Mapping of a complicated familial spastic paraplegia to locus SPG4 on chromosome 2p

Truncating mutations in SPAST patients are associated with a high rate of psychiatric comorbidities in hereditary spastic paraplegia

BACKGROUND

The hereditary spastic paraplegias (HSPs) are a rare and heterogeneous group of neurodegenerative disorders that are clinically characterised by progressive lower limb spasticity. They are classified as either 'pure' or 'complex' where spastic paraplegia is complicated with additional neurological features. Mutations in the spastin gene (SPAST) are the most common cause of HSP and typically present with a pure form.

METHODS

We assessed in detail the phenotypic and genetic spectrum of SPAST-related HSP focused on 118 patients carrying SPAST mutations.

RESULTS

This study, one of the largest cohorts of genetically confirmed spastin patients to date, contributes with the discovery of a significant number of novel SPAST mutations. Our data reveal a high rate of complex cases (25%), with psychiatric disorders among the most common comorbidity (10% of all SPASTpatients). Further, we identify a genotype-phenotype correlation between patients carrying loss-of-function mutations in SPAST and the presence of psychiatric disorders.

KIF1A missense mutations in SPG30, an autosomal recessive spastic paraplegia: distinct phenotypes according to the nature of the mutations

The hereditary spastic paraplegias (HSPs) are a clinically and genetically heterogeneous group of neurodegenerative diseases characterised by progressive spasticity in the lower limbs. The nosology of autosomal recessive forms is complex as most mapped loci have been identified in only one or a few families and account for only a small percentage of patients. We used next-generation sequencing focused on the SPG30 chromosomal region on chromosome 2q37.3 in two patients from the original linked family. In addition, wide genome scan and candidate gene analysis were performed in a second family of Palestinian origin. We identified a single homozygous mutation, p.R350G, that was found to cosegregate with the disease in the SPG30 kindred and was absent in 970 control chromosomes while affecting a strongly conserved amino acid at the end of the motor domain of KIF1A. Homozygosity and linkage mapping followed by mutation screening of KIF1A allowed us to identify a second mutation, p.A255V, in the second family. Comparison of the clinical features with the nature of the mutations of all reported KIF1A families, including those reported recently with hereditary sensory and autonomic neuropathy, suggests phenotype-genotype correlations that may help to understand the mechanisms involved in motor neuron degeneration. We have shown that mutations in the KIF1A gene are responsible for SPG30 in two autosomal recessive HSP families. In published families, the nature of the KIF1A mutations seems to be of good predictor of the underlying phenotype and vice versa.

Sequence alterations within CYP7B1 implicate defective cholesterol homeostasis in motor-neuron degeneration

The hereditary spastic paraplegias (HSPs) are a genetically and clinically heterogeneous group of upper-motor-neuron degenerative diseases characterized by selective axonal loss in the corticospinal tracts and dorsal columns. Although numerous mechanisms involving defective subcellular transportation, mitochondrial malfunction, and increased oxidative stress have been proposed, the pathogenic basis underlying the neuronal loss is unknown. We have performed linkage analysis to refine the extent of the SPG5 disease locus and conducted sequence analysis of the genes located within this region. This identified sequence alterations in the cytochrome P450-7B1 (CYP7B1) associated with this pure form of HSP. In the liver, CYP7B1 offers an alternative pathway for cholesterol degradation and also provides the primary metabolic route for the modification of dehydroepiandrosterone neurosteroids in the brain. These findings provide the first direct evidence of a pivotal role of altered cholesterol metabolism in the pathogenesis of motor-neuron degenerative disease and identify a potential for therapeutic intervention in this form of HSP.

Spastic paraplegia 5: Locus refinement, candidate gene analysis and clinical description

Thirty-three different loci for hereditary spastic paraplegias (HSP) have been mapped, and 15 responsible genes have been identified. Autosomal recessive spastic paraplegias (ARHSPs) usually have clinically complex phenotypes but the SPG5, SPG24, and SPG28 loci are considered to be associated with pure forms of the disease. We performed a genome-wide scan in a large French family. Fine mapping of the refined SPG5 region on chromosome 8q12 was performed in another 17 ARHSP families with additional microsatellite markers. After exclusion of known ARHSP loci, the genome-wide screen provided evidence of linkage with a maximal multipoint lod score of 2.6 in the D8S1113-D8S1699 interval. This interval partially overlapped SPG5 and reduced it to a 5.9 megabase (Mb)-region between D8S1113 and D8S544. In a family of Algerian origin from a series of 17 other ARHSP kindreds, linkage to the SPG5 locus was supported by a multipoint lod score of 2.3. The direct sequencing of the coding exons of seven candidate genes did not detect mutations/polymorphisms in the index cases of both linked families. The phenotype of the two SPG5-linked families consisted of spastic paraparesis associated with deep sensory loss. In several patients with long disease durations, there were also mild cerebellar signs. The frequency of SPG5 was approximately 10% (2/18) in our series of ARHSP families with pure or complex forms. We have refined the SPG5 locus to a 3.8 cM interval and extended the phenotype of this form of ARHSP to include slight cerebellar signs.

Hereditary spastic paraparesis and psychosis

Hereditary spastic paraparesis (HSP) is characterized by progressive spasticity and weakness of the legs with or without additional abnormalities. Reports of psychiatric disorders in patients with HSP are limited to mood disturbances rather than to psychosis. We had noted significant psychotic illness in several patients recruited to a survey of HSP in Ireland and therefore set about examining the frequency and nature of psychosis in our patients with HSP. Cases with HSP and psychotic illness were identified from a nationwide epidemiological and clinical study. Psychiatric case notes were reviewed and Operational Diagnostic Criteria Checklist (OPCRIT) applied. Six patients from four families with HSP had evidence of psychosis in addition to paraparesis. OPCRIT diagnoses were 'narrow schizophrenia' (n = 2), 'broad schizophrenia' (n = 2) and 'schizo-affective/manic disorder' (n = 2). Patients were from families with Kjellin's syndrome and SPG4-HSP but not other kindreds and psychosis was not evident in family members without HSP. We found a higher than expected rate of psychosis in the Irish HSP population. Two groups of HSP patients may have increased risk of developing psychosis: those with Kjellin's syndrome and those with SPG4-HSP.

Spastin in the human and mouse central nervous system with special reference to its expression in the hippocampus of mouse pilocarpine model of status epilepticus and temporal lobe epilepsy

In the present in situ hybridization and immunocytochemical studies in the mouse central nervous system (CNS), a strong expression of spastin mRNA and protein was found in Purkinje cells and dentate nucleus in the cerebellum, in hippocampal principal cells and hilar neurons, in amygdala, substantia nigra, striatum, in the motor nuclei of the cranial nerves and in different layers of the cerebral cortex except piriform and entorhinal cortices where only neurons in layer II were strongly stained. Spastin protein and mRNA were weakly expressed in most of the thalamic nuclei. In selected human brain regions such as the cerebral cortex, cerebellum, hippocampus, amygdala, substania nigra and striatum, similar results were obtained. Electron microscopy showed spastin immunopositive staining in the cytoplasma, dendrites, axon terminals and nucleus. In the mouse pilocarpine model of status epilepticus and subsequent temporal lobe epilepsy, spastin expression disappeared in hilar neurons as early as at 2h during pilocarpine induced status epilepticus, and never recovered. At 7 days and 2 months after pilocarpine induced status epilepticus, spastin expression was down-regulated in granule cells in the dentate gyrus, but induced expression was found in reactive astrocytes. The demonstration of widespread distribution of spastin in functionally different brain regions in the present study may provide neuroanatomical basis to explain why different neurological, psychological disorders and cognitive impairment occur in patients with spastin mutation. Down-regulation or loss of spastin expression in hilar neurons may be related to their degeneration and may therefore initiate epileptogenetic events, leading to temporal lobe epilepsy.

Hereditary spastic paraplegia

The hereditary spastic paraplegias (HSPs) comprise a large group of inherited neurologic disorders. HSP is classified according to the mode of inheritance, the HSP locus when known, and whether the spastic paraplegia syndrome occurs alone or is accompanied by additional neurologic or systemic abnormalities. Analysis of 11 recently discovered HSP genes provides insight into HSP pathogenesis. Hereditary spastic paraplegia is a clinical diagnosis for which laboratory confirmation is sometimes possible, and careful exclusion of alternate and co-existing disorders is an important element in HSP diagnosis. Treatment for HSP is presently limited to symptomatic reduction of muscle spasticity, reduction in urinary urgency, and strength and gait improvement through physical therapy. Prenatal genetic testing in HSP is possible for some individuals with the increasing availability of HSP gene analysis.

Reduced regional cerebral blood flow in SPG4-linked hereditary spastic paraplegia

Hereditary spastic paraplegia (HSP) linked to the spastic gait gene 4 (SPG4) is controversial, as the "pure" form traditionally has been considered confined to the long axons of the spinal cord. However, recent immunolabeling experiments have demonstrated extensive Spastin expression in the cortex and striatum. This could indicate a more widespread neuropathology from mutations in the SPG4 gene than previously assumed. The aim of this study was therefore to ascertain the extent of cerebral involvement in SPG4 linked HSP by neuropsychological examination and measurement of the regional cerebral blood flow (rCBF) as an indirect marker of regional neuronal activity. Eighteen SPG4 patients and 18 matched control subjects were studied. Resting state rCBF was measured using Positron Emission Tomography (PET) and the (15)O-labelled water bolus technique and relative group differences were explored using Statistical Parametric Mapping (SPM 99). Neuropsychological assessment was performed using established and nationally validated tests (RH Basic Battery). Compared to healthy controls, the patient group had significantly decreased rCBF in the left fronto-temporal cortex (P<0.05), and more extensive changes were observed in a separate analysis of the most disabled individuals. The neuropsychological assessment revealed only significantly impaired recognition memory for faces. In summary, the findings support cerebral pathology in SPG4-linked HSP, although the decreased rCBF in fronto-temporal cortex was not associated with severe cognitive impairment.

A novel NIPA1 mutation associated with a pure form of autosomal dominant hereditary spastic paraplegia

The hereditary spastic paraplegias (HSPs) are a clinically and genetically heterogeneous group of neurodegenerative disorders characterised by lower limb spasticity and weakness. Mutations in NIPA1 (Nonimprinted in Prader-Willi/Angelman syndrome 1) have recently been identified as a cause of autosomal dominant pure HSP, with one mutation described in two unrelated families. NIPA1 has no known function but is predicted to possess nine transmembrane domains and may function as a receptor or transporter. Here we present a large British pedigree in which linkage analysis conclusively demonstrates linkage to the NIPA1 locus (maximum multipoint LOD score 4.6). Subsequent mutation analysis identified a novel missense substitution in a highly conserved NIPA1 residue (G106R) which further confirms a causative link between NIPA1 mutation and autosomal dominant hereditary spastic paraplegia.

A novel locus for pure recessive hereditary spastic paraplegia maps to 10q22.1-10q24.1

The hereditary spastic paraplegias (HSPs) are a group of clinically and genetically heterogeneous disorders characterized by progressive lower-limb spasticity. In this study, we performed linkage analysis on an autosomal recessive pure HSP family and mapped the disease to chromosome 10q22.1-10q24.1, a locus partially overlapping the existing SPG9 locus. We have either identified a novel locus for pure recessive HSP (SPG27), or we have found the first case of allelic disorders with different mode of inheritance in HSP. If the disorders are indeed allelic, our results have reduced the SPG9 interval by 3Mb with D10S536 and D10S1758 as flanking markers.

Hereditary spastic paraplegia with cerebellar ataxia: a complex phenotype associated with a new SPG4 gene mutation

Complex forms of hereditary spastic paraplegia (HSP) are rare and usually transmitted in an autosomal recessive pattern. A family of four generations with autosomal dominant hereditary spastic paraplegia (AD-HSP) and a complex phenotype with variably expressed co-existing ataxia, dysarthria, unipolar depression, epilepsy, migraine, and cognitive impairment was investigated. Genetic linkage analysis and sequencing of the SPG4 gene was performed and electrophysiologic investigations were carried out in six individuals and positron emission tomography (PET) in one patient. The disease was linked to the SPG4 locus on chromosome 2p as previously reported for pure HSP. Sequence analysis of the SPG4 (spastin) gene identified a novel 1593 C > T (GLN490Stop) mutation leading to premature termination of exon 12 with ensuing truncation of the encoded protein. However, the mutation was only identified in those individuals who were clinically affected by a complex phenotype consisting of HSP and cerebellar ataxia. Other features noted in this kindred including epilepsy, cognitive impairment, depression, and migraine did not segregate with the HSP phenotype or mutation, and therefore the significance of these features to SPG4 is unclear. Electrophysiologic investigation showed increased central conduction time at somatosensory evoked potentials measured from the lower limbs as the only abnormal finding in two affected individuals with the SPG4 mutation. Moreover, PET of one patient showed significantly relatively decreased regional cerebral blood flow in most of the cerebellum. We conclude that this kindred demonstrates a considerable overlap between cerebellar ataxia and spastic paraplegia, emphasizing the marked clinical heterogeneity of HSP associated with spastin mutations.

Clinical signs and symptoms in a large hereditary spastic paraparesis pedigree with a novel spastin mutation

The most common form of autosomal dominant hereditary spastic paraparesis (HSP), SPG4, is caused by mutations in the spastin gene on chromosome 2p. This disease is characterized by intra- and interfamilial phenotypic variation. To determine the predictive values of clinical signs and symptoms in SPG4, we examined 43 members of a large pedigree with autosomal dominant HSP. We then identified the genetic etiology of the disorder in this family, a novel nonsense mutation in exon 1 of spastin, carried by 24 of the examined family members. The best clinical predictors of positive gene status were the presence of hyperreflexia in the lower extremities, >2 beats of ankle clonus, pes cavus, bladder symptoms and increased tone in the legs. The mean age of onset was 32.2 +/- 7.4 years, but the age of onset was earlier in children from 10 of 12 child-parent gene-positive pairs, with a mean difference of 10.8 +/- 3.3 years. The finding of leg weakness was especially common in older-onset affected family member with leg hyperreflexia. These results suggest that specific clinical signs and symptoms may be of value in differentiating individuals affected with SPG4 from family members with nonspecific neurological findings.

Genetic heterogeneity in inherited spastic paraplegia associated with epilepsy

We have recently mapped a new rare form of spastic paraplegia complicated by bilateral cataracts, gastroesophageal reflux with persistent vomiting, and amyotrophy to chromosome 10q23.3-q24.2. This locus, named SPG9, is located in an interval spanning about 12 cM of genomic DNA, between markers D10S536 and D10S603, where different neurological disorders have been mapped. In particular, a gene for partial epilepsy has been assigned to a 3 cM interval between markers D10S185 and D10S577, which is completely included in the SPG9 critical region. A few families affected with spastic paraplegia and epilepsy have been reported; in the present study, we tested a pedigree with concurrence of spastic paraplegia, epilepsy, and mental retardation inherited as an autosomal dominant trait, using markers located in the SPG9 interval. Haplotype reconstruction excluded the linkage to 10q23.3-q24.2. In addition, the seven different loci so far reported to be associated with autosomal dominant pure forms of spastic paraplegia have been tested and excluded by linkage analysis and haplotype reconstruction, including SPG4 on chromosome 2p22-p21, where a familial form of spastic paraplegia associated with dementia and epilepsy has been mapped. These data confirm genetic heterogeneity in familial spastic paraplegia with epilepsy and suggest a specific locus for the family here analyzed.

Three novel spastin (SPG4) mutations in families with autosomal dominant hereditary spastic paraplegia

Hereditary spastic paraplegia (HSP) is a clinically and genetically heterogeneous condition, characterised principally by progressive spasticity of the lower limbs. Forty percent of autosomal dominant (AD) pedigrees show linkage to the SPG4 locus on chromosome 2, which encodes spastin, an ATPase associated with diverse cellular activities (AAA) protein. We have performed a clinical and genetic study of three AD-HSP families linked to SPG4. Sequencing revealed three novel causative mutations. Two of the mutations were located in exon 5 (a 1-base pair (bp) insertion and a 5-bp deletion), resulting in frameshift and premature termination of translation, with the predicted protein lacking the entire AAA functional domain. The 5-bp deletion was associated with a later onset and mild cerebellar features. The third mutation was a 3-bp deletion in exon 9, resulting in the loss of a highly conserved phenylalanine residue within the AAA cassette and an apparently milder phenotype. This is the first example of a deletion of an amino acid in spastin.

Hereditary spastic paraplegia

The hereditary spastic paraplegias are a large group of clinically similar disorders. Seventeen different HSP loci have been discovered thus far. Different genetic forms of uncomplicated HSP are clinically very similar. Except for the average age at which symptoms appear, different genetic types of uncomplicated HSP cannot be distinguished reliably by clinical parameters alone. For most subjects, HSP is a diagnosis of exclusion. The differential diagnosis includes treatable disorders as well as those for which the prognosis is quite different from HSP. Even with the emerging availability of laboratory testing for HSP gene mutations, it is still essential that alternative disorders be excluded by careful history, examination, laboratory studies, neuroimaging, and neurophysiologic evaluation. Uncomplicated HSP is due to axonal degeneration at the ends of the longest motor (corticospinal tract) and sensory (dorsal column fibers) in the spinal cord. The observation that some forms begin in childhood and are essentially nonprogressive while other forms begin in adulthood and are slowly progressive raises the possibility that some forms of HSP (e.g.; those associated with LICAM gene mutations and possibly those due to SPG3A mutations) are neurodevelopmental disorders; and other forms are truly neurodegenerative disorders. The mechanisms by which spastin, atlastin, and paraplegin mutations cause axonal degeneration that results in clinically similar forms of HSP are not known. Nonetheless, the identification of these genes and the ability to generate animal models of these forms of HSP will permit direct exploration of the molecular basis of HSP.

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.

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.

Silver syndrome is not linked to any of the previously established autosomal dominant hereditary spastic paraplegia loci

The hereditary spastic paraplegias are a clinically variable and genetically heterogeneous group of disorders characterized by progressive and lower limb spasticity and weakness. Silver syndrome (SS) is a particularly disabling autosomal dominant form of the disease in which there is associated wasting of the hand muscles. In view of the fact that genes for hereditary spastic paraplegia can produce highly variable phenotypes, the eight known autosomal dominant loci were investigated for linkage to Silver syndrome. Genotyping of these loci in two large multigenerational families was incompatible with linkage to any of these regions, suggesting that an additional locus is responsible for this syndrome.

Atypical dementia and spastic paraplegia in a patient with primary lateral sclerosis and numerous necortical beta amyloid plaques: new disorder or Alzheimer's disease variant?

Primary lateral sclerosis (PLS) and hereditary spastic paraplegia (HSP) are clinically similar disorders in which progressive lower limb spasticity and corticospinal tract degeneration are characteristic. We report the occurrence of progressive spastic paraplegia and frontal systems dementia in a patient with postmortem features of PLS combined with moderate Alzheimer-like changes in neocortex and hippocampus. This combination of clinical and neuropathologic findings has not been described in PLS or HSP and varies from other cases in which spastic paraplegia, dementia, and Alzheimer neuropathology occurred concurrently. This 69-year-old woman developed spastic quadriplegia and dementia over 12 years. Left leg weakness progressed over 7 years to paraplegia, then quadriplegia by age 68. Sensory and cerebellar function were preserved and fasciculations were absent. Dementia characterized by concrete thinking, perseveration, and impaired executive function appeared in the seventh year and remained relatively stable until 6 months before death at age 69. Degeneration of the lateral corticospinal and dorsal spinocerebellar tracts confined to the spinal cord was evident at postmortem examination. Brain stem, midbrain, and cerebellum were normal. Numerous beta/A4 amyloid positive diffuse plaques (10-15/200x field) were apparent in neocortex, and neurofibrillary tangles immunopositive for paired helical filament were detected in hippocampus. This case broadens the spectrum of disorders associated with Alzheimer neuropathologic changes. The relationship between PLS, HSP, and Alzheimer's disease requires further study.

Clinical and genetic aspects of spinocerebellar degeneration

After decades of confusion as a result of the marked clinical variability of spinocerebellar degeneration, molecular analyses have permitted the identification of loci and genes, which constitute the basis of a new classification. However, even greater genetic heterogeneity is suspected and several phenotypes, such as complex forms of spastic paraplegia and autosomal recessive ataxias, have not yet been thoroughly explored. Unexpectedly, the genes responsible for Friedreich's ataxia and a form of autosomal recessive spastic paraplegia place these diseases in the category of mitochondrial disorders. The unstable mutations caused by trinucleotide repeat expansions are responsible for a growing number of inherited cerebellar ataxias.

Clinical and pathologic findings in hereditary spastic paraparesis with spastin mutation

OBJECTIVE

To describe a family with chromosome 2p-linked hereditary spastic paraparesis (HSP) associated with dementia and illustrate the cerebral pathology associated with this disorder.

BACKGROUND

HSP comprises a heterogeneous group of inherited disorders in which the main clinical feature is severe, progressive lower limb spasticity. Nongenetic classification relies on characteristics such as mode of inheritance, age at onset, and the presence or absence of additional neurologic features. Several loci have been identified for autosomal dominant pure HSP. The most common form, which links to chromosome 2p (SPG4), has recently been shown to be due to mutations in spastin, the gene encoding a novel AAA-containing protein.

RESULTS

The authors report four generations of a British family with autosomal dominant HSP in whom haplotype analysis indicates linkage to chromosome 2p. In addition, a missense mutation has been identified in exon 10 of the spastin gene (A1395G). Dementia was documented clinically in one member of the family, two other affected family members were reported to have had late onset memory loss, and a younger affected individual showed evidence of memory disturbance and learning difficulties. Autopsy of the demented patient confirmed changes in the spinal cord typical of HSP and also demonstrated specific cortical pathology. There was neuronal depletion and tau-immunoreactive neurofibrillary tangles in the hippocampus and tau-immunoreactive balloon cells were seen in the limbic and neocortex. The substantia nigra showed Lewy body formation. The pathologic findings are not typical of known tauopathies.

CONCLUSIONS

The authors confirm that chromosome 2p-linked HSP can be associated with dementia and that this phenotype may be associated with a specific and unusual cortical pathology.

Brazilian family with pure autosomal dominant spastic paraplegia maps to 8q: analysis of muscle beta 1 syntrophin

The autosomal dominant hereditary spastic paraplegias (AD-HSP) are a heterogeneous group of degenerative disorders of the central motor system, characterized by progressive spasticity of the lower limbs. Five loci for pure AD-HSP have been identified to date: SPG3 at 14q, SPG4 at 2p, SPG6 at 15q, SPG8 at 8q, and more recently SPG10 at 12q. We have analyzed a Brazilian family with 16 affected individuals by pure AD-HSP who developed progressive gait disturbance with onset at age 18-26 years. Linkage analysis performed with 13 relatives (6 affected and 7 normal) excluded SPG3, SPG4, and SPG6 as candidate regions. However, positive LOD scores were obtained with markers flanking the candidate region for the SPG8 locus [maximum two point Lod score (Zmax) = 3.3 at theta = 0 for D8S1804]. In this region lies the syntrophin beta 1 gene (SNT2B1), a widely expressed dystrophin-associated protein and therefore a good positional and functional candidate for this disease. Immunohistochemical and Western Blot (WB) studies showed that the distribution, expression, and apparent molecular weight of the beta 1 syntrophin protein were comparable to those of normal control individuals. Therefore, it is unlikely that defects in this protein are related to SPG8, at least in the present family.

Spastin, a new AAA protein, is altered in the most frequent form of autosomal dominant spastic paraplegia

Autosomal dominant hereditary spastic paraplegia (AD-HSP) is a genetically heterogeneous neurodegenerative disorder characterized by progressive spasticity of the lower limbs. Among the four loci causing AD-HSP identified so far, the SPG4 locus at chromosome 2p2-1p22 has been shown to account for 40-50% of all AD-HSP families. Using a positional cloning strategy based on obtaining sequence of the entire SPG4 interval, we identified a candidate gene encoding a new member of the AAA protein family, which we named spastin. Sequence analysis of this gene in seven SPG4-linked pedigrees revealed several DNA modifications, including missense, nonsense and splice-site mutations. Both SPG4 and its mouse orthologue were shown to be expressed early and ubiquitously in fetal and adult tissues. The sequence homologies and putative subcellular localization of spastin suggest that this ATPase is involved in the assembly or function of nuclear protein complexes.

A fine integrated map of the SPG4 locus excludes an expanded CAG repeat in chromosome 2p-linked autosomal dominant spastic paraplegia

Autosomal dominant hereditary spastic paraplegia (AD-HSP) is a genetically heterogeneous disorder characterized by progressive spasticity of the lower limbs. A major locus (SPG4) causing AD-HSP in about 40% of the families was mapped to chromosome 2p. The analysis of six SPG4-linked AD-HSP families using the RED procedure previously showed the expansion of a CAG repeat in affected individuals. To identify the gene responsible for this form of HSP, we have constructed a 3.5-Mb YAC contig flanked by loci D2S400 and D2S367, have subcloned five of these YACs spanning the candidate region into cosmids, and screened these cosmid libraries for the presence of CAG repeat sequences. Four CAG repeats have been identified but none of them is expanded in 26 patients from 13 SPG4-linked AD-HSP families. A gene map comprising 21 transcripts was established using expressed sequence tags (ESTs) assigned previously to this region of 2p21-p22 with radiation hybrid panels GeneBridge 4 and G3. Full-length cDNAs corresponding to the 14 ESTs mapping to the SPG4 interval flanked by loci D2S352 and D2S2347 were isolated and sequenced. None contains a CAG repeat in its coding sequence. Finally, we have assembled a BAC contig composed of 37 clones that were also screened for the presence of CAG repeats; this failed to detect additional repeats to those identified on YACs.

A new locus for autosomal dominant "pure" hereditary spastic paraplegia mapping to chromosome 12q13, and evidence for further genetic heterogeneity

Autosomal dominant pure hereditary spastic paraplegia (ADPHSP) is clinically characterized by slowly progressive lower-limb spasticity. The condition is genetically heterogeneous, and loci have been mapped at chromosomes 2p, 8q, 14q, and 15q. We have performed a genomewide linkage screen on a large family with ADPHSP, in which linkage to all four previously known loci was excluded. Analysis of markers on chromosome 12q gave a peak pairwise LOD score of 3.61 at D12S1691, allowing us to assign a new locus for ADPHSP (a locus that we have designated "SPG10") to this region. Haplotype construction and analysis of recombination events narrowed the SPG10 locus to a 9.2-cM region between markers D12S368 and D12S83. In addition, our data strongly suggest that there are at least six ADPHSP loci, since we describe a further family in which linkage to all five known ADPHSP loci has been excluded.