Familial occurrence of dementia and parkinsonism: a systematic review

Advancing the Genetics of Lewy Body Disorders with Disease-Modifying Treatments in Mind

In this article, a caveat for advancing the genetics of Lewy body disorders is raised, given the nosological controversy about whether to consider dementia with Lewy bodies (DLB) and Parkinson's disease (PD) as one entity or two separate entities. Using the framework of the sufficient and component causes model of causation, as further developed into an evolution-based model of causation, it is proposed that a disease of complex etiology is defined as having a relatively high degree of sharing of the component causes (a genetic or environmental factor), that is, a low degree of heterogeneity of the sufficient causes. Based on this definition, only if the sharing of component causes within each of two diseases is similar to their combined sharing can lumping be warranted. However, it is not known whether the separate and combined sharing are similar before conducting the etiologic studies. This means that lumping DLB and PD can be counterproductive as it can decrease the ability to detect component causes despite the potential benefit of conducting studies with larger sample sizes. In turn, this is relevant to the development of disease-modifying treatments, because non-overlapping causal genetic factors may result in distinct pathogenetic pathways providing promising targets for interventions.

Association between BDNF G196A (Val66Met) polymorphism and cognitive impairment in patients with Parkinson's disease: a meta-analysis

Brain-derived neurotrophic factor (BDNF) is widely expressed in the central nervous system and prolongs the survival of dopaminergic neurons in the substantia nigra. Several studies have recently investigated the association between BDNF G196A (Val66Met), a single nucleotide polymorphism influencing cognitive processes, and cognitive impairment in Parkinson's disease (PD), but with contradictory findings. Thus, this meta-analysis was performed to clarify the possible association. Relevant studies were identified by a systematic search of PubMed, Embase, and China National Knowledge Infrastructure (CNKI) databases. The strength of the association was evaluated using crude odds ratios and 95% confidence interval. Finally, six studies involving 532 cases and 802 controls were included. Our analyses suggested the G196A (Val66Met) polymorphism was significantly associated with cognitive impairment in PD, especially in Caucasian populations. In conclusion, BDNF G196A (Val66Met) is confirmed to be a risk factor for cognitive impairment in PD.

The relationship between four GWAS-identified loci in Alzheimer's disease and the risk of Parkinson's disease, amyotrophic lateral sclerosis, and multiple system atrophy

BACKGROUND

A number of genetic variants have previously been identified and associated with the risk of Alzheimer's disease (AD), including rs10838725 in CELF1, rs28834970 in PTK2B, rs17125944 in FERMT2, and rs10410544 in SIRT2 based on genome-wide association studies. Considering the overlap between the clinical manifestation and pathological characteristics of AD and Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS) and multiple system atrophy (MSA), we conducted a large sample study to investigate the associations between these variants and these three common neurodegenerative diseases in a Chinese population.

METHODS

A total of 2449 patients, including 1219 PD, 870 sporadic ALS, and 360 MSA, and 821 healthy controls were examined for this study. All cases were genotyped for single-nucleotide polymorphisms using Sequenom iPLEX assay technology.

RESULTS

No significant differences were found in genotype distribution and minor allele frequencies between the four candidate variants and the three neurodegenerative diseases. However, a significant difference was found in the minor allele frequency of rs28834970 in PTK2B between PD patients with normal and abnormal cognitive function (p = 0.001). Moreover, the minor allele "C" was associated with an increased risk for cognitive impairment in PD (OR = 1.84). Although this observation was not significant (p = 0.064), the mean Addenbrooke's Cognitive Examination-Revised (ACER) score of PD patients with the risk allele of rs28834970 was 2.913 ± 1.569 points lower than that of PD patients without the risk allele.

CONCLUSION

This study provides new insight into some of the phenotypes that may share the common pathogenesis of different neurodegenerative diseases.

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.

Cognitive impairment in patients with Parkinson's disease: diagnosis, biomarkers, and treatment

Dementia is one of the most common and important aspects of Parkinson's disease and has consequences for patients and caregivers, and has health-related costs. Mild cognitive impairment is also common and frequently progresses to dementia. The underlying mechanisms of dementia associated with Parkinson's disease are only partly known and no mechanism-based treatments are available. Both dysmetabolism of α-synuclein and amyloid-protein and cholinergic deficits contribute to cognitive impairment in Parkinson's disease, and preliminary findings show that imaging and neurophysiological and peripheral biomarkers could be useful in diagnosis and prognosis. Rivastigmine is the only licensed treatment for dementia in Parkinson's disease, but emerging evidence suggests that memantine might also be useful. Whether these or other treatments can delay the progression from mild cognitive impairment to dementia in Parkinson's disease is a key research question.

The epidemiology of dementia associated with Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative illness after Alzheimer's disease (AD). Cognitive impairment and dementia are common features in PD and characterized by a wide range of cognitive deficits distinct from those seen in AD. Mild cognitive impairment occurs even early in PD and is associated with shorter time to dementia. The purpose of this review is to present recent findings on clinical aspects of dementia in PD and to elucidate underlying clinical and neurobiological risk factors.

The epidemiology of dementia associated with Parkinson disease

Several recent studies have shown that dementia is common in Parkinson's disease (PD), and that in some patients, cognitive impairment occurs even at the time of diagnosis. The point prevalence of dementia in PD is close to 30% and the incidence rate is increased 4-6 times as compared to controls. The cumulative prevalence is very high, at least 75% of PD patients who survive for more than 10 years will develop dementia. The mean time from onset of PD to dementia is approximately 10 years. However, there are considerable variations, and some patients develop dementia early in the disease course. Earlier onset of dementia is associated with more structural brain changes. The most established risk factors for early dementia are old age, severity of motor symptoms, in particular postural and gait disturbances, mild cognitive impairment and visual hallucinations. The genetic contributions to dementia are currently not clear and need to be explored in future studies.

APOE alleles in Parkinson disease and their relationship to cognitive decline: a population-based, longitudinal study

Apolipoprotein E gene alleles have been linked to various cardiovascular and neurodegenerative disorders. There have been conflicting reports of associations between Apolipoprotein E alleles and Parkinson disease and Parkinson disease dementia. To investigate the role of Apolipoprotein E alleles in Parkinson disease and Parkinson disease dementia, we have determined Apolipoprotein E genotypes in a group of patients with Parkinson disease (n = 95) and compared them with those of healthy control participants (n = 73). Additionally, in 64 longitudinally followed patients with Parkinson disease, the allele types were correlated to development and progression of dementia and to time from onset of Parkinson disease to dementia using multivariate and survival analyses. The Apolipoprotein E e4e4 genotype was more common in patients with Parkinson disease (7.4%) than in healthy controls (1.4%; P = .03). No significant associations between the Apolipoprotein E genotype and development and progression of dementia or time to dementia were found. More studies with larger Parkinson disease samples are warranted.

A novel locus for dementia with Lewy bodies: a clinically and genetically heterogeneous disorder

Dementia with Lewy bodies (DLB) represents the second most frequent type of neurodegenerative dementia in the elderly. Although most patients have sporadic DLB, a limited number of DLB families have been described, suggesting that genetic factors may contribute to DLB pathogenesis. Here, we describe a three-generation Belgian family with prominent dementia and parkinsonism, consistent with a diagnosis of DLB, that was autopsy confirmed for the index patient. In a genome-wide scan and subsequent finemapping of candidate loci we obtained significant linkage to 2q35-q36 (Z = 3.01 at D2S1242). Segregation analysis defined a candidate region of 9.2 Mb between D2S433 and chr2q36.3-8, adjacent to the previously reported PARK11 locus. In addition, haplotype sharing studies in another DLB family of close geographical origin with similar clinical and neuropathological features highlighted the specificity of a 2q35-q36 haplotype harbouring a pathogenic mutation that causes DLB in the Belgian family. So far, extensive sequence analysis of five candidate genes within the 2q35-q36 region has not revealed a disease-causing mutation. Together, our data re-emphasize the genetic heterogeneity of DLB, and strongly support the existence of a gene for familial DLB on 2q35-q36. Once identified this will be the first novel causal gene for DLB and can be expected to open new avenues for biological studies of the disease process.

Associations between family history of Parkinson's disease and dementia and risk of dementia in Parkinson's disease: A community-based, longitudinal study

Dementia is common in patients with Parkinson's disease (PDD). The etiology of PDD is still unclear, but exciting advances have been made in discovering pathogenetic components in Parkinson's disease (PD), implicating the role of genetic factors. It is, however, still controversial whether genetic factors also contribute to the development of dementia in PD. Thus, we investigated the association between development of dementia and a positive family history of PD or dementia in a community-based study of PD in Rogaland County, Norway (n = 219). The patients were followed prospectively with neurological and neuropsychological assessments. Dementia was more common in patients with a strong family association of PD (first-degree relatives > second-degree relatives > no family history; P < 0.05). However, time to dementia did not differ between the two groups. No associations between dementia in PD and familial occurrence of dementia could be shown. Further studies with larger samples are needed to explore a possible relationship between a family history of PD and development of dementia in PD and its potential pathogenetic mechanisms.