Novel mutations in SPG11 cause hereditary spastic paraplegia associated with early-onset levodopa-responsive Parkinsonism

GBA-associated Parkinson's disease in Hungary: clinical features and genetic insights

INTRODUCTION

Parkinson's disease (PD) has a complex genetic background involving both rare and common genetic variants. Although a small percentage of cases show a clear Mendelian inheritance pattern, it is much more relevant to identify patients who present with a complex genetic profile of risk variants with different severity. The ß-glucocerebrosidase coding gene (GBA1) is recognized as the most frequent genetic risk factor for PD and Lewy body dementia, irrespective of reduction of the enzyme activity due to genetic variants.

METHODS

In a selected cohort of 190 Hungarian patients with clinical signs of PD and suspected genetic risk, we performed the genetic testing of the GBA1 gene. As other genetic hits can modify clinical features, we also screened for additional rare variants in other neurodegenerative genes and assessed the APOE-ε genotype of the patients.

RESULTS

In our cohort, we identified 29 GBA1 rare variant (RV) carriers. Out of the six different detected RVs, the highly debated E365K and T408M variants are composed of the majority of them (22 out of 32). Three patients carried two GBA1 variants, and an additional three patients carried rare variants in other neurodegenerative genes (SMPD1, SPG11, and SNCA). We did not observe differences in age at onset or other clinical features of the patients carrying two GBA1 variants or patients carrying heterozygous APOE-ε4 allele.

CONCLUSION

We need further studies to better understand the drivers of clinical differences in these patients, as this could have important therapeutic implications.

Movement disorders in hereditary spastic paraplegias

BACKGROUND

 Hereditary or familial spastic paraplegias (SPG) comprise a group of genetically and phenotypically heterogeneous diseases characterized by progressive degeneration of the corticospinal tracts. The complicated forms evolve with other various neurological signs and symptoms, including movement disorders and ataxia.

OBJECTIVE

 To summarize the clinical descriptions of SPG that manifest with movement disorders or ataxias to assist the clinician in the task of diagnosing these diseases.

METHODS

 We conducted a narrative review of the literature, including case reports, case series, review articles and observational studies published in English until December 2022.

RESULTS

 Juvenile or early-onset parkinsonism with variable levodopa-responsiveness have been reported, mainly in SPG7 and SPG11. Dystonia can be observed in patients with SPG7, SPG11, SPG22, SPG26, SPG35, SPG48, SPG49, SPG58, SPG64 and SPG76. Tremor is not a frequent finding in patients with SPG, but it is described in different types of SPG, including SPG7, SPG9, SPG11, SPG15, and SPG76. Myoclonus is rarely described in SPG, affecting patients with SPG4, SPG7, SPG35, SPG48, and SPOAN (spastic paraplegia, optic atrophy, and neuropathy). SPG4, SPG6, SPG10, SPG27, SPG30 and SPG31 may rarely present with ataxia with cerebellar atrophy. And autosomal recessive SPG such as SPG7 and SPG11 can also present with ataxia.

CONCLUSION

 Patients with SPG may present with different forms of movement disorders such as parkinsonism, dystonia, tremor, myoclonus and ataxia. The specific movement disorder in the clinical manifestation of a patient with SPG may be a clinical clue for the diagnosis.

Movement disorders in hereditary spastic paraplegia (HSP): a systematic review and individual participant data meta-analysis

BACKGROUND

Hereditary spastic paraplegia (HSP) is a rare genetic disorder associated with mutations in > 80 loci designated SPG (SPastic parapleGia). The phenotypic spectrum of HSP can extend to include other neurologic features, including movement disorders. Our aim was to investigate genotype-phenotype associations in HSP with a focus on movement disorders.

METHODS

We performed a systematic review and individual participant data (IPD)-level meta-analysis by retrieving publications from Medline/EMBASE/Web of Science on HSP with a SPG genotype. Studies were included only if individual-level information was accessible and at least one patient with a movement disorder was reported for that genotype. Out of 21,957 hits, 192 manuscripts with a total of 1413 HSP cases were eligible. Data were compared between two HSP groups: manifested with (HSP-MD, n = 767) or without (HSP-nMD, n = 646) a movement disorder.

RESULTS

The HSP-MD group had an older age of onset (20.5 ± 16.0 vs. 17.1 ± 14.2 yr, p < 0.001) and less frequent autosomal dominant inheritance (7.6% vs. 30.1%, p < 0.001) compared to HSP-nMD. SPG7 (31.2%) and SPG11 (23.8%) were the most frequent genotypes in the HSP-MD group. HSP-MD with SPG7 had higher frequency of later onset during adulthood (82.9% vs. 8.5%), ataxia (OR = 12.6), extraocular movement disturbances (OR = 3.4) and seizure (OR = 3.7) compared to HSP-MD with SPG11. Conversely, SPG11 mutations were more frequently associated with consanguinity (OR = 4.1), parkinsonism (OR = 7.8), dystonia (OR = 5.4), peripheral neuropathy (OR = 26.9), and cognitive dysfunction (OR = 34.5).

CONCLUSION

This systematic IPD-level meta-analysis provides the largest data on genotype-phenotype associations in HSP-MD. Several clinically relevant phenotypic differences were found between various genotypes, which can possibly facilitate diagnosis in resource-limited settings.

Early onset disease, anarthria, areflexia, and dystonia can be the distinctive features of SPG64, a very rare form of hereditary spastic paraplegias

Hereditary spastic paraplegias (HSP) are a group of inherited, neurodegenerative disorders characterized by progressive gait impairment, lower extremity spasticity and increased patellar reflexes. More than 80 types of HSP have been defined to date. In complicated forms, lower limb spasticity and gait impairment is accompanied by an additional neurological finding. Autosomal recessive (AR) HSPs are usually identified in complicated forms and occur more frequently in countries where consanguineous marriage is more widespread. Next generation sequencing techniques, developed in the last decade, have led to the identification of many new types of HSP and reduced the "diagnostic odyssey." Whole exome sequencing (WES) can diagnose up to 75% of undiagnosed HSP patients. Targeted genetic analysis with good clinical phenotyping gives the best diagnostic yields for rare diseases. Clinical heterogeneity is prominent in AR complicated HSP. However, some clinical features complicating the disease or magnetic resonance imaging findings, including thin corpus callosum or white matter abnormalities, can help to distinguish some types. AR spastic paraplegia type 64 (SPG64) is a very rare HSP, caused by a mutation in the ectonucleoside triphosphate diphosphohydrolase 1 (ENTPD1) gene, first described in 2014. To date only nine patients from five families have been reported. We present two siblings with a novel pathogenic variant in ENTPD1, diagnosed by WES, as the sixth published family. We propose that early onset in childhood, cognitive impairment, dysarthria/anarthria, dystonia and areflexia may be the distinctive features of SPG64 and more clinical evidence from families with pathogenic ENTPD1 variants is warranted.

Movement disorders and neuropathies: overlaps and mimics in clinical practice

Movement disorders as well as peripheral neuropathies are extremely frequent in the general population; therefore, it is not uncommon to encounter patients with both these conditions. Often, the coexistence is coincidental, due to the high incidence of common causes of peripheral neuropathy, such as diabetes and other age-related disorders, as well as of Parkinson disease (PD), which has a typical late onset. Nonetheless, there is broad evidence that PD patients may commonly develop a sensory and/or autonomic polyneuropathy, triggered by intrinsic and/or extrinsic mechanisms. Similarly, some peripheral neuropathies may develop some movement disorders in the long run, such as tremor, and rarely dystonia and myoclonus, suggesting that central mechanisms may ensue in the pathogenesis of these diseases. Although rare, several acquired or hereditary causes may be responsible for the combination of movement and peripheral nerve disorders as a unique entity, some of which are potentially treatable, including paraneoplastic, autoimmune and nutritional aetiologies. Finally, genetic causes should be pursued in case of positive family history, young onset or multisystemic involvement, and examined for neuroacanthocytosis, spinocerebellar ataxias, mitochondrial disorders and less common causes of adult-onset cerebellar ataxias and spastic paraparesis. Deep phenotyping in terms of neurological and general examination, as well as laboratory tests, neuroimaging, neurophysiology, and next-generation genetic analysis, may guide the clinician toward the correct diagnosis and management.

A Practical Approach to Early-Onset Parkinsonism

Early-onset parkinsonism (EO parkinsonism), defined as subjects with disease onset before the age of 40 or 50 years, can be the main clinical presentation of a variety of conditions that are important to differentiate. Although rarer than classical late-onset Parkinson’s disease (PD) and not infrequently overlapping with forms of juvenile onset PD, a correct diagnosis of the specific cause of EO parkinsonism is critical for offering appropriate counseling to patients, for family and work planning, and to select the most appropriate symptomatic or etiopathogenic treatments. Clinical features, radiological and laboratory findings are crucial for guiding the differential diagnosis. Here we summarize the most important conditions associated with primary and secondary EO parkinsonism. We also proposed a practical approach based on the current literature and expert opinion to help movement disorders specialists and neurologists navigate this complex and challenging landscape.

Axon-Specific Mitochondrial Pathology in SPG11 Alpha Motor Neurons

Pathogenic variants in SPG11 are the most frequent cause of autosomal recessive complicated hereditary spastic paraplegia (HSP). In addition to spastic paraplegia caused by corticospinal degeneration, most patients are significantly affected by progressive weakness and muscle wasting due to alpha motor neuron (MN) degeneration. Mitochondria play a crucial role in neuronal health, and mitochondrial deficits were reported in other types of HSPs. To investigate whether mitochondrial pathology is present in SPG11, we differentiated MNs from induced pluripotent stem cells derived from SPG11 patients and controls. MN derived from human embryonic stem cells and an isogenic SPG11 knockout line were also included in the study. Morphological analysis of mitochondria in the MN soma versus neurites revealed specific alterations of mitochondrial morphology within SPG11 neurites, but not within the soma. In addition, impaired mitochondrial membrane potential was indicative of mitochondrial dysfunction. Moreover, we reveal neuritic aggregates further supporting neurite pathology in SPG11. Correspondingly, using a microfluidic-based MN culture system, we demonstrate that axonal mitochondrial transport was significantly impaired in SPG11. Overall, our data demonstrate that alterations in morphology, function, and transport of mitochondria are an important feature of axonal dysfunction in SPG11 MNs.

iPLA2β Contributes to ER Stress-Induced Apoptosis during Myocardial Ischemia/Reperfusion Injury

Both calcium-independent phospholipase A2 beta (iPLA2β) and endoplasmic reticulum (ER) stress regulate important pathophysiological processes including inflammation, calcium homeostasis and apoptosis. However, their roles in ischemic heart disease are poorly understood. Here, we show that the expression of iPLA2β is increased during myocardial ischemia/reperfusion (I/R) injury, concomitant with the induction of ER stress and the upregulation of cell death. We further show that the levels of iPLA2β in serum collected from acute myocardial infarction (AMI) patients and in samples collected from both in vivo and in vitro I/R injury models are significantly elevated. Further, iPLA2β knockout mice and siRNA mediated iPLA2β knockdown are employed to evaluate the ER stress and cell apoptosis during I/R injury. Additionally, cell surface protein biotinylation and immunofluorescence assays are used to trace and locate iPLA2β. Our data demonstrate the increase of iPLA2β augments ER stress and enhances cardiomyocyte apoptosis during I/R injury in vitro and in vivo. Inhibition of iPLA2β ameliorates ER stress and decreases cell death. Mechanistically, iPLA2β promotes ER stress and apoptosis by translocating to ER upon myocardial I/R injury. Together, our study suggests iPLA2β contributes to ER stress-induced apoptosis during myocardial I/R injury, which may serve as a potential therapeutic target against ischemic heart disease.

GCH1 mutations in hereditary spastic paraplegia

GCH1 mutations have been associated with dopa-responsive dystonia (DRD), Parkinson's disease (PD) and tetrahydrobiopterin (BH₄ )-deficient hyperphenylalaninemia B. Recently, GCH1 mutations have been reported in five patients with hereditary spastic paraplegia (HSP). Here, we analyzed a total of 400 HSP patients (291 families) from different centers across Canada by whole exome sequencing (WES). Three patients with heterozygous GCH1 variants were identified: monozygotic twins with a p.(Ser77_Leu82del) variant, and a patient with a p.(Val205Glu) variant. The former variant is predicted to be likely pathogenic and the latter is pathogenic. The three patients presented with childhood-onset lower limb spasticity, hyperreflexia and abnormal plantar responses. One of the patients had diurnal fluctuations, and none had parkinsonism or dystonia. Phenotypic differences between the monozygotic twins were observed, who responded well to levodopa treatment. Pathway enrichment analysis suggested that GCH1 shares processes and pathways with other HSP-associated genes, and structural analysis of the variants indicated a disruptive effect. In conclusion, GCH1 mutations may cause HSP; therefore, we suggest a levodopa trial in HSP patients and including GCH1 in the screening panels of HSP genes. Clinical differences between monozygotic twins suggest that environmental factors, epigenetics, and stochasticity could play a role in the clinical presentation.

Pluripotent Stem Cell Derived Neurons as In Vitro Models for Studying Autosomal Recessive Parkinson's Disease (ARPD): PLA2G6 and Other Gene Loci

Parkinson's disease (PD) is a neurodegenerative motor disorder which is largely sporadic; however, some familial forms have been identified. Genetic PD can be inherited by autosomal, dominant or recessive mutations. While the dominant mutations mirror the prototype of PD with adult-onset and L-dopa-responsive cases, autosomal recessive PD (ARPD) exhibit atypical phenotypes with additional clinical manifestations. Young-onset PD is also very common with mutations in recessive gene loci. The main genes associated with ARPD are Parkin, PINK1, DJ-1, ATP13A2, FBXO7 and PLA2G6. Calcium dyshomeostasis is a mainstay in all types of PD, be it genetic or sporadic. Intriguingly, calcium imbalances manifesting as altered Store-Operated Calcium Entry (SOCE) is suggested in PLA2G6-linked PARK 14 PD. The common pathways underlying ARPD pathology, including mitochondrial abnormalities and autophagic dysfunction, can be investigated ex vivo using induced pluripotent stem cell (iPSC) technology and are discussed here. PD pathophysiology is not faithfully replicated by animal models, and, therefore, nigral dopaminergic neurons generated from iPSC serve as improved human cellular models. With no cure to date and treatments aiming at symptomatic relief, these in vitro models derived through midbrain floor-plate induction provide a platform to understand the molecular and biochemical pathways underlying PD etiology in a patient-specific manner.

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.

A case of spastic paraplegia type 11 with a variation in the SPG11 gene

Background

Spastic paraplegia 11 (SPG11) is defined as progressive spasticity and weakness of the lower limbs and also associated with mild intellectual disability with learning difficulties in childhood and/or progressive cognitive retardation, peripheral neuropathy, pseudobulbar symptoms, and increased reflexes in the upper limbs. We describe the clinical, laboratory, and radiological presentation of SPG11 through a report of a case and compare with previously reported SPG11 cases in the literature.

Case presentation

This case presents a homozygous variant in the SPG11 gene (NM_025137.4): c.1699C>T;p.(Gln567*).

Conclusion

The diagnosis was made based on molecular findings, thinning of corpus callosum (TCC) and in most cases, periventricular white matter abnormalities are detected in brain MRI. Therefore, the clinical and radiological findings are supporting the diagnosis. However, it should not be forgotten that TCC is not peculiar to SPG11.

Computational analysis of hereditary spastic paraplegia mutations in the kinesin motor domains of KIF1A and KIF5A

Hereditary spastic paraplegias (HSPs) are a genetically heterogeneous collection of neurodegenerative disorders categorized by progressive lower-limb spasticity and frailty. The complex HSP forms are characterized by various neurological features including progressive spastic weakness, urinary sphincter dysfunction, extra pyramidal signs and intellectual disability (ID). The kinesin superfamily proteins (KIFs) are microtubule-dependent molecular motors involved in intracellular transport. Kinesins directionally transport membrane vesicles, protein complexes, and mRNAs along neurites, thus playing important roles in neuronal development and function. Recent genetic studies have identified kinesin mutations in patients with HSPs. In this study, we used the computational approaches to investigate the 40 missense mutations associated with HSP and ID in KIF1A and KIF5A. We performed homology modeling to construct the structures of kinesin–microtubule binding domain and kinesin–tubulin complex. We applied structure-based energy calculation methods to determine the effects of missense mutations on protein stability and protein–protein interaction. The results revealed that the most of disease-causing mutations could change the folding free energy of kinesin motor domain and the binding free energy of kinesin–tubulin complex. We found that E253K associated with ID in KIF1A decrease the protein stability of kinesin motor domains. We showed that the HSP mutations located in kinesin–tubulin complex interface, such as K253N and R280C in KIF5A, can destabilize the kinesin–tubulin complex. The computational analysis provides useful information for understanding the roles of kinesin mutations in the development of ID and HSPs.

Bi-allelic variants in PNPLA6 possibly associated with Parkinsonian features in addition to spastic paraplegia phenotype

Variants in the PNPLA6 gene are known to cause 4 distinct phenotypes. One known phenotype is Hereditary Spastic Paraplegia type 39 (HSP 39), a rare neurodegenerative condition characterized by variable onset of lower limb spasticity, weakness and ataxia. Little is known about complications of HSP 39 in adulthood. Here, we report a family of three siblings who presented with bilateral lower limb spasticity in childhood, consistent with HSP, with confirmed bi-allellic PNPLA6 mutations. Two siblings developed parkinsonian features in middle age, a novel finding in this sibship. The proband had a positive dopamine transporter scan, indicating degeneration in dopaminergic neurons, and dopa-responsive extrapyramidal symptoms. Testing for known genetic causes of Parkinsonism was negative. The PNPLA6 gene encodes neuropathy target esterase, an enzyme involved in lipid metabolism that is critical to the stability of cell membranes. We hypothesize that the development of Parkinsonism in these patients may be related to the PNPLA6 mutations, as lipid dysregulation has been implicated in the pathogenesis of Parkinson disease.

Topiramate-Responsive Tremor in a Novel Pathogenic Variant of SPG15 Patient

Hereditary spastic paraplegia (HSP) is group of a rare neurodegenerative disorder with both genetically and clinically diverse neurologic features. Indeed, disease progression is varying greatly within the different forms and current treatment modalities are exclusively symptomatic for HSP. Tremor in HSP patients is only mentioned with rare case reports, so treatment option is lack in clinical ground. We reported a case of a HSP-15 girl with a previously reported novel mutation of SPG15 complained of a life disturbing tremor and topiramate as a drug therapy for tremor in our HSP patient.

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.

Overlapping spectrums: The clinicogenetic commonalities between Charcot-Marie-Tooth and other neurodegenerative diseases

Charcot-Marie-Tooth (CMT) disease is a progressive and heterogeneous inherited peripheral neuropathy. A myriad of genetic factors have been identified that contribute to the degeneration of motor and sensory axons in a length-dependent manner. Emerging biological themes underlying disease include defects in axonal trafficking, dysfunction in RNA metabolism and protein homeostasis, as well deficits in the cellular stress response. Moreover, genetic contributions to CMT can have overlap with other neuropathies, motor neuron diseases (MNDs) and neurodegenerative disorders. Recent progress in understanding the molecular biology of CMT and overlapping syndromes aids in the search for necessary therapeutic targets.

Clinical and neuroimaging phenotypes of genetic parkinsonism from infancy to adolescence

Genetic early-onset parkinsonism presenting from infancy to adolescence (≤21 years old) is a clinically diverse syndrome often combined with other hyperkinetic movement disorders, neurological and imaging abnormalities. The syndrome is genetically heterogeneous, with many causative genes already known. With the increased use of next-generation sequencing in clinical practice, there have been novel and unexpected insights into phenotype-genotype correlations and the discovery of new disease-causing genes. It is now recognized that mutations in a single gene can give rise to a broad phenotypic spectrum and that, conversely different genetic disorders can manifest with a similar phenotype. Accurate phenotypic characterization remains an essential step in interpreting genetic findings in undiagnosed patients. However, in the past decade, there has been a marked expansion in knowledge about the number of both disease-causing genes and phenotypic spectrum of early-onset cases. Detailed knowledge of genetic disorders and their clinical expression is required for rational planning of genetic and molecular testing, as well as correct interpretation of next-generation sequencing results. In this review we examine the relevant literature of genetic parkinsonism with ≤21 years onset, extracting data on associated movement disorders as well as other neurological and imaging features, to delineate syndromic patterns associated with early-onset parkinsonism. Excluding PRKN (parkin) mutations, &gt;90% of the presenting phenotypes have a complex or atypical presentation, with dystonia, abnormal cognition, pyramidal signs, neuropsychiatric disorders, abnormal imaging and abnormal eye movements being the most common features. Furthermore, several imaging features and extraneurological manifestations are relatively specific for certain disorders and are important diagnostic clues. From the currently available literature, the most commonly implicated causes of early-onset parkinsonism have been elucidated but diagnosis is still challenging in many cases. Mutations in ∼70 different genes have been associated with early-onset parkinsonism or may feature parkinsonism as part of their phenotypic spectrum. Most of the cases are caused by recessively inherited mutations, followed by dominant and X-linked mutations, and rarely by mitochondrially inherited mutations. In infantile-onset parkinsonism, the phenotype of hypokinetic-rigid syndrome is most commonly caused by disorders of monoamine synthesis. In childhood and juvenile-onset cases, common genotypes include PRKN, HTT, ATP13A2, ATP1A3, FBX07, PINK1 and PLA2G6 mutations. Moreover, Wilson’s disease and mutations in the manganese transporter are potentially treatable conditions and should always be considered in the differential diagnosis in any patient with early-onset parkinsonism.

Spastic Paraplegia Accompanied by Extrapyramidal Sign and Frontal Cognitive Dysfunction

A complicated form of spastic paraplegia is a neurodegenerative disorder presenting as progressive spasticity in the bilateral lower limbs accompanied by some clinical features. The present case showed spastic paralysis and hyperreflexia in all extremities as well as lead pipe rigidity in the neck and bilateral upper extremities (R < L), decreased scores on frontal cognitive tests, a decreased accumulation of the right dorsal putamen on a DAT scan, and hypoperfusion of the bilateral frontal lobes on ^99mTc-ECD single photon emission computed tomography (SPECT). The present case provides a new spectrum of spastic paraplegia based on the evidence of clinical scores and the findings of brain functional imaging.

Hereditary Myelopathies

PURPOSE OF REVIEW

Hereditary myelopathies are very diverse genetic disorders, and many of them represent a widespread neurodegenerative process rather than isolated spinal cord dysfunction. This article reviews various types of inherited myelopathies, with emphasis on hereditary spastic paraplegias and spastic ataxias.

RECENT FINDINGS

The ever-growing number of myelopathy-causing genes and broadening of phenotype-genotype correlations makes the molecular diagnosis of inherited myelopathies a daunting task. This article emphasizes the main phenotypic clusters among inherited myelopathies that can facilitate the diagnostic process. This article focuses on newly identified genetic causes and the most important identifying clinical features that can aid the diagnosis, including the presence of a characteristic age of onset and additional neurologic signs such as leukodystrophy, thin corpus callosum, or amyotrophy.

SUMMARY

The exclusion of potentially treatable causes of myelopathy remains the most important diagnostic step. Syndromic diagnosis can be supported by molecular diagnosis, but the genetic diagnosis at present does not change the management. Moreover, a negative genetic test does not exclude the diagnosis of a hereditary myelopathy because comprehensive molecular testing is not yet available, and many disease-causing genes remain unknown.

Current therapies and therapeutic decision making for childhood-onset movement disorders

Movement disorders differ in children to adults. First, neurodevelopmental movement disorders such as tics and stereotypies are more prevalent than parkinsonism, and second, there is a genomic revolution which is now explaining many early-onset dystonic syndromes. We outline an approach to children with movement disorders starting with defining the movement phenomenology, determining the level of functional impairment due to abnormal movements, and screening for comorbid psychiatric conditions and cognitive impairments which often contribute more to disability than the movements themselves. The rapid improvement in our understanding of the etiology of movement disorders has resulted in an increasing focus on precision medicine, targeting treatable conditions and defining modifiable disease processes. We profile some of the key disease-modifying therapies in metabolic, neurotransmitter, inflammatory, and autoimmune conditions and the increasing focus on gene or cellular therapies. When no disease-modifying therapies are possible, symptomatic therapies are often all that is available. These classically target dopaminergic, cholinergic, alpha-adrenergic, or GABAergic neurochemistry. Increasing interest in neuromodulation has highlighted that some clinical syndromes respond better to DBS, and further highlights the importance of "disease-specific" therapies with a future focus on individualized therapies according to the genomic findings or disease pathways that are disrupted. We summarize some pragmatic applications of symptomatic therapies, neuromodulation techniques, and some rehabilitative interventions and provide a contemporary overview of treatment in childhood-onset movement disorders. © 2019 International Parkinson and Movement Disorder Society.

Impaired mitochondrial dynamics underlie axonal defects in hereditary spastic paraplegias

Mechanisms by which long corticospinal axons degenerate in hereditary spastic paraplegia (HSP) are largely unknown. Here, we have generated induced pluripotent stem cells (iPSCs) from patients with two autosomal recessive forms of HSP, SPG15 and SPG48, which are caused by mutations in the ZFYVE26 and AP5Z1 genes encoding proteins in the same complex, the spastizin and AP5Z1 proteins, respectively. In patient iPSC-derived telencephalic glutamatergic and midbrain dopaminergic neurons, neurite number, length and branching are significantly reduced, recapitulating disease-specific phenotypes. We analyzed mitochondrial morphology and noted a significant reduction in both mitochondrial length and their densities within axons of these HSP neurons. Mitochondrial membrane potential was also decreased, confirming functional mitochondrial defects. Notably, mdivi-1, an inhibitor of the mitochondrial fission GTPase DRP1, rescues mitochondrial morphology defects and suppresses the impairment in neurite outgrowth and late-onset apoptosis in HSP neurons. Furthermore, knockdown of these HSP genes causes similar axonal defects, also mitigated by treatment with mdivi-1. Finally, neurite outgrowth defects in SPG15 and SPG48 cortical neurons can be rescued by knocking down DRP1 directly. Thus, abnormal mitochondrial morphology caused by an imbalance of mitochondrial fission and fusion underlies specific axonal defects and serves as a potential therapeutic target for SPG15 and SPG48.

Management of Hereditary Spastic Paraplegia: A Systematic Review of the Literature

The term hereditary spastic paraplegia (HSP) embraces a clinically and genetically heterogeneous group of neurodegenerative diseases characterized by progressive spasticity and weakness of the lower limbs. There currently exist no specific therapies for HSP, and treatment is exclusively symptomatic, aimed at reducing muscle spasticity, and improving strength and gait. The authors set out to perform a comprehensive systematic review of the available scientific literature on the treatment of HSP, applying Cochrane Collaboration methods. The Google Scholar, PubMed and Scopus electronic databases were searched to find relevant randomized control trials (RCTs) and open-label interventional studies, prospective, and retrospective observational studies of supplements, medications, and physical therapy, as well as case reports and case series. Two authors independently analyzed 27 articles selected on the basis of a series of inclusion criteria. Applying a best-evidence synthesis approach, they evaluated these articles for methodological quality. A standardized scoring system was used to obtain interrater assessments. Disagreements were resolved by discussion. The 27 articles focused on pharmacological treatment (n = 17 articles), physical therapy (n = 5), surgical treatment (n = 5). The drugs used in the 17 articles on pharmacological therapy were: gabapentin, progabide, dalfampridine, botulinum toxin, L-Dopa, cholesterol-lowering drugs, betaine, and folinic acid. Gabapentin, progabide, dalfampridine, and botulinum toxin were used as antispastic agents; the study evaluating gabapentin efficacy was well-designed, but failed to demonstrate any significant improvement. L-Dopa, cholesterol-lowering drugs, betaine, and folinic acid were only used in specific HSP subtypes. Two of the three studies evaluating cholesterol-lowering drugs (in SPG5 patients) were well-designed and showed a significant reduction of specific serum biomarkers (oxysterols), but clinical outcomes were not evaluated. The articles focusing on physical treatment and surgical therapy were found to be of low/medium quality and, accordingly, failed to clarify the role of these approaches in HSP. Despite recent advances in understanding of the pathogenesis of HSP and the possibility, in several centers, of obtaining more precise and rapid molecular diagnoses, there is still no adequate evidence base for recommending the various published therapies. Well-designed RCTs are needed to evaluate the efficacy of both symptomatic and pathogenetic treatments.

Clinical Trial Designs and Measures in Hereditary Spastic Paraplegias

Hereditary spastic paraplegias (HSPs) are a large group of genetically-diverse neurologic disorders characterized clinically by a common feature of lower extremity spasticity and gait difficulties. Current therapies are predominantly symptomatic, and even then usually provide inadequate relief of symptoms. Going forward, HSP therapeutics development requires a systematic analysis of quantifiable measures and tools to assess treatment response. This review summarizes promising therapeutic targets, assessment measures, and previous clinical trials for the HSPs. Oxidative stress, signaling pathways, microtubule dynamics, and gene rescue/replacement have been proposed as potential treatment targets or modalities. Quantitative evaluation of pre-clinical rodent HSP models emphasize rotarod performance, foot base angle, grip strength, stride length, beam walking, critical speed, and body weight. Clinical measures of HSP in humans include 10-m gait velocity, the Spastic Paraplegia Rating Scale (SPRS), Ashworth Spasticity Scale, Fugl-Meyer Scale, timed up-and-go, and the Gillette Functional Assessment Questionnaire. We conducted a broad search for past clinical trials in HSPs and identified trials that investigated pharmacological agents including atorvastatin, gabapentin, L-threonine, botulinum toxin, dalfampridine, methylphenidate, and baclofen. We provide recommendations for future HSP treatment directions based on these prior research experiences as well as regulatory insight.

SPG11-related parkinsonism: Clinical profile, molecular imaging and l-dopa response

BACKGROUND

Molecular imaging has proven to be a powerful tool to elucidate degenerated paths in a wide variety of neurological diseases and has not been systematically studied in hereditary spastic paraplegias.

OBJECTIVES

To investigate dopaminergic degeneration in a cohort of 22 patients with hereditary spastic paraplegia attributed to SPG11 mutations and evaluate treatment response to l-dopa.

METHODS

Patients and controls underwent single-photon emission computed tomography imaging utilizing ^99m Tc-TRODAT-1 tracer. A single-blind trial with 600 mg of l-dopa was performed comparing UPDRS scores.

RESULTS

Reduced dopamine transporter density was universal among patients. Nigral degeneration was symmetrical and correlated with disease duration and motor and cognitive handicap. No statistically significant benefit could be demonstrated with l-dopa intake during the trial.

CONCLUSION

Disruption of presynaptic dopaminergic pathways is a widespread phenomenon in patients with SPG11 mutations, even in the absence of parkinsonism. Unresponsiveness to treatment could be related to postsynaptic damage that needs to be further investigated.

Hereditary spastic paraplegia

The hereditary spastic paraplegias (HSPs) are a heterogeneous group of neurologic disorders with the common feature of prominent lower-extremity spasticity, resulting from a length-dependent axonopathy of corticospinal upper motor neurons. The HSPs exist not only in "pure" forms but also in "complex" forms that are associated with additional neurologic and extraneurologic features. The HSPs are among the most genetically diverse neurologic disorders, with well over 70 distinct genetic loci, for which about 60 mutated genes have already been identified. Numerous studies elucidating the molecular pathogenesis underlying HSPs have highlighted the importance of basic cellular functions - especially membrane trafficking, mitochondrial function, organelle shaping and biogenesis, axon transport, and lipid/cholesterol metabolism - in axon development and maintenance. An encouragingly small number of converging cellular pathogenic themes have been identified for the most common HSPs, and some of these pathways present compelling targets for future therapies.

Loss-of-function mutations in the ATP13A2/PARK9 gene cause complicated hereditary spastic paraplegia (SPG78)

Hereditary spastic paraplegias are heterogeneous neurodegenerative disorders characterized by progressive spasticity of the lower limbs due to degeneration of the corticospinal motor neurons. In a Bulgarian family with three siblings affected by complicated hereditary spastic paraplegia, we performed whole exome sequencing and homozygosity mapping and identified a homozygous p.Thr512Ile (c.1535C > T) mutation in ATP13A2. Molecular defects in this gene have been causally associated with Kufor-Rakeb syndrome (#606693), an autosomal recessive form of juvenile-onset parkinsonism, and neuronal ceroid lipofuscinosis (#606693), a neurodegenerative disorder characterized by the intracellular accumulation of autofluorescent lipopigments. Further analysis of 795 index cases with hereditary spastic paraplegia and related disorders revealed two additional families carrying truncating biallelic mutations in ATP13A2. ATP13A2 is a lysosomal P5-type transport ATPase, the activity of which critically depends on catalytic autophosphorylation. Our biochemical and immunocytochemical experiments in COS-1 and HeLa cells and patient-derived fibroblasts demonstrated that the hereditary spastic paraplegia-associated mutations, similarly to the ones causing Kufor-Rakeb syndrome and neuronal ceroid lipofuscinosis, cause loss of ATP13A2 function due to transcript or protein instability and abnormal intracellular localization of the mutant proteins, ultimately impairing the lysosomal and mitochondrial function. Moreover, we provide the first biochemical evidence that disease-causing mutations can affect the catalytic autophosphorylation activity of ATP13A2. Our study adds complicated hereditary spastic paraplegia (SPG78) to the clinical continuum of ATP13A2-associated neurological disorders, which are commonly hallmarked by lysosomal and mitochondrial dysfunction. The disease presentation in our patients with hereditary spastic paraplegia was dominated by an adult-onset lower-limb predominant spastic paraparesis. Cognitive impairment was present in most of the cases and ranged from very mild deficits to advanced dementia with fronto-temporal characteristics. Nerve conduction studies revealed involvement of the peripheral motor and sensory nerves. Only one of five patients with hereditary spastic paraplegia showed clinical indication of extrapyramidal involvement in the form of subtle bradykinesia and slight resting tremor. Neuroimaging cranial investigations revealed pronounced vermian and hemispheric cerebellar atrophy. Notably, reduced striatal dopamine was apparent in the brain of one of the patients, who had no clinical signs or symptoms of extrapyramidal involvement.

Modeling Axonal Defects in Hereditary Spastic Paraplegia with Human Pluripotent Stem Cells

BACKGROUND

Cortical motor neurons, also known as upper motor neurons, are large projection neurons whose axons convey signals to lower motor neurons to control the muscle movements. Degeneration of cortical motor neuron axons is implicated in several debilitating disorders, including hereditary spastic paraplegia (HSP) and amyotrophic lateral sclerosis (ALS). Since the discovery of the first HSP gene, SPAST that encodes spastin, over 70 distinct genetic loci associated with HSP have been identified. How the mutations of these functionally diverse genes result in axonal degeneration and why certain axons are affected in HSP remains largely unknown. The development of induced pluripotent stem cell (iPSC) technology has provided researchers an excellent resource to generate patient-specific human neurons to model human neuropathologic processes including axonal defects.

METHODS

In this article, we will frst review the pathology and pathways affected in the common forms of HSP subtypes by searching the PubMed database. We will then summurize the findings and insights gained from studies using iPSC-based models, and discuss the challenges and future directions.

RESULTS

HSPs, a heterogeneous group of genetic neurodegenerative disorders, are characterized by lower extremity weakness and spasticity that result from retrograde axonal degeneration of cortical motor neurons. Recently, iPSCs have been generated from several common forms of HSP including SPG4, SPG3A, and SPG11 patients. Neurons derived from HSP iPSCs exhibit disease-relevant axonal defects, such as impaired neurite outgrowth, increased axonal swellings, and reduced axonal transport.

CONCLUSION

These patient-derived neurons offer unique tools to study the pathogenic mechanisms and explore the treatments for rescuing axonal defects in HSP, as well as other diseases involving axonopathy.

Novel Compound Heterozygous Spatacsin Mutations in a Greek Kindred with Hereditary Spastic Paraplegia SPG11 and Dementia

SPG11 belongs to the autosomal recessive hereditary spastic paraplegias (HSP) and presents during childhood or puberty with a complex clinical phenotype encompassing learning difficulties, ataxia, peripheral neuropathy, amyotrophy, and mental retardation. We hereby present the case of a 30-year-old female patient with complex autosomal recessive HSP with thinning of the corpus callosum (TCC) and dementia that was compound heterozygous with two novel mutations in the SPG11 gene. Sequence analysis of the SPG11 gene revealed two novel mutations in a compound heterozygous state in the index patient (c.2431C>T/p.Gln811Ter and c.6755_6756insT/p.Glu2252Aspfs*88). MRI showed abnormal TCC, white matter (WM) hyperintensities periventricularly, and the 'ears of the lynx' sign. Diffusion tensor imaging showed a mild-to-moderate decrease in fractional anisotropy and an increase in mean diffusivity in WM compared to age-matched controls, while magnetic resonance spectroscopy showed abnormal findings in affected WM with a decrease in N-acetyl-aspartate in WM regions of interest. This is the first SPG11 kindred from the Greek population to be reported in the medical literature.

Genetic and phenotypic characterization of complex hereditary spastic paraplegia

The hereditary spastic paraplegias are a heterogeneous group of degenerative disorders that are clinically classified as either pure with predominant lower limb spasticity, or complex where spastic paraplegia is complicated with additional neurological features, and are inherited in autosomal dominant, autosomal recessive or X-linked patterns. Genetic defects have been identified in over 40 different genes, with more than 70 loci in total. Complex recessive spastic paraplegias have in the past been frequently associated with mutations in SPG11 (spatacsin), ZFYVE26/SPG15 , SPG7 (paraplegin) and a handful of other rare genes, but many cases remain genetically undefined. The overlap with other neurodegenerative disorders has been implied in a small number of reports, but not in larger disease series. This deficiency has been largely due to the lack of suitable high throughput techniques to investigate the genetic basis of disease, but the recent availability of next generation sequencing can facilitate the identification of disease-causing mutations even in extremely heterogeneous disorders. We investigated a series of 97 index cases with complex spastic paraplegia referred to a tertiary referral neurology centre in London for diagnosis or management. The mean age of onset was 16 years (range 3 to 39). The SPG11 gene was first analysed, revealing homozygous or compound heterozygous mutations in 30/97 (30.9%) of probands, the largest SPG11 series reported to date, and by far the most common cause of complex spastic paraplegia in the UK, with severe and progressive clinical features and other neurological manifestations, linked with magnetic resonance imaging defects. Given the high frequency of SPG11 mutations, we studied the autophagic response to starvation in eight affected SPG11 cases and control fibroblast cell lines, but in our restricted study we did not observe correlations between disease status and autophagic or lysosomal markers. In the remaining cases, next generation sequencing was carried out revealing variants in a number of other known complex spastic paraplegia genes, including five in SPG7 (5/97), four in FA2H (also known as SPG35 ) (4/97) and two in ZFYVE26 / SPG15 . Variants were identified in genes usually associated with pure spastic paraplegia and also in the Parkinson’s disease-associated gene ATP13A2 , neuronal ceroid lipofuscinosis gene TPP1 and the hereditary motor and sensory neuropathy DNMT1 gene, highlighting the genetic heterogeneity of spastic paraplegia. No plausible genetic cause was identified in 51% of probands, likely indicating the existence of as yet unidentified genes.

Clinical and genetic heterogeneity in hereditary spastic paraplegias: from SPG1 to SPG72 and still counting

Hereditary spastic paraplegias (HSPs) are genetically determined neurodegenerative disorders characterized by progressive weakness and spasticity of lower limbs, and are among the most clinically and genetically heterogeneous human diseases. All modes of inheritance have been described, and the recent technological revolution in molecular genetics has led to the identification of 76 different spastic gait disease-loci with 59 corresponding spastic paraplegia genes. Autosomal recessive HSP are usually associated with diverse additional features (referred to as complicated forms), contrary to autosomal dominant HSP, which are mostly pure. However, the identification of additional mutations and families has considerably enlarged the clinical spectra, and has revealed a huge clinical variability for almost all HSP; complicated forms have also been described for primary pure HSP subtypes, adding further complexity to the genotype-phenotype correlations. In addition, the introduction of next generation sequencing in clinical practice has revealed a genetic and phenotypic overlap with other neurodegenerative disorders (amyotrophic lateral sclerosis, neuropathies, cerebellar ataxias, etc.) and neurodevelopmental disorders, including intellectual disability. This review aims to describe the most recent advances in the field and to provide genotype-phenotype correlations that could help clinical diagnoses of this heterogeneous group of disorders.

SPG11 Mutations Associated With a Complex Phenotype Resembling Dopa-Responsive Dystonia

BACKGROUND

The aim of this study was to describe a case of hereditary spastic paraplegia (HSP) resulting from SPG11 mutations, presenting with a complex phenotype of dopa-responsive dystonia (DRD), diagnosed using whole exome sequencing (WES). HSP resulting from SPG11 typically presents with spasticity, cognitive impairment, and radiological evidence of thin corpus callosum. Initial presentation with DRD has not been previously reported on.

METHODS

This 11-year-old boy with delay in fine motor skills, presented at 8 years of age with progressive, generalized dystonia with diurnal variation, bradykinesia, and stiff gait. There was marked improvement in dystonia with levodopa, but he soon developed wearing-off phenomenon and l-dopa-induced dyskinesia. Family history was unremarkable.

RESULTS

Brain MRI showed thinning of the anterior corpus callosum with periventricular white matter changes. ¹²³I-ioflupane single-photon emission coupled tomography showed bilateral severe presynaptic dopamine deficiency. WES identified transheterozygous allelic variants in the SPG11 on chromosome 15, including a truncating STOP mutation (p.E1630X) and a second heterozygous coding variant (p.L2300R). Dystonia improved with globus pallidus internus (GPi) DBS surgery.

CONCLUSIONS

HSP resulting from SPG11 should be considered in the differential diagnosis of a patient presenting with DRD, parkinsonism, and spasticity. This case expands the HSP genotype and phenotype. GPi DBS may be a therapeutic option in selected patients.

Prevalence of inherited neurotransmitter disorders in patients with movement disorders and epilepsy: a retrospective cohort study

BACKGROUND

Inherited neurotransmitter disorders are primary defects of neurotransmitter metabolism. The main purpose of this retrospective cohort study was to identify prevalence of inherited neurotransmitter disorders.

METHODS

This retrospective cohort study does not have inclusion criteria; rather included all patients who underwent cerebrospinal fluid (CSF) homovanillic and 5-hydroxyindol acetic acid measurements. Patients with CSF neurotransmitter investigations suggestive of an inherited neurotransmitter disorder and patients with normal or non-diagnostic CSF neurotransmitter investigations underwent direct sequencing of single gene disorders.

RESULTS

There were 154 patients between October 2004 and July 2013. Four patients were excluded due to their diagnosis prior to this study dates. Two major clinical feature categories of patients who underwent lumbar puncture were movement disorders or epilepsy in our institution. Twenty out of the 150 patients (13.3%) were diagnosed with a genetic disorder including inherited neurotransmitter disorders (6 patients) (dihydropteridine reductase, 6-pyruvoyl-tetrahydropterin synthase, guanosine triphosphate cyclohydrolase I, tyrosine hydroxylase, pyridoxine dependent epilepsy due to mutations in the ALDH7A1 gene and pyridoxamine-5-phosphate oxidase deficiencies) and non-neurotransmitter disorders (14 patients).

CONCLUSION

Prevalence of inherited neurotransmitter disorders was 4% in our retrospective cohort study. Eight out of the 150 patients (5.3%) had one of the treatable inherited metabolic disorders with favorable short-term neurodevelopmental outcomes, highlighting the importance of an early and specific diagnosis. Whole exome or genome sequencing might shed light to unravel underlying genetic defects of new inherited neurotransmitter disorders in near future.

Genome-Wide Analyses of Working-Memory Ability: A Review

Working memory, a theoretical construct from the field of cognitive psychology, is crucial to everyday life. It refers to the ability to temporarily store and manipulate task-relevant information. The identification of genes for working memory might shed light on the molecular mechanisms of this important cognitive ability and-given the genetic overlap between, for example, schizophrenia risk and working-memory ability-might also reveal important candidate genes for psychiatric illness. A number of genome-wide searches for genes that influence working memory have been conducted in recent years. Interestingly, the results of those searches converge on the mediating role of neuronal excitability in working-memory performance, such that the role of each gene highlighted by genome-wide methods plays a part in ion channel formation and/or dopaminergic signaling in the brain, with either direct or indirect influence on dopamine levels in the prefrontal cortex. This result dovetails with animal models of working memory that highlight the role of dynamic network connectivity, as mediated by dopaminergic signaling, in the dorsolateral prefrontal cortex. Future work, which aims to characterize functional variants influencing working-memory ability, might choose to focus on those genes highlighted in the present review and also those networks in which the genes fall. Confirming gene associations and highlighting functional characterization of those associations might have implications for the understanding of normal variation in working-memory ability and also for the development of drugs for mental illness.

Striatal dopaminergic functioning in patients with sporadic and hereditary spastic paraplegias with parkinsonism

Sporadic spastic paraplegia (SSP) and hereditary spastic paraplegia (HSP) belong to a clinical and genetically heterogeneous group of disorders characterized by progressive spasticity and weakness in the lower extremities. The symptoms are associated with pyramidal tract dysfunction and degeneration of the corticospinal tracts. Parkinsonism is uncommon in SSP/HSP patients. However, both disorders are associated with damage to the nigrostriatal dopaminergic system. In the present study, the clinical features of patients with SSP/HSP were investigated, and nigrostriatal dopaminergic binding potential was assessed using dopamine transporter (DAT) single-photon emission computer tomography (SPECT). Nine patients with spastic paraplegia participated in the present study. The subjects underwent DAT SPECT using the agent [2-[[2-[[[3-(4-chlorophenyl)-8-methyl-8-azabicyclo[3,2,1]oct-2-yl]methyl](2-mercaptoethyl)amino]ethyl]amino]ethanethiolato (3-)-N2,N20,S2,S20]oxo-[IR-(exo-exo)])-[(99)mTc]technetium ([(99)mTc]TRODAT-1). The [(99)mTc]TRODAT-1 SPECT images of five patients appeared normal, whereas the images of four patients revealed reduced striatal ligand uptake. Among the four patients with reduced uptake, two had parkinsonism, and one exhibited periodic limb movements and restless leg syndrome. Our DAT SPECT imaging study shows that reduced DAT density may be observed in patients with parkinsonism. The results of the present study offer an explanation for the spectrum of spastic paraplegia symptoms and the progression of the disorder.

Immunohistochemical localization of spatacsin in α-synucleinopathies

Spatacsin (SPG11) is a major mutated gene in autosomal recessive spastic paraplegia with thin corpus callosum (ARHSP-TCC) and is responsible for juvenile Parkinsonism. To elucidate the role of spatacsin in the pathogenesis of α-synucleinopathies, an immunohistochemical investigation was performed on the brain of patients with Parkinson's disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy (MSA) using anti-spatacsin antibody. In PD, Lewy bodies (LBs) in the brain stem were positive for spatacsin. These LBs showed intense staining in their peripheral portions and occasionally in the central cores. Lewy neurites were also spatacsin-positive. In DLB, cortical LBs were immunolabeled by spatacsin. In MSA, glial cytoplasmic inclusions (GCI) and a small fraction of neuronal cytoplasmic inclusions (NCI) were positive for spatacsin. The widespread accumulation of spatacsin observed in pathologic α-synuclein-containing inclusions suggests that spatacsin may be involved in the pathogenesis of α-synucleinopathies.

Recognizing genetic forms of parkinsonism

SUMMARY It has been generally recognized that, in most cases of Parkinson’s disease (PD), the causes are a result of the complex interaction of genetic and environmental factors. Only approximately 10–15% of PD cases appear to be rare forms with a Mendelian genetic cause. There has been an increasing need and demand in daily clinical work to look for a molecular diagnosis, although a number of neurologists feel uneasy when dealing with the growing number of possible genes and risk factors related to PD that are accessible for diagnosis. Research has highlighted the consequences not only for hereditary but also sporadic forms of PD. This review will provide an overview of the principal aspects of the genetics of PD. It will focus on their differences and similarities, and discuss several useful tools for clinicians, and the role and importance of a neurogeneticist.

Monogenic Parkinson's disease and parkinsonism: clinical phenotypes and frequencies of known mutations

Mutations in seven genes are robustly associated with autosomal dominant (SNCA, LRRK2, EIF4G1, VPS35) or recessive (parkin/PARK2, PINK1, DJ1/PARK7) Parkinson's disease (PD) or parkinsonism. Changes in a long list of additional genes have been suggested as causes for parkinsonism or PD, including genes for hereditary ataxias (ATXN2, ATXN3, FMR1), frontotemporal dementia (C9ORF72, GRN, MAPT, TARDBP), DYT5 (GCH1, TH, SPR), and others (ATP13A2, CSF1R, DNAJC6, FBXO, GIGYF2, HTRA2, PLA2G6, POLG, SPG11, UCHL1). This review summarizes the clinical features of diseases caused by mutations in these genes, and their frequencies. Point mutations and multiplications in SNCA cause cognitive or psychiatric symptoms, parkinsonism, dysautonomia and myoclonus with widespread alpha-synuclein pathology in the central and peripheral nervous system. LRRK2 mutations may lead to a clinical phenotype closely resembling idiopathic PD with a puzzling variety in neuropathology. Mutations in parkin/PARK2, PINK1 or DJ1/PARK7 may cause early-onset parkinsonism with a low risk for cognitive decline and a pathological process usually restricted to the brainstem. Carriers of mutations in the other genes may develop parkinsonism with or without additional symptoms, but rarely a disease resembling PD. The pathogenicity of several mutations remains unconfirmed. Although some mutations occur with high frequency in specific populations, worldwide all are very rare. The genetic cause of the majority of patients with sporadic or hereditary PD remains unknown in most populations. Clinical genetic testing is useful for selected patients. Testing strategies need to be adapted individually based on clinical phenotype and estimated frequency of the mutation in the patient's population.