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The association between apolipoprotein ε4-TOMM40’523 haplotypes and multiple system atrophy
*Corresponding author: Yongbiao Zou, Department of Neurology, The Central Hospital of Shaoyang, Shaoyang, Hunan, China. 748818018@qq.com
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Received: ,
Accepted: ,
How to cite this article: Zhou X, Huang X, Zhou L, Zhou L, Zou Y. The association between apolipoprotein ε4-TOMM40’523 haplotypes and multiple system atrophy. J Neurosci Rural Pract. 2025;16:540-5. doi: 10.25259/JNRP_1_2025
Abstract
Objectives:
Accumulating evidence has increasingly indicated that apolipoprotein E (APOE) or TOMM40 poly-T genotypes are likely to be involved in the pathogenesis of several neurodegenerative disorders, rather than being exclusively associated with Alzheimer’s disease (AD), which was their initial and primary linked condition. This expanding understanding of their potential broader role has sparked growing interest in exploring their involvement across a wider spectrum of neurodegenerative conditions. Given the substantial overlap in multiple clinical manifestations between synucleinopathies and AD – such as shared features such as cognitive decline, motor impairments, and certain neuropsychiatric symptoms – we designed and conducted this case–control study. The specific aim was to investigate whether there exists a genetic association between APOE ε4-TOMM40’523 haplotypes and multiple system atrophy (MSA) within Chinese Han cohorts, thereby contributing to the understanding of MSA’s genetic underpinnings.
Materials and Methods:
We systematically genotyped APOE and TOMM40‘523 variants in a well-characterized cohort comprising 200 patients diagnosed with MSA, 66 patients with Parkinson’s disease (PD), and 320 healthy controls (HCs). All participants were carefully selected to ensure the reliability and representativeness of the study population.
Results:
Our analyses revealed no statistically significant differences in the distribution patterns of APOE ε4-TOMM40’523 haplotypes among the MSA patients, PD patients, and HCs. Furthermore, no significant correlations were observed between the ε4-’523L haplotype and key clinical parameters in MSA patients, including age at onset and disease severity scores assessed by standardized scales.
Conclusion:
Taken together, the findings of our study suggest that the APOE ε4-TOMM40’523L haplotype may not play a substantial role in the pathogenesis of MSA, providing valuable insights into the genetic factors that may or may not contribute to this complex neurodegenerative disorder.
Keywords
Apolipoprotein E
Multiple system atrophy
Parkinson’s disease
Poly-T polymorphism
TOMM40
INTRODUCTION
Multiple system atrophy (MSA), a sporadic and progressive neurodegenerative disorder, is characterized by diverse combinations of autonomic failure, parkinsonism, cerebellar ataxia, and corticospinal dysfunction.[1] Based on the predominant motor symptoms, the disease is classified into two subtypes: The MSA parkinsonism-predominant subtype (MSA-P) and the MSA cerebellar-predominant subtype (MSA-C).[2] A prominent pathological hallmark of MSA is the presence of glial cytoplasmic inclusions, which are composed of misfolded α-synuclein deposited in the olivopontocerebellar and/or striatonigral systems.[1] As such, MSA is recognized as a distinct synucleinopathy, alongside Parkinson’s disease (PD) and Lewy body dementia (DLB).[3] Emerging evidence has increasingly confirmed that patients with Alzheimer’s disease (AD), PD, and other neurodegenerative disorders share certain common genetic backgrounds, a finding that has garnered growing attention in the field.[4] Drawing inspiration from the numerous similarities between synucleinopathies and AD – including overlapping non-motor symptoms (such as cognitive impairment and neuropsychiatric disturbances) and abnormal protein accumulation (e.g., α-synuclein in synucleinopathies and β-amyloid/tau in AD) – several AD-associated genes, including apolipoprotein E (APOE), Microtubule-associated protein tau (MAPT), Presenilin 1 (PSEN1), Presenilin 2 (PSEN2), and Amyloid Beta Precursor Protein (APP) have become focal points of research in MSA.[5-9] However, further validation studies are required to clarify their potential roles in the pathogenesis of MSA.
APOE, a multifunctional protein integral to lipid metabolism and transport, is encoded on chromosome 19q13.2.[10] It plays a pivotal role in the recovery of brain function through diverse pathways, including lipid transfer, cholesterol metabolism, and the regulation of coagulation factors.[11] Each of the APOE alleles – ε2, ε3, and ε4 – exhibits distinct associations with the progression of AD.[12] Specifically, the APOE ε4 allele stands as the most well-validated genetic determinant of risk for late-onset AD (LOAD), while the APOE ε2 allele has been consistently reported to exert a protective effect against AD.[12,13]
Beyond AD, genetic association studies have implicated APOE ε4 as a risk factor for cognitive decline in PD.[14] In addition, previous evidence suggests that patients with DLB carrying the APOE ε4 allele develop dementia symptoms at an earlier age.[15] However, in contrast to these findings, researchers have not observed a significant association between APOE genetic variations and the risk of MSA.[7]
Translocase of outer mitochondrial membrane 40 (TOMM40), located approximately 15 kb upstream of the APOE gene, is in significant linkage disequilibrium (LD) with APOE.[16] This gene encodes the translocase of the outer mitochondrial membrane 40 homolog (TOOM40), a protein essential for facilitating the import of proteins into mitochondria.[16] A poly-T polymorphism, rs10524523, within the TOMM40 gene (referred to as TOMM40’523) has been increasingly recognized as a contributor to the pathogenesis of various neurodegenerative diseases.[17,18] For instance, a study focusing on PD revealed that the length of the TOMM40’523 poly-T repeat serves as a significant determinant of cognitive decline in PD patients.[18]
Notably, most existing studies have been limited to APOE ε3 carriers, primarily due to the strong linkage between the APOE ε4 allele and the TOMM40’523’-L allele. To the best of our knowledge, no previous research has investigated the potential effects of the APOE ε4-TOMM40’523 haplotype in patients with MSA. Therefore, the present study aimed to explore the association between this specific haplotype and MSA in a Chinese cohort.
MATERIALS AND METHODS
Participants
A total of 200 patients with MSA, 66 patients with PD, and 320 healthy controls (HCs) were enrolled in this study. All patients were consecutively recruited from the Central Hospital of Shaoyang between 2018 and 2023. MSA patients were subclassified into MSA-P and MSA-C subtypes in accordance with the consensus criteria for clinical diagnosis of probable and possible MSA established in 2008.[2] PD patients were diagnosed based on the Movement Disorder Society clinical diagnostic criteria for PD. HCs were recruited from the Physical Examination Center of the same hospital. Institutional Review Board approval is not required and all participants provided written informed consent before enrollment.
Clinical assessments
All patients were evaluated by two experienced neurologists. The symptoms of patients with MSA were assessed using multiple clinical scales, and all participants underwent comprehensive general and neurological examinations. A variety of rating scales were used to quantify neurological impairment and deficits, including the Unified PD Rating Scale for PD patients in the “on” state, the Unified MSA Rating Scale (UMSARS) for MSA patients, and the Mini– Mental State Examination (MMSE) for global cognitive assessment.
Genetic analysis
Genomic DNA was extracted from peripheral blood monocytes using standard protocols. APOE ε genotypes (rs429358 and rs7412) were determined through TaqMan genotyping assays. Based on the poly-T repeat length, TOMM40 poly-T repeats (rs10524523) were classified into three classes: Short (‘523-S: poly-T repeat ≤19), Long (‘523-L: 20 ≤ poly-T repeat ≤29), and Very long (‘523-VL: poly-T repeat ≥30).[17] Polymerase chain reaction (PCR) amplification was performed to analyze APOE and TOMM40 poly-T repeat genotypes. All PCR products were sequenced using an ABI 3100 automated sequencer (Applied Biosystems) and subsequently analyzed with SnapGene software (version 5.1.4).
Statistical analysis
All statistical analyses were performed using the Statistical Package for the Social Sciences software (version 22.0). Quantitative variables are presented as mean ± standard deviation or median (minimum and maximum) for normal or non-normal distributions, respectively. Categorical variables are presented as absolute numbers and percentages. The Shapiro–Wilk test was used to assess the normality of variables, while the Levene test was used to test the homogeneity of variances. Differences between groups were analyzed using the t-test (for two groups) or the Chi-square test (for more than two groups) when variables conformed to a normal distribution and variance homogeneity. Group comparisons were performed using a one-way analysis of covariance (analysis of variance). Cohen’s κ coefficients were used to evaluate the concordance between APOE ε4 and TOMM40’523-L genotypes. Spearman’s rank correlation and partial correlation were used for correlation analyses. Statistical significance was defined as a two-tailed P < 0.05. The Bonferroni method was used for multiple testing corrections in both the group comparisons and correlation analyses.
RESULTS
Participants and clinical characteristics
The demographic and clinical characteristics of the participants are summarized in Table 1. A statistically significant difference in mean age was observed among the three groups (P < 0.001), with post hoc analyses revealing that the PD group was significantly older than both the MSA group (P < 0.001) and the HC group (P < 0.001). In contrast, no significant difference was noted in the distribution of sex among the three groups (P = 0.719).
| HC (n=320) | MSA (n=200) | PD (n=66) | |
|---|---|---|---|
| Age, ya | 53.469±7.656 | 53.590±6.647 | 63.121±6.560 |
| Sex (female/male), nb | 114/206 | 73/127 | 27/39 |
| Age at onset, y | - | 51.295±6.154 | 59.697±5.716 |
| Duration, y | - | 2.250±1.406 | 3.272±1.776 |
| Subtype (MSA-C/P), n | - | 148/52 | - |
| UMSARS-I scores | - | 19.630±3.813 | - |
| UMSARS-II scores | - | 20.565±3.945 | - |
| UMSARS-IV scores | - | 2.780±1.130 | - |
| UPDRS-I scores | - | - | 3.197±1.056 |
| UPDRS-II scores | - | - | 11.333±2.592 |
| UPDRS-III scores | - | - | 21.455±5.550 |
| MMSE scores | - | 25.820±2.316 | 25.894±1.978 |
The APOE ε2/2 genotype was absent in both the MSA and PD groups, while in the HC group, the frequency of the ε2/2 genotype was 0.9% (n = 3). Further analyses showed no significant differences in APOE genotype frequencies between MSA patients, PD patients, and controls (P = 0.332 [Supplementary Table 1]). Similarly, the distribution of TOMM40 poly-T repeat lengths did not differ significantly among the three groups (P = 0.812 [Supplementary Table 1]).
Table 2 displays the frequencies of APOE and TOMM40’523 genotypes, which are stratified by APOE ε4 carrier status among individuals with complete genotyping data. Consistent with the well-documented LD between APOE ε4 and TOMM40’523-L, only 14.8% of ε4 non-carriers carried the ’523-L allele, while 94.5% of ε4 carriers had this allele. This classification exhibited a high level of concordance (Cohen’s κ = 0.871, standard error = 0.026). In Table 2, there are 8 cases in the MSA group, 8 cases in the HC group, and 2 cases in the PD group with missing data. These missing cases are carriers of the APOE ε2 or ε3 allele with the TOMM40 S/L or L/VL genotype and were excluded from the covariance analysis. Considering the relatively large overall sample size, we believe that the exclusion of these few samples is unlikely to affect the results.
| APOE-TOMM40 haplotypes | HC (%) | MSA (%) | PD (%) | P(95%CI) | Partial eta-squared (η2p) |
|---|---|---|---|---|---|
| Non ε4 carriersa | |||||
| S/S | 49 (15.7) | 23 (12.0) | 10 (15.6) | ||
| S/VL | 135 (43.3) | 90 (46.9) | 27 (42.2) | ||
| VL/VL | 71 (22.8) | 44 (22.9) | 11 (17.2) | ||
| ε4-‘523L haplotype | 57 (18.3) | 35 (18.2) | 16 (25.0) | ||
| Total | 312 | 192 | 64 | 0.753b(−0.180–0.399) | 0.001c |
Association between APOE-TOMM40’523 haplotypes and disease risk
Analysis of covariance, with age included as a covariate, revealed no significant association between APOETOMM40’523 haplotypes and the risk of MSA or PD when compared with HCs (P = 0.753, 95% confidence interval [CI] = −0.180–0.399, η2p = 0.001 [Table 2]). In addition, no significant correlation was observed between the APOE ε4-TOMM40’523L haplotype and the age at onset of MSA symptoms (P = 0.231, r = 0.087, 95% CI = −0.073 ~ 0.229 [Supplementary Table 2]).
Effects of the APOE ε4-TOMM40’523L haplotype on disease severity in MSA
We further explored the potential correlation between the APOE ε4-TOMM40’523L haplotype and key clinical parameters in MSA patients, including MMSE scores and UMSARS scores (UMSARS-I, UMSARS-II, and UMSARS-IV). However, no significant relationships were detected between the ε4-‘523L haplotype and these clinical scale scores. Detailed results are presented in Supplementary Table 2 and Figure 1.
- Comparsion of clinical parameters of MSA patients with different APOE-TOMM40’523 haplotypes. MSA: Multiple system atrophy, UMSARSI: Unified MSA rating scale, MMSE: Mini-Mental state examination
DISCUSSION
To the best of our knowledge, this is the first study to investigate the effect of APOE ε4-TOMM40 ‘523 haplotype variations on the risk of MSA. We confirmed the linkage between ε4 and ‘523-L in the Chinese Han population, which is consistent with findings in Caucasian Americans.[19] However, our results indicated that the APOE ε4-‘523-L haplotype was not significantly associated with the risk of developing MSA or the age of disease onset.
The APOE ε4 allele is well-known to be associated with an increased risk of AD and has been implicated in multiple aspects of AD pathophysiology, including tau-induced neurodegeneration, microglial and astrocytic responses, and blood–brain barrier disruption.[12] In contrast, research on the role of APOE ε4 in PD has yielded contradictory results. While some previous studies suggested that the APOE ε4 allele might contribute to PD risk, others demonstrated no association between APOE genotypes and PD susceptibility.[20,21] Notably, prior studies have identified APOE ε4 as a risk factor for PD dementia (PDD), potentially due to the distinct roles of APOE isoforms in α-synuclein clearance by microglia.[22] In addition, a study on rapid eye movement sleep behavior disorder (RBD)-associated neurodegeneration found that patients with PD, MSA, and DLB had similar frequencies of the APOE ε4 allele, and APOE genotypes were not associated with the risk of RBD-associated synucleinopathies.[23] Consistent with these previous findings, our results confirmed that the APOE ε4 allele is not a susceptibility factor for MSA.[7]
Although the extent to which common variants in TOMM40 exert APOE-independent effects on disease risk or disease modification remains unclear, accumulating evidence suggests that APOE and TOMM40 interact to influence AD risk, with APOE-TOMM40 ‘523 haplotypes modifying the age of onset in LOAD.[24,25] Recent studies have revealed that APOE’s contribution to AD risk likely involves mediating cell and tissue lipid transport, while TOMM40 is thought to contribute to mitochondrial dysfunction and protein accumulation in AD.[17] Despite the well-explored roles of APOE and TOMM40 in AD, there is a paucity of research investigating their potential roles in synuclein-associated neurodegeneration. Given the essential role of TOMM40 in mitochondrial import and mitophagy, Bender et al. demonstrated that the TOMM40 poly-T polymorphism might affect α-synuclein accumulation in mitochondria by participating in mitochondrial dysfunction, thereby potentially contributing to PD pathology.[26] Conversely, a previous study in a Polish PD cohort failed to detect any association between ‘523 alleles or haplotypes and PD risk or the age of symptom onset.[27] Furthermore, subsequent studies verified that APOE-TOMM40 ‘523 haplotypes do not contribute to the risk of developing PDD or DLB.[28] To date, knowledge regarding the relationship between APOETOMM40 ‘523 haplotypes and α-synucleinopathies remains limited. Therefore, future research exploring additional genes and genomic factors could provide novel insights into the understanding of these complex neurodegenerative disorders.
This study has several limitations. First, as a single-center study, it would be beneficial to expand to multicenter studies across different regions to enhance generalizability. Second, we only used the MMSE for cognitive assessment; thus, more comprehensive and systematic cognitive evaluations are warranted in future investigations.
CONCLUSION
In summary, our findings did not reveal any evidence of an association between the ε4-‘523L haplotype and the risk of developing MSA in the Chinese population. This observation leads us to speculate that the genetic underpinnings of MSA are likely complex and multifactorial, involving interactions among multiple genetic loci and potentially environmental factors. Moreover, it suggests that pathological processes related to tauopathy or β-amyloidopathy – key drivers in other neurodegenerative disorders such as AD – may play a less prominent or direct causal role in the pathogenesis of MSA.
Given the inherent complexity of MSA and the limitations of our current study, including its focus on a specific ethnic group, further investigations are warranted to validate our conclusions. These future studies should ideally encompass more diverse ethnic populations to account for potential genetic heterogeneity across different racial and ethnic backgrounds, as well as larger cohorts to enhance statistical power and robustness. Such efforts will help clarify the genetic landscape of MSA and contribute to a more comprehensive understanding of its underlying mechanisms.
Acknowledgments:
The authors are grateful to all subjects for their participation in our study.
Ethical approval:
The study was approved by the Ethics Committee of Shaoyang Central Hospital (Approval No. 201812230036; dated 23rd December 2018).
Declaration of patient consent:
The authors certify that they have obtained all appropriate patient consent.
Conflicts of interest:
There are no conflicts of interest.
Use of artificial intelligence (AI)-assisted technology for manuscript preparation:
The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.
Financial support and sponsorship: Nil.
References
- Second consensus statement on the diagnosis of multiple system atrophy. Neurology. 2008;71:670-6.
- [CrossRef] [PubMed] [Google Scholar]
- The role of alpha-synuclein in the pathogenesis of multiple system atrophy. Acta Neuropathol. 2005;109:129-40.
- [CrossRef] [PubMed] [Google Scholar]
- Alzheimer disease biomarkers and synucleinopathy. Neurology. 2018;90:537-8.
- [CrossRef] [PubMed] [Google Scholar]
- Multiple system atrophy with amyloid-β-predominant Alzheimer's disease neuropathologic change. Brain Commun. 2024;6:fcae141.
- [CrossRef] [PubMed] [Google Scholar]
- MAPT haplotype diversity in multiple system atrophy. Parkinsonism Relat Disord. 2016;30:40-5.
- [CrossRef] [PubMed] [Google Scholar]
- Multiple system atrophy and apolipoprotein E. Mov Disord. 2018;33:647-50.
- [CrossRef] [PubMed] [Google Scholar]
- Activation of Pgk1 results in reduced protein aggregation in diverse neurodegenerative conditions. Mol Neurobiol. 2023;60:5090-101.
- [CrossRef] [PubMed] [Google Scholar]
- Deep sequencing of proteotoxicity modifier genes uncovers a presenilin-2/beta-amyloid-actin genetic risk module shared among alpha-synucleinopathies. 2024:03.03.583145.
- [CrossRef] [Google Scholar]
- Apolipoprotein E: Structure and function in lipid metabolism, neurobiology, and Alzheimer's diseases. Neurobiol Dis. 2014;72 Pt A:3-12.
- [CrossRef] [PubMed] [Google Scholar]
- Apolipoprotein E regulates lipid metabolism and α-synuclein pathology in human iPSC-derived cerebral organoids. Acta Neuropathol. 2021;142:807-25.
- [CrossRef] [PubMed] [Google Scholar]
- APOE and Alzheimer's disease: Advances in genetics, pathophysiology, and therapeutic approaches. Lancet Neurol. 2021;20:68-80.
- [CrossRef] [PubMed] [Google Scholar]
- An inherited variable poly-T repeat genotype in TOMM40 in Alzheimer disease. Arch Neurol. 2010;67:536-41.
- [CrossRef] [PubMed] [Google Scholar]
- APOE genotype regulates pathology and disease progression in synucleinopathy. Sci Transl Med. 2020;12:eaay3069.
- [CrossRef] [PubMed] [Google Scholar]
- Relative survival in patients with dementia with Lewy bodies and Parkinson's disease dementia. PLoS One. 2018;13:e0202044.
- [CrossRef] [PubMed] [Google Scholar]
- The Alzheimer's disease mitochondrial cascade hypothesis: An update. Exp Neurol. 2009;218:308-15.
- [CrossRef] [PubMed] [Google Scholar]
- Alzheimer's disease pathology explains association between dementia with Lewy bodies and APOE-ε4/TOMM40 long poly-T repeat allele variants. Alzheimers Dement (N Y). 2019;5:814-24.
- [CrossRef] [PubMed] [Google Scholar]
- TOMM40 '523' poly-T repeat length is a determinant of longitudinal cognitive decline in Parkinson's disease. NPJ Parkinsons Dis. 2021;7:56.
- [CrossRef] [PubMed] [Google Scholar]
- APOE ε4TOMM40 '523 haplotypes and the risk of Alzheimer's disease in older Caucasian and African Americans. PLoS One. 2017;12:e0180356.
- [CrossRef] [PubMed] [Google Scholar]
- Apolipoprotein E polymorphisms and Parkinson disease with or without dementia: A meta-analysis including 6453 participants. J Geriatr Psychiatry Neurol. 2019;32:3-15.
- [CrossRef] [PubMed] [Google Scholar]
- Meta-analysis of the relationship between the APOE gene and the onset of Parkinson's disease dementia. Parkinsons Dis. 2018;2018:9497147.
- [CrossRef] [PubMed] [Google Scholar]
- Apolipoprotein E genotype as a risk factor for susceptibility to and dementia in Parkinson's disease. J Neurol. 2009;256:493-8.
- [CrossRef] [PubMed] [Google Scholar]
- The dementia-associated APOE ε4 allele is not associated with rapid eye movement sleep behavior disorder. Neurobiol Aging. 2017;49:218.e13-5.
- [CrossRef] [PubMed] [Google Scholar]
- Alzheimer's disease cortical morphological phenotypes are associated with TOMM40'523-APOE haplotypes. Neurobiol Aging. 2023;132:131-44.
- [CrossRef] [PubMed] [Google Scholar]
- TOMM40 and APOE: Requirements for replication studies of association with age of disease onset and enrichment of a clinical trial. Alzheimers Dement. 2013;9:132-6.
- [CrossRef] [PubMed] [Google Scholar]
- TOM40 mediates mitochondrial dysfunction induced by α-synuclein accumulation in Parkinson's disease. PLoS One. 2013;8:e62277.
- [CrossRef] [PubMed] [Google Scholar]
- TOMM40 and APOE common genetic variants are not Parkinson's disease risk factors. Neurobiol Aging. 2013;34:2078.e1-2.
- [CrossRef] [PubMed] [Google Scholar]
- Associations between TOMM40 poly-T repeat variants and dementia in cases with Parkinsonism. J Parkinsons Dis. 2016;6:99-108.
- [CrossRef] [PubMed] [Google Scholar]