Mutations in SPG11 are frequent in autosomal recessive spastic paraplegia with thin corpus callosum, cognitive decline and lower motor neuron degeneration

Intrauterine chromium exposure and cognitive developmental delay: The modifying effect of genetic predisposition

There is limited evidence on the effects of intrauterine chromium (Cr) exposure on children's cognitive developmental delay (CDD). Further, little is known about the genetic factors in modifying the association between intrauterine Cr exposure and CDD. The present study involved 2361 mother-child pairs, in which maternal plasma Cr concentrations were assessed, a polygenic risk score for the child was constructed, and the child's cognitive development was evaluated using the Bayley Scales of Infant Development. The risks of CDD conferred by intrauterine Cr exposure in children with different genetic backgrounds were evaluated by logistic regression. The additive interaction between intrauterine Cr exposure and genetic factors was evaluated by calculating the relative excess risk due to interaction (RERI), attributable proportion due to interaction (AP), and synergy index (SI). According to present study, higher intrauterine Cr exposure was significantly associated with increased CDD risk [each unit increase in ln-transformed maternal plasma Cr concentration (ln-Cr): adjusted OR (95 % CI), 1.18 (1.04-1.35); highest vs lowest quartile: adjusted OR (95 % CI), 1.57 (1.10-2.23)]. The dose-response relationship of intrauterine Cr exposure and CDD for children with high genetic risk was more prominent [each unit increased ln-Cr: adjusted OR (95 % CI), 1.36 (1.09-1.70)]. Joint effects between intrauterine Cr exposure and genetic factors were found. Specifically, for high genetic risk carriers, the association between intrauterine Cr exposure and CDD was more evident [highest vs lowest quartile: adjusted OR (95 % CI), 2.33 (1.43-3.80)]. For those children with high intrauterine Cr exposure and high genetic risk, the adjusted AP was 0.39 (95 % CI, 0.07-0.72). Conclusively, intrauterine Cr exposure was a high-risk factor for CDD in children, particularly for those with high genetic risk. Intrauterine Cr exposure and one's adverse genetic background jointly contribute to an increased risk of CDD in children.

Decreasing ganglioside synthesis delays motor and cognitive symptom onset in Spg11 knockout mice

Biallelic variants in the SPG11 gene account for the most common form of autosomal recessive hereditary spastic paraplegia characterized by motor and cognitive impairment, with currently no therapeutic option. We previously observed in a Spg11 knockout mouse that neurodegeneration is associated with accumulation of gangliosides in lysosomes. To test whether a substrate reduction therapy could be a therapeutic option, we downregulated the key enzyme involved in ganglioside biosynthesis using an AAV-PHP.eB viral vector expressing a miRNA targeting St3gal5. Downregulation of St3gal5 in Spg11 knockout mice prevented the accumulation of gangliosides, delayed the onset of motor and cognitive symptoms, and prevented the upregulation of serum levels of neurofilament light chain, a biomarker widely used in neurodegenerative diseases. Importantly, similar results were observed when Spg11 knockout mice were administrated venglustat, a pharmacological inhibitor of glucosylceramide synthase expected to decrease ganglioside synthesis. Downregulation of St3gal5 or venglustat administration in Spg11 knockout mice strongly decreased the formation of axonal spheroids, previously associated with impaired trafficking. Venglustat had similar effect on cultured human SPG11 neurons. In conclusion, this work identifies the first disease-modifying therapeutic strategy in SPG11, and provides data supporting its relevance for therapeutic testing in SPG11 patients.

AP2A2 mutation and defective endocytosis in a Malian family with hereditary spastic paraplegia

Hereditary spastic paraplegia (HSP) comprises a large group of neurogenetic disorders characterized by progressive lower extremity spasticity. Neurological evaluation and genetic testing were completed in a Malian family with early-onset HSP. Three children with unaffected consanguineous parents presented with symptoms consistent with childhood-onset complicated HSP. Neurological evaluation found lower limb weakness, spasticity, dysarthria, seizures, and intellectual disability. Brain MRI showed corpus callosum thinning with cortical and spinal cord atrophy, and an EEG detected slow background in the index patient. Whole exome sequencing identified a homozygous missense variant in the adaptor protein (AP) complex 2 alpha-2 subunit (AP2A2) gene. Western blot analysis showed reduced levels of AP2A2 in patient-iPSC derived neuronal cells. Endocytosis of transferrin receptor (TfR) was decreased in patient-derived neurons. In addition, we observed increased axon initial segment length in patient-derived neurons. Xenopus tropicalis tadpoles with ap2a2 knockout showed cerebral edema and progressive seizures. Immunoprecipitation of the mutant human AP-2-appendage alpha-C construct showed defective binding to accessory proteins. We report AP2A2 as a novel genetic entity associated with HSP and provide functional data in patient-derived neuron cells and a frog model. These findings expand our understanding of the mechanism of HSP and improve the genetic diagnosis of this condition.

Late-onset Kjellin syndrome: Diagnosis of SPG11 on fundus examination

INTRODUCTION

Spastic paraplegia (SPG) is a heterogenous group of neurodegenerative disorders, that may include ocular involvement. Here we report the clinical data of a patient with late-onset Kjellin syndrome, a peculiar form of hereditary SPG with macular dystrophy.

MATERIALS AND METHODS

Clinical, functional and multimodal retinal imaging data were collected. Genetic testing was performed by Whole Exome Sequencing (WES).

RESULTS

A 52-year-old female patient with SPG of unknown origin was referred for a progressive visual acuity loss. Multimodal fundus imaging revealed a peculiar macular dystrophy. Given the specific association of macular dystrophy and SPG, a Kjellin syndrome was suspected and genetic testing performed. WES revealed biallelic pathogenic variants in SPG11, co-segregating with disease in the family.

CONCLUSION

Careful ophthalmological examination prompted the diagnosis and guided molecular testing. This case underlines the importance of a neuro-ophthalmologic assessment in patients with SPG.

Identification and analyses of exonic and copy number variants in spastic paraplegia

Hereditary spastic paraplegias are a diverse group of degenerative disorders that are clinically categorized as isolated; with involvement of lower limb spasticity, or symptomatic, where spastic paraplegia is complicated by further neurological features. We sought to identify the underlying genetic causes of these disorders in the participating patients. Three consanguineous families with multiple affected members were identified by visiting special schools in the Punjab Province. DNA was extracted from blood samples of the participants. Exome sequencing was performed for selected patients from the three families, and the data were filtered to identify rare homozygous variants. ExomeDepth was used for the delineation of the copy number variants. All patients had varying degrees of intellectual disabilities, poor speech development, spasticity, a wide-based gait or an inability to walk and hypertonia. In family RDHR07, a homozygous deletion involving multiple exons and introns of SPG11 (NC000015.9:g.44894055_449028del) was found and correlated with the phenotype of the patients who had spasticity and other complex movement disorders, but not those who exhibited ataxic or indeterminate symptoms as well. In families ANMD03 and RDFA06, a nonsense variant, c.985C > T;(p.Arg329Ter) in DDHD2 and a frameshift insertion‒deletion variant of AP4B1, c.965-967delACTinsC;p.(Tyr322SerfsTer14), were identified which were homozygous in the patients while the obligate carriers in the respective pedigrees were heterozygous. All variants were ultra-rare with none, or very few carriers identified in the public databases. The three loss of function variants are likely to cause nonsense-mediated decay of the respective transcripts. Our research adds to the genetic variability associated with the SPG11 and AP4B1 variants and emphasizes the genetic heterogeneity of hereditary spastic paraplegia.

Unexpected complexity in the molecular diagnosis of spastic paraplegia 11

BACKGROUND

Spastic paraplegia 11 (SPG11) is the most prevalent form of autosomal recessive hereditary spastic paraplegia, resulting from biallelic pathogenic variants in the SPG11 gene (MIM *610844).

METHODS

The proband is a 36-year-old female referred for genetic evaluation due to cognitive dysfunction, gait impairment, and corpus callosum atrophy (brain MRI was normal at 25-years-old). Diagnostic approaches included CGH array, next-generation sequencing, and whole transcriptome sequencing.

RESULTS

CGH array revealed a 180 kb deletion located upstream of SPG11. Sequencing of SPG11 uncovered two rare single nucleotide variants: the novel variant c.3143C>T in exon 17 (in cis with the deletion), and the previously reported pathogenic variant c.6409C>T in exon 34 (in trans). Whole transcriptome sequencing revealed that the variant c.3143C>T caused exon 17 skipping.

CONCLUSION

We report a novel sequence variant in the SPG11 gene resulting in exon 17 skipping, which, along with a nonsense variant, causes Spastic Paraplegia 11 in our proband. In addition, a deletion upstream of SPG11 was identified in the patient, whose implication in the phenotype remains uncertain. Nonetheless, the deletion apparently affects cis-regulatory elements of the gene, suggesting a potential new pathogenic mechanism underlying the disease in a subset of undiagnosed patients. Our findings further support the hypothesis that the origin of thin corpus callosum in patients with SPG11 is of progressive nature.

Exome sequencing in four families with neurodevelopmental disorders: genotype-phenotype correlation and identification of novel disease-causing variants in VPS13B and RELN

Neurodevelopmental disorders (NDDs) are a clinically and genetically heterogeneous group of early-onset pediatric disorders that affect the structure and/or function of the central or peripheral nervous system. Achieving a precise molecular diagnosis for NDDs may be challenging due to the diverse genetic underpinnings and clinical variability. In the current study, we investigated the underlying genetic cause(s) of NDDs in four unrelated Pakistani families. Using exome sequencing (ES) as a diagnostic approach, we identified disease-causing variants in established NDD-associated genes in all families, including one hitherto unreported variant in RELN and three recurrent variants in VPS13B, DEGS1, and SPG11. Overall, our study highlights the potential of ES as a tool for clinical diagnosis.

Medical magnetic resonance imaging publications in Arab countries: A 25-year bibliometric analysis

Magnetic Resonance Imaging (MRI) is increasingly becoming a cornerstone in modern diagnostic healthcare, offering unparalleled capabilities in stroke, dementia, and cancer screening. Therefore, this study aims to map medical MRI literature affiliated with Arab countries, focusing on publication trends, top journals, author affiliations, study countries, and authors' collaboration, and keyword analysis. The scientific database used is the Scopus database. Microsoft Excel, VOSviewer software, and Biblioshiny for the Bibliometrix R package are the bibliometric tools used in this analysis. A total of 2592 publications were published between 1988 and 2022, with total citations of 22,115. Most of them were original articles (91,7%) and 89.9% were published in traditional journals. The number of total publications exhibited a steady increase over time, whereas total citations showed fluctuations, peaking in 2015 with 1571 citations for publications from that year. The most cited article was authored by Yaseen M. Arabi, receiving 286 citations. Saudi Arabia was the top active country. In addition, the most prolific author was Maha S Zaki, and the most prolific source was the "Egyptian Journal of Radiology and Nuclear Medicine". The most prolific affiliation was Cairo University. The "multiple sclerosis" and "case report" were the most trending keywords. The analysis revealed a significant growth in MRI research inside Arab countries, as shown by an increase in the total number of publications and international collaborations. Despite these developments, the results of this study suggest that there is still room for MRI research in the Arab region to advance. This can be achieved through increasing international collaboration and multidisciplinary work.

Pluripotent Stem Cells as a Preclinical Cellular Model for Studying Hereditary Spastic Paraplegias

Hereditary spastic paraplegias (HSPs) comprise a family of degenerative diseases mostly hitting descending axons of corticospinal neurons. Depending on the gene and mutation involved, the disease could present as a pure form with limb spasticity, or a complex form associated with cerebellar and/or cortical signs such as ataxia, dysarthria, epilepsy, and intellectual disability. The progressive nature of HSPs invariably leads patients to require walking canes or wheelchairs over time. Despite several attempts to ameliorate the life quality of patients that have been tested, current therapeutical approaches are just symptomatic, as no cure is available. Progress in research in the last two decades has identified a vast number of genes involved in HSP etiology, using cellular and animal models generated on purpose. Although unanimously considered invaluable tools for basic research, those systems are rarely predictive for the establishment of a therapeutic approach. The advent of induced pluripotent stem (iPS) cells allowed instead the direct study of morphological and molecular properties of the patient's affected neurons generated upon in vitro differentiation. In this review, we revisited all the present literature recently published regarding the use of iPS cells to differentiate HSP patient-specific neurons. Most studies have defined patient-derived neurons as a reliable model to faithfully mimic HSP in vitro, discovering original findings through immunological and -omics approaches, and providing a platform to screen novel or repurposed drugs. Thereby, one of the biggest hopes of current HSP research regards the use of patient-derived iPS cells to expand basic knowledge on the disease, while simultaneously establishing new therapeutic treatments for both generalized and personalized approaches in daily medical practice.

Liver-X-receptor agonists rescue axonal degeneration in SPG11-deficient neurons via regulating cholesterol trafficking

Spastic paraplegia type 11 (SPG11) is a common autosomal recessive form of hereditary spastic paraplegia (HSP) characterized by the degeneration of cortical motor neuron axons, leading to muscle spasticity and weakness. Impaired lipid trafficking is an emerging pathology in neurodegenerative diseases including SPG11, though its role in axonal degeneration of human SPG11 neurons remains unknown. Here, we established a pluripotent stem cell-based SPG11 model by knocking down the SPG11 gene in human embryonic stem cells (hESCs). These stem cells were then differentiated into cortical projection neurons (PNs), the cell types affected in HSP patients, to examine axonal defects and cholesterol distributions. Our data revealed that SPG11 deficiency led to reduced axonal outgrowth, impaired axonal transport, and accumulated swellings, recapitulating disease-specific phenotypes. In SPG11-knockdown neurons, cholesterol was accumulated in lysosome and reduced in plasma membrane, revealing impairments in cholesterol trafficking. Strikingly, the liver-X-receptor (LXR) agonists restored cholesterol homeostasis, leading to the rescue of subsequent axonal defects in SPG11-deficient cortical PNs. To further determine the implication of impaired cholesterol homeostasis in SPG11, we examined the cholesterol distribution in cortical PNs generated from SPG11 disease-mutation knock-in hESCs, and observed a similar cholesterol trafficking impairment. Moreover, LXR agonists rescued the aberrant cholesterol distribution and mitigated the degeneration of SPG11 disease-mutated neurons. Taken together, our data demonstrate impaired cholesterol trafficking underlying axonal degeneration of SPG11 human neurons, and highlight the therapeutic potential of LXR agonists for SPG11 through restoring cholesterol homeostasis.

Syringomyelia: A New Phenotype of SPG11-Related Hereditary Spastic Paraplegia?

Hereditary spastic paraplegia (HSP) refers to a group of neurodegenerative disorders affecting motor neurons in the central nervous system. HSP type 11 is the most frequent subtype of autosomal recessive HSPs. Caused by pathogenic variants in SPG11, HSP type 11 has a heterogeneous clinical presentation, including various degrees of cognitive dysfunction, spasticity and weakness predominantly in the lower extremities among other features. An 8-year-old boy visited our rehabilitation clinic with a chief complaint of intellectual impairment. Motor weakness was not apparent, but he exhibited a mild limping gait with physical signs of upper motor neuron involvement. Next generation sequencing revealed biallelic pathogenic variants, c.2163dupT and c.5866+1G>A in SPG11, inherited biparentally which was confirmed by Sanger sequencing. Brain imaging study showed thinning of corpus callosum, consistent with previous reports, however whole spine imaging study revealed extensive syringomyelia in his spinal cord, a rare finding in HSP type 11. Further studies are needed to determine whether this finding is a true phenotype associated with HSP type 11.

Upregulation of Heat-Shock Protein (hsp)-27 in a Patient with Heterozygous SPG11 c.1951C>T and SYNJ1 c.2614G>T Mutations Causing Clinical Spastic Paraplegia

We report a 49-year-old patient suffering from spastic paraplegia with a novel heterozygous mutation and analyzed the levels of heat shock proteins (hsp)-27, dopamine (DA), and its metabolites in their cerebrospinal fluid (CSF). The hsp27 protein concentration in the patient's CSF was assayed by an ELISA kit, while DA levels and its metabolites in the CSF, 3,4-dihydroxyphenylacetic acid (DOPAC), Cys-DA, and Cys-DOPA were measured by HPLC. Whole exome sequencing demonstrated SPG-11 c.1951C>T and novel SYNJ1 c.2614G>T mutations, both heterozygous recessive. The patient's DA and DOPAC levels in their CSF were significantly decreased (53.0 ± 6.92 and 473.3 ± 72.19, p < 0.05, respectively) while no differences were found in their Cys-DA. Nonetheless, Cys-DA/DOPAC ratio (0.213 ± 0.024, p < 0.05) and hsp27 levels (1073.0 ± 136.4, p < 0.05) were significantly higher. To the best of our knowledge, the c.2614G>T SYNJ1 mutation has not been previously reported. Our patient does not produce fully functional spatacsin and synaptojanin-1 proteins. In this line, our results showed decreased DA and DOPAC levels in the patient's CSF, indicating loss of DAergic neurons. Many factors have been described as being responsible for the increased cys-DA/DOPAC ratio, such as MAO inhibition and decreased antioxidant activity in DAergic neurons which would increase catecholquinones and consequently cysteinyl-catechols. In conclusion, haploinsufficiency of spatacsin and synaptojanin-1 proteins might be the underlying cause of neurodegeneration produced by protein trafficking defects, DA vesicle trafficking/recycling processes, autophagy dysfunction, and cell death leading to hsp27 upregulation as a cellular mechanism of protection and/or to balance impaired protein trafficking.

Clinical analysis in patients with SPG11 hereditary spastic paraplegia

Background

To analyze the clinical phenotype of hereditary spastic paraplegia (HSP) caused by SPG11 mutations (SPG11-HSP).

Methods

Among the 17 patients with sporadic HSP who performed whole exome sequencing analysis, six were diagnosed with SPG11-HSP. The clinical and radiologic findings and the results of the electrodiagnostic and neuropsychologic tests were reviewed retrospectively.

Results

The median age at onset was 16.5 years (range, 13-38 years). Progressive spastic paraparesis was a core feature, and the median spastic paraplegia rating scale score was 24/52 (range, 16-31 points). Additional major symptoms were pseudobulbar dysarthria, intellectual disability, bladder dysfunction, and being overweight. Minor symptoms included upper limbs rigidity and sensory axonopathy. The median body mass index was 26.2 kg/m² (range, 25.2-32.3 kg/m²). The thin corpus callosum (TCC) was predominant at the rostral body or anterior midbody, and the ears of the lynx sign was seen in all. The follow-up MRI showed the worsening of periventricular white matter (PVWM) signal abnormalities with ventricular widening or the extension of the TCC. Motor evoked potentials (MEP) to the lower limbs showed an absent central motor conduction time (CMCT) in all subjects. The upper limb CMCT was initially absent in three subjects, although it became abnormal in all at the follow-up. The mini-mental state examination median score was 27/30 (range, 26-28) with selective impairment of the attention/calculation domain. The median score of the full-scale intelligence quotient was 48 (range, 42-72) on the Wechsler Adult Intelligence Scale test.

Conclusion

Attention/calculation deficits and being overweight as well as pseudobulbar dysarthria were common additional symptoms in patients with SPG11-HSP. The rostral body and anterior midbody of the corpus callosum were preferentially thinned, especially in the early stage of the disease. The TCC, PVWM signal changes, and MEP abnormality worsened as the disease progressed.

Presence of Rare Variants is Associated with Poorer Survival in Chinese Patients with Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder with phenotypic and genetic heterogeneity. Recent studies have suggested an oligogenic basis of ALS, in which the co-occurrence of two or more genetic variants has additive or synergistic deleterious effects. To assess the contribution of possible oligogenic inheritance, we profiled a panel of 43 relevant genes in 57 sporadic ALS (sALS) patients and eight familial ALS (fALS) patients from five pedigrees in east China. We filtered rare variants using the combination of the Exome Aggregation Consortium, the 1000 Genomes and the HuaBiao Project. We analyzed patients with multiple rare variants in 43 known ALS causative genes and the genotype-phenotype correlation. Overall, we detected 30 rare variants in 16 different genes and found that 16 of the sALS patients and all the fALS patients examined harbored at least one variant in the investigated genes, among which two sALS and four fALS patients harbored two or more variants. Of note, the sALS patients with one or more variants in ALS genes had worse survival than the patients with no variants. Typically, in one fALS pedigree with three variants, the family member with three variants (Superoxide dismutase 1 (SOD1) p.V48A,  Optineurin (OPTN) p.A433V and TANK binding kinase 1 (TBK1) p.R573H) exhibited much more severe disease phenotype than the member carrying one variant (TBK1 p.R573H). Our findings suggest that rare variants could exert a negative prognostic effect, thereby supporting the oligogenic inheritance of ALS.

"Ear of the Lynx" Sign in Hereditary Spastic Paraparesis (HSP) 76

Background

Hereditary Spastic Paraparesis (HSP) are a group of genetically inherited disorders, clinically and genetically heterogenous and characterized by degeneration of corticospinal tracts, manifesting with progressive spasticity and lower limbs weakness. Most HSPs have an autosomal dominant inheritance. "Ear of the Lynx" sign describes the characteristic abnormality in the forceps minor region of the corpus callosum (CC) on MRI brain. These bear a striking resemblance to the ears of a lynx. This finding has previously been described with hereditary spastic paraparesis 11 and 15, both of which are autosomal recessive HSPs.

Cases

We describe this finding in two siblings with novel mutations causing HSP76, an extremely rare autosomal recessive HSP (less than 50 cases described worldwide), which has not been reported previously.

Conclusion

This sign suggests the presence of pathogenic genetic mutations and is likely indicative of autosomal recessive HSPs.

Case report: Novel mutations in the SPG11 gene in a case of autosomal recessive hereditary spastic paraplegia with a thin corpus callosum

A 24-year-old man presented with insidious onset progressive gait disturbance and was finally diagnosed with autosomal recessive hereditary spastic paraplegia. Two novel mutations, including a frameshift mutation (c.5687_5691del) and a non-sense mutation (c.751C>T), were identified in the SPG11 gene of the patient through whole genome sequencing. The frameshift mutation of c.5687_5691del leads to a change in amino acid synthesis beginning with amino acid No. 1896 arginine and terminating at the 8th amino acid after the change (p. Arg1896MetfsTer8). The non-sense mutation (c.751C>T) causes the conversion of codon 251st encoding the amino acid Gln into a stop codon (p. Gln251Ter), resulting in premature termination of peptide synthesis. Although confirmation of compound-heterozygosity could not be performed, our findings enriched the phenotypic spectrum of SPG11 mutations related to hereditary spastic paraplegia.

Neurometabolic Dysfunction in SPG11 Hereditary Spastic Paraplegia

BACKGROUND

Pathogenic variants in SPG11 cause the most common autosomal recessive complicated hereditary spastic paraplegia. Besides the prototypical combination of spastic paraplegia with a thin corpus callosum, obesity has increasingly been reported in this multisystem neurodegenerative disease. However, a detailed analysis of the metabolic state is lacking.

METHODS

In order to characterize metabolic alterations, a cross-sectional analysis was performed comparing SPG11 patients (n = 16) and matched healthy controls (n = 16). We quantified anthropometric parameters, body composition as determined by bioimpedance spectroscopy, and serum metabolic biomarkers, and we measured hypothalamic volume by high-field MRI.

RESULTS

Compared to healthy controls, SPG11 patients exhibited profound changes in body composition, characterized by increased fat tissue index, decreased lean tissue index, and decreased muscle mass. The presence of lymphedema correlated with increased extracellular fluid. The serum levels of the adipokines leptin, resistin, and progranulin were significantly altered in SPG11 while adiponectin and C1q/TNF-related protein 3 (CTRP-3) were unchanged. MRI volumetry revealed a decreased hypothalamic volume in SPG11 patients.

CONCLUSIONS

Body composition, adipokine levels, and hypothalamic volume are altered in SPG11. Our data indicate a link between obesity and hypothalamic neurodegeneration in SPG11 and imply that specific metabolic interventions may prevent obesity despite severely impaired mobility in SPG11.

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.

Cytosolic sequestration of spatacsin by Protein Kinase A and 14-3-3 proteins

Mutations in SPG11, encoding spatacsin, constitute the major cause of autosomal recessive Hereditary Spastic Paraplegia (HSP) with thinning of the corpus callosum. Previous studies showed that spatacsin orchestrates cellular traffic events through the formation of a coat-like complex and its loss of function results in lysosomal and axonal transport impairments. However, the upstream mechanisms that regulate spatacsin trafficking are unknown. Here, using proteomics and CRISPR/Cas9-mediated tagging of endogenous spatacsin, we identified a subset of 14-3-3 proteins as physiological interactors of spatacsin. The interaction is modulated by Protein Kinase A (PKA)-dependent phosphorylation of spatacsin at Ser1955, which initiates spatacsin trafficking from the plasma membrane to the intracellular space. Our study provides novel insight in understanding spatacsin physio-pathological roles with mechanistic dissection of its associated pathways.

Phenotypic and Genetic Heterogeneity of Adult Patients with Hereditary Spastic Paraplegia from Serbia

Hereditary spastic paraplegia (HSP) is among the most genetically diverse of all monogenic diseases. The aim was to analyze the genetic causes of HSP among adult Serbian patients. The study comprised 74 patients from 65 families clinically diagnosed with HSP during a nine-year prospective period. A panel of thirteen genes was analyzed: L1CAM (SPG1), PLP1 (SPG2), ATL1 (SPG3A), SPAST (SPG4), CYP7B1 (SPG5A), SPG7 (SPG7), KIF5A (SPG10), SPG11 (SPG11), ZYFVE26 (SPG15), REEP1 (SPG31), ATP13A2 (SPG78), DYNC1H1, and BICD2 using a next generation sequencing-based technique. A copy number variation (CNV) test for SPAST, SPG7, and SPG11 was also performed. Twenty-three patients from 19 families (29.2%) had conclusive genetic findings, including 75.0% of families with autosomal dominant and 25.0% with autosomal recessive inheritance, and 15.7% of sporadic cases. Twelve families had mutations in the SPAST gene, usually with a pure HSP phenotype. Three sporadic patients had conclusive findings in the SPG11 gene. Two unrelated patients carried a homozygous pathogenic mutation c.233T>A (p.L78*) in SPG7 that is a founder Roma mutation. One patient had a heterozygous de novo variant in the KIF5A gene, and one had a compound heterozygous mutation in the ZYFVE26 gene. The combined genetic yield of our gene panel and CNV analysis for HSP was around 30%. Our findings broaden the knowledge on the genetic epidemiology of HSP, with implications for molecular diagnostics in this region.

Neuroimaging in hereditary spastic paraplegias: from qualitative cues to precision biomarkers

INTRODUCTION

: Hereditary spastic paraplegias (HSP) include a clinically and genetically heterogeneous group of conditions. Novel imaging modalities have been increasingly applied to HSP cohorts which helps to quantitatively evaluate the integrity of specific anatomical structures and develop monitoring markers for both clinical care and future clinical trials.

AREAS COVERED

: Advances in HSP imaging are systematically reviewed with a focus on cohort sizes, imaging modalities, study design, clinical correlates, methodological approaches, and key findings.

EXPERT OPINION

: A wide range of imaging techniques have been recently applied to HSP cohorts. Common shortcomings of existing studies include the evaluation of genetically unconfirmed or admixed cohorts, limited sample sizes, unimodal imaging approaches, lack of postmortem validation, and a limited clinical battery, often exclusively focusing on motor aspects of the condition. A number of innovative methodological approaches have also be identified, such as robust longitudinal study designs, the implementation of multimodal imaging protocols, complementary cognitive assessments, and the comparison of HSP cohorts to MND cohorts. Collaborative multicentre initiatives may overcome sample limitations, and comprehensive clinical profiling with motor, extrapyramidal, cerebellar, and neuropsychological assessments would permit systematic clinico-radiological correlations. Academic achievements in HSP imaging have the potential to be developed into viable clinical applications to expedite the diagnosis and monitor disease progression.

An integrated modelling methodology for estimating global incidence and prevalence of hereditary spastic paraplegia subtypes SPG4, SPG7, SPG11, and SPG15

Background

Hereditary spastic paraplegias (HSPs) are progressively debilitating neurodegenerative disorders that follow heterogenous patterns of Mendelian inheritance. Available epidemiological evidence provides limited incidence and prevalence data, especially at the genetic subtype level, preventing a realistic estimation of the true social burden of the disease. The objectives of this study were to (1) review the literature on epidemiology of HSPs; and (2) develop an epidemiological model of the prevalence of HSP, focusing on four common HSP genetic subtypes at the country and region-level.

Methods

A model was constructed estimating the incidence at birth, survival, and prevalence of four genetic subtypes of HSP based on the most appropriate published literature. The key model parameters were assessed by HSP clinical experts, who provided feedback on the validity of assumptions. A model was then finalized and validated through comparison of outputs against available evidence. The global, regional, and national prevalence and patient pool were calculated per geographic region and per genetic subtype.

Results

The HSP global prevalence was estimated to be 3.6 per 100,000 for all HSP forms, whilst the estimated global prevalence per genetic subtype was 0.90 (SPG4), 0.22 (SPG7), 0.34 (SPG11), and 0.13 (SPG15), respectively. This equates to an estimated 3365 (SPG4) and 872 (SPG11) symptomatic patients, respectively, in the USA.

Conclusions

This is the first epidemiological model of HSP prevalence at the genetic subtype-level reported at multiple geographic levels. This study offers additional data to better capture the burden of illness due to mutations in common genes causing HSP, that can inform public health policy and healthcare service planning, especially in regions with higher estimated prevalence of HSP.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-022-02595-4.

A review of the genetic spectrum of hereditary spastic paraplegias, inherited neuropathies and spinal muscular atrophies in Africans

Background

Genetic investigations of inherited neuromuscular disorders in Africans, have been neglected. We aimed to summarise the published data and comment on the genetic evidence related to inherited neuropathies (Charcot-Marie-Tooth disease (CMT)), hereditary spastic paraplegias (HSP) and spinal muscular atrophy (SMA) in Africans.

Methods

PubMed was searched for relevant articles and manual checking of references and review publications were performed for African-ancestry participants with relevant phenotypes and identified genetic variants. For each case report we extracted phenotype information, inheritance pattern, variant segregation and variant frequency in population controls (including up to date frequencies from the gnomAD database).

Results

For HSP, 23 reports were found spanning the years 2000–2019 of which 19 related to North Africans, with high consanguinity, and six included sub-Saharan Africans. For CMT, 19 reports spanning years 2002–2021, of which 16 related to North Africans and 3 to sub-Saharan Africans. Most genetic variants had not been previously reported. There were 12 reports spanning years 1999–2020 related to SMN1-SMA caused by homozygous exon 7 ± 8 deletion. Interestingly, the population frequency of heterozygous SMN1-exon 7 deletion mutations appeared 2 × lower in Africans compared to Europeans, in addition to differences in the architecture of the SMN2 locus which may impact SMN1-SMA prognosis.

Conclusions

Overall, genetic data on inherited neuromuscular diseases in sub-Saharan Africa, are sparse. If African patients with rare neuromuscular diseases are to benefit from the expansion in genomics capabilities and therapeutic advancements, then it is critical to document the mutational spectrum of inherited neuromuscular disease in Africa.

Highlights

Review of genetic variants reported in hereditary spastic paraplegia in Africans

Review of genetic variants reported in genetic neuropathies in Africans

Review of genetic underpinnings of spinal muscular atrophies in Africans

Assessment of pathogenic evidence for candidate variants

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02280-2.

Molecular Characterization of Portuguese Patients with Hereditary Cerebellar Ataxia

Hereditary cerebellar ataxia (HCA) comprises a clinical and genetic heterogeneous group of neurodegenerative disorders characterized by incoordination of movement, speech, and unsteady gait. In this study, we performed whole-exome sequencing (WES) in 19 families with HCA and presumed autosomal recessive (AR) inheritance, to identify the causal genes. A phenotypic classification was performed, considering the main clinical syndromes: spastic ataxia, ataxia and neuropathy, ataxia and oculomotor apraxia (AOA), ataxia and dystonia, and ataxia with cognitive impairment. The most frequent causal genes were associated with spastic ataxia (SACS and KIF1C) and with ataxia and neuropathy or AOA (PNKP). We also identified three families with autosomal dominant (AD) forms arising from de novo variants in KIF1A, CACNA1A, or ATP1A3, reinforcing the importance of differential diagnosis (AR vs. AD forms) in families with only one affected member. Moreover, 10 novel causal-variants were identified, and the detrimental effect of two splice-site variants confirmed through functional assays. Finally, by reviewing the molecular mechanisms, we speculated that regulation of cytoskeleton function might be impaired in spastic ataxia, whereas DNA repair is clearly associated with AOA. In conclusion, our study provided a genetic diagnosis for HCA families and proposed common molecular pathways underlying cerebellar neurodegeneration.

Inhibiting mitochondrial fission rescues degeneration in hereditary spastic paraplegia neurons

Hereditary spastic paraplegias (HSPs) are characterized by lower limb spasticity resulting from degeneration of long corticospinal axons. SPG11 is one of the most common autosomal recessive HSPs, and the SPG11 protein spatacsin forms a complex with the SPG15 protein spastizin and heterotetrameric AP5 adaptor protein complex, which includes the SPG48 protein AP5Z1. Using the integration-free episomal method, we established SPG11 patient-specific induced pluripotent stem cells (iPSCs) from patient fibroblasts. We differentiated SPG11 iPSCs, as well as SPG48 iPSCs previously established, into cortical projection neurons (PNs) and examined protective effects by targeting mitochondrial dynamics using P110, a peptide that selectively inhibits mitochondrial fission GTPase Drp1. P110 treatment mitigates mitochondrial fragmentation, improves mitochondrial motility, and restores mitochondrial health and ATP levels in SPG11 and SPG48 neurons. Neurofilament (NF) aggregations are increased in SPG11 and SPG48 axons, and these are also suppressed by P110. Similarly, P110 mitigates NF disruption in both SPG11 and SPG48 knockdown cortical PNs, confirming the contribution of HSP gene deficiency to subsequent NF and mitochondrial defects. Strikingly, NF aggregations in SPG11 and SPG48 deficient neurons double stain with ubiquitin and autophagy related proteins, resembling the pathological hallmark observed in SPG11 autopsy brain sections. To confirm the cause-effect relationship between the SPG11 mutations and disease phenotypes, we knocked-in SPG11 disease mutations to human embryonic stem cells (hESCs) and differentiated these stem cells into cortical PNs. Reduced ATP levels and accumulated NF aggregations along axons are observed, and both are mitigated by P110. Furthermore, rescue experiment with expression of wildtype SPG11 in cortical PNs derived from both SPG11 patient iPSCs and SPG11 disease mutation knock-in hESCs leads to rescue of mitochondrial dysfunction and NF aggregations in these SPG11 neurons. Finally, in SPG11 and SPG48 long-term cultures, increased release of phosphoNF-H, a biomarker for nerve degeneration, is significantly reduced by inhibiting mitochondrial fission pharmacologically using P110 and genetically using Drp1 shRNA. Taken together, our results demonstrate that impaired mitochondrial dynamics underlie both cytoskeletal disorganization and axonal degeneration in SPG11 and SPG48 neurons, highlighting the importance of targeting these pathologies therapeutically.

Diagnosis of Genetic White Matter Disorders by Singleton Whole-Exome and Genome Sequencing Using Interactome-Driven Prioritization

Background and Objectives

Genetic white matter disorders (GWMD) are of heterogeneous origin, with >100 causal genes identified to date. Classic targeted approaches achieve a molecular diagnosis in only half of all patients. We aimed to determine the clinical utility of singleton whole-exome sequencing and whole-genome sequencing (sWES-WGS) interpreted with a phenotype- and interactome-driven prioritization algorithm to diagnose GWMD while identifying novel phenotypes and candidate genes.

Methods

A case series of patients of all ages with undiagnosed GWMD despite extensive standard-of-care paraclinical studies were recruited between April 2017 and December 2019 in a collaborative study at the Bellvitge Biomedical Research Institute (IDIBELL) and neurology units of tertiary Spanish hospitals. We ran sWES and WGS and applied our interactome-prioritization algorithm based on the network expansion of a seed group of GWMD-related genes derived from the Human Phenotype Ontology terms of each patient.

Results

We evaluated 126 patients (101 children and 25 adults) with ages ranging from 1 month to 74 years. We obtained a first molecular diagnosis by singleton WES in 59% of cases, which increased to 68% after annual reanalysis, and reached 72% after WGS was performed in 16 of the remaining negative cases. We identified variants in 57 different genes among 91 diagnosed cases, with the most frequent being RNASEH2B, EIF2B5, POLR3A, and PLP1, and a dual diagnosis underlying complex phenotypes in 6 families, underscoring the importance of genomic analysis to solve these cases. We discovered 9 candidate genes causing novel diseases and propose additional putative novel candidate genes for yet-to-be discovered GWMD.

Discussion

Our strategy enables a high diagnostic yield and is a good alternative to trio WES/WGS for GWMD. It shortens the time to diagnosis compared to the classical targeted approach, thus optimizing appropriate management. Furthermore, the interactome-driven prioritization pipeline enables the discovery of novel disease-causing genes and phenotypes, and predicts novel putative candidate genes, shedding light on etiopathogenic mechanisms that are pivotal for myelin generation and maintenance.

An autopsied case report of spastic paraplegia with thin corpus callosum carrying a novel mutation in the SPG11 gene: widespread degeneration with eosinophilic inclusions

Background

The detailed neuropathological features of patients with autosomal recessive hereditary spastic paraplegia with a thin corpus callosum (TCC) and SPG11 mutations are poorly understood, as only a few autopsies have been reported. Herein, we describe the clinicopathological findings of a patient with this disease who received long-term care at our medical facility.

Case presentation

A Japanese man exhibited a mild developmental delay in early childhood and intellectual disability, followed by the appearance of a spastic gait by age 13. At the age of 25 years, he became bedridden and needed a ventilator. Genetic analysis revealed a homozygous splice site variant in the SPG11 gene (c. 4162–2A > G) after the provision of genetic counselling and acquisition of informed consent from his parents. He died of pneumonia at the age of 44. His brain weighed 967 g and was characterized by a TCC, and his spinal cord was flattened. Microscopically, degeneration was observed in the posterior spinocerebellar tract, the gracile fasciculus, and the posterior column in addition to the corticospinal tract. Marked neuronal loss and gliosis were observed in the anterior horn, Clarke’s column, and hypoglossal and facial nuclei. Various types of neurons, in addition to motor neurons, showed coarse eosinophilic granules that were immunoreactive for p62. The loss of pigmented neurons with gliosis was apparent in both the substantia nigra and locus coeruleus. Lateral geniculate body degeneration was a characteristic feature of this patient. Furthermore, peripheral Lewy body-related α-synucleinopathy and scattered α-synuclein–immunoreactive neurites in the locus coeruleus and reticular formation of the brainstem were observed.

Conclusions

In patients with hereditary spastic paraplegia with SPG11 mutations, a variety of clinical phenotypes develop due to widespread lesions containing p62-immunoreactive neuronal cytoplasmic inclusions. We herein report the lateral geniculate body as another degenerative site related to SPG11-related pathologies that should be studied in future investigations.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-021-02514-z.

Mitochondrial enzyme GPT2 regulates metabolic mechanisms required for neuron growth and motor function in vivo

The metabolic needs for postnatal growth of the human nervous system are vast. Recessive loss-of-function mutations in the mitochondrial enzyme glutamate pyruvate transaminase 2 (GPT2) in humans cause postnatal undergrowth of brain, and cognitive and motor disability. We demonstrate that GPT2 governs critical metabolic mechanisms in neurons required for neuronal growth and survival. These metabolic processes include neuronal alanine synthesis and anaplerosis, the replenishment of tricarboxylic acid (TCA) cycle intermediates. We performed metabolomics across postnatal development in Gpt2-null mouse brain to identify the trajectory of dysregulated metabolic pathways: alterations in alanine occur earliest; followed by reduced TCA cycle intermediates and reduced pyruvate; followed by elevations in glycolytic intermediates and amino acids. Neuron-specific deletion of GPT2 in mice is sufficient to cause motor abnormalities and death pre-weaning, a phenotype identical to the germline Gpt2-null mouse. Alanine biosynthesis is profoundly impeded in Gpt2-null neurons. Exogenous alanine is necessary for Gpt2-null neuronal survival in vitro, but is not needed for Gpt2-null astrocytes. Dietary alanine supplementation in Gpt2-null mice enhances animal survival, and improves the metabolic profile of Gpt2-null brain, but does not alone appear to correct motor function. In surviving Gpt2-null animals, we observe smaller upper and lower motor neurons in vivo. We also observe selective death of lower motor neurons in vivo with worsening motor behavior with age. In conclusion, these studies of the pathophysiology of GPT2 Deficiency have identified metabolic mechanisms required for neuronal growth and that potentially underlie selective neuronal vulnerabilities in motor neurons.

Transactivation response DNA-binding protein of 43 kDa proteinopathy and lysosomal abnormalities in spastic paraplegia type 11

Spastic paraplegia type 11 (SPG11) is the most common autosomal recessive hereditary spastic paraplegia with thinning of the corpus callosum. Spatacsin, a protein encoded by the SPG11 gene, is associated with autophagy. SPG11 patients show spastic paraplegia, intellectual disability, dementia, and parkinsonism. A previous neuropathological analysis of SPG11 cases reported neurodegeneration mimicking amyotrophic lateral sclerosis without transactivation response DNA-binding protein of 43 kDa (TDP-43) deposits and unique sequestosome 1 (SQSTM1)-positive neuronal inclusions. We performed a neuropathological examination of two Japanese patients with complicated spastic paraplegia with thinning of the corpus callosum from different families, and one was genetically diagnosed as having SPG11. Both cases showed diffuse atrophy of the brain and spinal cord. Depigmentation of the substantia nigra was also observed. Immunohistochemistry revealed widespread distribution of areas showing TDP-43 aggregation in the central nervous system. The TDP-43 deposits in the thalamus and substantia nigra especially resembled skein-like inclusions. Unique SQSTM1-positive neuronal inclusions, as previously reported, were widespread in the whole central nervous system as well as the dorsal root ganglia. Double-labeling immunofluorescence of the dorsal root ganglia revealed that the unique, large SQSTM1-positive cytoplasmic inclusions of the ganglion cells were labeled with lysosome-associated membrane protein 1 and lysosome-associated membrane protein 2. This is the first report showing TDP-43 pathology in SPG11. The common neuropathological findings of TDP-43-positive inclusions in both the cases imply a causal connection between the TDP-43 proteinopathy and autophagy dysfunction in SPG11.

Neuroimaging patterns in paediatric onset hereditary spastic paraplegias

Hereditary spastic paraplegias (HSPs) are a clinically and genetically heterogeneous group of neurodegenerative disorders characterized by progressive spasticity and weakness of the lower limbs with a notable phenotypic variation and an autosomal recessive (AR), autosomal dominant (AD), and X-linked inheritance pattern. The recent clinical use of next generation sequencing methods has facilitated the diagnostic approach to HSPs, but the diagnosis remains quite challenging considering its wide clinical and genetic heterogeneity. In this scenario, magnetic resonance imaging (MRI) emerges as a valuable tool in helping to exclude mimicking disorders and to guide genetic testing. The aim of this study is to investigate the presence of possible patterns of morphostructural MRI findings that may provide relevant clues for a specific genetic HSP subtype. In our cohort, for example, white matter abnormalities were the most common finding followed by the thinning of the corpus callosum, which, interestingly, presented different thinning characteristics depending on the HSP subtype.

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.

Hereditary spastic paraplegia type 11: Clinicogenetic lessons from 339 patients

Hereditary spastic paraplegia type 11 (SPG11) is the most common subtype of autosomal recessive hereditary spastic paraplegia (HSP), to date, there are more than 181 different KIAA1840 gene mutations detected, and yet the genetic landscape of SPG11 is far from complete. To find the clinical and genetic characteristics of SPG11, we performed a reanalysis of the clinical features and genotype-phenotype correlations in all reported studies exhibiting SPG11 mutations. A total of 339 patients were collected, their mean age at onset was 13.10 ± 3.65 years, with initial symptoms like gait disturbance (107/195, 54.87%) and mental retardation (47/195, 24.10%). Cognitive decline (228/270, 84.44%) was the most common complex manifestation stepped by dysarthria (134/195, 68.72%), neuropathy (112/177, 63.28%), amyatrophy, sphincter disturbance (60/130, 46.15%) and ataxia (90/194, 46.39%). The most common brain MRI abnormality is thinning of the corpus callosum (TCC) (173/190, 91.05%), followed by periventricular white matter changes (130/158, 82.28%), cerebral or cerebellar cortical atrophy (55/107, 51.40%). The mutational spectrum associated with KIAA1840 gene is wide, and frameshift mutations are the most common type followed by nonsense mutations. Our reanalysis demonstrated that SPG11 exhibited significant clinical and genetic heterogeneity, and no clear genotype-phenotype correlation was observed. There is no mutational hot spot in the KIAA1840 gene, which emphasizes the need to analyse the whole gene in clinical practice. In addition to conventional genetic testing methods, further mRNA analysis should be conducted on some cases to yield a definitive diagnosis.

Mild cognitive impairment in novel SPG11 mutation-related sporadic hereditary spastic paraplegia with thin corpus callosum: case series

BACKGROUND

SPG11 mutation-related autosomal recessive hereditary spastic paraplegia with thin corpus callosum (HSP-TCC) is the most common cause in complicated forms of HSP, usually presenting comprehensive mental retardation on early-onset stage preceding spastic paraplegias in childhood. However, there are many instances of sporadic late-onset HSP-TCC cases with a negative family history, and potential mild cognitive deficits in multiple domains may be easily neglected and inaccurately described.

METHODS

In this study, we performed next generation sequencing in four sporadic late-onset patients with HSP-TCC, and combined Mini-Mental State Examination (MMSE) and Montreal Cognitive Assessment (MoCA) to evaluate cognition of the patients.

RESULTS

By evolutionary conservation and structural modeling analysis, we have revealed 4 novel pathogenic SPG11 mutations, and firstly confirmed mild cognitive impairment (MCI) with normal MMSE scores (≥27) and decreased MoCA scores (< 26) in these SPG11 mutation-related HSP-TCC patients, predominantly presenting impairment of executive function, delayed recall, abstraction and language.

CONCLUSIONS

The results expand the mutational spectrum of SPG11-associated HSP-TCC from sporadic cases, and confirm MCI with combination of decreased MoCA and normal MMSE assessment, suggesting that clinicians should consider doing a MoCA to detect MCI in patients with HSP, particularly those with HSP-TCC.

Janus-faced spatacsin (SPG11): involvement in neurodevelopment and multisystem neurodegeneration

Hereditary spastic paraplegia (HSP) is a heterogeneous group of rare motor neuron disorders characterized by progressive weakness and spasticity of the lower limbs. HSP type 11 (SPG11-HSP) is linked to pathogenic variants in the SPG11 gene and it represents the most frequent form of complex autosomal recessive HSP. The majority of SPG11-HSP patients exhibit additional neurological symptoms such as cognitive decline, thin corpus callosum, and peripheral neuropathy. Yet, the mechanisms of SPG11-linked spectrum diseases are largely unknown. Recent findings indicate that spatacsin, the 280 kDa protein encoded by SPG11, may impact the autophagy-lysosomal machinery. In this update, we summarize the current knowledge of SPG11-HSP. In addition to clinical symptoms and differential diagnosis, our work aims to link the different clinical manifestations with the respective structural abnormalities and cellular in vitro phenotypes. Moreover, we describe the impact of localization and function of spatacsin in different neuronal systems. Ultimately, we propose a model in which spatacsin bridges between neurodevelopmental and neurodegenerative phenotypes of SPG11-linked disorders.

Homozygous frameshift mutation of SPG11 as a cause of progressive flaccid paralysis, ataxia and dysphagia

Hereditary spastic paraplegias (HSP) are phenotypically and genotypically diverse. We describe a unique case of autosomal recessive HSP (ARHSP) diagnosed at age 44 in a patient previously described as having "spinal muscular ataxia" [sic]. Predominant lower motor neuron findings and lack of clinical spasticity reduced suspicion for HSP in early life. The identified SPG11 mutation was novel and the presentation was atypical for HSP in general and SPG11 disease specifically.

Clinical and molecular characterization of hereditary spastic paraplegia in a spanish southern region

Spastic paraplegia (SPG) is a syndrome characterised by lower limb spasticity, occurring alone or in association with other neurological manifestations. Despite of the new molecular technologies, many patients remain yet undiagnosed. The purpose of this study was to describe the clinical presentation and molecular characteristics of a cohort of 27 patients from 18 different families with SPG in the south of Spain. We used a targeted next-generation sequencing (NGS) approach to study a proband from each family. Variants in SPG11 gene were the most common cause of SPG in our area. We made a genetic diagnosis in 52% of cases, identified 3 novel variants and reclassified one uncertain variant in SPG11 gene as pathogenic variant. We identified a patient with two truncanting mutation in SPG11 gene and late onset disease and report another missense mutation outside of motor domain of KIF1A gene in a family with pure SPG. Our study contributes to enhance the scientific knowledge of SPG. It is important to note the large group of cases (48%) that were not genetically diagnosed in our cohort. Therefore NGS approach is an efficient diagnostic tool, but it still large the number of non-diagnosed subjects, suggesting further genetic heterogeneity.

Defining the clinical, molecular and imaging spectrum of adaptor protein complex 4-associated hereditary spastic paraplegia

Bi-allelic loss-of-function variants in genes that encode subunits of the adaptor protein complex 4 (AP-4) lead to prototypical yet poorly understood forms of childhood-onset and complex hereditary spastic paraplegia: SPG47 (AP4B1), SPG50 (AP4M1), SPG51 (AP4E1) and SPG52 (AP4S1). Here, we report a detailed cross-sectional analysis of clinical, imaging and molecular data of 156 patients from 101 families. Enrolled patients were of diverse ethnic backgrounds and covered a wide age range (1.0-49.3 years). While the mean age at symptom onset was 0.8 ± 0.6 years [standard deviation (SD), range 0.2-5.0], the mean age at diagnosis was 10.2 ± 8.5 years (SD, range 0.1-46.3). We define a set of core features: early-onset developmental delay with delayed motor milestones and significant speech delay (50% non-verbal); intellectual disability in the moderate to severe range; mild hypotonia in infancy followed by spastic diplegia (mean age: 8.4 ± 5.1 years, SD) and later tetraplegia (mean age: 16.1 ± 9.8 years, SD); postnatal microcephaly (83%); foot deformities (69%); and epilepsy (66%) that is intractable in a subset. At last follow-up, 36% ambulated with assistance (mean age: 8.9 ± 6.4 years, SD) and 54% were wheelchair-dependent (mean age: 13.4 ± 9.8 years, SD). Episodes of stereotypic laughing, possibly consistent with a pseudobulbar affect, were found in 56% of patients. Key features on neuroimaging include a thin corpus callosum (90%), ventriculomegaly (65%) often with colpocephaly, and periventricular white-matter signal abnormalities (68%). Iron deposition and polymicrogyria were found in a subset of patients. AP4B1-associated SPG47 and AP4M1-associated SPG50 accounted for the majority of cases. About two-thirds of patients were born to consanguineous parents, and 82% carried homozygous variants. Over 70 unique variants were present, the majority of which are frameshift or nonsense mutations. To track disease progression across the age spectrum, we defined the relationship between disease severity as measured by several rating scales and disease duration. We found that the presence of epilepsy, which manifested before the age of 3 years in the majority of patients, was associated with worse motor outcomes. Exploring genotype-phenotype correlations, we found that disease severity and major phenotypes were equally distributed among the four subtypes, establishing that SPG47, SPG50, SPG51 and SPG52 share a common phenotype, an 'AP-4 deficiency syndrome'. By delineating the core clinical, imaging, and molecular features of AP-4-associated hereditary spastic paraplegia across the age spectrum our results will facilitate early diagnosis, enable counselling and anticipatory guidance of affected families and help define endpoints for future interventional trials.

Clinical and genetic update of hereditary spastic paraparesis

Hereditary spastic paraparesis is a group of inherited neurological diseases characterized by underlying wide genetic heterogeneity. It should be suspected if there is a positive familial history, a common genetic alteration (i.e. SPG4, the most overall frequent form), or association with other signs, such as cerebellar ataxia (i.e. SPG7), early cognitive impairment or even cognitive deficit (i.e. SPG11), or peripheral neuropathy (i.e. SACS). The natural history is known for certain genetic subgroups, with genotype-phenotype correlations partially explaining childhood or late onset. However, the search for genetic modifying factors, in addition to the causal pathogenic variant or environmental influencers, is still needed. Novel approaches to provide etiological treatment are in the pipeline for SPG11. Symptomatic treatments are available but would benefit from randomized controlled trials.

Genetic mutation analysis of hereditary spastic paraplegia: A retrospective study

Hereditary spastic paraplegias are heterogeneous disorders with diversified clinical manifestations, and genetic testing is important for the diagnosis and typing of hereditary spastic paraplegias.Gene panel sequencing containing 55 hereditary spastic paraplegias-related genes was performed to screen the pathogenic genes for hereditary spastic paraplegias. Sanger sequencing was adopted to validate if the family member carried the same pathogenic gene as the proband.Fifteen out of 53 patients carried mutation(s) in the screened hereditary spastic paraplegias-related genes. Among the 23 identified mutations, only one mutation had been previously reported as a pathogenic mutation. In the pedigree of case 6, the proband, his mother and uncle all carried the same novel deletion mutation (c.1459delA) at SPAST gene. Based on the pedigree, the disease was inherited in an AD pattern. In the pedigree of case 53, the family disease may be in an X-linked recessive inheritance pattern. The proband (case 53) carried two novel mutations in ALT1 gene and L1CAM gene (c.2511C>A), respectively. The L1CAM gene is the causative gene for the SPG1 X-linked recessive-hereditary spastic paraplegias.Our data confirm the genetic heterogeneity of hereditary spastic paraplegias, and SPG4/SPAST were the most frequent forms. The pathogenicity of the novel mutations is worth to be further investigated.

Description of combined ARHSP/JALS phenotype in some patients with SPG11 mutations

Background

SPG11 mutations can cause autosomal recessive hereditary spastic paraplegia (ARHSP) and juvenile amyotrophic lateral sclerosis (JALS). Because these diseases share some clinical presentations and both can be caused by SPG11 mutations, it was considered that definitive diagnosis may not be straight forward.

Methods

The DNAs of referred ARHSP and JALS patients were exome sequenced. Clinical data of patients with SPG11 mutations were gathered by interviews and neurological examinations including electrodiagnosis (EDX) and magnetic resonance imaging (MRI).

Results

Eight probands with SPG11 mutations were identified. Two mutations are novel. Among seven Iranian probands, six carried the p.Glu1026Argfs*4‐causing mutation. All eight patients had features known to be present in both ARHSP and JALS. Additionally and surprisingly, presence of both thin corpus callosum (TCC) on MRI and motor neuronopathy were also observed in seven patients. These presentations are, respectively, key suggestive features of ARHSP and JALS.

Conclusion

We suggest that rather than ARHSP or JALS, combined ARHSP/JALS is the appropriate description of seven patients studied. Criteria for ARHSP, JALS, and combined ARHSP/JALS designations among patients with SPG11 mutations are suggested. The importance of performing both EDX and MRI is emphasized. Initial screening for p.Glu1026Argfs*4 may facilitate SPG11 screenings in Iranian patients.

Burden of Rare Variants in ALS and Axonal Hereditary Neuropathy Genes Influence Survival in ALS: Insights from a Next Generation Sequencing Study of an Italian ALS Cohort

Although the genetic architecture of amyotrophic lateral sclerosis (ALS) is incompletely understood, recent findings suggest a complex model of inheritance in ALS, which is consistent with a multistep pathogenetic process. Therefore, the aim of our work is to further explore the architecture of ALS using targeted next generation sequencing (NGS) analysis, enriched in motor neuron diseases (MND)-associated genes which are also implicated in axonal hereditary motor neuropathy (HMN), in order to investigate if disease expression, including the progression rate, could be influenced by the combination of multiple rare gene variants. We analyzed 29 genes in an Italian cohort of 83 patients with both familial and sporadic ALS. Overall, we detected 43 rare variants in 17 different genes and found that 43.4% of the ALS patients harbored a variant in at least one of the investigated genes. Of note, 27.9% of the variants were identified in other MND- and HMN-associated genes. Moreover, multiple gene variants were identified in 17% of the patients. The burden of rare variants is associated with reduced survival and with the time to reach King stage 4, i.e., the time to reach the need for percutaneous endoscopic gastrostomy (PEG) positioning or non-invasive mechanical ventilation (NIMV) initiation, independently of known negative prognostic factors. Our data contribute to a better understanding of the molecular basis of ALS supporting the hypothesis that rare variant burden could play a role in the multistep model of disease and could exert a negative prognostic effect. Moreover, we further extend the genetic landscape of ALS to other MND-associated genes traditionally implicated in degenerative diseases of peripheral axons, such as HMN and CMT2.

First-line exome sequencing in Palestinian and Israeli Arabs with neurological disorders is efficient and facilitates disease gene discovery

A high rate of consanguinity leads to a high prevalence of autosomal recessive disorders in inbred populations. One example of inbred populations is the Arab communities in Israel and the Palestinian Authority. In the Palestinian Authority in particular, due to limited access to specialized medical care, most patients do not receive a genetic diagnosis and can therefore neither receive genetic counseling nor possibly specific treatment. We used whole-exome sequencing as a first-line diagnostic tool in 83 Palestinian and Israeli Arab families with suspected neurogenetic disorders and were able to establish a probable genetic diagnosis in 51% of the families (42 families). Pathogenic, likely pathogenic or highly suggestive candidate variants were found in the following genes extending and refining the mutational and phenotypic spectrum of these rare disorders: ACO2, ADAT3, ALS2, AMPD2, APTX, B4GALNT1, CAPN1, CLCN1, CNTNAP1, DNAJC6, GAMT, GPT2, KCNQ2, KIF11, LCA5, MCOLN1, MECP2, MFN2, MTMR2, NT5C2, NTRK1, PEX1, POLR3A, PRICKLE1, PRKN, PRX, SCAPER, SEPSECS, SGCG, SLC25A15, SPG11, SYNJ1, TMCO1, and TSEN54. Further, this cohort has proven to be ideal for prioritization of new disease genes. Two separately published candidate genes (WWOX and PAX7) were identified in this study. Analyzing the runs of homozygosity (ROHs) derived from the Exome sequencing data as a marker for the rate of inbreeding, revealed significantly longer ROHs in the included families compared with a German control cohort. The total length of ROHs correlated with the detection rate of recessive disease-causing variants. Identification of the disease-causing gene led to new therapeutic options in four families.

Lipids in the Physiopathology of Hereditary Spastic Paraplegias

Hereditary spastic paraplegias (HSP) are a group of neurodegenerative diseases sharing spasticity in lower limbs as common symptom. There is a large clinical variability in the presentation of patients, partly underlined by the large genetic heterogeneity, with more than 60 genes responsible for HSP. Despite this large heterogeneity, the proteins with known function are supposed to be involved in a limited number of cellular compartments such as shaping of the endoplasmic reticulum or endolysosomal function. Yet, it is difficult to understand why alteration of such different cellular compartments can lead to degeneration of the axons of cortical motor neurons. A common feature that has emerged over the last decade is the alteration of lipid metabolism in this group of pathologies. This was first revealed by the identification of mutations in genes encoding proteins that have or are supposed to have enzymatic activities on lipid substrates. However, it also appears that mutations in genes affecting endoplasmic reticulum, mitochondria, or endolysosome function can lead to changes in lipid distribution or metabolism. The aim of this review is to discuss the role of lipid metabolism alterations in the physiopathology of HSP, to evaluate how such alterations contribute to neurodegenerative phenotypes, and to understand how this knowledge can help develop therapeutic strategy for HSP.