Clinical features and genetic spectrum in Chinese patients with recessive hereditary spastic paraplegia

Biallelic variants in the COQ4 gene caused hereditary spastic paraplegia predominant phenotype

INTRODUCTION

Hereditary spastic paraplegias (HSPs) comprise a group of neurodegenerative disorders characterized by progressive degeneration of upper motor neurons. Homozygous or compound heterozygous variants in COQ4 have been reported to cause primary CoQ10 deficiency-7 (COQ10D7), which is a mitochondrial disease.

AIMS

We aimed to screened COQ4 variants in a cohort of HSP patients.

METHODS

A total of 87 genetically unidentified HSP index patients and their available family members were recruited. Whole exome sequencing (WES) was performed in all probands. Functional studies were performed to identify the pathogenicity of those uncertain significance variants.

RESULTS

In this study, five different COQ4 variants were identified in three Chinese HSP pedigrees and two variants were novel, c.87dupT (p.Arg30*), c.304C>T (p.Arg102Cys). More importantly, we firstly described two early-onset pure HSP caused by COQ4 variants. Functional studies in patient-derived fibroblast lines revealed a reduction cellular CoQ10 levels and the abnormal mitochondrial structure.

CONCLUSIONS

Our findings revealed that bilateral variants in the COQ4 gene caused HSP predominant phenotype, expanding the phenotypic spectrum of the COQ4-related disorders.

Hereditary spastic paraparesis type 46 (SPG46): new GBA2 variants in a large Italian case series and review of the literature

Hereditary spastic paraparesis (HSP) is a group of central nervous system diseases primarily affecting the spinal upper motor neurons, with different inheritance patterns and phenotypes. SPG46 is a rare, early-onset and autosomal recessive HSP, linked to biallelic GBA2 mutations. About thirty families have been described worldwide, with different phenotypes like complicated HSP, recessive cerebellar ataxia or Marinesco-Sjögren Syndrome. Herein, we report five SPG46 patients harbouring five novel GBA2 mutations, the largest series described in Italy so far. Probands were enrolled in five different centres and underwent neurological examination, clinical cognitive assessment, column imaging for scoliosis assessment, ophthalmologic examination, brain imaging, GBA2 activity in peripheral blood cells and genetic testing. Their phenotype was consistent with HSP, with notable features like upper gaze palsy and movement disorders. We review demographic, genetic, biochemical and clinical information from all documented cases in the existing literature, focusing on the global distribution of cases, the features of the syndrome, its variable presentation, new potential identifying features and the significance of measuring GBA2 enzyme activity.

The mutational profile in a South African cohort with inherited neuropathies and spastic paraplegia

Introduction

Limited diagnostics are available for inherited neuromuscular diseases (NMD) in South Africa and (excluding muscle disease) are mainly aimed at the most frequent genes underlying genetic neuropathy (GN) and spastic ataxias in Europeans. In this study, we used next-generation sequencing to screen 61 probands with GN, hereditary spastic paraplegia (HSP), and spastic ataxias for a genetic diagnosis.

Methods

After identifying four GN probands with PMP22 duplication and one spastic ataxia proband with SCA1, the remaining probands underwent whole exome (n = 26) or genome sequencing (n = 30). The curation of coding/splice region variants using gene panels was guided by allele frequencies from internal African-ancestry control genomes (n = 537) and the Clinical Genome Resource's Sequence Variant Interpretation guidelines.

Results

Of 32 GN probands, 50% had African-genetic ancestry, and 44% were solved: PMP22 (n = 4); MFN2 (n = 3); one each of MORC2, ATP1A1, ADPRHL2, GJB1, GAN, MPZ, and ATM. Of 29 HSP probands (six with predominant ataxia), 66% had African-genetic ancestry, and 48% were solved: SPG11 (n = 3); KIF1A (n = 2); and one each of SPAST, ATL1, SPG7, PCYT2, PSEN1, ATXN1, ALDH18A1, CYP7B1, and RFT1. Structural variants in SPAST, SPG11, SPG7, MFN2, MPZ, KIF5A, and GJB1 were excluded by computational prediction and manual visualisation.

Discussion

In this preliminary cohort screening panel of disease genes using WES/WGS data, we solved ~50% of cases, which is similar to diagnostic yields reported for global cohorts. However, the mutational profile among South Africans with GN and HSP differs substantially from that in the Global North.

Power of NGS-based tests in HSP diagnosis: analysis of massively parallel sequencing in clinical practice

Hereditary spastic paraplegia (HSP) refers to a group of heterogeneous neurological disorders mainly characterized by corticospinal degeneration (pure forms), but sometimes associated with additional neurological and extrapyramidal features (complex HSP). The advent of next-generation sequencing (NGS) has led to huge improvements in knowledge of HSP genetics and made it possible to clarify the genetic etiology of hundreds of "cold cases," accelerating the process of reaching a molecular diagnosis. The different NGS-based strategies currently employed as first-tier approaches most commonly involve the use of targeted resequencing panels and exome sequencing, whereas genome sequencing remains a second-tier approach because of its high costs. The question of which approach is the best is still widely debated, and many factors affect the choice. Here, we aim to analyze the diagnostic power of different NGS techniques applied in HSP, by reviewing 38 selected studies in which different strategies were applied in different-sized cohorts of patients with genetically uncharacterized HSP.

Hereditary spastic paraplegia (SPG 48) with deafness and azoospermia: A case report

Hereditary spastic paraplegias (HSP) are inherited neurodegenerative disorders characterized by progressive paraplegia and spasticity in the lower limbs. SPG48 represents a rare genotype characterized by mutations in AP5Z1, a gene playing a role in intracellular membrane trafficking. This study describes a case of a 53-year-old male patient with SPG48 presenting spastic paraplegia, infertility, hearing impairment, cognitive abnormalities and peripheral neuropathy. The Sanger sequencing revealed a homozygous deletion in the chr 7:4785904-4786677 region causing a premature stop codon in exon 10. The patient's brother was heterozygous for the mutation. The brain magnetic resonance imaging found a mild brain atrophy and white matter lesions. In the analysis of the auditory thresholds, we found a significant hearing decrease in both ears.

Clinical and genetic spectrum of hereditary spastic paraplegia in Chinese children

AIM

To explore the clinical and genetic spectrum of hereditary spastic paraplegia (HSP) in Chinese children.

METHOD

This retrospective study was conducted between January 2014 and October 2021 in children clinically diagnosed with either pure HSP (pHSP) or complex HSP (cHSP).

RESULTS

We investigated 45 children (32 males, 13 females; mean age [SD] at symptom onset 4 years [7 months]). clinically diagnosed with HSP and identified genetic causes in 35 patients. Most patients with autosomal dominant HSP had pHSP (16/18), whereas most patients with autosomal recessive HSP tended to have cHSP (14/16). SPG11 was the most common autosomal recessive subtype, followed by FA2H/SPG35, whereas SPAST/SPG4 was the most frequent cause of autosomal dominant HSP. Two patients with CPT1C mutations presented with a complex phenotype. Meanwhile, 10 patients were found to have likely pathogenic variants/variants of uncertain clinical significance in six genes related to HSP.

INTERPRETATION

SPG11 and SPG4 were the most frequent subtypes in Chinese children with autosomal recessive HSP and autosomal dominant HSP. However, the prevalence of SPG4 was much lower than that in adults, which might be explained by the late onset of the disease. On the other hand, FA2H/SPG35 was common in our cohort, while it contributed to only a small proportion of adult cases, which might be explained by its rapid progression and early death in some patients. We also expanded the genetic and clinical spectra of SPG73.

Identification and functional characterization of novel variants of MAPT and GRN in Chinese patients with frontotemporal dementia

Frontotemporal dementia (FTD) is the second most common cause of dementia after Alzheimer's disease, characterized by distinct changes in behavior, personality, and language. Our study performed whole exome sequencing and repeat-primed PCR analysis in 29 unrelated FTD patients. Consequently, 2 known pathogenic variants (MAPT: p.P301L; TBK1: p.I450Kfs), and 4 novel variants (MAPT: p.R406Q, p.D430H, p.A330D; GRN: c.350-2A>G) were identified. The functional analysis results showed that phosphorylated tau levels were higher in cells expressing p.R406Q and p.D430H tau than those expressing wild-type tau, especially at the Thr205, Thr231, and Ser396 phosphorylation epitopes. Besides, the p.R406Q and p.D430H variants of MAPT impaired the ability of tau to bind to the microtubules and increased tau self-aggregation. Furthermore, we found that the c.350-2A>G variant caused exon 5 skipping. Our results showed that p.R406Q, p.D430H, and c.350-2A>G variants were classified as pathogenic. Finally, we summarized the clinical characterization of patients carrying pathogenic variants of MAPT in the East Asia populations. Our results broaden the genetic spectrum of FTD with MAPT and GRN variants.

P5B-ATPases in the mammalian polyamine transport system and their role in disease

Polyamines (PAs) are physiologically relevant molecules that are ubiquitous in all organisms. The vitality of PAs to the healthy functioning of a cell is due to their polycationic nature causing them to interact with a vast plethora of cellular players and partake in numerous cellular pathways. Naturally, the homeostasis of such essential molecules is tightly regulated in a strictly controlled interplay between intracellular synthesis and degradation, uptake from and secretion to the extracellular compartment, as well as intracellular trafficking. Not surprisingly, dysregulated PA homeostasis and signaling are implicated in multiple disorders, ranging from cancer to neurodegeneration; leading many to propose rectifying the PA balance as a potential therapeutic strategy. Despite being well characterized in bacteria, fungi and plants, the molecular identity and properties of the PA transporters in animals are poorly understood. This review brings together the current knowledge of the cellular function of the mammalian PA transport system (PTS). We will focus on the role of P5B-ATPases ATP13A2-5 which are PA transporters in the endosomal system that have emerged as key players in cellular PA uptake and organelle homeostasis. We will discuss recent breakthroughs on their biochemical and structural properties as well as their implications for disease and therapy.

Two novel mutations in ALDH18A1 and SPG11 gene found by whole-exome sequencing in spastic paraplegia disease patients in Iran

Hereditary spastic paraplegia is a not common inherited neurological disorder with heterogeneous clinical expressions. ALDH18A1 (located on 10q24.1) gene-related spastic paraplegias (SPG9A and SPG9B) are rare metabolic disorders caused by dominant and recessive mutations that have been found recently. Autosomal recessive hereditary spastic paraplegia is a common and clinical type of familial spastic paraplegia linked to the SPG11 locus (locates on 15q21.1). There are different symptoms of spastic paraplegia, such as muscle atrophy, moderate mental retardation, short stature, balance problem, and lower limb weakness. Our first proband involves a 45 years old man and our second proband involves a 20 years old woman both are affected by spastic paraplegia disease. Genomic DNA was extracted from the peripheral blood of the patients, their parents, and their siblings using a filter-based methodology and quantified and used for molecular analysis and sequencing. Sequencing libraries were generated using Agilent SureSelect Human All ExonV7 kit, and the qualified libraries are fed into NovaSeq 6000 Illumina sequencers. Sanger sequencing was performed by an ABI prism 3730 sequencer. Here, for the first time, we report two cases, the first one which contains likely pathogenic NM_002860: c.475C>T: p.R159X mutation of the ALDH18A1 and the second one has likely pathogenic NM_001160227.2: c.5454dupA: p.Glu1819Argfs Ter11 mutation of the SPG11 gene and also was identified by the whole-exome sequencing and confirmed by Sanger sequencing. Our aim with this study was to confirm that these two novel variants are direct causes of spastic paraplegia.

Clinical and genetic characterization of a Taiwanese cohort with spastic paraparesis combined with cerebellar involvement

Hereditary spastic paraplegias (HSPs) are a heterogeneous group of neurodegenerative disorders clinically characterized by progressive lower-limb spasticity. Cerebellar ataxia commonly co-occurs with complicated HSPs. HSP with concurrent cerebellar ataxia has significant clinical and genetic overlaps with hereditary cerebellar ataxia (HCA) and other inherited neurological diseases, adding to the challenge of planning genetic testing for the disease. In this study, we characterized clinical features of a cohort of 24 patients (male/female: 15/9) from 22 families who presented spastic paraparesis combined with cerebellar involvement, with a median disease onset age 20.5 (range 5–53) years. Aside from the core phenotype, 18 (75%) patients had additional neuropsychiatric and systemic manifestations. A stepwise genetic testing strategy stratified by mode of inheritance, distinct neuroimaging features (e.g., thin corpus callosum), population-specific prevalence and whole-exome sequencing was utilized to investigate the genetic etiology. Causative mutations in up to 10 genes traditionally related to HSP, HCA and other neurogenetic diseases (autosomal recessive spastic ataxia of Charlevoix-Saguenay, neurodegeneration with brain iron accumulation, and progressive encephalopathy with brain atrophy and thin corpus callosum) were detected in 16 (73%) of the 22 pedigrees. Our study revealed the genetic complexity of HSP combined with cerebellar involvement. In contrast to the marked genetic diversity, the functions of the causative genes are restricted to a limited number of physiological themes. The functional overlap might reflect common underlying pathogenic mechanisms, to which the corticospinal tract and cerebellar neuron circuits may be especially vulnerable.

Nomenclature of Genetic Movement Disorders: Recommendations of the International Parkinson and Movement Disorder Society Task Force - An Update

In 2016, the Movement Disorder Society Task Force for the Nomenclature of Genetic Movement Disorders presented a new system for naming genetically determined movement disorders and provided a criterion-based list of confirmed monogenic movement disorders. Since then, a substantial number of novel disease-causing genes have been described, which warrant classification using this system. In addition, with this update, we further refined the system and propose dissolving the imaging-based categories of Primary Familial Brain Calcification and Neurodegeneration with Brain Iron Accumulation and reclassifying these genetic conditions according to their predominant phenotype. We also introduce the novel category of Mixed Movement Disorders (MxMD), which includes conditions linked to multiple equally prominent movement disorder phenotypes. In this article, we present updated lists of newly confirmed monogenic causes of movement disorders. We found a total of 89 different newly identified genes that warrant a prefix based on our criteria; 6 genes for parkinsonism, 21 for dystonia, 38 for dominant and recessive ataxia, 5 for chorea, 7 for myoclonus, 13 for spastic paraplegia, 3 for paroxysmal movement disorders, and 6 for mixed movement disorder phenotypes; 10 genes were linked to combined phenotypes and have been assigned two new prefixes. The updated lists represent a resource for clinicians and researchers alike and they have also been published on the website of the Task Force for the Nomenclature of Genetic Movement Disorders on the homepage of the International Parkinson and Movement Disorder Society (https://www.movementdisorders.org/MDS/About/Committees--Other-Groups/MDS-Task-Forces/Task-Force-on-Nomenclature-in-Movement-Disorders.htm). © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson Movement Disorder Society.

The emerging genetic diversity of hereditary spastic paraplegia in Korean patients

Hereditary Spastic Paraplegias (HSP) are a group of rare inherited neurological disorders characterized by progressive loss of corticospinal motor-tract function. Numerous patients with HSP remain undiagnosed despite screening for known genetic causes of HSP. Therefore, identification of novel genetic variations related to HSP is needed. In this study, we identified 88 genetic variants in 54 genes from whole-exome data of 82 clinically well-defined Korean HSP families. Fifty-six percent were known HSP genes, and 44% were composed of putative candidate HSP genes involved in the HSPome and originally reported neuron-related genes, not previously diagnosed in HSP patients. Their inheritance modes were 39, de novo; 33, autosomal dominant; and 10, autosomal recessive. Notably, ALDH18A1 showed the second highest frequency. Fourteen known HSP genes were firstly reported in Koreans, with some of their variants being predictive of HSP-causing protein malfunction. SPAST and REEP1 mutants with unknown function induced neurite abnormality. Further, 54 HSP-related genes were closely linked to the HSP progression-related network. Additionally, the genetic spectrum and variation of known HSP genes differed across ethnic groups. These results expand the genetic spectrum for HSP and may contribute to the accurate diagnosis and treatment for rare HSP.

Spastic paraplegia type 46: novel and recurrent GBA2 gene variants in a compound heterozygous Italian patient with spastic ataxia phenotype

INTRODUCTION

Spastic paraplegia type 46 (SPG46) is a rare autosomal recessive hereditary spastic paraplegia, caused by mutations in the non-lysosomal glucosylceramidase β2 (GBA2) gene. Worldwide, approximately twenty SPG46 families have been identified so far.

CASE REPORT

We describe a compound heterozygous Italian patient carrying a novel (p.Arg879Gln) and a recurrent (p.Arg399 *) GBA2 gene variant. The patient presented unsteady gait at age 2, and progressively manifested spastic-ataxia, scoliosis, mild intellectual decline, and bilateral cataract.

DISCUSSION

Clinical manifestations associated with GBA2 gene variants encompass a spectrum of overlapping phenotypes including cerebellar ataxia, spastic paraplegia, and Marinesco-Sjogren-like syndrome. We review previously reported cases of SPG46 and discuss possible genetic differential diagnosis.

Genetic, clinical and neuroimaging profiles of sporadic and autosomal recessive hereditary spastic paraplegia cases in Chinese

Spastic paraplegias (SPGs) are a group of clinically and genetically heterogeneous neurodegenerative diseases. Mutations in 78 genes have been identified in autosomal dominant hereditary SPG (AD-HSP) and autosomal recessive hereditary SPG (AR-HSP). Compared to familial HSP, much less is known about the genetic and clinical profiles of sporadic SPGs. In this study, we have screened mutations for 18 sporadic SPGs or AR-HSP patients (mainly Northern Chinese) by whole-exome sequencing. We identified 12 mutations in five genes in 9 (50%) patients, including 9 novel ones: SPG5A/CYP7B1 (c.851C > A; c.122 + 2 T > G), SPG11/KIAA1840 (c.1735 + 3_ 1735 + 6del AAGT); SPG7/SPG7 (c.1454G > A; c.1892_ 1906dup GAGGACGGGCCTCGG); SPG39/PNPLA6 (c.1591G > A; c. 2990C > T); SPG15/ ZFYVE26 (c. 4804C > T; c. 4278 G > A). Among all the mutations, 7 were detected in the SPG5A and SPG11. Age at onset was significantly younger in cases with mutations (15.45 ± 6.78 years) than those without mutations (25.56 ± 10.90 years) (P = 0.03). Except for two cases with the SPG5A mutations, all cases presented with complicated SPGs. Three cases carrying mutations in SPG7, SPG15, SPG39 showed symptoms and signs of ataxia. One case carrying the homozygous c.259 + 2 T > C mutation in CYP7B1 showed serum parameters indicating liver impairment. Magnetic resonance imaging showed significantly thinned corpus callosum in cases with SPG11 and SPG15, but not in those with SPG5A, SPG7 or SPG39. In contrast, cerebellar atrophy was prominent in the SPG7 and SPG39 cases. These findings expand the spectrum of genetic, clinical and imaging features of sporadic SPG and AR-HSP, and have important implications in genetic counselling, molecular mechanisms and precise diagnosis of the disease.

Novel Compound Missense and Intronic Splicing Mutation in ALDH18A1 Causes Autosomal Recessive Spastic Paraplegia

Background: Hereditary spastic paraplegia (HSP) caused by mutations in ALDH18A1 have been reported as spastic paraplegia 9 (SPG9), with autosomal dominant and autosomal recessive transmission (SPG9A and SPG9B). SPG9 is rare and has shown phenotypic and genotypic heterogeneity in previous reports.

Methods: This study screened ALDH18A1 mutations in autosomal recessive HSP patients using combined whole exome sequencing and RNA splicing analysis. We conducted in silico investigations, co-segregation analysis, and ELISA-based analysis of P5CS (Δ1-pyrroline-5-carboxylate synthetase; encoded by ALDH18A1) concentration to validate the pathogenicity of the detected ALDH18A1 variants. All previously reported bi-allelic ALDH18A1 mutations and cases were reviewed to summarize the genetic and clinical features of ALDH18A1-related HSP.

Results: A novel missense mutation c.880T>C, p.S294P and an intronic splicing mutation c.-28-13A>G were both detected in ALDH18A1 in an autosomal recessive family presenting with a complicated form HSP. ELISA assays revealed significantly decreased P5CS concentration in the proband's plasma compared with that in the healthy controls. Moreover, review of previously reported recessive cases showed that SPG9B patients in our cohort presented with milder symptoms, i.e., later age at onset and without cognitive impairment.

Conclusion: The present study expands the genetic and clinical spectrum of SPG9B caused by ALDH18A1 mutation. Our work defines new genetic variants to facilitate future diagnoses, in addition to demonstrating the highly informative value of splicing mutation prediction in the characterization of disease-related intronic variants.

The investigation of genetic and clinical features in patients with hereditary spastic paraplegia in central-Southern China

Objective

Hereditary spastic paraplegias (HSP) is a clinically and genetically heterogeneous group of neurodegenerative disorders. We describe the genetic and clinical features of a cohort of five HSP families from central‐southern China.

Methods

Using targeted exome‐sequencing technology, we investigated the genetic and clinical features in five HSP families. We reviewed the clinical histories of these patients as well as the molecular and functional characterization of the associated gene variants. We also performed functional analysis of an intron variant of SPAST in vitro.

Results

We identified a known SPAST mutation (p.Pro435Leu) in a family with autosomal dominant HSP (AD‐HSP) and four novel variants in two HSP families and a sporadic case. These identified four novel variants included a variant in SPG11 (p.Val1979Ter), two variants in B4GALNT1 (p.Ser475Phe and c.1002 + 2 T > G), and a splicing site variant in SPAST (c.1245+5G>A). Minigene analysis of the splicing variant in SPAST (c.1245+5G>A) revealed that the mutation resulted in mRNAs with a loss of exon 9. The SPG4 family carrying c.1245+5G>A variant in SPAST exhibited genetic anticipation, with a decreased age at onset and increased severity in successive generations. The proband with p.Val1979Ter variant in SPG11 showed characteristic clinical features of early‐onset, severe spasticity, and corpus callosum atrophy which were highly suggestive of the diagnosis of SPG11‐associated HSP.

Conclusions

Our findings strongly support variable phenotype of B4GALNT1‐related SPG26 and also expand the clinical and mutation spectrum of HSP caused by mutations in SPAST, SPG11, and B4GALNT1. These results will help to improve the efficiency of early diagnosis in patients clinically suspected of HSP.

We investigated the genetic and clinical features in five families with HSP from central‐southern China using targeted exome‐sequencing technology. We identified a known mutation (p.Pro435Leu) in SPAST in a family with autosomal dominant HSP (AD‐HSP) and four novel variants in three independent HSP families and a sporadic case. These identified four novel variants include a nonsense variant (p.Val1979Ter) in SPG11, two variants (p.Ser475Phe and c.1002 + 2 T > G) in B4GALNT1, and a splicing site variants in SPAST (c.1245 + 5G>A). Minigene analysis of the splicing variant (c.1245 + 5G>A) in SPAST revealed that the mutation resulted in mRNAs with a loss of exon 9

Application of a Clinical Workflow May Lead to Increased Diagnostic Precision in Hereditary Spastic Paraplegias and Cerebellar Ataxias: A Single Center Experience

The molecular characterization of Hereditary Spastic Paraplegias (HSP) and inherited cerebellar ataxias (CA) is challenged by their clinical and molecular heterogeneity. The recent application of Next Generation Sequencing (NGS) technologies is increasing the diagnostic rate, which can be influenced by patients’ selection. To assess if a clinical diagnosis of CA/HSP received in a third-level reference center might impact the molecular diagnostic yield, we retrospectively evaluated the molecular diagnostic rate reached in our center on 192 unrelated families (90 HSP and 102 CA) (i) before NGS and (ii) with the use of NGS gene panels. Overall, 46.3% of families received a genetic diagnosis by first-tier individual gene screening: 43.3% HSP and 50% spinocerebellar ataxias (SCA). The diagnostic rate was 56.7% in AD-HSP, 55.5% in AR-HSP, and 21.2% in sporadic HSP. On the other hand, 75% AD-, 52% AR- and 33% sporadic CA were diagnosed. So far, 32 patients (24 CA and 8 HSP) were further assessed by NGS gene panels, and 34.4% were diagnosed, including 29.2% CA and 50% HSP patients. Eleven novel gene variants classified as (likely) pathogenic were identified. Our results support the role of experienced clinicians in the diagnostic assessment and the clinical research of CA and HSP even in the next generation era.

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.

Tremor as an early sign of hereditary spastic paraplegia due to mutations in ALDH18A1

BACKGROUND

The ALDH18A1 gene is located at 10q24.1 and encodes delta-1-pyrroline-5-carboxylate synthetase (P5CS), a mitochondrial bifunctional enzyme that catalyzes the first two steps in de novo biosynthesis of proline, ornithine, citrulline, and arginine. ALDH18A1-related disorders have been classified into four groups, such as autosomal dominant and recessive hereditary spastic paraplegia (SPG9A and SPG9B, respectively), as well as autosomal dominant and recessive cutis laxa (ADCL3 and ARCL3A, respectively). Neurodegeneration is a characteristic feature of all groups.

CASE REPORT

Here, we report a girl with compound heterozygous disease-causing variants (c.-28-2A>G and c.383G>A, p.Arg128His) in the ALDH18A1 gene, revealed by whole exome sequencing. The c.-28-2A>G variant in intron 1, inherited from the mother, is a novel mutation, while the c.383G>A variant in exon 4, inherited from the father, has already been reported. The patient presented with vigorous infantile tremor preceding progressive spastic paraplegia. Dysmorphic features included elongated face, deep-set ears, upturned nose, long philtrum and pointed chin. Intrauterine and postnatal growth retardation, microcephaly, global developmental delay and profound intellectual disability were also noticed. Blood fasting ammonia level, plasma proline, ornithine and arginine levels were normal, while citrulline level was slightly decreased. Brain MRI revealed moderate hypoplasia of the corpus callosum and reduction of white matter volume.

CONCLUSIONS

The patient represents SPG9B, a rare form of autosomal recessive hereditary spastic paraplegias. The early onset tremor, preceding lower limb spasticity appears to be a unique early manifestation of neurodegeneration in this case.

Paediatric-onset hereditary spastic paraplegias: a retrospective cohort study

AIM

To describe the clinical and neurogenetic spectrum of paediatric-onset hereditary spastic paraplegias (HSPs) diagnosed in our unit.

METHOD

We report on 47 patients (30 males, 17 females; mean [SD] age 12y 7mo [6y 2mo], range 4-34y) clinically diagnosed with an HSP at the Child Neurology Unit, IRCCS-ASMN (Reggio Emilia, Italy) between 1990 and 2018, who were genetically investigated by means of single-gene direct sequencing and/or next-generation sequencing technologies (targeted panels, whole-exome sequencing [WES]).

RESULTS

Complex forms prevailed slightly (n=26), autosomal dominant being the main inheritance pattern (n=11), followed by recessive (n=5) and X-linked (n=1). A definite genetic diagnosis was achieved in 17 patients. Spastic paraplegia 3A (n=4) was the most frequent cause of autosomal dominant HSP in our cohort, while no genetic variant prevailed in autosomal recessive forms and pathogenic/likely pathogenic variants were disclosed in a wide range of different genes.

INTERPRETATION

We found wide phenotypic and genetic heterogeneity. With increasing accessibility to WES, a higher number of patients receive a diagnosis, allowing detection of variants in ultra-rare disease-causing genes and refining genotype-phenotype correlations.

WHAT THIS PAPER ADDS

A genetic diagnosis of paediatric-onset hereditary spastic paraplegia was achieved in one-third of patients. Pathogenic/likely pathogenic variants in rare genes were found. Genotypic and phenotypic heterogeneity favours targeted panel/whole-exome sequencing for diagnosis.

Novel CAPN1 mutations extend the phenotypic heterogeneity in combined spastic paraplegia and ataxia

OBJECTIVE

Recessive mutations in the CAPN1 gene have recently been identified in spastic paraplegia 76 (SPG76), a complex hereditary spastic paraplegia (HSP) that is combined with cerebellar ataxia, resulting in an ataxia-spasticity disease spectrum. This study aims to assess the influence of CAPN1 variants on the occurrence of SPG76 and identify factors potentially contributing to phenotypic heterogeneity.

METHODS

We screened a cohort of 240 unrelated HSP families for variants in CAPN1 using high-throughput sequencing analysis. We described in detail the clinical and genetic features of the SPG76 patients in our cohort and summarized all reported cases.

RESULTS

Six unreported CAPN1-associated families containing eight patients with or without cerebellar ataxia were found in our cohort of HSP cases. These patients carried three previously reported homozygous truncating mutations (p.V64Gfs^* 103, c.759+1G>A, and p.R285^* ), and three additional novel compound heterozygous missense mutations (p.R481Q, p.P498L, and p.R618W). Lower limbs spasticity, hyperreflexia, and Babinski signs developed in about 94% of patients, with ataxia developing in 63% of cases. In total, 33 pathogenic mutations were distributed along the three reported functional domains of calpain-1 protein, encoded by CAPN1, with no hotspot region. A comparison of gender distribution between the two groups indicated that female SPG76 patients were significantly more likely to present with complicated HSP than male patients (P = 0.015).

INTERPRETATION

Our study supports the clinically heterogeneous inter- and intra-family variability of SPG76 patients, and demonstrates that gender and calpain-1 linker structure may contribute to clinical heterogeneity in SPG76 cases.

[A case of spastic paraplegia 48 with a novel mutation in the AP5Z1 gene]

We describe an additional patient with spastic paraplegia 48 (SPG48). A 52-year-old woman with gradually increasing gait disturbance was admitted to our hospital. When she was 47 years old, acquaintances noted a shuffling gait. Gait worsening was evident at 48 years. Spastic gait was apparent at 50, and she required a walking stick at 54. Her elder brother had similar gait disturbance. No consanguinity was known. Neurologic examination at 52 disclosed spasticity and moderate weakness in the lower limbs. Spasticity and brisk reflexes in all limbs. Laboratory studies including HTLV-1 titer detected no abnormalities. MRI demonstrated mild corpus callosum narrowing and prominent anterior periventricular hyperintensities in fluid attenuation inversion recovery images. In limb muscles, electromyography (EMG) showed a chronic neurogenic pattern including reduced interference. Gene analysis identified compound homozygosity in exon 7 of adaptor-related protein complex 5 subunit zeta 1 (AP5Z1), including a novel frameshift mutation, c.1662_1672del;p.Glu554Hfs*15 in the patient, and a heterozygous missense mutation in asymptomatic family members, including her mother, two siblings, and a daughter. The frameshift mutation is considered a pathogenic variant according to American College of Medical Genetics and Genomics standards and guidelines. Based on clinical features, imaging findings and genetic abnormalities, we diagnosed this patient with SPG48. Mutations in AP5Z1, which encodes the ζ subunit of AP-5, underlie SPG48. The AP-5 adaptor protein complex, which is mutated in SPG48, binds to both spastizin and spatacsin. While hereditary spastic paraplegias generally are clinically and genetically heterogenous, SPG48, SPG11, and SPG15 are clinically similar.

Δ1 -Pyrroline-5-carboxylate synthetase deficiency: An emergent multifaceted urea cycle-related disorder

The bifunctional homooligomeric enzyme Δ¹ -pyrroline-5-carboxylate synthetase (P5CS) and its encoding gene ALDH18A1 were associated with disease in 1998. Two siblings who presented paradoxical hyperammonemia (alleviated by protein), mental disability, short stature, cataracts, cutis laxa, and joint laxity, were found to carry biallelic ALDH18A1 mutations. They showed biochemical indications of decreased ornithine/proline synthesis, agreeing with the role of P5CS in the biosynthesis of these amino acids. Of 32 patients reported with this neurocutaneous syndrome, 21 familial ones hosted homozygous or compound heterozygous ALDH18A1 mutations, while 11 sporadic ones carried de novo heterozygous ALDH18A1 mutations. In 2015 to 2016, an upper motor neuron syndrome (spastic paraparesis/paraplegia SPG9) complicated with some traits of the neurocutaneous syndrome, although without report of cutis laxa, joint laxity, or herniae, was associated with monoallelic or biallelic ALDH18A1 mutations with, respectively, dominant and recessive inheritance. Of 50 SPG9 patients reported, 14 and 36 (34/2 familial/sporadic) carried, respectively, biallelic and monoallelic mutations. Thus, two neurocutaneous syndromes (recessive and dominant cutis laxa 3, abbreviated ARCL3A and ADCL3, respectively) and two SPG9 syndromes (recessive SPG9B and dominant SPG9A) are caused by essentially different spectra of ALDH18A1 mutations. On the bases of the clinical data (including our own prior patients' reports), the ALDH18A1 mutations spectra, and our knowledge on the P5CS protein, we conclude that the four syndromes share the same pathogenic mechanisms based on decreased P5CS function. Thus, these syndromes represent a continuum of increasing severity (SPG9A < SPG9B < ADCL3 ≤ ARCL3A) of the same disease, P5CS deficiency, in which the dominant mutations cause loss-of-function by dominant-negative mechanisms.

Truncated mutants of beta-glucosidase 2 (GBA2) are localized in the mitochondrial matrix and cause mitochondrial fragmentation

The enzyme β-glucosidase 2 (GBA2) is clinically relevant because it is targeted by the drug miglustat (Zavesca^®) and because it is involved in inherited diseases. Mutations in the GBA2 gene are associated with two neurological diseases on the ataxia-spasticity spectrum, hereditary spastic paraplegia 46 (SPG46) and Marinesco-Sjögren-like syndrome (MSS). To establish how GBA2 mutations give rise to neurological pathology, we have begun to investigate mutant forms of GBA2 encoded by disease-associated GBA2 alleles. Previously, we found that five GBA2 missense mutants and five C-terminally truncated mutants lacked enzyme activity. Here we have examined the cellular locations of wild-type (WT) and mutant forms of GBA2 by confocal and electron microscopy, using transfected cells. Similar to GBA2-WT, the D594H and M510Vfs*17 GBA2 mutants were located at the plasma membrane, whereas the C-terminally truncated mutants terminating after amino acids 233 and 339 (GBA2-233 and -339) were present in the mitochondrial matrix, induced mitochondrial fragmentation and loss of mitochondrial transmembrane potential. Deletional mutagenesis indicated that residues 161–200 are critical for the mitochondrial fragmentation of GBA2-233 and -339. Considering that the mitochondrial fragmentation induced by GBA2-233 and -339 is consistently accompanied by their localization to the mitochondrial matrix, our deletional analysis raises the possibility that that GBA2 residues 161–200 harbor an internal targeting sequence for transport to the mitochondrial matrix. Altogether, our work provides new insights into the behaviour of GBA2-WT and disease-associated forms of GBA2.