Mutation analysis of SPG4 and SPG3A genes and its implication in molecular diagnosis of Korean patients with hereditary spastic paraplegia

BACKGROUND: Hereditary spastic paraplegia (HSP), a genetically and clinically heterogeneous group of neurodegenerative disorders, is characterized by progressive lower limb weakness and spasticity. Among the 8 loci associated with the autosomal dominant uncomplicated HSP (AD-HSP), the spastin (SPG4) and atlastin (SPG3A) genes have been known to account for approximately 40% and 10% of all cases, respectively. OBJECTIVE: To investigate the contribution of these 2 genes in the occurrence of HSP in Korean patients. DESIGN: Clinical and genetic study. SETTING: Tertiary care center. PATIENTS: Eighteen patients with uncomplicated HSP (11 AD and 7 sporadic) underwent screening for gene mutation. MAIN OUTCOME MEASURES: Mutations in the SPG4 and SPG3A genes as detected by direct sequencing of all coding exons and flanking intronic sequences. RESULTS: We identified 8 different SPG4 mutations, 7 of which have not been reported elsewhere. Among the detected mutations were 3 missense mutations, 2 in-frame deletions, 2 frameshift mutations, and 1 splice-site mutation. No mutation was found in the SPG3A gene. CONCLUSION: Compared with previous studies, a higher frequency of SPG4 gene mutations in AD-HSP (7/11; 64%) was observed, suggesting that a mutation analysis for the SPG4 gene might be helpful for molecular diagnosis of AD-HSP in Korean patients.     

White matter lesions in spastic paraplegia with mutations in SPG5/CYP7B1

Hereditary spastic paraplegias (HSPs) are relatively frequent disorders presenting great genetic heterogeneity. The recent identification of mutations in SPG5/CYP7B1 in six autosomal recessive kindred linked to the SPG5 locus on chromosome 8q prompted us to test the relative frequency of SPG5/CYP7B1 variants in 12 families and in sporadic HSP patients by high-resolution melting screening combined with direct sequencing. We present two patients who harbored three mutations (including two novel variants) in SPG5/CYP7B1 and white matter involvement evidenced at brain MRI. In HSP patients in whom no other genes were mutated, screening of SPG5/CYP7B1 seems to have a low diagnostic yield in autosomal recessive (8%) and sporadic (<1%) cases, even in those with complicated clinical features.     

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 mutations in SPG4 in whom 4 other genes were analyzed (SPG3A, SPG6, SPG10, and SPG13) indicate that these genes are not frequently mutated in sporadic pure HSP.     

Targeted next generation sequencing in SPAST-negative hereditary spastic paraplegia

Molecular characterization is important for an accurate diagnosis in hereditary spastic paraplegia (HSP). Mutations in the gene SPAST (SPG4) are the most common cause of autosomal dominant forms. We performed targeted next generation sequencing (NGS) in a SPAST-negative HSP sample. Forty-four consecutive HSP patients were recruited from an adult neurogenetics clinic in Sydney, Australia. SPAST mutations were confirmed in 17 subjects, and therefore 27 SPAST-negative patients were entered into this study. Patients were screened according to mode of inheritance using a PCR-based library and NGS (Roche Junior 454 sequencing platform). The screening panel included ten autosomal dominant (AD) and nine autosomal recessive (AR) HSP-causing genes. A genetic cause for HSP was identified in 25.9 % (7/27) of patients, including 1/12 classified as AD and 6/15 as AR or sporadic inheritance. Several forms of HSP were identified, including one patient with SPG31, four with SPG7 (with one novel SPG7 mutation) and two with SPG5 (including two novel CYP7B1 frameshift mutations). Additional clinical features were noted, including optic atrophy and ataxia for patients with SPG5 and ataxia and a chronic progressive external ophthalmoplegia-like phenotype for SPG7. This protocol enabled the identification of a genetic cause in approximately 25 % of patients in whom one of the most common genetic forms of HSP (SPG4) was excluded. Targeted NGS may be a useful method to screen for mutations in multiple genes associated with HSP. More studies are warranted to determine the optimal approach to achieve a genetic diagnosis in this condition.     

Novel SPG3A and SPG4 mutations in dominant spastic paraplegia families

Objectives – The hereditary spastic paraplegias (HSP) are a genetically and clinically heterogeneous group of neurodegenerative disorders, mainly characterized by a progressive spasticity and weakness of the lower limbs. Mutations in the SPG4 and SPG3A genes are responsible for approximately 50% of autosomal dominant HSP. To genetically diagnose the Portuguese families with HSP, mutation analysis was performed for the SPG4 and SPG3A genes. Patients and methods – Analysis was performed by polymerase chain reaction, followed by denaturing high performance liquid chromatography (DHPLC), in 61 autosomal dominant (AD)‐HSP families and 19 unrelated patients without family history. Results – Ten novel mutations were identified: one in the SPG3A and nine in the SPG4 genes; three known mutations in the SPG4 were also found. Most of the novel mutations were frameshift or nonsense (80%), resulting in a dysfunctional protein. Conclusions – The SPG4 and SPG3A analysis allowed the identification of 10 novel mutations and the genetic diagnosis of approximately a quarter of our AD‐HSP families.     

Two novel mutations in the Spastin gene of Chinese patients with hereditary spastic paraplegia

Background and purpose: Hereditary spastic paraplegia (HSP) is a clinically and genetically heterogeneous group of neurodegenerative diseases. Mutations in the spastin (SPG4) gene are responsible for approximately 40% of autosomal dominant HSP (AD‐HSP) and 6.5–18% of sporadic cases. Methods: Spastin mutations were screened in 11 AD‐HSP families and 11 sporadic cases by direct sequencing and MLPA assay. Novel mutations were detected in 100 healthy controls by PCR‐RFLP. Results: We identified seven different spastin mutations in five probands and one sporadic patient. Two of seven mutations were novel. The c.458delT was a pathogenic mutation, but the effect of c.1724 G>T remained unknown. Conclusions: This study allowed us to estimate the frequency of the SPG4 mutations in Chinese at 45% (5/11) in families with AD‐HSP and 9% (1/11) in sporadic cases. In addition, our data showed p.T614I was not associated with congenital arachnoid cysts.     

Genetics of hereditary spastic paraplegias

Hereditary spastic paraplegias (HSPs) are clinically and genetically highly heterogeneous. The key symptom of spastic paraparesis of lower limbs can be complicated by a variety of signs and symptoms including cognitive impairment, optic atrophy, cerebellar ataxia, peripheral nerve involvement, or seizures. At least 48 loci have been identified, termed SPG1-SPG48. Ten genes for autosomal dominant HSP are currently known, SPG4 being by far the most common subtype accounting for ～50% of cases. SPG3 is especially common in young-onset cases. Autosomal recessive HSP seems to be even more heterogeneous. The known 12 autosomal recessive HSP genes collectively explain about one third of cases only. The most common causes for pure autosomal recessive HSP are SPG7 and SPG5. Mental retardation and thin corpus callosum on magnetic resonance imaging point toward SPG11 and SPG15. The authors provide an overview on clinical, neurophysiologic, and neuroradiologic characteristics of the more common HSP subtypes. More details are given in the tables for quick reference, and a genetic testing strategy is proposed.     

Identification of a Mutation in SPG11 in an Iranian Patient with Spastic Paraplegia and Ears of the Lynx Sign

Hereditary spastic paraplegia (HSP) includes a number of inherited disorders which are characterized by stiffness in the lower extremities and progressive gait disturbance. Mutations in terms of spastic gait genes (SPGs) are responsible for occurrence of different types of HPS with autosomal recessive, X-linked recessive, and autosomal dominant modes of inheritance. In the current case report, we identified a mutation in SPG11 gene in a female patient with progressive stiffness of lower extremities and atrophy of corpus callosum and the “lynx ear” sign in brain MRI. Whole exome sequencing (WES) revealed a homozygote frameshift deletion variant in SPG11 gene (NM001160227: exon 28: c.4746delT, p.N1583Tfs*23). This variant is a null variant classified as a pathogenic variant (PVS1) according to ACMG standards and guidelines. The frequency of this variant in 1000G, ExAC, and Iranome databases was 0. This study shows the role of WES in the identification of disease-causing mutations in a disease such as HSP which can be caused by diverse mutations in several genes.     

Early onset autosomal dominant spastic paraplegia caused by novel mutations in SPG3A

Hereditary spastic paraplegia (HSP) is a group of neurodegenerative disorders mainly characterized by progressive spasticity of the lower limbs. The major features of HSP are a marked phenotypic variability both among and within families and an extended genetic heterogeneity. More than 20 HSP loci and 10 spastic paraplegia genes ( SPG) have been identified to date, including the genes responsible for the two most frequent forms of autosomal dominant spastic paraplegia (AD-HSP), encoding spastin ( SPG4) and atlastin ( SPG3A), respectively. To date, only eight mutations have been described in the atlastin gene, which was reported to account for about 10% of all AD-HSP families. We investigated 15 German and French AD-HSP families, including the 3 large pedigrees that allowed the mapping and subsequent refinement of the SPG3A locus. Three novel mutations were found in exons 4, 9, and 12 of the atlastin gene and the common R239C mutation located in exon 7 was confirmed in a 7th family of European origin. Overall, the comparison of the clinical data for all SPG3A-HSP families reported to date failed to reveal any genotype/phenotype correlation as demonstrated for other forms of AD-HSP. However, it confirmed the early onset of this form of HSP, which was observed in almost all affected individuals with a mutation in the atlastin gene.     

Further clinical and genetic characterization of SPG11: hereditary spastic paraplegia with thin corpus callosum

Hereditary spastic paraplegias (HSPs) are a heterogeneous group of neurodegenerative disorders leading to progressive spasticity of the lower limbs. Clinically, HSPs are divided into "pure" and "complicated" forms. In pure HSP, the spasticity of the lower limbs is the sole symptom, whereas in complicated forms additional neurological and non-neurological features are observed. Genetically, HSPs are divided into autosomal dominant (AD), autosomal recessive (AR) and X-linked (XL) forms. Up to date, 30 different HSPs are linked to different chromosomal loci and 11 genes could be defined for AR-HSP, AD-HSP and XL-HSP. SPG11, an AR-HSP (synonym: HSP11), is a complicated HSP associated with a slowly progressive spastic paraparesis, mental impairment and the development of a thin corpus callosum (TCC) during the course of the disease. SPG11 has been previously linked to chromosomal region 15q13 - 15. First, we applied rigid diagnostic criteria to systematically examine 20 Turkish families with autosomal recessive HSP for characteristic features of SPG11. We detected four large Turkish families with AR-HSP and TCC consistent with SPG11. Subsequent genetic linkage analysis of those 4 families refines the SPG11 locus further down to a small region of 2.93 cM with a maximum lod score of 11.84 at marker D15S659 and will guide further candidate gene analysis.     

Novel mutations in SPG11 cause hereditary spastic paraplegia associated with early‐onset levodopa‐responsive Parkinsonism

Background: Autosomal recessive hereditary spastic paraplegia with thin corpus callosum is a neurodegenerative disorder characterized by spastic paraparesis, cognitive impairment, and peripheral neuropathy. The neuroradiologic hallmarks are thin corpus callosum and periventricular white matter changes. Mutations in the SPG11 gene have been identified to be a major cause of autosomal recessive hereditary spastic paraplegia with thin corpus callosum and recently also proven to be responsible for juvenile parkinsonism associated with spastic paraplegia. Methods: We describe one Italian autosomal recessive hereditary spastic paraplegia with thin corpus callosum patient who unusually presented at onset, 16 years, with parkinsonism‐like features, responsive to dopaminergic therapy. Then the clinical picture evolved and became more complex. A brain magnetic resonance imaging scan showed thin corpus callosum and hyperintense T₂‐weighted lesions in periventricular regions, and the ¹²³I‐ioflupane single‐photon emission coupled tomography was abnormal. Results: Genetic analysis detected two novel mutations, a c.3664insT variant in compound heterozygosity with a c.6331insG mutation, in SPG11. Discussion: This case confirms the high genetic and clinical heterogeneity associated with SPG11 mutations. It also offers further evidence that parkinsonism may initiate autosomal recessive hereditary spastic paraplegia with thin corpus callosum and that parkinsonian symptoms can have variable dopaminergic response in these patients. © 2011 Movement Disorder Society     

Analysis of CYP7B1 in non-consanguineous cases of hereditary spastic paraplegia

Hereditary spastic paraplegia (HSP) is a neurodegenerative condition defined clinically by lower limb spasticity and weakness. Homozygous mutations in CYP7B1 have been identified in several consanguineous families that represented HSP type 5 (SPG5), one of the many genetic forms of the disease. We used direct sequencing and multiplex ligation-dependent probe amplification to screen for CYP7B1 alterations in apparently sporadic HSP patients (n = 12) as well as index patients from non-consanguineous families with recessive (n = 8) and dominant (n = 8) transmission of HSP. One sporadic patient showing HSP as well as optic atrophy carried a homozygous nonsense mutation. Compound heterozygosity was observed in a recessive family with a clinically pure phenotype. A heterozygous missense change segregated in a small dominant family. We also found a significant association of a known coding polymorphism with cerebellar signs complicating a primary HSP phenotype. Our findings suggest CYP7B1 alterations to represent a rather frequent cause of HSP that should be considered in patients with various clinical presentations.     

Mapping of a new form of pure autosomal recessive spastic paraplegia (SPG28)

Pure hereditary spastic paraplegias are characterized by isolated and progressive spasticity in the lower limbs. We mapped the spastic paraplegia 28 (SPG28) locus to chromosome 14q21.3-q22.3 in a Moroccan family with autosomal recessive hereditary spastic paraplegia. Affected patients experienced development of progressive spastic gait during childhood and required help walking in their early 40s. Nine additional hereditary spastic paraplegia families were not linked to this locus, demonstrating further genetic heterogeneity. No mutations were found in exons of GCH1 and SPG3A, two genes from the candidate region involved in movement disorders.     

Motor system abnormalities in hereditary spastic paraparesis type 4 (SPG4) depend on the type of mutation in the spastin gene

BACKGROUND: Hereditary spastic paraparesis (HSP) denotes a group of inherited neurological disorders with progressive lower limb spasticity as their clinical hallmark; a large proportion of autosomal dominant HSP belongs to HSP type 4, which has been linked to the SPG4 locus on chromosome 2. A variety of mutations have been identified within the SPG4 gene product, spastin. OBJECTIVE: Correlation of genotype and electrophysiological phenotype. MATERIAL: Two large families with HSP linked to the SPG4 locus with a very similar disease with respect to age of onset, progression, and severity of symptoms. METHODS: Mutation analysis was performed by PCR from genomic DNA and cDNA, and direct sequencing. The motor system was evaluated using transcranial magnetic stimulation. RESULTS: Patients differ in several categories depending on the type of mutation present. CONCLUSIONS: For the first time in hereditary spastic paraparesis, a phenotypic correlate of a given genetic change in the spastin gene has been shown.     

Narrowing of the critical region in autosomal recessive spastic paraplegia linked to the SPG5 locus

Hereditary spastic paraplegias are neurodegenerative disorders characterized clinically by progressive spasticity of the lower limbs. They are inherited as autosomal dominant, autosomal recessive, and X-linked traits. Four Italian families with autosomal recessive pure spastic paraplegia are reported. We show evidence of linkage to the SPG5 locus on chromosome 8p and our data reduce the candidate interval for SPG5 to the11-cM interval spanned by D8S285 and D8S544. We also report the search for mutations in five genes located in the region and their exclusion as candidates for SPG5.     

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.     

The high prevalence of hereditary spastic paraplegia in Sardinia, insular Italy

The few epidemiological studies conducted to date on the heterogeneous group of hereditary spastic paraplegias (HSPs) indicate a prevalence of 1.27–12.1 per 100,000. This study aims to explore the epidemiological, clinical, and genetic variability of HSPs among Sardinians, a population of peculiar ethnicity.A population-based prevalence study was performed in north-western Sardinia between January 2000 and December 2010. Multiple sources were used for case ascertainment. Familial and sporadic cases were diagnosed according to generally accepted criteria, and clinical diagnoses were validated by expert neurological examination. Clinical data and pedigree information were recorded and blood samples drawn for genetic testing.Sixty-seven HSP patients were included in the study: 59 belonged to 11 families with autosomal dominant transmission (AD-HSP), three cases were from two unrelated autosomal recessive families, and the remaining five cases were apparently sporadic. On 31 December 2010, the total crude prevalence was 19.9 per 100,000 (95 % CI 18.4–21.4), while the crude prevalence of AD-HSP was 17.5 (24.4 M, 15.7 F; M:F ratio 1.55). The mean age at examination was 48.4 years, and the mean age at onset of HSP was 36.6 years. A molecular diagnosis was obtained in 82.1 % of the cases (52 cases with mutations in SPAST/SPG4, two in SPG7, and one in SPG11).The prevalence of HSP among Sardinians is high compared with other Western European populations. The multiple search strategy used in this study and the specific socio-demographic characteristics of Sardinians may account for this finding.     

Novel spastin (SPG4) mutations in Italian patients with hereditary spastic paraplegia

Spastic paraplegia type 4 is caused by mutations in the gene that encodes spastin (SPG4), a member of the AAA protein family. A cohort of 34 unrelated Italian patients with pure spastic paraplegia, of which 18 displayed autosomal dominant inheritance and 16 were apparently sporadic, were screened for mutations in the SPG4 gene by denaturing high performance liquid chromatography. We identified a previously reported mutation in a sporadic patient with pure hereditary spastic paraplegia. We also identified eight unrelated patients with pure autosomal dominant hereditary spastic paraplegia carrying five novel mutations in the SPG4 gene (one missense mutation, c.1304 C>T; one nonsense mutation, c.807C>A; two frameshift mutations, c.1281dupT, c.1514_1515insATA; and one splicing mutation, c.1322-2A>C). The frequency for SPG4 mutations detected in autosomal dominant hereditary spastic paraplegia was 44.4%. This study contributes to expand the spectrum of SPG4 mutations in Italian population.     

SPG11: a consistent clinical phenotype in a family with homozygous Spatacsin truncating mutation

Hereditary spastic paraplegias (HSP) are a heterogeneous group of neurodegenerative disorders leading to progressive spasticity of the lower limbs. Here, we describe clinical and genetic features in an Italian family affected by autosomal recessive HSP (ARHSP) with mental impairment and thin corpus callosum (TCC). In both affected subjects, genetic analysis revealed the presence of a homozygous small deletion (733_734delAT) leading to a frameshift (M245VfsX) within the coding region of SPG11 gene, encoding spatacsin. This finding is the first independent confirmation that spatacsin loss of function mutations cause ARHPS-TCC. Roberto Del Bo and Alessio Di Fonzo, These two authors equally contributed to the present work.     

SPG3A is the most frequent cause of hereditary spastic paraplegia with onset before age 10 years

Seven families with six different SPG3A mutations were identified among 106 with autosomal dominant hereditary spastic paraplegia (HSP). Two mutations were novel (T162P, C375R). SPG3A was twice as frequent as SPG4 in patients with onset before age 10 years (31.8%). Later onset was not observed. The phenotype was pure HSP, but disease duration was longer than in non-SPG3A/SPG4 patients, leading ultimately to greater handicap.