The emerging role of SMPD1 mutations in Parkinson's disease: Implications for future studies

Exome sequencing in Asian populations identifies low-frequency and rare coding variation influencing Parkinson's disease risk

Parkinson's disease (PD) is an incurable, progressive and common movement disorder that is increasing in incidence globally because of population aging. We hypothesized that the landscape of rare, protein-altering variants could provide further insights into disease pathogenesis. Here we performed whole-exome sequencing followed by gene-based tests on 4,298 PD cases and 5,512 controls of Asian ancestry. We showed that GBA1 and SMPD1 were significantly associated with PD risk, with replication in a further 5,585 PD cases and 5,642 controls. We further refined variant classification using in vitro assays and showed that SMPD1 variants with reduced enzymatic activity display the strongest association (<44% activity, odds ratio (OR) = 2.24, P = 1.25 × 10-15) with PD risk. Moreover, 80.5% of SMPD1 carriers harbored the Asian-specific p.Pro332Arg variant (OR = 2.16; P = 4.47 × 10-8). Our findings highlight the utility of performing exome sequencing in diverse ancestry groups to identify rare protein-altering variants in genes previously unassociated with disease.

Ceramide lowering rescues respiratory defects in a Drosophila model of acid sphingomyelinase deficiency

Types A and B Niemann-Pick disease (NPD) are inherited multisystem lysosomal storage disorders due to mutations in the SMPD1 gene. Respiratory dysfunction is a key hallmark of NPD, yet the mechanism for this is underexplored. SMPD1 encodes acid sphingomyelinase (ASM), which hydrolyses sphingomyelin to ceramide and phosphocholine. Here, we present a Drosophila model of ASM loss-of-function, lacking the fly orthologue of SMPD1, dASM, modelling several aspects of the respiratory pathology of NPD. dASM is expressed in the late-embryonic fly respiratory network, the trachea, and is secreted into the tracheal lumen. Loss of dASM results in embryonic lethality, and the tracheal lumen fails to fill normally with gas prior to eclosion. We demonstrate that the endocytic clearance of luminal constituents prior to gas-filling is defective in dASM mutants, and is coincident with autophagic, but not lysosomal defects, in late stage embryonic trachea. Finally, we show that although bulk sphingolipids are unchanged, dietary loss of lipids in combination with genetic and pharmacological block of ceramide synthesis rescues the airway gas-filling defects. We highlight myriocin as a potential therapeutic drug for the treatment of the developmental respiratory defects associated with ASM deficiency, and present a new NPD model amenable to genetic and pharmacological screens.

Genetic-based diagnostics of Parkinson's disease and other Parkinsonian syndromes

INTRODUCTION

Parkinson's disease (PD) is a complex disorder with vast clinical heterogeneity. Recent genetic, imaging and clinical evidence suggest that there are multiple subtypes of PD, and perhaps even distinct clinical entities, which are being diagnosed under the umbrella of PD. These might have similar clinical presentation, but potentially different underlying mechanisms, which, in future, will require different treatments. Despite extensive genetic research progress, genetic testing is still not a common practice in clinical patient care.

AREAS COVERED

This review examines the numerous genes that have been discovered to affect the risk of, or cause, PD. We also outline genetic variants that affect PD age at onset, its progression, and the presence or severity of motor and non-motor symptoms. We differentiate between PD, other synucleinopathies, and atypical parkinsonism syndromes, and describe genes responsible for familial forms of typical PD and atypical parkinsonism. Lastly, we present current clinical trails that are underway for targeted therapies, particularly for GBA1-PD and LRRK2-PD which are the most significant subtypes.

EXPERT OPINION

While genetic studies alone cannot be diagnostic for PD, proper utilization of genetic screening for PD could improve diagnostic accuracy and predictions for prognosis, guide treatment, and identify individuals that qualify for clinical trials.

Late-onset Krabbe disease presenting as spastic paraplegia - implications of GCase and CTSB/D

OBJECTIVE

Krabbe disease (KD) is a multisystem neurodegenerative disorder with severe disability and premature death, mostly with an infancy/childhood onset. In rare cases of late-onset phenotypes, symptoms are often milder and difficult to diagnose. We here present a translational approach combining diagnostic and biochemical analyses of a male patient with a progressive gait disorder starting at the age of 44 years, with a final diagnosis of late-onset KD (LOKD).

METHODS

Additionally to cerebral MRI, protein structural analyses of the β-galactocerebrosidase protein (GALC) were performed. Moreover, expression, lysosomal localization, and activities of β-glucocerebrosidase (GCase), cathepsin B (CTSB), and cathepsin D (CTSD) were analyzed in leukocytes, fibroblasts, and lysosomes of fibroblasts.

RESULTS

Exome sequencing revealed biallelic likely pathogenic variants: GALC exons 11-17: 33 kb deletion; exon 4: missense variant (c.334A>G, p.Thr112Ala). We detected a reduced GALC activity in leukocytes and fibroblasts. While histological KD phenotypes were absent in fibroblasts, they showed a significantly decreased activities of GCase, CTSB, and CTSD in lysosomal fractions, while expression levels were unaffected.

INTERPRETATION

The presented LOKD case underlines the age-dependent appearance of a mildly pathogenic GALC variant and its interplay with other lysosomal proteins. As GALC malfunction results in reduced ceramide levels, we assume this to be causative for the here described decrease in CTSB and CTSD activity, potentially leading to diminished GCase activity. Hence, we emphasize the importance of a functional interplay between the lysosomal enzymes GALC, CTSB, CTSD, and GCase, as well as between their substrates, and propose their conjoined contribution in KD pathology.

Peripheral Upregulation of Parkinson's Disease-Associated Genes Encoding α-Synuclein, β-Glucocerebrosidase, and Ceramide Glucosyltransferase in Major Depression

Due to the high comorbidity of Parkinson's disease (PD) with major depressive disorder (MDD) and the involvement of sphingolipids in both conditions, we investigated the peripheral expression levels of three primarily PD-associated genes: α-synuclein (SNCA), lysosomal enzyme β-glucocerebrosidase (GBA1), and UDP-glucose ceramide glucosyltransferase (UGCG) in a sex-balanced MDD cohort. Normalized gene expression was determined by quantitative PCR in patients suffering from MDD (unmedicated n = 63, medicated n = 66) and controls (remitted MDD n = 39, healthy subjects n = 61). We observed that expression levels of SNCA (p = 0.036), GBA1 (p = 0.014), and UGCG (p = 0.0002) were higher in currently depressed patients compared to controls and remitted patients, and expression of GBA1 and UGCG decreased in medicated patients during three weeks of therapy. Additionally, in subgroups, expression was positively correlated with the severity of depression and anxiety. Furthermore, we identified correlations between the gene expression levels and PD-related laboratory parameters. Our findings suggest that SNCA, GBA1, and UGCG analysis could be instrumental in the search for biomarkers of MDD and in understanding the overlapping pathological mechanisms underlying neuro-psychiatric diseases.

Sex-specific pleiotropic changes in emotional behavior and alcohol consumption in human α-synuclein A53T transgenic mice during early adulthood

Point mutations in the α-synuclein coding gene may lead to the development of Parkinson's disease (PD). PD is often accompanied by other psychiatric conditions, such as anxiety, depression, and drug use disorders, which typically emerge in adulthood. Some of these point mutations, such as SNCA and A30T, have been linked to behavioral effects that are not commonly associated with PD, especially regarding alcohol consumption patterns. In this study, we investigated whether the familial PD point mutation A53T is associated with changes in alcohol consumption behavior and emotional states at ages not yet characterized by α-synuclein accumulation. The affective and alcohol-drinking phenotypes remained unaltered in female PDGF-hA53T-synuclein-transgenic (A53T) mice during both early and late adulthood. Brain region-specific activation of ceramide-producing enzymes, acid sphingomyelinase (ASM), and neutral sphingomyelinase (NSM), known for their neuroprotective properties, was observed during early adulthood but not in late adulthood. In males, the A53T mutation was linked to a reduction in alcohol consumption in both early and late adulthood. However, male A53T mice displayed increased anxiety- and depression-like behaviors during both early and late adulthood. Enhanced ASM activity in the dorsal mesencephalon and ventral hippocampus may potentially contribute to these adverse behavioral effects of the mutation in males during late adulthood. In summary, the A53T gene mutation was associated with diverse changes in emotional states and alcohol consumption behavior long before the onset of PD, and these effects varied by sex. These alterations in behavior may be linked to changes in brain ceramide metabolism.

LRRK2 exonic variants are associated with lysosomal hydrolase activities and lysosphingolipid alterations in Parkinson's disease

Last data demonstrated that exonic variants of LRRK2 (p.G2019S, p.M1646T) may affect the catalytic activity of lysosomal enzyme glucocerebrosidase (GCase) probably through the phosphorylation of Rab10 protein. We aimed to evaluate an association of LRRK2 exonic variants previously associated with alteration of phosphorylation levels for Rab10Thr73 with PD risk in Russian population and analyze an impact of p.G2019S mutation and selected LRRK2 variants on lysosomal hydrolase activities. LRRK2 variants were determined by full sequencing of LRRK2 in 508 PD patients and 470 controls from Russian population. Activity of lysosomal enzymes (glucocerebrosidase (GCase), alpha-galactosidase A (GLA), acid sphingomyelinase (ASMase) and concentrations of their corresponded substrates (hexosylsphingosine (HexSph), globotriaosylsphingosine (LysoGb3), lysosphingomyelin (LysoSM), respectively) were estimated in 211 PD patients and 179 controls by liquid chromatography with tandem mass spectrometry (LC-MS-MS) in dry blood spots. p.M1646T and p.N2081D were associated with PD (OR = 2.33, CI 95%: 1.1215 to 4.8253, p = 0.023; OR = 1.89, 95%CI: 1.0727 to 3.3313, p = 0.028, respectively) in Russian population. An increased LysoGb3 concentration was found in p.G2019S and p.N2081D LRRK2 carriers among PD patients compared to both PD patients and controls (p.G2019S: p = 0.00086, p = 0.0004, respectively; p.N2081D: p = 0.012, p = 0.0076, respectively). A decreased ASMase activity in p.G2019S LRRK2 carriers among PD patients (p = 0.014) was demonstrated as well. Our study supported possible involvement of LRRK2 dysfunction in an alteration of sphingolipid metabolism in PD.

Genetic Evidence for Endolysosomal Dysfunction in Parkinson’s Disease: A Critical Overview

Parkinson’s disease (PD) is the second most common neurodegenerative disorder in the aging population, and no disease-modifying therapy has been approved to date. The pathogenesis of PD has been related to many dysfunctional cellular mechanisms, however, most of its monogenic forms are caused by pathogenic variants in genes involved in endolysosomal function (LRRK2, VPS35, VPS13C, and ATP13A2) and synaptic vesicle trafficking (SNCA, RAB39B, SYNJ1, and DNAJC6). Moreover, an extensive search for PD risk variants revealed strong risk variants in several lysosomal genes (e.g., GBA1, SMPD1, TMEM175, and SCARB2) highlighting the key role of lysosomal dysfunction in PD pathogenesis. Furthermore, large genetic studies revealed that PD status is associated with the overall “lysosomal genetic burden”, namely the cumulative effect of strong and weak risk variants affecting lysosomal genes. In this context, understanding the complex mechanisms of impaired vesicular trafficking and dysfunctional endolysosomes in dopaminergic neurons of PD patients is a fundamental step to identifying precise therapeutic targets and developing effective drugs to modify the neurodegenerative process in PD.

LRRK2 and GBA1 variant carriers have higher urinary bis(monacylglycerol) phosphate concentrations in PPMI cohorts

We quantified concentrations of three isoforms of the endolysosomal lipid, bis(monoacylglycerol) phosphate (BMP) in the urine of deeply phenotyped cohorts in the Parkinson's Progression Markers Initiative: LRRK2 G2019S PD (N = 134) and non-manifesting carriers (NMC) (G2019S+ NMC; N = 182), LRRK2 R1441G PD (N = 15) and R1441G+ NMC (N = 15), GBA1 N409S PD (N = 76) and N409S+ NMC (N = 178), sporadic PD (sPD, N = 379) and healthy controls (HC) (N = 190). The effects of each mutation and disease status were analyzed using nonparametric methods. Longitudinal changes in BMP levels were analyzed using linear mixed models. At baseline, all LRRK2 carriers had 3-7× higher BMP levels compared to HC, irrespective of the disease status. GBA1 N409S carriers also showed significant, albeit smaller, elevation (~30-40%) in BMP levels compared to HC. In LRRK2 G2019S PD, urinary BMP levels remained stable over two years. Furthermore, baseline BMP levels did not predict disease progression as measured by striatal DaT imaging, MDS-UPDRS III Off, or MoCA in any of the cohorts. These data support the utility of BMP as a target modulation biomarker in therapeutic trials of genetic and sPD but not as a prognostic or disease progression biomarker.

Disease mechanisms as subtypes: Lysosomal dysfunction in the endolysosomal Parkinson's disease subtype

Parkinson's disease (PD) remains one of the most prevalent neurodegenerative disorders. It has become increasingly recognized that PD is not one disease but a constellation of many, with distinct cellular mechanisms driving pathology and neuronal loss in each given subtype. Endolysosomal trafficking and lysosomal degradation are crucial to maintain neuronal homeostasis and vesicular trafficking. It is clear that deficits in endolysosomal signaling data support the existence of an endolysosomal PD subtype. This chapter describes how cellular pathways involved in endolysosomal vesicular trafficking and lysosomal degradation in neurons and immune cells can contribute to PD. Last, as inflammatory processes including phagocytosis and cytokine release are central in glia-neuron interactions, a spotlight on the role of neuroinflammation plays in the pathogenesis of this PD subtype is also explored.

The Protein-Protein Interaction Network of Hereditary Parkinsonism Genes Is a Hierarchical Scale-Free Network

PURPOSE

Hereditary parkinsonism genes consist of causative genes of familial Parkinson's disease (PD) with a locus symbol prefix (PARK genes) and hereditary atypical parkinsonian disorders that present atypical features and limited responsiveness to levodopa (non-PARK genes). Although studies have shown that hereditary parkinsonism genes are related to idiopathic PD at the phenotypic, gene expression, and genomic levels, no study has systematically investigated connectivity among the proteins encoded by these genes at the protein-protein interaction (PPI) level.

MATERIALS AND METHODS

Topological measurements and physical interaction enrichment were performed to assess PPI networks constructed using some or all the proteins encoded by hereditary parkinsonism genes (n=96), which were curated using the Online Mendelian Inheritance in Man database and literature.

RESULTS

Non-PARK and PARK genes were involved in common functional modules related to autophagy, mitochondrial or lysosomal organization, catecholamine metabolic process, chemical synapse transmission, response to oxidative stress, neuronal apoptosis, regulation of cellular protein catabolic process, and vesicle-mediated transport in synapse. The hereditary parkinsonism proteins formed a single large network comprising 51 nodes, 83 edges, and three PPI pairs. The probability of degree distribution followed a power-law scaling behavior, with a degree exponent of 1.24 and a correlation coefficient of 0.92. LRRK2 was identified as a hub gene with the highest degree of betweenness centrality; its physical interaction enrichment score was 1.28, which was highly significant.

CONCLUSION

Both PARK and non-PARK genes show high connectivity at the PPI and biological functional levels.

The Multiple Roles of Sphingomyelin in Parkinson's Disease

Advances over the past decade have improved our understanding of the role of sphingolipid in the onset and progression of Parkinson's disease. Much attention has been paid to ceramide derived molecules, especially glucocerebroside, and little on sphingomyelin, a critical molecule for brain physiopathology. Sphingomyelin has been proposed to be involved in PD due to its presence in the myelin sheath and for its role in nerve impulse transmission, in presynaptic plasticity, and in neurotransmitter receptor localization. The analysis of sphingomyelin-metabolizing enzymes, the development of specific inhibitors, and advanced mass spectrometry have all provided insight into the signaling mechanisms of sphingomyelin and its implications in Parkinson's disease. This review describes in vitro and in vivo studies with often conflicting results. We focus on the synthesis and degradation enzymes of sphingomyelin, highlighting the genetic risks and the molecular alterations associated with Parkinson's disease.

Neurodegenerative Disease Risk in Carriers of Autosomal Recessive Disease

Genetics has driven significant discoveries in the field of neurodegenerative diseases (NDDs). An emerging theme in neurodegeneration warrants an urgent and comprehensive update: that carrier status of early-onset autosomal recessive (AR) disease, typically considered benign, is associated with an increased risk of a spectrum of late-onset NDDs. Glucosylceramidase beta (GBA1) gene mutations, responsible for the AR lysosomal storage disorder Gaucher disease, are a prominent example of this principle, having been identified as an important genetic risk factor for Parkinson disease. Genetic analyses have revealed further examples, notably GRN, TREM2, EIF2AK3, and several other LSD and mitochondria function genes. In this Review, we discuss the evidence supporting the strikingly distinct allele-dependent clinical phenotypes observed in carriers of such gene mutations and its impact on the wider field of neurodegeneration.

Murine Models of Lysosomal Storage Diseases Exhibit Differences in Brain Protein Aggregation and Neuroinflammation

Genetic, epidemiological and experimental evidence implicate lysosomal dysfunction in Parkinson’s disease (PD) and related synucleinopathies. Investigate several mouse models of lysosomal storage diseases (LSDs) and evaluate pathologies reminiscent of synucleinopathies. We obtained brain tissue from symptomatic mouse models of Gaucher, Fabry, Sandhoff, Niemann–Pick A (NPA), Hurler, Pompe and Niemann–Pick C (NPC) diseases and assessed for the presence of Lewy body-like pathology (proteinase K-resistant α-synuclein and tau aggregates) and neuroinflammation (microglial Iba1 and astrocytic GFAP) by immunofluorescence. All seven LSD models exhibited evidence of proteinopathy and/or inflammation in the central nervous system (CNS). However, these phenotypes were divergent. Gaucher and Fabry mouse models displayed proteinase K-resistant α-synuclein and tau aggregates but no neuroinflammation; whereas Sandhoff, NPA and NPC showed marked neuroinflammation and no overt proteinopathy. Pompe disease animals uniquely displayed widespread distribution of tau aggregates accompanied by moderate microglial activation. Hurler mice also demonstrated proteinopathy and microglial activation. The present study demonstrated additional links between LSDs and pathogenic phenotypes that are hallmarks of synucleinopathies. The data suggest that lysosomal dysregulation can contribute to brain region-specific protein aggregation and induce widespread neuroinflammation in the brain. However, only a few LSD models examined exhibited phenotypes consistent with synucleinopathies. While no model can recapitulate the complexity of PD, they can enable the study of specific pathways and mechanisms contributing to disease pathophysiology. The present study provides evidence that there are existing, previously unutilized mouse models that can be employed to study pathogenic mechanisms and gain insights into potential PD subtypes, helping to determine if they are amenable to pathway-specific therapeutic interventions.

The Emerging Role of the Lysosome in Parkinson's Disease

Lysosomal function has a central role in maintaining neuronal homeostasis, and, accordingly, lysosomal dysfunction has been linked to neurodegeneration and particularly to Parkinson’s disease (PD). Lysosomes are the converging step where the substrates delivered by autophagy and endocytosis are degraded in order to recycle their primary components to rebuild new macromolecules. Genetic studies have revealed the important link between the lysosomal function and PD; several of the autosomal dominant and recessive genes associated with PD as well as several genetic risk factors encode for lysosomal, autophagic, and endosomal proteins. Mutations in these PD-associated genes can cause lysosomal dysfunction, and since α-synuclein degradation is mostly lysosomal-dependent, among other consequences, lysosomal impairment can affect α-synuclein turnover, contributing to increase its intracellular levels and therefore promoting its accumulation and aggregation. Recent studies have also highlighted the bidirectional link between Parkinson’s disease and lysosomal storage diseases (LSD); evidence includes the presence of α-synuclein inclusions in the brain regions of patients with LSD and the identification of several lysosomal genes involved in LSD as genetic risk factors to develop PD.

Lysosomal Storage Disorders Shed Light on Lysosomal Dysfunction in Parkinson's Disease

The lysosome is a central player in the cell, acting as a clearing house for macromolecular degradation, but also plays a critical role in a variety of additional metabolic and regulatory processes. The lysosome has recently attracted the attention of neurobiologists and neurologists since a number of neurological diseases involve a lysosomal component. Among these is Parkinson’s disease (PD). While heterozygous and homozygous mutations in GBA1 are the highest genetic risk factor for PD, studies performed over the past decade have suggested that lysosomal loss of function is likely involved in PD pathology, since a significant percent of PD patients have a mutation in one or more genes that cause a lysosomal storage disease (LSD). Although the mechanistic connection between the lysosome and PD remains somewhat enigmatic, significant evidence is accumulating that lysosomal dysfunction plays a central role in PD pathophysiology. Thus, lysosomal dysfunction, resulting from mutations in lysosomal genes, may enhance the accumulation of α-synuclein in the brain, which may result in the earlier development of PD.

Genetic perspective on the synergistic connection between vesicular transport, lysosomal and mitochondrial pathways associated with Parkinson's disease pathogenesis

Parkinson's disease (PD) and atypical parkinsonian syndromes (APS) are symptomatically characterized by parkinsonism, with the latter presenting additionally a distinctive range of atypical features. Although the majority of patients with PD and APS appear to be sporadic, genetic causes of several rare monogenic disease variants were identified. The knowledge acquired from these genetic factors indicated that defects in vesicular transport pathways, endo-lysosomal dysfunction, impaired autophagy-lysosomal protein and organelle degradation pathways, α-synuclein aggregation and mitochondrial dysfunction play key roles in PD pathogenesis. Moreover, membrane dynamics are increasingly recognized as a key player in the disease pathogenesis due lipid homeostasis alterations, associated with lysosomal dysfunction, caused by mutations in several PD and APS genes. The importance of lysosomal dysfunction and lipid homeostasis is strengthened by both genetic discoveries and clinical epidemiology of the association between parkinsonism and lysosomal storage disorders (LSDs), caused by the disruption of lysosomal biogenesis or function. A synergistic coordination between vesicular trafficking, lysosomal and mitochondria defects exist whereby mutations in PD and APS genes encoding proteins primarily involved one PD pathway are frequently associated with defects in other PD pathways as a secondary effect. Moreover, accumulating clinical and genetic observations suggest more complex inheritance patters of familial PD exist, including oligogenic and polygenic inheritance of genes in the same or interconnected PD pathways, further strengthening their synergistic connection.Here, we provide a comprehensive overview of PD and APS genes with functions in vesicular transport, lysosomal and mitochondrial pathways, and highlight functional and genetic evidence of the synergistic connection between these PD associated pathways.

Lysosomal Ceramide Metabolism Disorders: Implications in Parkinson's Disease

Ceramides are a family of bioactive lipids belonging to the class of sphingolipids. Sphingolipidoses are a group of inherited genetic diseases characterized by the unmetabolized sphingolipids and the consequent reduction of ceramide pool in lysosomes. Sphingolipidoses include several disorders as Sandhoff disease, Fabry disease, Gaucher disease, metachromatic leukodystrophy, Krabbe disease, Niemann Pick disease, Farber disease, and GM2 gangliosidosis. In sphingolipidosis, lysosomal lipid storage occurs in both the central nervous system and visceral tissues, and central nervous system pathology is a common hallmark for all of them. Parkinson’s disease, the most common neurodegenerative movement disorder, is characterized by the accumulation and aggregation of misfolded α-synuclein that seem associated to some lysosomal disorders, in particular Gaucher disease. This review provides evidence into the role of ceramide metabolism in the pathophysiology of lysosomes, highlighting the more recent findings on its involvement in Parkinson’s disease.

Probiotic Bacillus subtilis Protects against α-Synuclein Aggregation in C. elegans

Recent discoveries have implicated the gut microbiome in the progression and severity of Parkinson's disease; however, how gut bacteria affect such neurodegenerative disorders remains unclear. Here, we report that the Bacillus subtilis probiotic strain PXN21 inhibits α-synuclein aggregation and clears preformed aggregates in an established Caenorhabditis elegans model of synucleinopathy. This protection is seen in young and aging animals and is partly mediated by DAF-16. Multiple B. subtilis strains trigger the protective effect via both spores and vegetative cells, partly due to a biofilm formation in the gut of the worms and the release of bacterial metabolites. We identify several host metabolic pathways differentially regulated in response to probiotic exposure, including sphingolipid metabolism. We further demonstrate functional roles of the sphingolipid metabolism genes lagr-1, asm-3, and sptl-3 in the anti-aggregation effect. Our findings provide a basis for exploring the disease-modifying potential of B. subtilis as a dietary supplement.

Understanding the links between cardiovascular disease and Parkinson's disease

Studies investigating the associations between genetic or environmental factors and Parkinson's disease (PD) have uncovered a number of factors shared with cardiovascular disease, either as risk factors or manifestations of cardiovascular disease itself. Older age, male sex, and possibly type 2 diabetes are examples. On the other hand, coffee consumption and physical activity are each associated with a lower risk of both PD and cardiovascular disease. This observation raises questions about the underlying pathophysiological links between cardiovascular disease and PD. There is evidence for common mechanisms in the areas of glucose metabolism, cellular stress, lipid metabolism, and inflammation. On the other hand, smoking and total/low-density lipoprotein cholesterol appear to have opposite associations with cardiovascular disease and PD. Thus, it is uncertain whether the treatment of cardiovascular risk factors will impact on the onset or progression of PD. The available data suggest that a nuanced approach is necessary to manage risk factors such as cholesterol levels once the associations are better understood. Ultimately, the choice of therapy may be tailored to a patient's comorbidity profile. This review presents the epidemiological evidence for both concordant and discordant associations between cardiovascular disease and PD, discusses the cellular and metabolic processes that may underlie these links, and explores the implications this has for patient care and future research. © 2019 International Parkinson and Movement Disorder Society.

Do heterozygous mutations of Niemann-Pick type C predispose to late-onset neurodegeneration: a review of the literature

BACKGROUND/METHODS

Monogenic diseases are important models for the study of neurodegenerative diseases, such as Parkinson's disease (PD) and dementia. Notably, for some disorders, homozygosity is associated with a complex metabolic disease, while heterozygosity predisposes to late-onset neurodegeneration. For instance, biallelic glucocerebrosidase gene mutations cause Gaucher's disease, while heterozygous mutations are a common genetic risk factor for late-onset PD. Little is known about similar risks of related diseases, such as Niemann-Pick type C (NPC). Given that both conditions map into related, i.e., lysosomal, pathways, we hypothesize a similar risk of single-NPC gene mutations. Indeed, there is increasing evidence based on clinical observations in humans and animal studies. Here we review the current knowledge of NPC heterozygosity.

RESULTS

Family history studies suggest a high proportion of late-onset neurodegenerative diseases in NPC families. We identified 19 cases with heterozygous NPC mutations in the literature who presented with a neurodegenerative disease, including levodopa-responsive PD, atypical parkinsonism (PSP, CBD), dystonia or dementia with a mean age at onset of about 57 years (range 8-87). Consistent splenomegaly and mildly abnormal filipin staining results have also been reported in heterozygous gene mutation carriers. Imaging and pathological data support this notion.

DISCUSSION/CONCLUSION

This finding has wider implications in so far as NPC-related forms of Parkinsonian syndromes, dementia, motor neuron disease and other neurodegenerative disorders may benefit from NPC-mechanistic therapies, in particular related to lysosomal dysfunction. Further research is warranted to generate systematic data of heterozygous mutation carriers, including longitudinal data.

Emerging links between pediatric lysosomal storage diseases and adult parkinsonism

Lysosomal storage disorders comprise a clinically heterogeneous group of autosomal-recessive or X-linked genetic syndromes caused by disruption of lysosomal biogenesis or function resulting in accumulation of nondegraded substrates. Although lysosomal storage disorders are diagnosed predominantly in children, many show variable expressivity with clinical presentations possible later in life. Given the important role of lysosomes in neuronal homeostasis, neurological manifestations, including movement disorders, can accompany many lysosomal storage disorders. Over the last decade, evidence from genetics, clinical epidemiology, cell biology, and biochemistry have converged to implicate links between lysosomal storage disorders and adult-onset movement disorders. The strongest evidence comes from mutations in Glucocerebrosidase, which cause Gaucher's disease and are among the most common and potent risk factors for PD. However, recently, many additional lysosomal storage disorder genes have been similarly implicated, including SMPD1, ATP13A2, GALC, and others. Examination of these links can offer insight into pathogenesis of PD and guide development of new therapeutic strategies. We systematically review the emerging genetic links between lysosomal storage disorders and PD. © 2019 International Parkinson and Movement Disorder Society.

SMPD1 mutations, activity, and α-synuclein accumulation in Parkinson's disease

BACKGROUND

SMPD1 (acid-sphingomyelinase) variants have been associated with Parkinson's disease in recent studies. The objective of this study was to further investigate the role of SMPD1 mutations in PD.

METHODS

SMPD1 was sequenced in 3 cohorts (Israel Ashkenazi Jewish cohort, Montreal/Montpellier, and New York), including 1592 PD patients and 975 controls. Additional data were available for 10,709 Ashkenazi Jewish controls. Acid-sphingomyelinase activity was measured by a mass spectrometry-based assay in the New York cohort. α-Synuclein levels were measured in vitro following CRISPR/Cas9-mediated knockout and siRNA knockdown of SMPD1 in HeLa and BE(2)-M17 cells. Lysosomal localization of acid-sphingomyelinase with different mutations was studied, and in silico analysis of their effect on acid-sphingomyelinase structure was performed.

RESULTS

SMPD1 mutations were associated with PD in the Ashkenazi Jewish cohort, as 1.4% of PD patients carried the p.L302P or p.fsP330 mutation, compared with 0.37% in 10,709 Ashkenazi Jewish controls (OR, 3.7; 95%CI, 1.6-8.2; P = 0.0025). In the Montreal/Montpellier cohort, the p.A487V variant was nominally associated with PD (1.5% versus 0.14%; P = 0.0065, not significant after correction for multiple comparisons). Among PD patients, reduced acid-sphingomyelinase activity was associated with a 3.5- to 5.8-year earlier onset of PD in the lowest quartile versus the highest quartile of acid-sphingomyelinase activity (P = 0.01-0.001). We further demonstrated that SMPD1 knockout and knockdown resulted in increased α-synuclein levels in HeLa and BE(2)-M17 dopaminergic cells and that the p.L302P and p.fsP330 mutations impair the traffic of acid-sphingomyelinase to the lysosome.

CONCLUSIONS

Our results support an association between SMPD1 variants, acid-sphingomyelinase activity, and PD. Furthermore, they suggest that reduced acid-sphingomyelinase activity may lead to α-synuclein accumulation. © 2019 International Parkinson and Movement Disorder Society.

Recommendations for clinical monitoring of patients with acid sphingomyelinase deficiency (ASMD)

BACKGROUND

Acid sphingomyelinase deficiency (ASMD), a rare lysosomal storage disease, results from mutations in SMPD1, the gene encoding acid sphingomyelinase (ASM). As a result, sphingomyelin accumulates in multiple organs including spleen, liver, lung, bone marrow, lymph nodes, and in the most severe form, in the CNS and peripheral nerves. Clinical manifestations range from rapidly progressive and fatal infantile neurovisceral disease, to less rapidly progressing chronic neurovisceral and visceral forms that are associated with significant morbidity and shorter life span due to respiratory or liver disease.

OBJECTIVES

To provide a contemporary guide of clinical assessments for disease monitoring and symptom management across the spectrum of ASMD phenotypes.

METHODS

An international group of ASMD experts in various research and clinical fields used an evidence-informed consensus process to identify optimal assessments, interventions, and lifestyle modifications.

RESULTS

Clinical assessment strategies for major organ system involvement, including liver, spleen, cardiovascular, pulmonary, and neurological/developmental are described, as well as symptomatic treatments, interventions, and/or life style modifications that may lessen disease impact.

CONCLUSIONS

There is currently no disease-specific treatment for ASMD, although enzyme replacement therapy with a recombinant human ASM (olipudase alfa) is in clinical development. Current monitoring addresses symptoms and multisystem involvement. Recommended interventions and lifestyle modifications are designed to address morbidity and disease complications and improve patient quality of life. While infantile neurovisceral ASMD is uniformly fatal in early childhood, patients with chronic visceral and chronic neurovisceral ASMD require appropriate management throughout childhood and adulthood by an interdisciplinary clinical team.

The Role of Ceramide and Sphingosine-1-Phosphate in Alzheimer's Disease and Other Neurodegenerative Disorders

Bioactive sphingolipids-ceramide, sphingosine, and their respective 1-phosphates (C1P and S1P)-are signaling molecules serving as intracellular second messengers. Moreover, S1P acts through G protein-coupled receptors in the plasma membrane. Accumulating evidence points to sphingolipids' engagement in brain aging and in neurodegenerative disorders such as Alzheimer's, Parkinson's, and Huntington's diseases and amyotrophic lateral sclerosis. Metabolic alterations observed in the course of neurodegeneration favor ceramide-dependent pro-apoptotic signaling, while the levels of the neuroprotective S1P are reduced. These trends are observed early in the diseases' development, suggesting causal relationship. Mechanistic evidence has shown links between altered ceramide/S1P rheostat and the production, secretion, and aggregation of amyloid β/α-synuclein as well as signaling pathways of critical importance for the pathomechanism of protein conformation diseases. Sphingolipids influence multiple aspects of Akt/protein kinase B signaling, a pathway that regulates metabolism, stress response, and Bcl-2 family proteins. The cross-talk between sphingolipids and transcription factors including NF-κB, FOXOs, and AP-1 may be also important for immune regulation and cell survival/death. Sphingolipids regulate exosomes and other secretion mechanisms that can contribute to either the spread of neurotoxic proteins between brain cells, or their clearance. Recent discoveries also suggest the importance of intracellular and exosomal pools of small regulatory RNAs in the creation of disturbed signaling environment in the diseased brain. The identified interactions of bioactive sphingolipids urge for their evaluation as potential therapeutic targets. Moreover, the early disturbances in sphingolipid metabolism may deliver easily accessible biomarkers of neurodegenerative disorders.

GBA-Associated Parkinson's Disease and Other Synucleinopathies

PURPOSE OF REVIEW

GBA mutations are the most common known genetic cause of Parkinson's disease (PD). Its biological pathway may be important in idiopathic PD, since activity of the enzyme encoded by GBA, glucocerebrosidase, is reduced even among PD patients without GBA mutations. This article describes the structure and function of GBA, reviews recent literature on the clinical phenotype of GBA PD, and suggests future directions for research, counseling, and treatment.

RECENT FINDINGS

Several longitudinal studies have shown that GBA PD has faster motor and cognitive progression than idiopathic PD and that this effect is dose dependent. New evidence suggests that GBA mutations may be important in multiple system atrophy. Further, new interventional studies focusing on GBA PD are described. These studies may increase the interest of PD patients and caregivers in genetic counseling. GBA mutation status may help clinicians estimate PD progression, though mechanisms underlying GBA and synucleinopathy require further understanding.

Alpha galactosidase A activity in Parkinson's disease

Glucocerebrosidase (GCase, deficient in Gaucher disease) enzymatic activity measured in dried blood spots of Parkinson's Disease (PD) cases is within healthy range but reduced compared to controls. It is not known whether activities of additional lysosomal enzymes are reduced in dried blood spots in PD. To test whether reduction in lysosomal enzymatic activity in PD is specific to GCase, we measured GCase, acid sphingomyelinase (deficient in Niemann-Pick disease types A and B), alpha galactosidase A (deficient in Fabry), acid alpha-glucosidase (deficient in Pompe) and galactosylceramidase (deficient in Krabbe) enzymatic activities in dried blood spots of PD patients (n = 648) and controls (n = 317) recruited from Columbia University. Full sequencing of glucocerebrosidase (GBA) and the LRRK2 G2019S mutation was performed. Enzymatic activities were compared between PD cases and controls using t-test and regression models adjusted for age, gender, and GBA and LRRK2 G2019S mutation status. Alpha galactosidase A activity was lower in PD cases compared to controls both when only non-carriers were included (excluding all GBA and LRRK2 G2019S carriers and PD cases with age-at-onset below 40) [2.85 μmol/l/h versus 3.12 μmol/l/h, p = 0.018; after controlling for batch effect, p = 0.006 (468 PD cases and 296 controls)], and when including the entire cohort (2.89 μmol/l/h versus 3.10 μmol/l/h, p = 0.040; after controlling for batch effect, p = 0.011). Because the alpha galactosidase A gene is X-linked, we stratified the analyses by sex. Among women who were non-carriers of GBA and LRRK2 G2019S mutations (PD, n = 155; control, n = 194), alpha galactosidase A activity was lower in PD compared to controls (2.77 μmol/l/h versus 3.10 μmol/l/h, p = 0.044; after controlling for a batch effect, p = 0.001). The enzymatic activity of acid sphingomyelinase, acid alpha-glucosidase and galactosylceramidase was not significantly different between PD and controls. In non-carriers, most lysosomal enzyme activities were correlated, with the strongest association in GCase, acid alpha-glucosidase, and alpha galactosidase A (Pearson correlation coefficient between 0.382 and 0.532). In a regression model with all five enzymes among non-carriers (adjusted for sex and age), higher alpha galactosidase A activity was associated with lower odds of PD status (OR = 0.54; 95% CI:0.31-0.95; p = 0.032). When LRRK2 G2019S PD carriers (n = 37) were compared to non-carriers with PD, carriers had higher GCase, acid sphingomyelinase and alpha galactosidase A activity. We conclude that alpha galactosidase A may have a potential independent role in PD, in addition to GCase.

Novel homozygous variants in ATCAY, MCOLN1, and SACS in complex neurological disorders

BACKGROUND

Neurological disorders comprise a large group of clinically and genetically heterogeneous disorders, many of which have a genetic cause. In addition to a detailed neurological examination, exome sequencing is being increasingly used as a complementary diagnostic tool to identify the underlying genetic cause in patients with unclear, supposedly genetically determined disorders.

OBJECTIVE

To identify the genetic cause of a complex movement disorder in five consanguineous Pakistani families.

METHODS

We included five consanguineous Pakistani families with complex recessively inherited movement disorders. Clinical investigation including videotaping was carried out in a total of 59 family members (4-21 per family) and MRI in six patients. Exome sequencing was performed in 4-5 family members per pedigree to explore the underlying genetic cause.

RESULTS

Patients presented a wide spectrum of neurological symptoms including ataxia and/or dystonia. We identified three novel homozygous, segregating variants in ATCAY (p.Pro200Profs*20), MCOLN1 (p.Ile184Thr), and SACS (p.Asn3040Lysfs*4) in three of the families. Thus, we were able to identify the likely cause of the disease in a considerable number of families (60%) with the relatively simple and nowadays widely available method of exome sequencing. Of note, close collaboration of neurologists and geneticists was instrumental for proper data interpretation.

CONCLUSIONS

We expand the phenotypic, genotypic, and ethnical spectrum of mutations in these genes. Our findings alert neurologists that rare genetic causes should be considered in complex phenotypes regardless of ethnicity.

Adaptive Sparse Multiple Canonical Correlation Analysis With Application to Imaging (Epi)Genomics Study of Schizophrenia

Finding correlations across multiple data sets in imaging and (epi)genomics is a common challenge. Sparse multiple canonical correlation analysis (SMCCA) is a multivariate model widely used to extract contributing features from each data while maximizing the cross-modality correlation. The model is achieved by using the combination of pairwise covariances between any two data sets. However, the scales of different pairwise covariances could be quite different and the direct combination of pairwise covariances in SMCCA is unfair. The problem of "unfair combination of pairwise covariances" restricts the power of SMCCA for feature selection. In this paper, we propose a novel formulation of SMCCA, called adaptive SMCCA, to overcome the problem by introducing adaptive weights when combining pairwise covariances. Both simulation and real-data analysis show the outperformance of adaptive SMCCA in terms of feature selection over conventional SMCCA and SMCCA with fixed weights. Large-scale numerical experiments show that adaptive SMCCA converges as fast as conventional SMCCA. When applying it to imaging (epi)genetics study of schizophrenia subjects, we can detect significant (epi)genetic variants and brain regions, which are consistent with other existing reports. In addition, several significant brain-development related pathways, e.g., neural tube development, are detected by our model, demonstrating imaging epigenetic association may be overlooked by conventional SMCCA. All these results demonstrate that adaptive SMCCA are well suited for detecting three-way or multiway correlations and thus can find widespread applications in multiple omics and imaging data integration.

LRRK2, GBA and SMPD1 Founder Mutations and Parkinson's Disease in Ashkenazi Jews

BACKGROUND/AIM

Parkinson's disease (PD) is associated with mutations in LRRK2, GBA, and SMPD1 genes. We describe the clinical characteristics of PD patients related to their carrier status of the Ashkenazi founder mutations in the aforementioned genes.

METHODS

Ashkenazi PD patients (n = 270) were recruited following informed consent, and tested for the founder Ashkenazi mutations in the above genes. Clinical characteristics were compared between carriers and noncarriers. Homozygotes for mutations in GBA or LRRK2, and those who carried mutations in two causative genes were excluded from the analysis.

RESULTS

Five (1.85%), 54 (20%), and 22 (8.1%) PD patients carried mutations in SMPD1, GBA or LRRK2, respectively. By post hoc Bonferroni analysis, GBA carriers were singled at a significantly earlier age at diagnosis compared to noncarriers (58.06 ± 10.84 and 62.65 ± 10.86 years, respectively; p = 0.036), and due to bilateral manifestation at diagnosis compared to all other PD groups (n = 8, 15.7% compared to n = 2, 1.1%, respectively; p < 0.001). Other clinical manifestations were comparable between groups.

CONCLUSION

Although only GBA mutation carriers, compared to noncarriers, reached statistical significance regarding age at diagnosis, it appears that LRRK2 and SMPD1 mutation carriers may reach significance with larger group numbers.

Excessive burden of lysosomal storage disorder gene variants in Parkinson's disease

Mutations in the glucocerebrosidase gene (GBA), which cause Gaucher disease, are also potent risk factors for Parkinson's disease. We examined whether a genetic burden of variants in other lysosomal storage disorder genes is more broadly associated with Parkinson's disease susceptibility. The sequence kernel association test was used to interrogate variant burden among 54 lysosomal storage disorder genes, leveraging whole exome sequencing data from 1156 Parkinson's disease cases and 1679 control subjects. We discovered a significant burden of rare, likely damaging lysosomal storage disorder gene variants in association with Parkinson's disease risk. The association signal was robust to the exclusion of GBA, and consistent results were obtained in two independent replication cohorts, including 436 cases and 169 controls with whole exome sequencing and an additional 6713 cases and 5964 controls with exome-wide genotyping. In secondary analyses designed to highlight the specific genes driving the aggregate signal, we confirmed associations at the GBA and SMPD1 loci and newly implicate CTSD, SLC17A5, and ASAH1 as candidate Parkinson's disease susceptibility genes. In our discovery cohort, the majority of Parkinson's disease cases (56%) have at least one putative damaging variant in a lysosomal storage disorder gene, and 21% carry multiple alleles. Our results highlight several promising new susceptibility loci and reinforce the importance of lysosomal mechanisms in Parkinson's disease pathogenesis. We suggest that multiple genetic hits may act in combination to degrade lysosomal function, enhancing Parkinson's disease susceptibility.

Disease manifestations and burden of illness in patients with acid sphingomyelinase deficiency (ASMD)

Acid sphingomyelinase deficiency (ASMD), a rare lysosomal storage disease, is an autosomal recessive genetic disorder caused by different SMPD1 mutations. Historically, ASMD has been classified as Niemann-Pick disease (NPD) types A (NPD A) and B (NPD B). NPD A is associated with a uniformly devastating disease course, with rapidly progressing psychomotor degeneration, leading to death typically by the age of 3 years, most often from respiratory failure. In contrast, the clinical phenotype and life expectancy of patients with NPD B may vary widely. Almost all patients have hepatosplenomegaly and an atherogenic lipid profile, and most patients have interstitial lung disease with progressive impairment of pulmonary function and hematologic abnormalities including cytopenias. Other common clinical manifestations include liver dysfunction, heart disease, skeletal abnormalities and growth delays. Some patients with ASMD who survive beyond early childhood have intermediate phenotypes (variant NPD B) characterized by combinations of non-neurologic and mild to severe neurologic symptoms. The physical and psychosocial burden of illness in patients with NPD B is substantial. Common symptoms include shortness of breath, joint or limb pain, abdominal pain, bleeding and bruising. The disease often leads to chronic fatigue, limited physical or social activity and difficulties in performing daily activities or work. Many patients die before or in early adulthood, often from pneumonia/respiratory failure or liver failure. Available treatments are limited to symptom management and supportive care. An enzyme replacement therapy currently in clinical development is expected to be the first treatment addressing the underlying pathology of the disease. Early diagnosis and appropriate management are essential for reducing the risk of complications. While knowledge about ASMD is evolving, more evidence about ASMD and the natural history across the disease spectrum is needed, to improve disease recognition, timely diagnosis and appropriate disease management.