HSP60 is a rare cause of hereditary spastic paraparesis, but may act as a genetic modifier

A novel REEP1 splicing mutation with broad clinical variability in a family with hereditary spastic paraplegia

Hereditary spastic paraplegia (HSP) is a heterogeneous group of genetic disorders characterized by lower-limb spastic paralysis. We report on a family with three generations of autosomal dominant inheritance of HSP caused by a novel heterozygous splice-site mutation (c.303 + 2 T > C) in REEP1 that was confirmed by RFLP analysis. Carriers of the mutation, including one asymptomatic individual, showed a mild HSP phenotype with a wide range of intrafamilial variation. All symptomatic carriers had ankle contractures in addition to other classical clinical symptoms of HSP. Clinicians should suspect REEP1-related HSP in patients who show ankle contractures with other symptoms of HSP and should consider that these patients have asymptomatic carriers within their family.

Independent occurrence of de novo HSPD1 and HIP1 variants in brothers with different neurological disorders - leukodystrophy and autism

Consecutive occurrence of de novo variants in the same family is an extremely rare phenomenon. Two siblings, a younger brother with hypomyelinating leukodystrophy and an elder brother with severe intellectual disability and autistic features, had independent de novo variants of HSPD1 c.139T > G (p.Leu47Val) and HIP1 c.1393G > A (p.Glu465Lys), respectively. These novel variants were predicted to be pathogenic. Both patients also had a known MECP2 variant, c.499C > T (p.Arg167Trp).

Erbliche spastische Spinalparalysen: aktuelle Erkenntnisse und Entwicklungen

Die erblichen spastischen Spinalparalysen („hereditary spastic paraplegias“, HSPs) sind Bewegungsstörungen, die aus der Degeneration der Axone oberer Motoneuronen resultieren. Sie sind klinisch und genetisch sehr heterogen. Der vorliegende Übersichtsartikel fasst aktuelle Strategien zur genetischen Diagnostik der HSPs zusammen, erörtert mögliche Mutationsmechanismen, diskutiert Erklärungen für die klinische Variabilität innerhalb ausgewählter Formen und verweist auf noch ungeklärte und zum Teil wenig beachtete Phänomene. Außerdem wird die Notwendigkeit eines tieferen Verständnisses der zellulären und molekularen Mechanismen für die Entwicklung neuer Therapien dargestellt.

Mutation and clinical characteristics of autosomal-dominant hereditary spastic paraplegias in China

BACKGROUND

Hereditary spastic paraplegias constitute a heterogeneous group of inherited neurodegenerative disorders. To date, there has been no systematic mutation and clinical analysis for a large group of autosomal-dominant hereditary spastic paraplegias in China.

OBJECTIVE

The purpose of this study was to investigate the mutation frequencies and the clinical phenotypes of Chinese spastic paraplegia patients.

METHODS

Direct sequencing and a multiplex ligation-dependent probe amplification assay were applied to detect the mutations of SPAST and ATL1 in 54 autosomal-dominant hereditary spastic paraplegia probands and 66 isolated cases. Next, mutations in NIPA1, KIF5A, REEP1 and SLC33A1 were detected in the negative patients. Subsets of spastic paraplegia patients were genotyped for the modifying variants. Further, detailed clinical data regarding the genetically diagnosed families were analysed.

RESULTS

Altogether, 27 families were diagnosed as SPG4, 3 as SPG3A and 1 as SPG6. No mutations in KIF5A, REEP1 or SLC33A1 were found; 9 SPAST mutations were novel. There was no p.S44L or p.P45Q variant in SPAST and no p.G563A variant in HSPD1 in either the 120 spastic paraplegia patients or the 500 controls. There was a remarkable clinical difference between the SPG4 and non-SPG4 patients and even between genders among the SPG4 patients. Non-penetrance and remarkable gender difference were observed in some SPG4 and SPG3A families.

CONCLUSIONS

Our data confirm that hereditary spastic paraplegias in China represent a heterogeneous group of genetic neurodegenerative disorders in autosomal-dominant and apparently sporadic forms. Novel genotype-phenotype correlations were established. © 2014 S. Karger AG, Basel.

Large deletion mutation of SPAST in a multi-generation family from Sardinia

BACKGROUND AND PURPOSE

The hereditary spastic paraplegias (HSP) are characterized by progressive spasticity of the lower limbs, mostly inherited as an autosomal dominant trait. Analyses of large HSP pedigrees could help to better characterize the phenotype due to a single causative mutation. Patients in a seven-generation kindred carrying a large deletion in SPAST/SPG4 are described.

METHODS

Individuals originating from Sardinia were clinically and genetically studied.

RESULTS

Sixty-seven subjects carried a heterozygous deletion encompassing exons 2-17 of SPAST. Fifty patients (53.2 ± 15.4 years) presented a pure form of spastic paraparesis characterized by mild impairment and slow progression. Most patients showed spasticity, increased tendon reflexes in the lower limbs and Babinski sign, whilst weakness was rarely detected and urinary disturbances occasionally reported. Amongst the 17 asymptomatic carriers of the mutation, minimal neurological signs were detected in 11 cases.

CONCLUSIONS

A focus on spasticity, increased tendon reflexes and Babinski sign, more than on weakness, could help clinicians to promote early diagnosis in asymptomatic carriers of SPAST deletions.

Novel SPAST deletion and reduced DPY30 expression in a Spastic Paraplegia type 4 kindred

BACKGROUND

The hereditary spastic paraplegias (HSPs) are pleiomorphic disorders of motor pathway and a large number of affected genes have been discovered. Yet, mutations in SPG4/SPAST represent the most frequent molecular etiology in autosomal dominant (AD) patients and sporadic cases. We describe a large, AD-HSP Sardinian family where 5 out of several living members harbored a novel deletion affecting also the 5'UTR of SPAST and resulting in reduced expression of DPY30, the gene located upstream SPAST in a head-to-head manner.

CASE PRESENTATION

A 54-year-old woman manifested leg stiffness at age 39 and required a cane to walk at age 50. Neurological examination disclosed mild spasticity and weakness in the legs, hyperreflexia in all limbs, and bilateral Babinski sign. She also complained of urinary urgency, but no additional neurological symptoms or signs were detected at examination. The clinical examination of 24 additional relatives disclosed three further affected individuals, two men and one woman. In the four symptomatic patients the initial manifestations were walking abnormalities and leg stiffness with a mean age at onset (SD) of 46.75 (5.44) years (range 39-51). The mean disease duration was 13.2 (13.4) years (range 6-35), and it correlated well with clinical severity (SPRS score) (r = 0.975, p = 0.005). One patient was confined to bed and displayed knee and ankle contractures, another case needed a cane to walk, and two individuals were able to walk without aids. Interestingly, a patient had also had a miscarriage during her first pregnancy.Gene testing revealed an heterozygous deletion spanning from the 5'-UTR to intron 4 of SPAST in the affected individuals and in one clinically unaffected woman. In three affected patients, the deletion also determined low mRNA levels of SPAST and DPY30, a component of the Set1-like multiprotein histone methyltransferase complex located upstream, head-to-head with SPAST.

CONCLUSION

Together with data described in a Japanese family, our findings seem to suggest that genes close to spastin might be candidates in modulating the clinical phenotype. This report endorses future research on the role of neighboring genes as potential players in SPG4 disease variability.

Alu-specific microhomology-mediated deletion of the final exon of SPAST in three unrelated subjects with hereditary spastic paraplegia

PURPOSE

Autosomal dominant spastic paraplegia, type 4 (SPG4), a debilitating disorder of progressive spasticity and weakness of the lower limbs, results from heterozygous mutations in the SPAST gene. The full spectrum of SPAST mutations causing SPG4 and their mechanisms of formation remain to be determined.

METHODS

We used multiplex ligation-dependent probe amplification, locus-specific array comparative genomic hybridization, and breakpoint DNA sequencing to identify and describe genomic rearrangements in three patients with a clinical presentation of hereditary spastic paraplegia.

RESULTS

We describe three SPG4 patients with intragenic rearrangements in SPAST; all specifically delete the final exon, exon 17. Breakpoint sequence analyses provide evidence for Alu-specific microhomology-mediated deletion as the mechanism of exon loss; one complex rearrangement apparently occurred by multiple Alu-facilitated template switches.

CONCLUSION

We hypothesize that the high concentration of Alu family members in the introns and flanking sequence of SPAST may predispose to intragenic rearrangements. Thus, Alu-specific microhomology-mediated intragenic rearrangements in SPAST may be a common cause of SPG4. Furthermore, we propose that genomic deletions encompassing the final exon of SPAST may affect expression of SLC30A6, the most proximal downstream locus and a gene that has been implicated in the pathogenesis of Alzheimer disease, potentially explaining recent reports of dementia in selected SPG4 patients.

Evaluating the effect of spastin splice mutations by quantitative allele-specific expression assay

BACKGROUND

mutations in the SPG4/SPAST gene are the most common cause for hereditary spastic paraplegia (HSP). The splice-site mutations make a significant contribution to HSP and account for 17.4% of all types of mutations and 30.8% of point mutations in the SPAST gene. However, only few studies with limited molecular approach were conducted to investigate and decipher the role of SPAST splice-site mutations in HSP.

METHODS

a reverse transcriptase-polymerase chain reaction (RT-PCR) analysis and quantitative allele-specific expression assay were performed.

RESULTS

we have characterized the consequence of two novel splice-site mutations (c.1493 + 1G>A and c.1414-1G>A) in the SPAST gene in two different families with pure HSP. The RT-PCR analysis revealed that both spastin mutations are indeed splice-site mutations and cause skipping of exon 12. Furthermore, RT-PCR data suggested that these splice-site mutations may cause leaky splicing. By means of a quantitative allele-specific expression assay, we could confirm that both splice-site mutations cause leaky splicing, as the relative expression of the exon 12-skipped transcript was reduced (21.1 ± 3.6 compared to expected 50%).

CONCLUSIONS

our finding supports a "threshold-effect-model" for functional spastin in HSP. A higher level (78.8 ± 3.9%) of functional spastin than the expected ratio of 50% owing to leaky splicing might cause late age at onset of HSP. Remarkably, we could show that a quantitative allele-specific expression assay is a simple and effective tool to evaluate the role of most types of spastin splice-site mutations in HSP.

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.

Sequence variants in SPAST, SPG3A and HSPD1 in hereditary spastic paraplegia

Hereditary spastic paraplegia (HSP) is a group of clinically and genetically heterogeneous neurodegenerative disorders characterized by progressive spasticity and weakness in the lower limbs. The most common forms of autosomal dominant HSP, SPG4 and SPG3, are caused by sequence variants in the SPAST and SPG3A genes, respectively. The pathogenic variants are scattered all over these genes and many variants are unique to a specific family. The phenotype in SPG4 patients can be modified by a variant in SPAST (p.Ser44Leu) and recently, a variant in HSPD1, the gene underlying SPG13, was reported as a second genetic modifier in SPG4 patients. In this study HSP patients were screened for variants in SPG3A, SPAST and HSPD1 in order to identify disease causing variations. SPAST was sequenced in all patients whereas subsets were sequenced in HSPD1 and in selected exons of SPG3A. SPG4 patients and their HSP relatives were genotyped for the modifying variant in HSPD1. We report six new sequence variants in SPAST including a fourth non synonymous sequence variant in exon 1 and two synonymous changes of which one has been found in a HSP patient previously, but never in controls. Of the novel variants in SPAST four were interpreted as disease causing. In addition one new disease causing sequence variant and one non pathogenic non synonymous variant were found in SPG3A. In HSPD1 we identified a sporadic patient homozygote for the potential modifying variation. The effect of the modifying HSPD1 variation was not supported by identification in one SPG4 family.

New pedigrees and novel mutation expand the phenotype of REEP1-associated hereditary spastic paraplegia (HSP)

The hereditary spastic paraplegias (HSP) are a heterogeneous group of conditions in which the main feature is a progressive spastic paraparesis. Mutations in the receptor expression enhancing protein 1 (REEP1) gene have recently been reported to be associated with an autosomal dominant HSP phenotype (SPG31). The objective of this study was to identify the frequency of REEP1 mutations in both autosomal dominant HSP (ADHSP) and sporadic spastic paraparesis (SSP) cases and to analyse the genotype/phenotype correlation of mutations so far described in REEP1. One hundred thirty-three index cases from large ADHSP pedigrees and 80 SSP cases were screened for mutation in REEP1 by direct sequencing. Three mutations were identified in REEP1 in the ADHSP group. A novel nonsense mutation in exon 5, c.[337C>T] (p.[Arg113X]), was associated with spastic paraparesis, amyotrophy and mitochondrial dysfunction. A second previously reported mutation, c.[606+43G>T], was identified in two pedigrees. The index case of one of these pedigrees had a peripheral neuropathy in association with spastic paraparesis, and the proband of the second pedigree had a severe spastic tetraparesis and bulbar dysfunction. No mutations were detected in the SSP cases. We report a mutation frequency of 2.3% in REEP1 in ADHSP, suggesting REEP1 mutation is a relatively uncommon cause of ADHSP in a population of patients drawn from the UK. The phenotype of ADHSP associated with REEP1 mutation is broader than initially reported. The spastic paraparesis in SPG31 may be complicated by the presence of amyotrophy, bulbar palsy and/or peripheral neuropathy.

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.