Phenotypic variability in a large kindred with spastic paraplegia associated with a novel REEP1 variant

Background and objectives

The aim of this study is to provide a comprehensive characterization of a large Estonian family spanning five generations with seventeen individuals affected by spastic paraplegia associated with a novel variant in the receptor expression-enhancing protein-1 (REEP1) gene.

Methods

Comprehensive clinical evaluation, neuroimaging, and neurophysiological studies were performed on six patients who provided oral and written consent. Whole-exome sequencing was performed on the index case. Targeted carrier testing was done in all other available affected and at-risk relatives.

Results

Four individuals presented with pure spastic paraplegia, with onset from early childhood to adult age. None had bladder or bowel dysfunction. Two subjectively asymptomatic mutation carriers displayed pyramidal signs on examination. Imaging of the neuroaxis was normal in three patients, three had MRI findings interpreted as unrelated. Motor evoked potential (MEP) was abnormal in five; the patient with the longest disease duration had additional somatosensory evoked potential (SSEP) abnormalities. The novel splice-site variant, c.32 + 1G > C in the REEP1 gene, found in the index case, co-segregates with disease in the family. Expressivity in this family is variable.

Conclusion

Our findings are in keeping with previous descriptions of the SPG31 spectrum. The phenotype associated with splice variants is not necessarily more severe than other conventional REEP1 variants. As for other forms of familial spastic paraplegias, the factors modulating variable expressivity in SPG31 are still unknown.

AP4B1-associated hereditary spastic paraplegia: Expansion of clinico-genetic phenotype and geographic range

BACKGROUND

Hereditary spastic paraplegias (HSP) are a group of neurodegenerative diseases that present with weakness and stiffness in the lower limb muscles and lead to progressive neurological decline. Bi-allelic loss-of-function variants in genes that encode subunits of the adaptor protein complex 4 (AP-4) lead to complex HSP. This study aimed to identify causative genetic variants in consanguineous families with HSP from Azerbaijan and Pakistan.

METHODS

We performed a thorough clinical and neuroradiological characterization followed by exome sequencing in 7 patients from 3 unrelated families. Segregation analysis was subsequently performed by Sanger sequencing.

RESULTS

We describe 7 patients (4 males, 2-31 years of age) with developmental delay and spasticity. Similar to the previously reported cases with AP4B1-associated HSP, cases in the present report besides spasticity in the lower limbs had additional features including microcephaly, facial dysmorphism, infantile hypotonia, and epilepsy. The imaging findings included thin corpus callosum, white matter loss, and ventriculomegaly.

CONCLUSION

In this study, we report 7 novel cases of HSP caused by bi-allelic variants in AP4B1 in Azerbaijani and Pakistani families. Our observations will help clinicians observe and compare common and unique clinical features of AP4B1-associated HSP patients, further improving our current understanding of HSP.

A novel homozygous mutation in ERLIN1 gene causing spastic paraplegia 62 and literature review

Hereditary spastic paraplegia (HSP) is a group of genetic neurodegenerative disorders, which is characterized by the presence of progressive spasticity and weakness in bilateral lower limbs. Spastic paraplegia 62 (SPG62) caused by the endoplasmic reticulum lipid raft associated 1 (ERLIN1) gene mutation is a rare subtype of HSP. Herein, we report the case of the first Chinese SPG62 patient, explore the potential pathogenic mechanism and review ERLIN1-related HSP patients. A 23-year-old man had progressive difficulty in walking and gait abnormalities for more than 11 years. Physical examination showed slightly reduced muscle strength (5^-/5) and elevated muscle tone in the lower limbs and hyperreflexia in four limbs. Genetic analysis identified a novel splicing site mutation in ERLIN1 gene (c.504+1G > A), which was predicted to disturb the normal splicing process of mRNA by bioinformatic tools. Minigene experiment further confirmed the mutation c.504+1G > A could cause erroneous deletion of Exon 7 in the mRNA, which may change the conserved prohibitin (PHB) domain of erlin-1 and affect the function of erlin1/2 complex. Thus, we identified a pathogenic mutation of ERLIN1 splicing site causing delayed-onset pure HSP. This study widened the genetic and phenotypic spectrum of SPG62.

Neuropsychology and MRI correlates of neurodegeneration in SPG11 hereditary spastic paraplegia

Background

SPG11-linked hereditary spastic paraplegia is characterized by multisystem neurodegeneration leading to a complex clinical and yet incurable phenotype of progressive spasticity and weakness. Severe cognitive symptoms are present in the majority of SPG11 patients, but a systematic and multidimensional analysis of the neuropsychological phenotype in a larger cohort is lacking. While thinning of the corpus callosum is a well-known structural hallmark observed in SPG11 patients, the neuroanatomical pattern of cortical degeneration is less understood. We here aimed to integrate neuropsychological and brain morphometric measures in SPG11.

Methods

We examined the neuropsychological profile in 16 SPG11 patients using a defined neuropsychological testing battery. Long-term follow up testing was performed in 7 patients. Cortical and subcortical degeneration was analyzed using an approved, artificial intelligence based magnetic resonance imaging brain morphometry, comparing patients to established reference values and to matched controls.

Results

In SPG11 patients, verbal fluency and memory as well as frontal-executive functions were severely impaired. Later disease stages were associated with a global pattern of impairments. Interestingly, reaction times correlated significantly with disease progression. Brain morphometry showed a significant reduction of cortical and subcortical parenchymal volume following a rostro-caudal gradient in SPG11. Whereas performance in memory tasks correlated with white matter damage, verbal fluency measures showed strong associations with frontal and parietal cortical volumes.

Conclusions

The present data will help define neuropsychological and imaging read out parameters in early as well as in advanced clinical stages for future interventional trials in SPG11.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02451-1.

Genetic, structural and clinical analysis of spastic paraplegia 4

INTRODUCTION

Spastic paraplegia type 4 (SPG4), resulting from heterozygous mutations in the SPAST gene, is the most common form among the heterogeneous group of hereditary spastic paraplegias (HSPs). We aimed to study genetic and clinical characteristics of SPG4 across Canada.

METHODS

The SPAST gene was analyzed in a total of 696 HSP patients from 431 families by either HSP-gene panel sequencing or whole exome sequencing (WES). We used Multiplex ligation-dependent probe amplification to analyze copy number variations (CNVs), and performed in silico structural analysis of selected mutations. Clinical characteristics of patients were assessed, and long-term follow-up was done to study genotype-phenotype correlations.

RESULTS

We identified 157 SPG4 patients from 65 families who carried 41 different SPAST mutations, six of which are novel and six are CNVs. We report novel aspects of mutations occurring in Arg499, a case with homozygous mutation, a family with probable compound heterozygous mutations, three patients with de novo mutations, three cases with pathogenic synonymous mutation, co-occurrence of SPG4 and clinically isolated syndrome, and novel or rarely reported signs and symptoms seen in SPG4 patients.

CONCLUSION

Our study demonstrates that SPG4 is a heterogeneous type of HSP, with diverse genetic features and clinical manifestations. In rare cases, biallelic inheritance, de novo mutation, pathogenic synonymous mutations and CNVs should be considered.

Age-Dependent Increase in Schmidt-Lanterman Incisures and a Cadm4-Associated Membrane Skeletal Complex in Fatty Acid 2-hydroxylase Deficient Mice: a Mouse Model of Spastic Paraplegia SPG35

PNS and CNS myelin contain large amounts of galactocerebroside and sulfatide with 2-hydroxylated fatty acids. The underlying hydroxylation reaction is catalyzed by fatty acid 2-hydroxylase (FA2H). Deficiency in this enzyme causes a complicated hereditary spastic paraplegia, SPG35, which is associated with leukodystrophy. Mass spectrometry-based proteomics of purified myelin isolated from sciatic nerves of Fa2h-deficient (Fa2h^−/−) mice revealed an increase in the concentration of the three proteins Cadm4, Mpp6 (Pals2), and protein band 4.1G (Epb41l2) in 17-month-old, but not in young (4 to 6-month-old), Fa2h^−/− mice. These proteins are known to form a complex, together with the protein Lin7, in Schmidt-Lanterman incisures (SLIs). Accordingly, the number of SLIs was significantly increased in 17-month-old but not 4-month-old Fa2h^−/− mice compared to age-matched wild-type mice. On the other hand, the relative increase in the SLI frequency was less pronounced than expected from Cadm4, Lin7, Mpp6 (Pals2), and band 4.1G (Epb41l2) protein levels. This suggests that the latter not only reflect the higher SLI frequency but that the concentration of the Cadm4 containing complex itself is increased in the SLIs or compact myelin of Fa2h^−/− mice and may potentially play a role in the pathogenesis of the disease. The proteome data are available via ProteomeXchange with identifier PXD030244.

HACE1, GLRX5, and ELP2 gene variant cause spastic paraplegies

Hereditary spastic paraplegias (HSPs) are a clinically and genetically heterogeneous group of conditions that are characterized by lower limb spasticity and weakness. Considering the clinical overlap between metabolic causes, genetic diseases, and autosomal recessive HSP, differentiation between these types can be difficult based solely on their clinical characteristics. This study aimed to investigate the genetic etiology of patients with clinically suspected HSP. The study group was composed of seven Turkish families who each had two affected children and three families who each had a single affected child (17 total patients). The 17 probands (14 males, 3 females) underwent whole exome sequencing. Five typical HSP genes (FA2H, AP4M1, AP4E1, CYP7B1, and MAG) and three genes not previously related to HSP (HACE1, GLRX5, ad ELP2) were identified in 14 probands. Eight novel variants were identified in seven families: c.653 T > C (p.Leu218Pro) in the FA2H gene, c.347G > A (p.Gly116Asp) in the GLRX5 gene, c.2581G > C (p.Ala861Pro) in the HACE1 gene, c.1580G > A (p.Arg527Gln) and c.1189-1G > A in the ELP2 gene, c.10C > T (p.Gln4*) and c.1025 + 1G > A in the AP4M1 gene, c.1291delG (p.Gly431Alafs*3) and c.3250delA (p.Ile1084*) in the AP4E1 gene, and c.475 T > G (p.Cys159Gly) in the MAG gene. The growing use of next-generation sequencing improved diagnosis but also led to the continual identification of new causal genes for neurogenetic diseases associated with lower limb spasticity. The increasing number of HSP genes identified thus far highlights the extreme genetic heterogeneity of these disorders and their clinical and functional overlap with other neurological conditions. Our findings suggest that the HACE1, GLRX5, and ELP2 genes are genetic causes of HSP.

Malformations of cerebral development and clues from the peripheral nervous system: A systematic literature review

Clinical manifestations of malformations of cortical development (MCD) are variable and can range from mild to severe intellectual disability, cerebral palsy and drug-resistant epilepsy. Besides common clinical features, non-specific or more subtle clinical symptoms may be present in association with different types of MCD. Especially in severely affected individuals, subtle but specific underlying clinical symptoms can be overlooked or overshadowed by the global clinical presentation. To facilitate the interpretation of genetic variants detailed clinical information is indispensable. Detailed (neurological) examination can be helpful in assisting with the diagnostic trajectory, both when referring for genetic work-up as well as when interpreting data from molecular genetic testing. This systematic literature review focusses on different clues derived from the neurological examination and potential further work-up triggered by these signs and symptoms in genetically defined MCDs. A concise overview of specific neurological findings and their associations with MCD subtype and genotype are presented, easily applicable in daily clinical practice. The following pathologies will be discussed: neuropathy, myopathy, muscular dystrophies and spastic paraplegia. In the discussion section, tips and pitfalls are illustrated to improve clinical outcome in the future.

GLRX5-associated [Fe-S] cluster biogenesis disorder: further characterisation of the neurological phenotype and long-term outcome

Background

Identification and characterisation of monogenic causes of complex neurological phenotypes are important for genetic counselling and prognostication. Bi-allelic pathogenic variants in the gene encoding GLRX5, a protein involved in the early steps of Fe-S cluster biogenesis, are rare and cause two distinct phenotypes: isolated sideroblastic anemia and a neurological phenotype with variant non-ketotic hyperglycinemia. In this study, we analysed the evolution of clinical and MRI findings and long-term outcome of patients with GLRX5 mutations.

Methods

Four patients from three Australian families of Lebanese descent were identified. All patients presented in childhood and were followed up into adult life through multiple clinical assessments. All were prescribed sodium benzoate.

Results

All patients (all females, age range 18–56 years) showed a complex neurological phenotype characterised by varying combinations of spastic paraparesis, length-dependent motor/sensory-motor axonal polyneuropathy, and psychiatric disturbances with variable intellectual disability. All had non-ketotic hyperglycinemia and a homozygous pathogenic c.151_153delAAG (p.K51del) change in GLRX5. Motor disability gradually progressed reaching moderate disability during adolescence and moderately severe disability during adult life. The major MRI finding was the upper cervical spinal cord signal changes with contrast enhancement noted in all and additional leukoencephalopathy in one. On follow up MRI, the white matter lesions diminished on a subsequent scan and then remained static over time. The spinal cord showed gliotic changes. Two patients have previously demonstrated low pyruvate dehydrogenase complex deficiency but none had plasma lactate elevation, nor biochemical evidence of branch-chain keto-dehydrogenase deficiency. Glycine levels reduced in patients that tolerated sodium benzoate, possibly stabilising clinical manifestations.

Conclusions

This report demonstrates that the p.K51del GLRX5 variant causes a distinct and predictable neurological phenotype. The clinical assessments spanning from childhood to adult life enable physicians to infer the natural history of GLRX5 related neurological disorder. There may be widespread metabolic consequences, and optimal management is unknown.

Clinical and genetic characteristics of 21 Spanish patients with biallelic pathogenic SPG7 mutations

Spastic paraplegia type 7 (SPG7) is one of the most common hereditary spastic paraplegias. SPG7 mutations most often lead to spastic paraparesis (HSP) and/or hereditary cerebellar ataxia (HCA), frequently with mixed phenotypes. We sought to clinically and genetically characterize a Spanish cohort of SPG7 patients. Patients were recruited from our HCA and HSP cohorts. We identified twenty-one patients with biallelic pathogenic SPG7 mutations. Mean age at onset was 37.4 years (SD ± 14.3). The most frequent phenotype was spastic ataxia (57%), followed by pure spastic paraplegia (19%) and complex phenotypes (19%). Isolated patients presented with focal or multifocal dystonia, subclinical myopathy or ophthalmoplegia. p.Ala510Val was the most frequent pathogenic variant encountered. Compound heterozygous for p.Ala510Val displayed younger onset (p < 0.05) and more complex phenotypes (p < 0.05) than p.Ala510Val homozygotes. Two novel variants were found: p.Lys559Argfs*33 and p.Ala312Glu. In conclusion, spastic ataxia is the most common phenotype found in Spanish patients. Nonetheless, SPG7 analysis should also be considered in patients with less frequent clinical findings such as dystonia or ophthalmoplegia especially when these symptoms are associated with mild spastic ataxia.

Potential markers for sample size estimations in hereditary spastic paraplegia type 5

Background

Aim to identify potential biomarkers to assess therapeutic efficacy for hereditary spastic paraplegias type 5 (SPG5) by investigating the clinical, cerebrospinal fluid (CSF) and magnetic resonance imaging (MRI) features.

Methods

We performed a cross-sectional study to compare SPG5 patients with age- and sex-matched healthy controls who underwent conventional and quantitative MRI techniques of spinal cord (C1-T9) and brain. SPG5 patients also underwent assessment for clinical status and CSF biomarkers (27-hydroxycholesterol, neurofilament light). We identified a set of markers with standardized effect sizes (|t|> 0.5) to estimate sample sizes for disease progression (disease duration > 14 years vs. ≤ 14 years).

Results

Seventeen genetically confirmed SPG5 patients (11 men, 6 women; age range, 13–49 years; median disease duration, 14 years) were enrolled. Compared to healthy controls, the total spinal cord area (SCA) of SPG5 patients was reduced particularly at the thoracic levels (cervical levels: 12–27%; thoracic levels 41–60%). Patients did not show significant alterations of brain signal abnormalities or atrophy relative to controls. A total of 10 surrogate markers were selected and a minimum sample size was achieved with the measurement of SCA on T9 (n = 22) much less that what would be required if using clinical disability assessment (n = 124).

Conclusions

SPG5 patients showed distinct MRI features of spinal cord atrophy without significant brain alterations. Our finding supports the measurements of spinal cord on T9 level as potential endpoint for SPG5 clinical trials.

Trial registration ClinicalTrials.gov, NCT04006418. Registered 05 July 2019, https://clinicaltrials.gov/ct2/show/NCT04006418?term=NCT04006418&draw=2&rank=1.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-02014-w.

A new family with spastic paraplegia type 51 and novel mutations in AP4E1

Background

Autosomal recessive mutations in the AP-4 (adaptor protein complex 4) complex subunit ϵ − 1 (AP-4E1) gene on chromosome 15q21.2 are known to cause spastic paraplegia 51 (SPG51). The exact phenotype of SPG51 remains poorly characterized, because only a few families have been reported as carriers of the mutation. In addition, a previous study identified an autosomal dominant mutation in the AP4E1 gene as being associated with persistent stuttering. The aim of the current study was to characterize the phenotype of a paediatric patient with an identified novel AP4E1 mutation presenting with significant psychomotor retardation, intellectual disability and paraplegia.

Methods

Magnetic resonance imaging was used to identify hypoplasia of the corpus callosum. The DNA sample was tested using multiplex ligation-dependent probe amplification (MLPA) and array comparative genomic hybridization (aCGH). In addition, next-generation sequencing (NGS) was performed using the patient’s DNA, and Sanger sequencing was performed using that of his family members.

Results

The phenotype was identified to be associated with a novel pathogenic variant c.942_943 + 3delinsCC in the AP4E1 gene. The patient manifested severely delayed psychomotor development, impaired global physical development and general illness. Movement disorders were evident during the neonatal period.

Conclusions

The present study identifies a previously unknown disease-inducing AP4E1 gene mutation.

Recent advances in understanding hereditary spastic paraplegias and emerging therapies

Hereditary spastic paraplegias (HSPs) are a group of rare, inherited, neurological diseases characterized by broad clinical and genetic heterogeneity. Lower-limb spasticity with first motoneuron involvement is the core symptom of all HSPs. As spasticity is a syndrome and not a disease, it develops on top of other neurological signs (ataxia, dystonia, and parkinsonism). Indeed, the definition of genes responsible for HSPs goes beyond the 79 identified SPG genes. In order to avoid making a catalog of the different genes involved in HSP in any way, we have chosen to focus on the HSP with cerebellar ataxias since this is a frequent association described for several genes. This overlap leads to an intermediary group of spastic ataxias which is actively genetically and clinically studied. The most striking example is SPG7, which is responsible for HSP or cerebellar ataxia or both. There are no specific therapies against HSPs, and there is a dearth of randomized trials in patients with HSP, especially on spasticity when it likely results from other mechanisms. Thus far, no gene-specific therapy has been developed for HSP, but emerging therapies in animal models and neurons derived from induced pluripotent stem cells are potential treatments for patients.

Thalamic atrophy in patients with pure hereditary spastic paraplegia type 4

SPG4 is an autosomal dominant pure form of hereditary spastic paraplegia (HSP) caused by mutations in the SPAST gene. HSP is considered an upper motor neuron disorder characterized by progressive spasticity and weakness of the lower limbs caused by degeneration of the corticospinal tract. In other neurodegenerative motor disorders, the thalamus and basal ganglia are affected, with a considerable impact on disease progression. However, only a few works have studied these brain structures in HSP, mainly in complex forms of this disease. Our research aims to detect potential alterations in the volume and shape of the thalamus and various basal ganglia structures by comparing 12 patients with pure HSP and 18 healthy controls. We used two neuroimaging procedures: automated segmentation of the subcortical structures (thalamus, hippocampus, caudate nucleus, globus pallidus, and putamen) in native space and shape analysis of the structures. We found a significant reduction in thalamic volume bilaterally, as well as an inward deformation, mainly in the sensory-motor thalamic regions in patients with pure HSP and a mutation in SPG4. We also observed a significant negative correlation between the shape of the thalamus and clinical scores (the Spastic Paraplegia Rating Scale score and disease duration). Moreover, we found a 'Group × Age' interaction that was closely related to the severity of the disease. No differences in volume or in shape were found in the remaining subcortical structures studied. Our results suggest that changes in structure of the thalamus could be an imaging biomarker of disease progression in pHSP.

Increasing involvement of CAPN1 variants in spastic ataxias and phenotype-genotype correlations

Spastic ataxias are rare neurogenetic disorders involving spinocerebellar and pyramidal tracts. Many genes are involved. Among them, CAPN1, when mutated, is responsible for a complex inherited form of spastic paraplegia (SPG76). We report the largest published series of 21 novel patients with nine new CAPN1 disease-causing variants and their clinical characteristics from two European university hospitals (Paris and Stockholm). After a formal clinical examination, causative variants were identified by next-generation sequencing and confirmed by Sanger sequencing. CAPN1 variants are a rare cause (~ 1.4%) of young-adult-onset spastic ataxia; however, together with all published cases, they allowed us to better describe the clinical and genetic spectra of this form. Truncating variants are the most frequent, and missense variants lead to earlier age at onset in favor of an additional deleterious effect. Cerebellar ataxia with cerebellar atrophy, dysarthria and lower limb weakness are often associated with spasticity. We also suggest that cognitive impairment and depression should be assessed specifically in the follow-up of SPG76 cases.

Coexistence of Hereditary Spastic Paraplegia Type 4 and Narcolepsy: A Case Report

Spastic paraplegia type 4 (SPG4) is the most common type of hereditary spastic paraplegia (HSP) caused by the mutations in the SPAST gene, which encodes a microtubule-severing protein named spastin. Spastin regulates the number and mobility of microtubules and is essential for axonal outgrowth and neuronal morphogenesis. Herein, we report a patient with SPG4 harboring a novel donor splice site mutation in the SPAST gene (c.1616+1dupG). Although SPG4 usually manifests itself as a pure form of HSP, this patient exhibited a slow progressive cognitive decline and also developed narcolepsy type 2 (narcolepsy without cataplexy) prior to the onset of SPG4. Recently, cognitive decline has attracted attention as a main non-motor symptom of SPG4. However, this is the first reported case of a patient developing both SPG4 and narcolepsy, although it remains unclear whether the manifestation of the two diseases is a coincidence or an association. In this report, we describe the clinical symptoms and genetic background of the patient.

Treatment options and long-term outcomes in pediatric spinal cord vascular malformations: a case report and review of the literature

A 16-month-old female was admitted for prolonged fever, gait ataxia, and neurogenic bowel and bladder. Neurological exam was significant for decreased sensory and motor functions in bilateral lower extremities. Initial MRI showed a thoracic spine hematoma and diagnostic angiogram revealed a large AVM and aneurysm. The patient underwent surgical resection of the hematoma and AVM, as well as clipping and later endovascular coiling of the aneurysm. Due to significant hemorrhage perioperatively, she developed spastic paraplegia improved by baclofen and onabotulinumtoxin A injections. The aims of this paper were to conduct a systematic review of the literature on pediatric spinal cord vascular malformations and analyze trends in treatment options and long-term neurological outcomes. PubMed searches were conducted using keywords "pediatric spinal vascular malformation" and "pediatric spinal AVM", yielding 34 results after abstract screening and cross-reference. Endovascular embolization was determined to have better long-term outcomes, with 10/19 (52.6%) patients with postoperative complications associated with open vascular surgeries. Open versus endovascular surgical decisions can be difficult with unique spinal AVM pathologies in pediatric patients. Important considerations such as size, location, neurological deficits, and risk of rupture are important factors to consider in treating these patients. We recommend endovascular treatment as a first-line approach due to lower risk of hemorrhage and postoperative deficits.

Co-incident primary progressive multiple sclerosis and hereditary spastic paraplegia (SPG4) - a case report

The cause of progressive disability in Primary Progressive Multiple Sclerosis (PPMS) is unknown. Pathogenic genes have been described in some MS cases that may contribute to progressive disability, independent of immune - mediated mechanisms (Jia et al., 2018). The autosomal dominant SPG4 (Spastin) mutation is the most common genotype in Hereditary Spastic Paraplegia (Solowska and Baas, 2015) and has been found in some patients with Relapsing Remitting Multiple Sclerosis (Mead et al., 2001, Yazici et al., 2013). Here, we describe the novel association of PPMS and the SPG4 (Spastin) mutation, in a patient with a family history of Hereditary Spastic Paraplegia, and discuss the therapeutic implications. While this single case report cannot discrimiate between simple co-occurence and the possibility of a pathogenic association, our report invites larger scale investigation.

X-linked myotubular myopathy mimics hereditary spastic paraplegia in two female manifesting carriers of pathogenic MTM1 variant

X-linked myotubular myopathy (XLMTM) is a rare congenital myopathy caused by pathogenic variants in the myotubularin 1 (MTM1) gene. XLMTM leads to severe weakness in male infants and majority of them die in the early postnatal period due to respiratory failure. Disease manifestations in female carriers vary from asymptomatic to severe, generalized congenital weakness. The symptomatic female carriers typically have limb-girdle weakness, asymmetric muscle weakness and skeletal size, urinary incontinence, facial weakness, ptosis and ophthalmoplegia. Here we describe a Finnish family with two females with lower limb spasticity and hyperreflexia resembling spastic paraplegia, gait difficulties and asymmetric muscle weakness in the limbs. A whole exome sequencing identified a heterozygous pathogenic missense variant MTM1 c.1262G > A, p.(Arg421Gln) segregating in the family. The variant has previously been detected in male and female patients with XLMTM. Muscle biopsy of one of the females showed variation in the myofiber diameter, atrophic myofibers, central nuclei and necklace fibers consistent with a diagnosis of XLMTM. This report suggests association between spastic paraplegia and pathogenic MTM1 variants expanding the phenotypic spectrum potentially associated with XLMTM, but the possible association needs to be confirmed by additional cases.

Recessive null-allele variants in MAG associated with spastic ataxia, nystagmus, neuropathy, and dystonia

INTRODUCTION

The gene encoding myelin-associated glycoprotein (MAG) has been implicated in autosomal-recessive spastic paraplegia type 75. To date, only four families with biallelic missense variants in MAG have been reported. The genotypic and phenotypic spectrum of MAG-associated disease awaits further elucidation.

METHODS

Four unrelated patients with complex neurologic conditions underwent whole-exome sequencing within research or diagnostic settings. Following determination of the underlying genetic defects, in-depth phenotyping and literature review were performed.

RESULTS

In all case subjects, we detected ultra-rare homozygous or compound heterozygous variants in MAG. The observed nonsense (c.693C > A [p.Tyr231*], c.980G > A [p.Trp327*], c.1126C > T [p.Gln376*], and 1522C > T [p.Arg508*]) and frameshift (c.517_521dupAGCTG [p.Trp174*]) alleles were predicted to result in premature termination of protein translation. Affected patients presented with variable combinations of psychomotor delay, ataxia, eye movement abnormalities, spasticity, dystonia, and neuropathic symptoms. Cerebellar signs, nystagmus, and pyramidal tract dysfunction emerged as unifying features in the majority of MAG-mutated individuals identified to date.

CONCLUSIONS

Our study is the first to describe biallelic null variants in MAG, confirming that loss of myelin-associated glycoprotein causes severe infancy-onset disease with central and peripheral nervous system involvement.

Dystonia as initial presentation of compound heterozygous GBA2 mutations: Expanding the phenotypic spectrum of SPG46

GBA2 associated spastic paraplegia type 46 (SPG46) is an autosomal-recessive disorder associated with a clinical presentation of spastic gait, muscle weakness as well as an array of clinical symptoms including pseudobulbar palsy and progressive cognitive decline. Several neurological and non-neurological symptoms are associated with GBA2 mutations. An initial presentation with dystonia has not been reported so far. We report clinical, genetic and brain imaging findings in two siblings with hereditary spastic paraparesis. One sister presented with juvenile-onset leg spasticity and progressed to spastic tetraparesis, cervical and jaw opening dystonia, pseudobulbar symptoms and dementia. The other sister initially developed cervical dystonia in adulthood followed by gait spasticity and cognitive decline in the disease course. Molecular genetic testing revealed novel compound heterozygous variants in GBA2 in both sisters. The initial presentation with cervical dystonia and the differing clinical disease progression expand the clinical phenotype of GBA2 associated SPG46.

A novel mutation in the GBA2 gene in a Japanese patient with SPG46: A case report

Hereditary spastic paraplegia (HSP) is a neurodegenerative disorder characterized by pyramidal weakness and spasticity of the lower limbs. SPG46, one of autosomal recessive HSP, is clinically characterized by spasticity and pyramidal weakness of the lower limbs, mental retardation, congenital bilateral cataract, thin corpus callosum, and hypogonadism in males. Mutations in the nonlysosomal glucosylceramidase β2 (GBA2) gene have been identified in patients with SPG46. A Japanese woman was identified with bilateral cataracts when she was in an elementary school. She felt falling easily, speaking unclearness, and difficulty in walking and raising her left leg in her 30s. Her neurological examination at the age of 44 revealed dysarthria, spasticity in the upper and lower extremities, increased jaw jerk and tendon reflexes in the extremities, bilateral extensor plantar reflexes, ataxia, and pollakiuria. Magnetic resonance imaging showed thinning of the corpus callosum body as well as atrophy in the pons and cerebellum. A novel homozygous c.1838A > G (p.D613G) missense mutation was detected at exon 12 in GBA2. We diagnosed her illness as an autosomal-recessive form of hereditary SPG46. The clinical features matched previously reported phenotype of SPG46. This is the first report of a Japanese patient with SPG46 with a novel mutation in GBA2. We presume that the novel GBA2 missense mutation found in our patient would cause loss of GBA2 activity, resulting in the neurological manifestations of SPG46.

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SPG46 is a rare autosomal recessive hereditary spastic paraplegia.

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In Japan, clinical cases of SPG46 have never been reported.

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We report a case of a Japanese patient with SPG46 with a novel mutation in GBA2.

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She showed cataracts, mild cognitive impairment, spasticity, and cerebellar ataxia.

Autosomal dominant GCH1 mutations causing spastic paraplegia at disease onset

BACKGROUND

Autosomal dominant GCH1 mutations are known to cause dopa-responsive dystonia (DRD). In this case series, we confirm a variant phenotype, characterized by predominant spastic paraplegia at disease onset with development of dystonia and/or parkinsonism only decades later.

METHODS

Clinical trajectories of four patients from three families with pathogenic variants in GCH1 are described, illustrated by videos of the motor phenotype before and during treatment with levodopa. An extensive literature review was performed on previous reports of spasticity in patients with autosomal dominant GCH1 mutations.

RESULTS

All patients presented during childhood or early adolescence with gait and leg spasticity. Three patients developed basal ganglia signs only in the fifth decade; the youngest patient has not yet developed dystonia, bradykinesia or hypokinesia. All patients responded to levodopa/carbidopa with improvement of gait and of dystonia, hypokinesia and/or rigidity. In all patients, spasticity decreased but did not disappear. Spasticity has been described previously in DRD, but in most cases co-existent basal ganglia signs were identified early in the disease course.

CONCLUSION

GCH1 mutations may cause a phenotype initially resembling hereditary spastic paraplegia (HSP) rather than DRD, with basal ganglia signs developing only after decades. In order not to miss this treatable condition, GCH1 should be included in HSP gene panels and its testing is pivotal in patients with spastic paraplegia, especially if there are concomitant basal ganglia signs and/or diurnal fluctuation.

Autosomal dominant SPG9: intrafamilial variability and onset during pregnancy

INTRODUCTION

The ALDH18A1 gene, encoding delta-1-pyrroline-5-carboxylate synthase (P5CS), is responsible for an autosomal recessive disease with severe developmental delay; more recently, ALDH18A1 was found to be responsible for SPG9, an autosomal dominant (AD) spastic paraplegia.

CASE REPORT

We report a three-generation family with AD SPG9, initially suspected because of low citrulline on fasting plasma amino acid chromatography (AAC). Interestingly, in two patients, the spastic paraplegia appeared during pregnancy. One subject presented a severe childhood-onset form while another subject had a mild late-onset disease.

CONCLUSION

The description of this family is of particular interest: it highlights the possibility of transient or permanent aggravation of spastic paraplegia due to SPG9 during pregnancy, suggesting a direct link between neurological symptoms and amino acid defect in a period of higher requirements and the potential benefit of amino acid supplementation; it underscores the value of plasma citrulline on fasting plasma AAC as a biomarker for this disease; it shows the variable expression of the disease.

Motor impairment in a rare form of spastic paraplegia (Spoan syndrome): a 10-year follow-up

Background

Spastic paraplegia, optic atrophy and neuropathy (Spoan syndrome) is an autosomal recessive disease with approximately 70 cases recorded in Brazil and Egypt.

Methods

This is a prospective longitudinal study performed with 47 patients affected with Spoan syndrome of seven communities of Rio Grande do Norte (Brazil) to investigate changes in motor function based on comparative data obtained from a 10-year follow-up.

Results

The mean age of the participants was 47.21 ± 12.42 years old, and the mean age at loss of ambulation and hand function were 10.78 ± 5.55 and 33.58 ± 17.47 years old, respectively. Spearman’s correlation analysis between the score on the Modified Barthel Index and the investigated variables evidenced statistical significance for age (p < 0.001) and right- and left-hand grip strength (p = 0.042 and p = 0.021, respectively). Statistical significance was not evidenced for the remainder of the variables, including age at onset of symptoms (p = 0.634), age at loss of ambulation (p = 0.664) and age at loss of hand function (p = 0.118).

Conclusions

Our analysis allows asserting that the participants exhibited slight dependence until age 35. The greatest losses occurred from ages 35 to 41, and starting at 50, practically all patients become completely dependent. These findings are relevant for determining the prognosis as well as suitable treatment, rehabilitation and assistive technology for these individuals.

ATP13A2 missense variant in Australian Cattle Dogs with late onset neuronal ceroid lipofuscinosis

The neuronal ceroid lipofuscinoses (NCLs) are lysosomal storage disorders characterized by progressive neurodegeneration and declines in neurological functions. Pathogenic sequence variants in at least 13 genes underlie different forms of NCL, almost all of which are recessively inherited. To date 13 sequence variants in 8 canine orthologs of human NCL genes have been found to occur in 11 dog breeds in which they result in progressive neurological disorders similar to human NCLs. Canine NCLs can serve as models for preclinical evaluation of therapeutic interventions for these disorders. In most NCLs, the onset of neurological signs occurs in childhood, but some forms have adult onsets. Among these is CLN12 disease, also known as Kufor-Rakeb syndrome, PARK9, and spastic paraplegia78. These disorders result from variants in ATP13A2 which encodes a putative transmembrane ion transporter important for lysosomal function. Three Australian Cattle Dogs (a female and two of her offspring) were identified with a progressive neurological disorder with an onset of clinical signs at approximately 6 years of age. The affected dogs exhibited clinical courses and histopathology characteristic of the NCLs. Whole genome sequence analysis of one of these dogs revealed a homozygous c.1118C > T variant in ATP13A2 that predicts a nonconservative p.(Thr373Ile) amino acid substitution. All 3 affected dogs were homozygous for this variant, which was heterozygous in 42 of 394 unaffected Australian Cattle Dogs, the remainder of which were homozygous for the c.1118C allele. The high frequency of the mutant allele in this breed suggests that further screening for this variant should identify additional homozygous dogs and indicates that it would be advisable to perform such screening prior to breeding Australian Cattle Dogs.

FARS2 deficiency; new cases, review of clinical, biochemical, and molecular spectra, and variants interpretation based on structural, functional, and evolutionary significance

An increasing number of mitochondrial diseases are found to be caused by pathogenic variants in nuclear encoded mitochondrial aminoacyl-tRNA synthetases. FARS2 encodes mitochondrial phenylalanyl-tRNA synthetase (mtPheRS) which transfers phenylalanine to its cognate tRNA in mitochondria. Since the first case was reported in 2012, a total of 21 subjects with FARS2 deficiency have been reported to date with a spectrum of disease severity that falls between two phenotypes; early onset epileptic encephalopathy and a less severe phenotype characterized by spastic paraplegia. In this report, we present an additional 15 individuals from 12 families who are mostly Arabs homozygous for the pathogenic variant Y144C, which is associated with the more severe early onset phenotype. The total number of unique pathogenic FARS2 variants known to date is 21 including three different partial gene deletions reported in four individuals. Except for the large deletions, all variants but two (one in-frame deletion of one amino acid and one splice-site variant) are missense. All large deletions and the single splice-site variant are in trans with a missense variant. This suggests that complete loss of function may be incompatible with life. In this report, we also review structural, functional, and evolutionary significance of select FARS2 pathogenic variants reported here.

Novel ABCD1 Gene Mutation in Adrenomyeloneuropathy with Hypoplasia and Agenesis of the Corpus Callosum

BACKGROUND

Adult adrenomyeloneuropathy (AMN) is caused by mutations in the ABCD1 gene. Some pure AMN patients develop cerebral demyelination late in life. However, hypoplasia and agenesis of the corpus callosum (CC) has never been reported in AMN patients.

OBJECTIVE

To describe a new clinical variant of AMN that is possibly caused by a novel ABCD1 gene mutation.

METHODS

A total of 10 members in an X-linked inherited family were examined. The age at onset, progression of disability, and clinical manifestations were collected. Blood tests of the index case were conducted in an academic hospital. Cerebral and spinal MRI was performed in 4 affected members using a Siemens 3.0-T or Hitachi 1.0-T MR scanner. Whole-exome sequencing was conducted in the index case, which was subsequently validated by Sanger sequencing in the family.

RESULTS

The patients displayed typical degenerative spastic paraparesis and peripheral sensorimotor neuropathy with some intrafamilial variations. In addition to neurological deficits, all male patients displayed alopecia since adolescence. Furthermore, an increase in plasma long-chain fatty acids was observed. Based on these presentations, adult AMN was diagnosed for the patients. Intriguingly, cerebral MRI showed multiple types of hypoplasia and agenesis of the CC including anterior remnant CC agenesis, truncated corpus and splenium, anterior remnant CC agenesis along with thin corpus and splenium. Whole-exome sequencing revealed a nonsense mutation (c.231G>A) which results in a truncated protein product (p.W77X) that might be nonfunctional. No other mutations associated with alopecia or hypoplasia and agenesis of the CC were identified in the exome-sequencing database.

CONCLUSION

In addition to the typical symptoms such as spastic myelopathy, cognitive impairment, mixed neuropathy, and alopecia, AMN patients can also display hypoplasia and agenesis of the CC, which was not described in the other AMN patients reported before.

Isolated spinal cord compression syndrome revealing delayed extensive superficial siderosis of the central nervous system secondary to cervical root avulsion

CONTEXT

Cervical root avulsion secondary to traumatic plexus injury is a rare etiology of superficial siderosis (SS) of the central nervous system (CNS). We describe the case of an isolated progressive compressive myelopathy revealing this complication and discuss the pathogenesis of such a presentation, its clinical and imaging peculiarities with a literature review.

FINDINGS

We report on the case of a 48-year-old man with history of left brachial plexus injury at the age of 2 years. Since the age of 38 years, he had presented with a progressive paraplegia, bladder and erectile dysfunction, neuropathic pain and sensory level. The diagnosis was made by spinal cord and brain magnetic resonance follow-up imaging revealing hypointensity T2-weighted gradient echo linear dark rim around the entire neuraxis and cervical dural pseudomeningoceles. These MRI findings were suggestive of extensive hemosiderin deposition consolidating the diagnosis of SS of CNS.

CONCLUSION/CLINICAL RELEVANCE

Our case report illustrates diagnosis difficulties in unusual or paucisymptomatic presentations of SS. A history of brachial plexus trauma with nerve root avulsion should prompt gradient-echo T2-weighted imaging to bring out such a complication. Superficial siderosis of the CNS should be included in the panel of differential diagnosis of the parethospastic syndromes and compressive myelopathy.

Dorsal Longitudinal T-Myelotomy (Bischof II Technique): A Useful, Antiquated Procedure for the Treatment of Intractable Spastic Paraplegia

OBJECTIVE

Dorsal longitudinal T-myelotomy is a long-established operation to treat severe spastic paraplegia. The present study aimed to report this surgical technique and investigate the efficacy of T-myelotomy for spasticity relief.

METHODS

All cases undergoing T-myelotomy for treatment of intractable spastic paraplegia during 2009-2017 were included. The severity of spasticity was evaluated with the Modified Ashworth Scale, Penn Spasm Frequency Scale, Adductor Tone Rating Scale, degree of passive range of motion, and occurrence of abdominal muscle spasms. Other clinical assessments included deep tendon reflex assessed by the National Institute of Neurological Disorders and Stroke scale, Babinski sign, healing of decubitus ulcers, and ambulatory status.

RESULTS

Fourteen patients with a mean age of 39.3 ± 13.4 years were included. The 7 patients with abdominal muscle spasms before surgery had no spasms after surgery. The Babinski sign was absent in all cases after surgery. Unhealed pressure ulcers in all 9 cases were healed after surgery. All 4 patients with a preoperative bed-bound condition were able to ambulate with a wheelchair. A statistically significant improvement in mean Modified Ashworth Scale score, degree of passive range of motion, and National Institute of Neurological Disorders and Stroke scale score was found in the subgroup and overall analyses. There was also a statistically significant improvement in the Penn Spasm Frequency Scale and Adductor Tone Rating Scale scores.

CONCLUSIONS

Dorsal longitudinal T-myelotomy remains an effective option for the treatment of intractable spastic paraplegia. It is suitable for, and may be an alternative to, intrathecal baclofen therapy for patients with complete spinal cord lesion or patients without hope of regaining motor function.

Brain diffusion tensor imaging changes in cerebrotendinous xanthomatosis reversed with treatment

Cerebrotendinous xanthomatosis (CTX, MIM 213700) is a rare autosomal recessive lipid storage disorder caused by CYP27A1 mutations. Treatment with chenodeoxycholic acid (CDCA) may slow the progression of the disease and reverse some symptoms in a proportion of patients. In a non-consanguineous Caucasian family, two siblings with CTX were evaluated before treatment and prospectively followed-up every 6 months after starting CDCA therapy, using systematic clinical examination, neuropsychological tests, laboratory tests, electroencephalography (EEG) and brain MRI, diffusion tensor imaging (DTI) and tractography. A 30-year-old patient and her 27-year-old brother were referred for progressive spastic paraparesis. Both had epilepsy, learning difficulties, chronic diarrhoea and juvenile-onset cataracts. CTX was diagnosed by increased cholestanol levels and compound heterozygosity for CYP27A1 mutations. Therapy with CDCA led to resolution of chronic diarrhoea, normalisation of serum cholestanol and EEG, and a progressive improvement in gait, cognition and seizure control. Before treatment, conventional brain MRI showed no CTX-related abnormalities for the proband and no cerebellar abnormalities for the brother, while DTI showed reduced fractional anisotropy (FA) and tract-density in the cerebellum and widespread cerebral reductions of FA in both patients, compared to a group of 35 healthy controls. Repeated DTI after starting therapy showed progressive increases of cerebellar tract density and of cerebral FA. In patients with CTX, therapy with CDCA may lead to significant clinical improvement, with normalisation of biochemical and electrophysiological biomarkers. DTI and tractography may detect changes when the conventional MRI is unremarkable and may provide potential neuroimaging biomarkers for monitoring treatment response in CTX, while the conventional MRI remains unchanged.

Brain diffusion tensor imaging changes in cerebrotendinous xanthomatosis reversed with treatment

Cerebrotendinous xanthomatosis (CTX, MIM 213700) is a rare autosomal recessive lipid storage disorder caused by CYP27A1 mutations. Treatment with chenodeoxycholic acid (CDCA) may slow the progression of the disease and reverse some symptoms in a proportion of patients. In a non-consanguineous Caucasian family, two siblings with CTX were evaluated before treatment and prospectively followed-up every 6 months after starting CDCA therapy, using systematic clinical examination, neuropsychological tests, laboratory tests, electroencephalography (EEG) and brain MRI, diffusion tensor imaging (DTI) and tractography. A 30-year-old patient and her 27-year-old brother were referred for progressive spastic paraparesis. Both had epilepsy, learning difficulties, chronic diarrhoea and juvenile-onset cataracts. CTX was diagnosed by increased cholestanol levels and compound heterozygosity for CYP27A1 mutations. Therapy with CDCA led to resolution of chronic diarrhoea, normalisation of serum cholestanol and EEG, and a progressive improvement in gait, cognition and seizure control. Before treatment, conventional brain MRI showed no CTX-related abnormalities for the proband and no cerebellar abnormalities for the brother, while DTI showed reduced fractional anisotropy (FA) and tract-density in the cerebellum and widespread cerebral reductions of FA in both patients, compared to a group of 35 healthy controls. Repeated DTI after starting therapy showed progressive increases of cerebellar tract density and of cerebral FA. In patients with CTX, therapy with CDCA may lead to significant clinical improvement, with normalisation of biochemical and electrophysiological biomarkers. DTI and tractography may detect changes when the conventional MRI is unremarkable and may provide potential neuroimaging biomarkers for monitoring treatment response in CTX, while the conventional MRI remains unchanged.

Hereditary Spastic Paraplegia: Clinical and Genetic Hallmarks

Hereditary spastic paraplegia comprises a wide and heterogeneous group of inherited neurodegenerative and neurodevelopmental disorders resulting from primary retrograde dysfunction of the long descending fibers of the corticospinal tract. Although spastic paraparesis and urinary dysfunction represent the most common clinical presentation, a complex group of different neurological and systemic compromise has been recognized recently and a growing number of new genetic subtypes were described in the last decade. Clinical characterization of individual and familial history represents the main step during diagnostic workup; however, frequently, few and unspecific data allows a low rate of definite diagnosis based solely in clinical and neuroimaging basis. Likewise, a wide group of neurological acquired and inherited disorders should be included in the differential diagnosis and properly excluded after a complete laboratorial, neuroimaging, and genetic evaluation. The aim of this review article is to provide an extensive overview regarding the main clinical and genetic features of the classical and recently described subtypes of hereditary spastic paraplegia (HSP).

A de novo mosaic mutation in SPAST with two novel alternative alleles and chromosomal copy number variant in a boy with spastic paraplegia and autism spectrum disorder

Here we report a 12 year old male with an extreme presentation of spastic paraplegia along with autism and dysmorphisms. Whole exome sequencing identified a predicted pathogenic pair of missense variants in SPAST at the same chromosomal location, each with a different alternative allele, while a chromosome microarray identified a 1.73 Mb paternally inherited copy gain of 1q21.1q21.2 resulting in a blended phenotype of both Spastic paraplegia 4 and 1q21.1 microduplication syndrome. We believe that the extreme phenotype observed is likely caused by the presence of cells which contain only mutant SPAST, but that the viability of the patient is possible due mosaicism of mutant alleles observed in different proportions across tissues.

A novel mutation in ALS2 associated with severe and progressive infantile onset of spastic paralysis

Infantile onset ascending spastic paralysis (IAHSP) is a type of recessively inherited spastic paraplegia. We investigated the clinical and genetic cause of a recessively inherited disorder in two siblings manifesting severe spasticity in the lower limbs which hindered their gait. A novel homozygous nonsense mutation c.1918 C > T (p.Arg640*) was identified after whole-exome sequencing within ALS2 in the DNA of both patients. The obligate carriers were heterozygous for the mutation and other unaffected members were homozygous for the wild type allele. The variant was absent from 100 control chromosomes and all public databases. This report extends the allelic heterogeneity of ALS2 mutations and emphasizes the importance of genetic testing for diagnosis of pediatric disorders.

Rapidly progressive psychotic symptoms triggered by infection in a patient with methylenetetrahydrofolate reductase deficiency: a case report

Background

Methylenetetrahydrofolate reductase (MTHFR) deficiency is a rare inborn error of metabolism inherited in autosomal recessive pattern and is associated with a wide spectrum of neurological abnormalities.

Case presentation

We herein describe a 15-year-old boy with MTHFR deficiency who presented with a slowly progressive decline of school performance and a spastic gait. Rapidly deteriorating psychosis and repetitive seizures triggered by a febrile infection prompted neurological investigation. He had significantly elevated total plasma homocysteine and urinary homocystine levels, as well as a decreased plasma methionine level. Brain magnetic resonance imaging (MRI) revealed leukoencephalopathy. DNA gene sequencing showed c.446_447 del GC ins TT and c.137G > A, and c.665C > T heterozygous mutations in the MTHFR gene of the patient. Oral administration of betaine drastically improved his clinical symptoms within a few months. After 8 months of treatment, his total plasma homocysteine level moderately decreased; and the plasma methionine concentration became normalized. Furthermore, the white matter lesions on MRI had disappeared.

Conclusion

This patient demonstrates the possibility that MTHFR deficiency should be considered in mentally retarded adolescents who display an abnormally elevated plasma level of homocysteine in association with progressive neurological dysfunction and leukoencephalopathy. Febrile infections may be an aggravating factor in patients with MTHFR deficiency.

Classifications of neurogenetic diseases: An increasingly complex problem

Neurodegenerative disorders represent a wide group of diseases affecting the central and/or peripheral nervous system. Many of these disorders were described in the 19th century, but our genetic knowledge of them is recent (over the past 25 years). However, the continual discovery of disease-causing gene mutations has led to difficulties in the classification of these diseases. For this reason, our present proposals for updating and simplifying the classification of some of these conditions (Charcot-Marie-Tooth diseases, distal hereditary motor neuropathies, hereditary sensory and autonomic neuropathies, hereditary spastic ataxias, hereditary spastic paraplegias and hereditary spastic ataxias) are expounded here.

Genetic background of the hereditary spastic paraplegia phenotypes in Hungary - An analysis of 58 probands

BACKGROUND

Hereditary spastic paraplegias (HSPs) are a clinically and genetically heterogeneous group of neurodegenerative diseases with progressive lower limb spasticity and weakness. The aim of this study is to determine the frequency of different SPG mutations in Hungarian patients, and to provide further genotype-phenotype correlations for the known HSP causing genes.

METHODS

We carried out genetic testing for 58 probands with clinical characteristics of HSP. For historical reasons, three different approaches were followed in different patients: 1) Sanger sequencing of ATL1 and SPAST genes, 2) whole exome, and 3) targeted panel sequencing by next generation sequencing.

RESULTS

Genetic diagnosis was established for 20 probands (34.5%). We detected nine previously unreported mutations with high confidence for pathogenicity. The most frequently affected gene was SPAST with pathogenic or likely pathogenic mutations in 10 probands. The most frequently detected variant in our cohort was the SPG7 p.Leu78*, observed in four probands. Altogether five probands were diagnosed with SPG7. Additional mutations were detected in SPG11, ATL1, NIPA1, and ABCD1.

CONCLUSION

This is the first comprehensive genetic epidemiological study of patients with HSP in Hungary. Next generation sequencing improved the yield of genetic diagnostics in this disease group even when the phenotype was atypical. However, considering the frequency of the HSP-causing gene defects, SPG4, the most common form of the disease, should be tested first to be cost effective in this economic region.

TFG-Related Neurologic Disorders: New Insights Into Relationships Between Endoplasmic Reticulum and Neurodegeneration

The tropomyosin-receptor kinase fused gene(TFG), which is located on chromosome 3q12.2, was originally identified as a fusion partner that results in the formation of oncogenic products associated with multiple cancers. TFG protein interacts directly with Sec16, the scaffolding protein for coat protein II-coated vesicles that regulate endoplasmic reticulum (ER)-to-Golgi transport at ER exit sites. In 2012, a heterozygous mutation of TFG was identified as the causative gene for autosomal-dominant hereditary motor and sensory neuropathy with proximal dominant involvement. In 2013, a homozygous mutation of TFG was reported in a family with early onset spastic paraplegia, optic atrophy, and neuropathy. Another novel mutation in TFG was discovered in 2014 as a cause of dominant axonal Charcot-Marie-Tooth disease type 2. These findings suggest that mutations of TFG cause ER dysfunction and neurodegeneration in this disease spectrum, which is tightly associated with ER function. Here, we review the clinical phenotypes of these diseases and present recent insights that suggest causal roles of ER dysfunction in TFG-related neurologic disorders. Although the precise pathogenetic mechanisms underlying these TFG mutations remain to be elucidated, experimental manipulations suggest that the dysregulations of ER homeostasis that occur due to mutations in TFG lead to neurodegeneration.

Glial expression of Swiss cheese (SWS), the Drosophila orthologue of neuropathy target esterase (NTE), is required for neuronal ensheathment and function

Mutations in Drosophila Swiss cheese (SWS) or its vertebrate orthologue neuropathy target esterase (NTE), respectively, cause progressive neuronal degeneration in Drosophila and mice and a complex syndrome in humans that includes mental retardation, spastic paraplegia and blindness. SWS and NTE are widely expressed in neurons but can also be found in glia; however, their function in glia has, until now, remained unknown. We have used a knockdown approach to specifically address SWS function in glia and to probe for resulting neuronal dysfunctions. This revealed that loss of SWS in pseudocartridge glia causes the formation of multi-layered glial whorls in the lamina cortex, the first optic neuropil. This phenotype was rescued by the expression of SWS or NTE, suggesting that the glial function is conserved in the vertebrate protein. SWS was also found to be required for the glial wrapping of neurons by ensheathing glia, and its loss in glia caused axonal damage. We also detected severe locomotion deficits in glial sws-knockdown flies, which occurred as early as 2 days after eclosion and increased further with age. Utilizing the giant fibre system to test for underlying functional neuronal defects showed that the response latency to a stimulus was unchanged in knockdown flies compared to controls, but the reliability with which the neurons responded to increasing frequencies was reduced. This shows that the loss of SWS in glia impairs neuronal function, strongly suggesting that the loss of glial SWS plays an important role in the phenotypes observed in the sws mutant. It is therefore likely that changes in glia also contribute to the pathology observed in humans that carry mutations in NTE.

Biotinidase deficiency should be considered in individuals exhibiting myelopathy with or without and vision loss

Multiple symptomatic children with biotinidase deficiency have exhibited spastic para- or tetraplegia due to myelopathy with and without vision loss. Although this has been a feature of what has been designated as delayed onset-biotinidase deficiency, myelopathy is likely also on the continuum of clinical features seen in younger children who have had these features attributed to dysfunction of the upper brain rather than of the spinal cord. Because many countries are still not screening their newborns for biotinidase deficiency, the disorder should be included in the differential diagnosis of individuals with myelopathic symptoms. Many of these children have gone weeks to months before they were correctly diagnosed with biotinidase deficiency. Rapid recognition that a child with myelopathy with and without vision loss has biotinidase deficiency will undoubtedly facilitate prompt treatment, increase the possibility of complete recovery and avoid potential residual permanent neurological damage. Newborn screening for biotinidase deficiency would avoid the delay in the diagnosis and treatment of individuals who otherwise may present with myelopathic or other neurological symptoms.

Identification of two novel KIF5A mutations in hereditary spastic paraplegia associated with mild peripheral neuropathy

Spastic paraplegia type 10 (SPG10) is a rare form of autosomal dominant hereditary spastic paraplegia (AD-HSP) due to mutations in KIF5A, a gene encoding the neuronal kinesin heavy-chain involved in axonal transport. KIF5A mutations have been associated with a wide clinical spectrum, ranging from pure HSP to isolated peripheral nerve involvement or complicated HSP phenotypes. Most KIF5A mutations are clustered in the motor domain of the protein that is necessary for microtubule interaction. Here we describe two Spanish families with an adult onset complicated AD-HSP in which neurological studies revealed a mild sensory neuropathy. Intention tremor was also present in both families. Molecular genetic analysis identified two novel mutations c.773 C>T and c.833 C>T in the KIF5A gene resulting in the P258L and P278L substitutions respectively. Both were located in the highly conserved kinesin motor domain of the protein which has previously been identified as a hot spot for KIF5A mutations. This study adds to the evidence associating the known occurrence of mild peripheral neuropathy in the adult onset SPG10 type of AD-HSP.

Lack of enzyme activity in GBA2 mutants associated with hereditary spastic paraplegia/cerebellar ataxia (SPG46)

Glucosylceramide is a membrane glycolipid made up of the sphingolipid ceramide and glucose, and has a wide intracellular distribution. Glucosylceramide is degraded to ceramide and glucose by distinct, non-homologous enzymes, including glucocerebrosidase (GBA), localized in the endolysosomal pathway, and β-glucosidase 2 (GBA2), which is associated with the plasma membrane and/or the endoplasmic reticulum. It is well established that mutations in the GBA gene result in endolysosomal glucosylceramide accumulation, which triggers Gaucher disease. In contrast, the biological significance of GBA2 is less well understood. GBA2-deficient mice present with male infertility, but humans carrying mutations in the GBA2 gene are affected with a combination of cerebellar ataxia and spastic paraplegia, as well as with thin corpus callosum and cognitive impairment (SPastic Gait locus #46, SPG46). To improve our understanding of the biochemical consequences of the GBA2 mutations, we have evaluated five nonsense and five missense GBA2 mutants for their enzyme activity. In transfected cells, the mutant forms of GBA2 were present in widely different amounts, ranging from overabundant to very minor, compared to the wild type enzyme. Nevertheless, none of the GBA2 mutant cDNAs raised the enzyme activity in transfected cells, in contrast to the wild-type enzyme. These results suggest that SPG46 patients have a severe deficit in GBA2 activity, because the GBA2 mutants are intrinsically inactive and/or reduced in amount. This assessment of the expression levels and enzyme activities of mutant forms of GBA2 offers a first insight in the biochemical basis of the complex pathologies seen in SPG46.