No association between a polymorphism in the presenilin 1 gene and dementia with Lewy bodies

Genetic Architecture and Molecular, Imaging and Prodromic Markers in Dementia with Lewy Bodies: State of the Art, Opportunities and Challenges

Dementia with Lewy bodies (DLB) is one of the most common causes of dementia and belongs to the group of α-synucleinopathies. Due to its clinical overlap with other neurodegenerative disorders and its high clinical heterogeneity, the clinical differential diagnosis of DLB from other similar disorders is often difficult and it is frequently underdiagnosed. Moreover, its genetic etiology has been studied only recently due to the unavailability of large cohorts with a certain diagnosis and shows genetic heterogeneity with a rare contribution of pathogenic mutations and relatively common risk factors. The rapid increase in the reported cases of DLB highlights the need for an easy, efficient and accurate diagnosis of the disease in its initial stages in order to halt or delay the progression. The currently used diagnostic methods proposed by the International DLB consortium rely on a list of criteria that comprises both clinical observations and the use of biomarkers. Herein, we summarize the up-to-now reported knowledge on the genetic architecture of DLB and discuss the use of prodromal biomarkers as well as recent promising candidates from alternative body fluids and new imaging techniques.

Systematic review of genetic association studies in people with Lewy body dementia

OBJECTIVES

Lewy body dementia (LBD) causes more morbidity, disability, and earlier mortality than Alzheimer disease. Molecular mechanisms underlying neurodegeneration in LBD are poorly understood. We aimed to do a systematic review of all genetic association studies that investigated people with LBD for improving our understanding of LBD molecular genetics and for facilitating discovery of novel biomarkers and therapeutic targets for LBD.

METHODS

We systematically reviewed five online databases (PROSPERO protocol: CRD42018087114) and completed the quality assessment using the quality of genetic association studies tool.

RESULTS

Eight thousand five hundred twenty-one articles were screened, and 75 articles were eligible to be included. Genetic associations of LBD with APOE, GBA, and SNCA variants have been replicated by two or more good quality studies. Our meta-analyses confirmed that APOE-ε4 is significantly associated with dementia with Lewy bodies (pooled odds ratio [POR] = 2.70; 95% CI, 2.37-3.07; P < .001) and Parkinson's disease dementia (POR = 1.60; 95% CI, 1.21-2.11; P = .001). Other reported genetic associations that need further replication include variants in A2M, BCHE-K, BCL7C, CHRFAM7A, CNTN1, ESR1, GABRB3, MAPT, mitochondrial DNA (mtDNA) haplogroup H, NOS2A, PSEN1, SCARB2, TFAM, TREM2, and UCHL1.

CONCLUSIONS

The reported genetic associations and their potential interactions indicate the importance of α-synuclein, amyloid, and tau pathology, autophagy lysosomal pathway, ubiquitin proteasome system, oxidative stress, and mitochondrial dysfunction in LBD. There is a need for larger genome-wide association study (GWAS) for identifying more LBD-associated genes. Future hypothesis-driven studies should aim to replicate reported genetic associations of LBD and to explore their functional implications.

Genetic Association between Presenilin 2 Polymorphisms and Alzheimer's Disease and Dementia of Lewy Body Type in a Japanese Population

Background/Aims

Mutations in the presenilin 2 (PSEN2) gene cause familial Alzheimer's disease (AD). Common polymorphisms affect gene activity and increase the risk of AD. Nonsynonymous polymorphisms in the PSEN2 gene showed Lewy body dementia (LBD) phenotypes clinically. Therefore, we aimed to investigate whether PSEN2 gene polymorphisms were associated with AD or LBD.

Methods

Seven single nucleotide polymorphisms (SNPs) of the gene were analyzed using a case-control study design comprising 288 AD patients, 76 LBD patients, and 105 age-matched controls.

Results

Linkage disequilibrium (LD) examination showed strong LD from rs1295645 to rs8383 on the gene in our cases from Japan. There were no associations between the SNPs studied here and AD onset, and haplotypic analyses did not detect genetic associations between AD and the PSEN2 gene. Although the number of the cases was small, the SNPs studied did not modify the risk of developing LBD in a Japanese population.

Conclusion

The common SNPs of the PSEN2 gene did not affect the risk of AD or LBD in a Japanese population. Because genetic variability of the PSEN2 gene is associated with behavioral and psychological symptoms of dementia (BPSD) in AD and LBD, further detailed analyses considering BPSD of both diseases would be required.

Association between presenilin-1 −48C/T polymorphism and Down’s syndrome

Individuals with Down's syndrome (DS), i.e., trisomy 21, over 40 years of age, are likely to develop neuropathological changes characteristic of Alzheimer's disease (AD). The involvement of chromosome 21 both in DS and AD suggests a shared genetic susceptibility to these disorders, but genetic determinants are still undefined. The -48C/T polymorphism in the PSEN1 promoter is a possible candidate, since it has recently been associated with an increased risk of early onset AD. Based on the assumption that the excess of dementia in DS might be a consequence of a different distribution of the -48C/T polymorphism, we investigated the association between DS and this polymorphism in patients with trisomy 21 and controls. Overall, 260 DS patients and 197 controls were recruited at the Department of Neurosciences, Tor Vergata University of Rome. Cases and controls had similar age and gender distribution. High molecular weight DNA was extracted from whole blood samples collected in EDTANa(2) and -48C/T genotypes were determined. Genotype and allele frequencies were compared between cases and controls. Cases were less likely than controls to have the CC genotype ( P = 0.05). A significant difference for allele distribution between DS cases and controls was found, with DS showing a lower frequency of the allele C compared with the control population (OR: 0.57; 95% CI: 0.35-0.91; P = 0.01). No significant interaction of PSEN1 with age, gender, ApoE and -850 TNF-alpha polymorphisms was found. The association found suggests that the -48C/T polymorphism in the PSN1 gene promoter, which is involved in the modulation of amyloid beta load in human AD, is associated with DS. However, the biological role of this polymorphism in DS-related dementia remains unclear and merits further investigation.

Progress in clinical neurosciences: Parkinson's disease with dementia and dementia with Lewy bodies

Dementia occurs in up to 30% of people with Parkinson's disease and is a major cause of disability. Pathologically, Parkinson's dementia, where dementia follows the onset of parkinsonism by at least one year, overlaps with dementia with Lewy bodies. We review the functional impact, definitions, neuropsychology, epidemiology and pathophysiology of Parkinson's dementia, dementia with Lewy bodies and their overlap. Associated psychiatric and imaging findings are also considered. Lastly, current and emerging approaches to assessment and treatment in patients with these Lewy body associated dementias are presented.

No evidence of an association between CYP2D6 polymorphisms among Japanese and dementia with Lewy bodies

Dementia with Lewy bodies (DLB) is the second most frequent degenerative dementia among the elderly, following Alzheimer-type dementia (ATD). An association of DLB with CYP2D6*4, one of the cytochrome P450IID6 (debrisoquine 4-hydroxylase; CYP2D6) gene polymorphisms, was reported previously, but this is controversial. Moreover, these reports have been restricted to Caucasian populations. Therefore, we compared frequencies of CYP2D6*3, *4, and *10 mutant alleles in 17 Japanese DLB patients to those among Alzheimer-type dementia (ATD) patients and healthy controls. Polymerase chain reaction amplification and restriction fragment length polymorphism analyses were used for genotyping. No significant difference of genotype or mutant allele frequencies was detected between DLB, ATD, and healthy controls. The present results do not support the suggestion that the CYP2D6 gene is related to DLB susceptibility, at least in the Japanese population.

Presenilin-1 in late-onset depressive disorder

Late-onset depressive disorder (LOD) is thought to be associated with dementia. Allele 1 in the presenilin-1 (PS-1) gene is a risk factor for Alzheimer's disease. An association study on this polymorphism was performed in depressive patients and control subjects. The patients were subdivided into those with early onset and late onset, using 50 years as the cut-off age. There was no statistically significant difference in the age of onset of depressive disorders according to the PS-1 genotype. There was also no association between early/late-onset depressive disorders and the PS-1 genotype. Our results suggest there is no association between the PS-1 allele and LOD.

Dementia with Lewy bodies. A distinct non-Alzheimer dementia syndrome?

Lewy body formation is central to the pathological phenotype of a spectrum of disorders. The most familiar of these is the extrapyramidal syndrome of idiopathic Lewy-body Parkinson's disease (PD). Studies of dementia in the elderly suggest that another manifestation of Lewy body pathology is equally or more common than Parkinson's disease. This syndrome of Dementia with Lewy bodies (DLB) has been given a number of diagnostic labels and is characterised by dementia, relatively mild parkinsonism, visual hallucinations, and fluctuations in conscious level. Although many of these features can arise in Parkinson's disease, the patients with DLB tend to have early neuropsychiatric features which predominate the clinical picture, and the diagnosis of the syndrome in practice is more concerned with the differential diagnosis of Alzheimer's disease (AD). Distinction from AD has clinical importance because of potentially differing therapeutic implications. Diagnostic guidelines for the clinical diagnosis and pathological evaluation of DLB are reviewed. Research into the disorder has centered around characterising the clinical, neuropsychological, pathological, neurochemical and genetic relationships with Alzheimer's disease on the one hand, and Parkinson's disease on the other. Many cases of DLB have prominent pathological features of AD and there are some shared genetic risk factors. Differences from the pathology of PD are predominantly quantitative rather than qualitative and evidence is discussed which suggests that DLB represents a clinicopathological syndrome within the spectrum of Lewy body disorders. The possibility that the syndrome represents a chance association of PD and AD is not supported by published studies.