Hereditary spastic paraparesis in adults. A clinical and genetic perspective from Tuscany

OBJECTIVE

Hereditary spastic paraparesis or paraplegias (HSPs) are a group of neurogenetic conditions with prominent involvement of the pyramidal tracts. Aim of this study is the clinical and molecular characterization of a cohort of patients with HSP. Moreover, we aim to study the minimum prevalence of HSP in our area and to propose a schematic diagnostic approach to HSP patients based on the available data from the literature.

METHODS

Retrospective/perspective study on the subjects with clinical signs and symptoms indicative of pure or complicated HSP, in whom other possible diagnosis were excluded by appropriate neuroradiological, neurophysiologic and laboratory studies, who have been evaluated by the Neurogenetic Service of our Clinic in last two years (2011-2012).

RESULTS

45 patients were identified. The minimum prevalence of HSP in our area was of about 2.17-3.43/100,000. The SF-36 (quality of life) and SPRS (disease progression) scores were inversely related; the time-saving, four-stage scale of motor disability could predict the SPRS scores with a high statistical significance, and we encourage its use in HSP. Our study confirms SPG4 as the major cause of HSP. All SPG4 patients had a pure HSP phenotype, and the dominant inheritance was evident in the great majority of these subjects. SPG7 was the second genetic cause. Other genotypes were rarer (SPG10, SPG11, SPG17).

CONCLUSION

Exact molecular diagnosis will allow a more accurate patient counseling and, hopefully, will lead to specific, targeted, therapeutic options for these chronic, still incurable diseases.

A novel mutation in STXBP1 gene in a child with epileptic encephalopathy and an atypical electroclinical pattern

Mutations in STXBP1 gene, encoding the syntaxin binding protein 1, have been recently described in Ohtahara syndrome, or early infantile epileptic encephalopathy with suppression-burst pattern, and in other early-onset epileptic encephalopathies. A 3-year-old boy affected by epileptic encephalopathy started at 8 months of age is described. Focal epilepsy was characterized by drug resistance seizures with multifocal interictal and ictal electroencephalographic (EEG) features and variable EEG focus. Direct sequencing of the STXBP1 gene showed a novel de novo mutation (c.751G>A), leading to a p.Ala251Thr substitution. Based on reported data, treatment with vigabatrin was attempted and patient became immediately seizure free for 4 months. The present case further expands the clinical spectrum of "STXBP1-related encephalopathy" suggesting molecular analysis of STXBP1 in early onset epileptic encephalopathies of unknown etiology (with onset within the first year of life). In addition, the case provides valuable suggestions on seizures treatment in STXBP1 mutated subjects.

Mutations in CYP2U1, DDHD2 and GBA2 genes are rare causes of complicated forms of hereditary spastic paraparesis

Complicated hereditary spastic paraplegias (HSP) are a heterogeneous group of HSP characterized by spasticity associated with a variable combination of neurologic and extra-neurologic signs and symptoms. Among them, HSP with thin corpus callosum and intellectual disability is a frequent subtype, often inherited as a recessive trait (ARHSP-TCC). Within this heterogeneous subgroup, SPG11 and SPG15 represent the most frequent subtypes. We analyzed the mutation frequency of three genes associated with early-onset forms of ARHSP with and without TCC, CYP2U1/SPG56, DDHD2/SPG54 and GBA2/SPG46, in a large population of selected complicated HSP patients by using a combined approach of traditional-based and amplicon-based high-throughput pooled-sequencing. Three families with mutations were identified, one for each of the genes analyzed. Novel homozygous mutations were identified in CYP2U1 (c.1A>C/p.Met1?) and in GBA2 (c.2048G>C/p.Gly683Arg), while the homozygous mutation found in DDHD2 (c.1978G>C/p.Asp660His) had been previously reported in a compound heterozygous state. The phenotypes associated with the CYP2U1 and DDHD2 mutations overlap the SPG56 and the SPG54 subtypes, respectively, with few differences. By contrast, the GBA2 mutated patients show phenotypes combining typical features of both the SPG46 subtype and the recessive ataxia form, with marked intrafamilial variability thereby expanding the spectrum of clinical entities associated with GBA2 mutations. Overall, each of three genes analyzed shows a low mutation frequency in a general population of complicated HSP (<1 % for either CYP2U1 or DDHD2 and approximately 2 % for GBA2). These findings underline once again the genetic heterogeneity of ARHSP-TCC and the clinical overlap between complicated HSP and the recessive ataxia syndromes.

Cerebroretinal microangiopathy with calcifications and cysts associated with CTC1 and NDP mutations

Mutations in the conserved telomere maintenance component 1 (CTC1) gene were recently described in Coats plus syndrome and in cerebroretinal microangiopathy with calcifications and cysts. Norrie disease protein (NDP) gene was found mutated in Norrie disease, in Familial Exudative Vitreoretinopathy, and in Coats syndrome. Here we describe a boy affected by Norrie disease who developed typical features of cerebroretinal microangiopathy with calcifications and cysts. Direct sequencing of the CTC1 and NDP genes in this patient shows the presence of compound heterozygosity for 2 mutations in CTC1 (c.775G>A, pV259M and a novel microdeletion c.1213delG) and a missense mutation in the NDP gene (c.182T>C, p.L61P). Based on these genetic findings and on the expression of both genes in endothelial cells, we postulate that microangiopathy might be a primary underlying pathologic abnormality in cerebroretinal microangiopathy with calcifications and cysts. This hypothesis is further supported by magnetic resonance imaging (MRI) data showing multiple minute calcifications in the deep gray nuclei and in terminal arteriolar zones.

ZFYVE26/SPASTIZIN: a close link between complicated hereditary spastic paraparesis and autophagy

Defective autophagy is associated with neurodegenerative disorders including Alzheimer, Parkinson and Huntington diseases, amyotrophic lateral sclerosis and SCA (spinocerebellar ataxias). Autophagy defects were detected also in SPG49, a complicated form of hereditary spastic paraparesis (cHSP) associated with mutations in the TECPR2 gene, suggesting a role of autophagy also in this heterogeneous group of neurodegenerative diseases. We recently found defective autophagy in SPG15, another HSP subtype associated with mutations in the ZFYVE26/SPG15 gene. Patient-derived cells (fibroblasts/lymphoblasts) carrying different ZFYVE26 mutations show accumulation of immature autophagosomes and increased MAP1LC3B-II and SQSTM1/p62 levels. These findings indicate that ZFYVE26 is a key determinant of autophagosome maturation, which is impaired when the protein is defective or absent. Replication of these findings in primary neurons supports the relevance of defective autophagy in SPG15-related neurodegeneration.

Defective autophagy in spastizin mutated patients with hereditary spastic paraparesis type 15

Hereditary spastic paraparesis type 15 is a recessive complicated form of the disease clinically characterized by slowly progressive spastic paraparesis and mental deterioration with onset between the first and second decade of life. Thinning of corpus callosum is the neuroradiological distinctive sign frequently associated with white matter abnormalities. The causative gene, ZFYVE26, encodes a large protein of 2539 amino acid residues, termed spastizin, containing three recognizable domains: a zinc finger, a leucine zipper and a FYVE domain. Spastizin protein has a diffuse cytoplasmic distribution and co-localizes partially with early endosomes, the endoplasmic reticulum, microtubules and vesicles involved in protein trafficking. In addition, spastizin localizes to the mid-body during the final step of mitosis and contributes to successful cytokinesis. Spastizin interacts with Beclin 1, a protein required for cytokinesis and autophagy, which is the major lysosome-mediated degradation process in the cell. In view of the Beclin 1-spastizin interaction, we investigated the possible role of spastizin in autophagy. We carried out this analysis by using lymphoblast and fibroblast cells derived from four different spastizin mutated patients (p.I508N, p.L243P, p.R1209fsX, p.S1312X) and from control subjects. Of note, the truncating p.R1209fsX and p.S1312X mutations lead to loss of spastizin protein. The results obtained indicate that spastizin interacts with the autophagy related Beclin 1-UVRAG-Rubicon multiprotein complex and is required for autophagosome maturation. In cells lacking spastizin or with mutated forms of the protein, spastizin interaction with Beclin 1 is lost although the formation of the Beclin 1-UVRAG-Rubicon complex can still be observed. However, in these cells we demonstrate an impairment of autophagosome maturation and an accumulation of immature autophagosomes. Autophagy defects with autophagosome accumulation can be observed also in neuronal cells upon spastizin silencing. These results indicate that autophagy is a central process in the pathogenesis of complicated forms of hereditary spastic paraparesis with thin corpus callosum.

A novel ATP1A2 gene mutation in familial hemiplegic migraine and epilepsy

BACKGROUND

Familial hemiplegic migraine (FHM) is a rare autosomal dominant migraine subtype, characterized by fully reversible motor weakness as a specific symptom of aura. Mutations in the ion transportation coding genes CACNA1A , ATP1A2 and SCN1A are responsible for the FHM phenotype. Moreover, some mutations in ATP1A2 or SCN1A also may lead to epilepsy.

CASE

Here we report on a three-generation family with five patients having a novel ATP1A2 mutation on exon 19, causing guanine-to-adenine substitution (c.2620G>A, p.Gly874Ser) that co-segregated in the five living relatives with migraine, four of whom had hemiplegic migraine. Moreover, three patients presented with epilepsy, one of whom had generalized epilepsy with febrile seizures plus (GEFS+).

CONCLUSIONS

The present study provides further evidence on the involvement of ATP1A2 mutations in both migraine and epilepsy, underlying the relevance of genetic analysis in families with a comorbidity of both disorders.

A 66-year-old patient with vanishing white matter disease due to the p.Ala87Val EIF2B3 mutation

Vanishing white matter (VWM; OMIM # 603896) is one of the most prevalent inherited childhood leukoencephalopathies. It has, however, become evident that VWM has a wider clinical spectrum, with age at onset inversely related to clinical severity. Many affected women experience a combination of leukoencephalopathy and primary amenorrhea or premature ovarian failure, a condition named ovarioleukodystrophy. Mutations in any of the genes encoding the 5 subunits of the Eukaryotic Initiation Factor 2B gene (EIF2B1, 2, 3, 4, and 5) can independently cause VWM.(1).

Considerations on a mutation in the NOTCH3 gene sparing a cysteine residue: a rare polymorphism rather than a CADASIL variant

Some missense mutations and small deletions in the NOTCH3 gene, not involving cysteine residues, have been described in patients considered to be affected by paucisymptomatic CADASIL. However, the significance of such molecular variants is still unclear. We describe a 49-year-old woman with a CADASIL-like phenotype, carrying a novel cysteine-sparing mutation in exon 29 of the NOTCH3 gene, and discuss the possible pathogenetic role of this molecular variant. Even though atypical clinical and MRI findings make a diagnosis of CADASIL unlikely in this patient, our report nevertheless underlines the intriguing genotype-phenotype relationship in NOTCH3 mutations and the importance of functional investigation to ascertain the role of new NOTCH3 mutations in CADASIL pathogenesis.

A novel mutation in the β-tubulin gene TUBB2B associated with complex malformation of cortical development and deficits in axonal guidance

Neurological disorders characterized by abnormal neuronal migration, organization, axon guidance, and maintenance have recently been associated with missense and splice-site mutations in the genes encoding α- and β-tubulin isotypes TUBA1A, TUBB2B, TUBB3, and TUBA8. We found a novel heterozygous mutation c.419G > C in exon 4 of the gene encoding TUBB2B in a female with microcephaly, agenesis of the corpus callosum, open-lip schizencephaly of the left parietal lobe, extensive polymicrogyria, basal ganglia and thalami dysmorphisms, and vermis and right third nerve hypoplasia. The missense change results in a glycine to alanine substitution; the mutated residue falls within an invariant glycine-rich region and therefore is likely to result in impaired protein function and possibly microtubule formation. This study expands the spectrum of brain malformations associated with mutations in the β-tubulin gene TUBB2B, supporting its critical role in migration/organization and axon guidance processes. In addition, it suggests a possible genetic aetiology of schizencephaly, thus strengthening the hypothesis that there is a common pathophysiological base in polymicrogyria and schizencephaly.

Nitric oxide sustains long-term skeletal muscle regeneration by regulating fate of satellite cells via signaling pathways requiring Vangl2 and cyclic GMP

Satellite cells are myogenic precursors that proliferate, activate, and differentiate on muscle injury to sustain the regenerative capacity of adult skeletal muscle; in this process, they self-renew through the return to quiescence of the cycling progeny. This mechanism, while efficient in physiological conditions does not prevent exhaustion of satellite cells in pathologies such as muscular dystrophy where numerous rounds of damage occur. Here, we describe a key role of nitric oxide, an important signaling molecule in adult skeletal muscle, on satellite cells maintenance, studied ex vivo on isolated myofibers and in vivo using the α-sarcoglycan null mouse model of dystrophy and a cardiotoxin-induced model of repetitive damage. Nitric oxide stimulated satellite cells proliferation in a pathway dependent on cGMP generation. Furthermore, it increased the number of Pax7⁺/Myf5⁻ cells in a cGMP-independent pathway requiring enhanced expression of Vangl2, a member of the planar cell polarity pathway involved in the Wnt noncanonical pathway. The enhanced self-renewal ability of satellite cells induced by nitric oxide is sufficient to delay the reduction of the satellite cell pool during repetitive acute and chronic damages, favoring muscle regeneration; in the α-sarcoglycan null dystrophic mouse, it also slowed disease progression persistently. These results identify nitric oxide as a key messenger in satellite cells maintenance, expand the significance of the Vangl2-dependent Wnt noncanonical pathway in myogenesis, and indicate novel strategies to optimize nitric oxide-based therapies for muscular dystrophy. Stem Cells 2012; 30:197–209.

SMC1A codon 496 mutations affect the cellular response to genotoxic treatments

Cornelia de Lange syndrome is a pleiotropic developmental syndrome characterized by growth and cognitive impairment, facial dysmorphic features, limb anomalies, and other malformations. Mutations in core cohesin genes SMC1A and SMC3, and the cohesin regulatory gene, NIPBL, have been identified in Cornelia de Lange syndrome probands. Patients with NIPBL mutations have more severe phenotypes when compared to those with mutations in SMC1A or SMC3. To date, 26 distinct SMC1A mutations have been identified in patients with Cornelia de Lange syndrome. Here, we describe a 3-year-old girl with psychomotor and cognitive impairment, mild facial dysmorphic features but no limb anomaly, heterozygous for a c.1487G>A mutation in SMC1A which predicts p.Arg496His. We show that this mutation leads to an impairment of the cellular response to genotoxic treatments.

Mutations in the motor and stalk domains of KIF5A in spastic paraplegia type 10 and in axonal Charcot-Marie-Tooth type 2

Spastic paraplegia type 10 (SPG10) is an autosomal dominant form of hereditary spastic paraplegia (HSP) due to mutations in KIF5A, a gene encoding the neuronal kinesin heavy chain implicated in anterograde axonal transport. KIF5A mutations were found in both pure and complicated forms of the disease; a single KIF5A mutation was also detected in a CMT2 patient belonging to an SPG10 mutant family. To confirm the involvement of the KIF5A gene in both CMT2 and SPG10 phenotypes and to define the frequency of KIF5A mutations in an Italian HSP patient population, we performed a genetic screening of this gene in a series of 139 HSP and 36 CMT2 affected subjects. We identified five missense changes, four in five HSP patients and one in a CMT2 subject. All mutations, including the one segregating in the CMT2 patient, are localized in the kinesin motor domain except for one, falling within the stalk domain and predicted to generate protein structure destabilization. The results obtained indicate a KIF5A mutation frequency of 8.8% in the Italian HSP population and identify a region of the kinesin protein, the stalk domain, as a novel target for mutation. In addition, the mutation found in the CMT2 patient strengthens the hypothesis that CMT2 and SPG10 are the extreme phenotypes resulting from mutations in the same gene.

Senataxin modulates neurite growth through fibroblast growth factor 8 signalling

Senataxin is encoded by the SETX gene and is mainly involved in two different neurodegenerative diseases, the dominant juvenile form of amyotrophic lateral sclerosis type 4 and a recessive form of ataxia with oculomotor apraxia type 2. Based on protein homology, senataxin is predicted to be a putative DNA/RNA helicase, while senataxin interactors from patients' lymphoblast cell lines suggest a possible involvement of the protein in different aspects of RNA metabolism. Except for an increased sensitivity to oxidative DNA damaging agents shown by some ataxia with neuropathy patients' cell lines, no data are available about possible functional consequences of dominant SETX mutations and no studies address the function of senataxin in neurons. To start elucidating the physiological role of senataxin in neurons and how disease-causing mutations in this protein lead to neurodegeneration, we analysed the effect of senataxin on neuronal differentiation in primary hippocampal neurons and retinoic acid-treated P19 cells by modulating the expression levels of wild-type senataxin and three different dominant mutant forms of the protein. Wild-type senataxin overexpression was required and sufficient to trigger neuritogenesis and protect cells from apoptosis during differentiation. These actions were reversed by silencing of senataxin. In contrast, overexpression of the dominant mutant forms did not affect the regular differentiation process in primary hippocampal neurons. Analysis of the cellular pathways leading to neuritogenesis and cytoprotection revealed a role of senataxin in modulating the expression levels and signalling activity of fibroblast growth factor 8. Silencing of senataxin reduced, while overexpression enhanced, fibroblast growth factor 8 expression levels and the phosphorylation of related target kinases and effector proteins. The effects of senataxin overexpression were prevented when fibroblast growth factor 8 signalling was inhibited, while exogenous fibroblast growth factor 8 reversed the effects of senataxin silencing. Overall, these results reveal a key role of senataxin in neuronal differentiation through the fibroblast growth factor 8 signalling and provide initial molecular bases to explain the neurodegeneration associated with loss-of-function mutations in senataxin found in recessive ataxia. The lack of effect on neuritogenesis observed with the overexpression of the dominant mutant forms of senataxin apparently excludes a dominant negative effect of these mutants while favouring haploinsufficiency as the pathogenic mechanism implicated in the amyotrophic lateral sclerosis 4-related degenerative condition. Alternatively, a different protein function, other than the one involved in neuritogenesis, may be implicated in these dominant degenerative processes.

Clinical phenotype variability in patients with hereditary spastic paraplegia type 5 associated with CYP7B1 mutations

Spastic paraplegia type 5 (SPG5) is caused by mutations in CYP7B1, a gene encoding the cytochrome P-450 oxysterol 7-α-hydroxylase, CYP7B1, an enzyme implicated in the cholesterol metabolism. Mutations in CYP7B1 were found in both pure and complicated forms of the disease with a mutation frequency of 7.7% in pure recessive cases. The mutation frequency in complex forms, approximately 6.6%, is more controversial and needs to be refined. We studied in more detail the SPG5-related spectrum of complex phenotypes by screening CYPB1 for mutations in a large cohort of 105 Italian hereditary spastic paraplegias (HSPs) index patients including 50 patients with a complicated HSP (cHSP) phenotype overlapping the SPG11- and the SPG15-related forms except for the lack of thin corpus callosum and 55 pure patients. Five CYP7B1 mutations, three of which are novel, were identified in four patients, two with a complex form of the disease and two with a pure phenotype. The CYP7B1 mutation frequencies obtained in both complicated and pure familial cases are comparable to the known ones. These results obtained extend the range of SPG5-related phenotypes and reveal variability in clinical presentation, disease course and functional profile in the SPG5-related patients while providing with some clues for molecular diagnosis in cHSP.

A novel mutation in KIF5A gene causing hereditary spastic paraplegia with axonal neuropathy

Hereditary spastic paraplegias (HSPs) include a group of neurodegenerative diseases, and so far 46 SPG loci have been mapped and 17 genes isolated. Among the autosomal dominant HSPs (AD-HSPs), SPG10 is a rare form due to mutations in KIF5A gene (locus 12q13.3). We describe the clinical, neurophysiological, morphological and genetic study of an Italian family with AD-HSP. The proband presented with an adult onset spastic paraparesis and diffuse paresthesias where neurophysiological and nerve biopsy morphological studies revealed an axonal neuropathy. Molecular genetic analysis identified a new missense mutation (c.608C>G) of KIF5A gene resulting in a serine to cysteine substitution, S203C, located in a highly conserved domain of the protein. This pedigree confirms the occurrence of an axonal peripheral neuropathy in SPG10.

Syntaxin 4 is required for acid sphingomyelinase activity and apoptotic function

Acid sphingomyelinase (A-SMase) is an important enzyme in sphingolipid metabolism and plays key roles in apoptosis, immunity, development, and cancer. In addition, it mediates cytotoxicity of cisplatin and some other chemotherapeutic drugs. The mechanism of A-SMase activation is still undefined. We now demonstrate that, upon CD95 stimulation, A-SMase is activated through translocation from intracellular compartments to the plasma membrane in an exocytic pathway requiring the t-SNARE protein syntaxin 4. Indeed, down-regulation of syntaxin 4 inhibits A-SMase translocation and activation induced by CD95 stimulation. This leads to inhibition of the CD95-triggered signaling events, including caspase 3 and 9 activation and apoptosis, activation of the survival pathway involving the protein kinase Akt, and important changes in cell cycle and proliferation. The molecular interaction between A-SMase and syntaxin 4 was not known and clarifies the mechanism of A-SMase activation. The novel actions of syntaxin 4 in sphingolipid metabolism and exocytosis we describe here define signaling mechanisms of broad relevance in cell pathophysiology.

The low-affinity receptor for neurotrophins p75NTR plays a key role for satellite cell function in muscle repair acting via RhoA

Regeneration of muscle fibers, lost during pathological muscle degeneration or after injuries, is mediated by the production of new myofibres. This process, sustained by the resident stem cells of the muscle, the satellite cells, is finely regulated by local cues, in particular by cytokines and growth factors. Evidence in the literature suggests that nerve growth factor (NGF) is involved in muscle fiber regeneration; however, its role and mechanism of action were unclear. We have investigated this issue in in vivo mouse models of muscle regeneration and in primary myogenic cells. Our results demonstrate that NGF acts through its low-affinity receptor p75(NTR) in a developmentally regulated signaling pathway necessary to myogenic differentiation and muscle repair in vivo. We also demonstrate that this action of NGF is mediated by the down-regulation of RhoA-GTP signaling in myogenic cells.

Point mutations and a large intragenic deletion in SPG11 in complicated spastic paraplegia without thin corpus callosum

BACKGROUND

Hereditary spastic paraplegia (HSP) with thin corpus callosum (HSP-TCC) is a frequent subtype of complicated HSP clinically characterised by slowly progressive spastic paraparesis with cognitive impairment and thin corpus callosum (TCC). SPG11, the gene associated with the major locus involved, encodes spatacsin, a protein of unknown function.

METHODS

Different types of mutations were identified in patients with the complex form of HSP (cHSP) including TCC. We screened a series of 45 index patients with different types of cHSP with (n = 10) and without (n = 35) TCC.

RESULTS

Ten mutations, of which five are novel, were detected in seven patients. Of importance, three out of seven mutated patients present with cHSP without TCC. Among the novel mutations identified, we characterised a large intragenic rearrangement deleting 2.6 kb of the SPG11 gene. The rearrangement is due to non-allelic homologous recombination between Alu sequences flanking the breakpoints.

CONCLUSIONS

These findings expand the mutation spectrum of SPG11 and suggest that SPG11 mutations may occur more frequently in familial than sporadic forms of cHSP without TCC. This helps to define further clinical and molecular criteria for a correct diagnosis of the SPG11 related form of cHSP. In addition, the intragenic deletion detected here, and the mechanism involved, both provide clues to address the issue of SPG11 missing mutant alleles previously reported.

Cornelia de Lange syndrome mutations in SMC1A or SMC3 affect binding to DNA

Cornelia de Lange syndrome (CdLS) is a clinically heterogeneous developmental disorder characterized by facial dysmorphia, upper limb malformations, growth and cognitive retardation. Mutations in the sister chromatid cohesion factor genes NIPBL, SMC1A and SMC3 are present in approximately 65% of CdLS patients. In addition to their canonical roles in chromosome segregation, the cohesin proteins are involved in other biological processes such as regulation of gene expression, DNA repair and maintenance of genome stability. To gain insights into the molecular basis of CdLS, we analyzed the affinity of mutated SMC1A and SMC3 hinge domains for DNA. Mutated hinge dimers bind DNA with higher affinity than wild-type proteins. SMC1A- and SMC3-mutated CdLS cell lines display genomic instability and sensitivity to ionizing radiation and interstrand crosslinking agents. We propose that SMC1A and SMC3 CdLS mutations affect the dynamic association between SMC proteins and DNA, providing new clues to the underlying molecular cause of CdLS.