; disease mutations abolish or partially interfere with these activities .

Recent advances in hereditary spastic paraplegia. (2001 Jul)
recent advances in hereditary spastic paraplegia . The hereditary spastic paraplegias are a group of rare disorders that are characterized by great clinical and genetic heterogeneity . there has been an exponential increase in the number of HSP loci mapped in recent years , with nine out of the 17 loci reported during the past 2 years . eight loci have now been identified for the autosomal dominant form , and seven of these are associated with pure HSP . spastic paraplegia 4 remains the most frequent locus , and is usually associated with a pure phenotype . although the corresponding spastin gene was only recently identified , over 50 mutations have been described to date , which renders molecular diagnosis difficult . Five loci are known for autosomal recessive HSP , and four of these are associated with complex forms , all with different phenotypes . Two genes have been identified : paraplegin and sacsin . finally , three loci have been identified in X linked HSP , two of which are complex forms . The genes that encode L1 and PLP were the first to be identified in HSP disorders . surprisingly , the five genes encode proteins of different families , making understanding and diagnosis of HSP even more difficult . The discovery of new genes should hopefully help to clarify the pathophysiology of these disorders .

Mutations in a newly identified gtpase gene cause autosomal dominant hereditary spastic paraplegia. (2001 Nov)
mutations in a newly identified gtpase gene cause autosomal dominant hereditary spastic paraplegia . The hereditary spastic paraplegias ( HSPs ; strümpell lorrain syndrome , MIM number 18260 ) are a diverse class of disorders characterized by insidiously progressive lower extremity spastic weakness ( reviewed in refs . 1 3 ) . eight autosomal dominant HSP ( adhsp ) loci have been identified , the most frequent of which is that linked to the SPG4 locus on chromosome 2p22 ( found in approximately 42 ) , followed by that linked to the spg3a locus on chromosome 14q11 q21 ( in approximately 9 ) . Only SPG4 has been identified as a causative gene in adhsp . Its protein ( spastin ) is predicted to participate in the assembly or function of nuclear protein complexes . Here we report the identification of mutations in a newly identified gtpase gene , spg3a , in adhsp affected individuals .

SPG4 founder effect in french canadians with hereditary spastic paraplegia. (2007 Jun)
SPG4 founder effect in french canadians with hereditary spastic paraplegia . background : The most common cause of autosomal dominant hereditary spastic paraplegia ( HSP ) is mutations in the SPG4 gene . We have previously identified novel SPG4 mutations in a collection of north american families including the c . g1801a mutation present in two families from quebec . The aim of this study is to estimate the frequency of the c . g1801a mutation in the french canadian ( FC ) population and to determine whether this mutation originates from a common ancestor . methods : We collected and sequenced exon 15 in probands of 37 families . genotypes of markers flanking the SPG4 gene were used to construct haplotypes in five families . clinical information was reviewed by a neurologist with expertise in HSP . results : We have identified three additional unrelated families with the c . g1801a mutation and haplotype analysis revealed that all five families share a common ancestor . The mutation is present in 7 of all our FC families and explains half of our spastin linked FC families . The phenotype associated with the c . g1801a genotype is pure HSP with bladder involvement . conclusion : In this study we have determined that the relative frequency of the c . g1801a mutation in our FC collection is 7 , and approximately 50 in the spastin positive FC group . This mutation is the most common HSP mutation identified in this population …

A novel missense mutation ( i344k ) in the spg4gene in a korean family with autosomal dominant hereditary spastic paraplegia. (2002 Aug)
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 .

Prenatal diagnosis of autosomal dominant hereditary spastic paraplegia ( SPG4 ) using direct mutation detection. (2004 May)
prenatal diagnosis of autosomal dominant hereditary spastic paraplegia ( SPG4 ) using direct mutation detection . objective : To present a report on prenatal diagnosis using direct SPG4 gene analysis in a family with autosomal dominant hereditary spastic paraplegia ( AD HSP ) . methods : genetic linkage and haplotype analysis were previously carried out with chromosome 2p markers . DNA was obtained from affected individuals , the affected father , the mother , and fetal DNA from an ongoing pregnancy by chorionic villus sampling ( CVS ) in the first trimester . The spastin gene ( SPG4 ) was completely sequenced . results : A novel 832insgdelaa frameshift mutation , predicted to cause loss of functional protein , was identified in the affected father and in the fetal DNA . conclusions : This is the first report on direct prenatal diagnosis of chromosome 2p linked AD HSP ( SPG4 ) . In addition , we report a novel SPG4 combined small insertion / deletion mutation in exon 5 , which may be the first SPG4 mutational hot spot .

Seven novel mutations and four exon deletions in a collection of norwegian patients with SPG4 hereditary spastic paraplegia. (2007 Jun)
seven novel mutations and four exon deletions in a collection of norwegian patients with SPG4 hereditary spastic paraplegia . To establish the phenotypic variation and frequency of spast mutations or deletions in norwegian patients with hereditary spastic paraplegia ( HSP ) , we examined 59 unrelated patients with HSP and screened for DNA point mutations and microdeletions in SPG4 . forty one had a familial history , 35 had a clear dominant inheritance , six had other affected sibs and 18 were sporadic . We found 12 mutations in SPG4 , seven of them novel , and four different heterozygous exon deletions , two of them novel . mutations were found in 16 families showing autosomal dominant ( AD ) inheritance , and in one sporadic case . In two non SPG4 families the S44L polymorphism / modifier was found in both affected and unaffected individuals . This is the first study of norwegian patients with HSP since the 1970s , and the first report on SPG4 in norway . Our results show that SPG4 mutations and deletions are a significant cause of HSP in our population and warrant SPG4 screening in AD families and selected sporadic cases .

A novel mutation in the spastin gene in a family with spastic paraplegia. (2002 May)
A novel mutation in the spastin gene in a family with spastic paraplegia . hereditary spastic paraplegia ( HSP ) is a degenerative neuromuscular disease characterized by progressive lower extremity weakness , spasticity and hyperreflexia . inheritance of HSP is commonly autosomal dominant , spastin was identified as the defective gene in chromosome 2p linked autosomal dominant hereditary spastic paraplegia ( AD HSP ) . In a large american family with AD HSP , we have identified a novel spastin mutation at a splice acceptor site in intron 6 ( 1130 1 g a ) and detected a corresponding aberrant transcript generated from a cryptic splice site . This is predicted to cause a frameshift and premature truncation of the abnormal spastin protein . Our data are the first to confirm that a mutation in an acceptor site in the spastin gene results in activation of a cryptic acceptor site and a translational frameshift . The clinical phenotype of this pedigree is also discussed .

Atlastin1 mutations are frequent in young onset autosomal dominant spastic paraplegia. (2004 Dec)
atlastin1 mutations are frequent in young onset autosomal dominant spastic paraplegia . background : hereditary spastic paraplegias are disorders that are very heterogeneous , both clinically and genetically . The atlastin1 gene has recently been implicated in spg3a , a form of autosomal dominant pure spastic paraplegia . atlastin1 mutations have been identified in 8 families so far . objectives : To determine the relative frequency , phenotype , and mutation spectrum of spg3a in patients with pure autosomal dominant spastic paraplegia and onset before age 20 years . patients AND methods : We sequenced the atlastin1 gene in a large series of patients ( 31 families ) in which mutations in the spastin gene , corresponding to the frequent SPG4 locus , had previously been excluded . The phenotype was compared with 126 SPG4 patients . results : We identified 12 families ( 39 ) including 34 patients with 9 different missense atlastin1 mutations , 7 of which are newly described . The main clinical characteristic of these spg3a patients was pure spasticity with very young onset of symptoms ( mean age , 4 . 6 / 3 . 9 years ) and slow progression . however , additional signs such as decreased vibration sense and wasting in lower limbs , sphincter disturbances , and scoliosis were found in a minority of patients . In addition , several gene carriers were clinically affected but still asymptomatic ( n 5 ) or had no clinical signs ( n 2 ) …

Four mutations of the spastin gene in japanese families with spastic paraplegia. (2006 Aug)
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 .

Hereditary spastic paraparesis : disrupted intracellular transport associated with spastin mutation. (2003 Dec)
hereditary spastic paraparesis : disrupted intracellular transport associated with spastin mutation . The commonest cause of hereditary spastic paraplegia ( HSP ) is mutation in the spastin gene . Both the normal function of spastin in the central nervous system and the mechanism by which mutation in spastin causes axonal degeneration are unknown . One hypothesis is that mutant spastin disrupts microtubule dynamics , causing an impairment of organelle transport on the microtubule network , which leads to degeneration in the distal parts of long axons . To study this neuronal and non neuronal cells were transfected with either wild type or mutant spastin proteins . We demonstrated evidence of a transient interaction of wild type spastin with microtubules , with resulting disassembly of microtubules , supporting a role for wild type spastin as a microtubule severing protein . mutant spastin demonstrated an abnormal interaction with microtubules , colocalizing with but no longer severing microtubules . The abnormal interaction of mutant spastin with microtubules was demonstrated to be associated with an abnormal perinuclear clustering of mitochondria and peroxisomes , suggestive of an impairment of kinesin mediated intracellular transport . Our findings indicate that an abnormal interaction of mutant spastin with microtubules , which disrupts organelle transport on the microtubule cytoskeleton , is likely to be the primary disease mechanism in HSP caused by missense mutations in the spastin gene .

Quantitative and functional analyses of spastin in the nervous system : implications for hereditary spastic paraplegia. (2008 Feb)
quantitative and functional analyses of spastin in the nervous system : implications for hereditary spastic paraplegia . spastin and P60 katanin are two distinct microtubule severing proteins . autosomal dominant mutations in the SPG4 locus corresponding to spastin are the most common cause of hereditary spastic paraplegia ( HSP ) , a neurodegenerative disease that afflicts the adult corticospinal tracts . Here we sought to evaluate whether SPG4 based HSP is best understood as a loss of function disease . using various rat tissues , we found that P60 katanin levels are much higher than spastin levels during development . In the adult , P60 katanin levels plunge dramatically but spastin levels decline only slightly . quantitative data of spastin expression in specific regions of the nervous system failed to reveal any obvious explanation for the selective sensitivity of adult corticospinal tracts to loss of spastin activity . An alternative explanation relates to the fact that the mammalian spastin gene has two start codons , resulting in a 616 amino acid protein called M1 and a slightly shorter protein called M85 . We found that M1 is almost absent from developing neurons and most adult neurons but comprises 20 25 of the spastin in the adult spinal cord , the location of the axons that degenerate during HSP . experimental expression in cultured neurons of a short dysfunctional M1 polypeptide ( but not a short dysfunctional M85 peptide ) is deleterious to normal axonal growth . In squid axoplasm , …

Spg3a hereditary spastin paraplegia with genetic anticipation and incomplete penetrance objective : To analyze the spg3a coding sequence and clinical … (2007 Feb)
spg3a hereditary spastin paraplegia with genetic anticipation and incomplete penetrance objective : To analyze the spg3a coding sequence and clinical features in a family with dominantly inherited hereditary spastin paraplegia ( HSP ) characterized by incomplete genetic penetrance and genetic anticipation . methods : analysis of the spg3a coding sequence , being sequence variations in SPG4 / spastin ( S44L and P45Q ) and SPG6 / nipa1 ( GCG 5 11 ) genes were performed for the proband , his affected son , his unaffected parents and unaffected brother . One hundred normal individuals were selected as controls . results : spg3a mutation v253i in the proband , his affected son , and unexpectedly , in his asymptomatic , 72 year old father was identified . No mutation at the same site was found in the other members of this family as well as the control . conclusion : incomplete genetic penetrance due to spg3a mutation v253i was observed in this family . This is the second report . marked phenotype variation ( genetic non penetrance , adult versus childhood onset symptoms ) between subjects with the same spg3a mutation indicates the influence of modifying genetic or environmental factors . progressively earlier symptom onset and increasing symptom severity in this family is consistent with genetic anticipation which has not been previously reported in spg3a HSP .

Identification of nuclear localisation sequences in spastin ( SPG4 ) using a novel tetra GFP reporter system. (2004 May)
identification of nuclear localisation sequences in spastin ( SPG4 ) using a novel tetra GFP reporter system . mutations in the human spastin gene ( SPG4 ) cause the most prevalent form of autosomal dominant hereditary spastic paraplegia ( HSP ) , a neurodegenerative disorder characterised by progressive weakness and spasticity of the lower limbs . We address the question of intracellular localisation of spastin . using polyclonal antibodies against N terminal spastin sequences , we find that the native protein is localised in both the perinuclear cytoplasm and the nucleus . To identify structural motifs within the protein that can explain entry into the nucleus , we developed a reporter system to test nuclear localisation sequence ( NLS ) functionality based on four in frame fused copies of green fluorescent protein . using this novel tool we demonstrate that spastin carries two NLSs located in exons 1 and 6 . Both are independently functional in mediating nuclear entry .

Phenotype of AD HSP due to mutations in the spast gene : comparison with AD HSP without mutations. (2001 Jan)
phenotype of AD HSP due to mutations in the spast gene : comparison with AD HSP without mutations . background : Pure autosomal dominant hereditary spastic paraparesis ( AD HSP ) is clinically and genetically heterogeneous . there are at least seven genetic loci with varying ages at onset and disability . The spast gene at the SPG4 locus on chromosome 2p is the major disease gene for AD HSP . objectives : To investigate whether there are distinct clinical features among families with AD HSP due to spast mutations compared with families excluded from SPG4 . methods : nineteen families with pure AD HSP were identified , and the clinical features of family members were compared using a standard protocol . With use of genetic studies , the families were divided into two groups for comparison : those with mutations in spast , the mutation positive group , and those excluded from SPG4 on the basis of linkage studies , the SPG4 excluded group . results : twenty nine individuals from four families had mutations in spast , whereas 22 individuals from three families comprised the SPG4 excluded group ; in 11 families , the pattern of linkage was unknown . In the one remaining family , no mutations were found despite strong linkage to SPG4 . different mutations were identified in the four spast pedigrees , but the clinical picture was similar in each . comparison of the mutation positive group with the SPG4 excluded group revealed an …

Eight novel mutations in SPG4 in a large sample of patients with hereditary spastic paraplegia. (2006 May)
eight novel mutations in SPG4 in a large sample of patients with hereditary spastic paraplegia . background : hereditary spastic paraplegia ( HSP ) is a group of genetically heterogeneous disorders characterized by progressive spasticity of the lower limbs . mutations in the SPG4 gene , which encodes spastin protein , are responsible for up to 45 of autosomal dominant cases . objective : To search for disease causing mutations in a large series of italian patients with HSP . design : samples of DNA were analyzed by direct sequencing of all exons in SPG4 . samples from a subset of patients were also analyzed by direct sequencing of all exons in spg3a , SPG6 , spg10 , and spg13 . setting : molecular testing facility in italy . patients : sixty unrelated italian patients with pure ( n 50 ) and complicated ( n 10 ) HSP . MAIN outcome measures : mutations in SPG4 , spg3a , SPG6 , spg10 , and spg13 . results : We identified 12 different mutations , 8 of which were novel , in 13 patients . No mutations of any of the other HSP genes tested were found in 15 patients with sporadic pure HSP who did not have mutations in the SPG4 gene . conclusions : The overall rate of mutation in the SPG4 gene within our sample was 22 , rising to 26 when only patients with pure HSP were considered . The negative result obtained in 15 patients without …

Human spastin has multiple microtubule related functions. (2005 Nov)
human spastin has multiple microtubule related functions . hereditary spastic paraplegias ( HSPs ) are neurodegenerative diseases caused by mutations in more than 20 genes , which lead to progressive spasticity and weakness of the lower limbs . The most frequently mutated gene causing autosomal dominant HSP is SPG4 , which encodes spastin , a protein that belongs to the family of atpases associated with various cellular activities ( AAAs ) . A number of studies have suggested that spastin regulates microtubule dynamics . We have studied the atpase activity of recombinant human spastin and examined the effect of taxol stabilized microtubules on this activity . We used spastin translated from the second ATG and provide evidence that this is the physiologically relevant form . We showed that microtubules enhance the atpase activity of the protein , a property also described for katanin , an AAA of the same spastin subgroup . furthermore , we demonstrated that human spastin has a microtubule destabilizing activity and can bundle microtubules in vitro , providing new insights into the molecular pathogenesis of HSP .

Spastin mutations are frequent in sporadic spastic paraparesis and their spectrum is different from that observed in familial cases. (2006 Mar)
spastin mutations are frequent in sporadic spastic paraparesis and their spectrum is different from that observed in familial cases . background : SPG4 encodes spastin , a member of the AAA protein family , and is the major gene responsible for autosomal dominant spastic paraplegia . It accounts for 10 40 of families with pure ( or eventually complicated ) hereditary spastic paraparesis ( HSP ) . objective : To assess the frequency of SPG4 mutation in patients with spastic paraplegia but without family histories . methods : 146 mostly european probands with progressive spastic paraplegia were studied ( 103 with pure spastic paraplegia and 43 with additional features ) . major neurological causes of paraplegia were excluded . None had a family history of paraplegia . DNA was screened by dhplc for mutations in the 17 coding exons of the SPG4 gene . sequence variants were characterised by direct sequencing . A panel of 600 control chromosomes was used to rule out polymorphisms . results : The overall rate of mutations was 12 ; 19 different mutations were identified in 18 patients , 13 of which were novel . In one family , where both parents were examined and found to be normal , the mutation was transmitted by the asymptomatic mother , indicating reduced penetrance . The parents of other patients were not available for analysis but were reported to be normal . there was no evidence for de novo mutations . The mutations found in these apparently …