SNCA,MAPT, and GSK3B in Parkinson disease: a gene–gene interaction study

Background and purpose: Recent evidence suggests that variation in the SNCA, MAPT, and GSK3B genes interacts in affecting risk for Parkinson disease (PD). In the current study, we attempt to validate previously published findings, evaluating gene–gene interactions between SNCA, MAPT, and GSK3B in association with PD. Methods: Three Caucasian PD patient–control series from the United States, Ireland, and Norway (combined n = 1020 patients and 1095 controls) were genotyped for SNCA rs356219, MAPT H1/H2‐discriminating SNP rs1052553, and GSK3B rs334558 and rs6438552. Results: Our findings indicate that as previously reported, the SNCA rs356219‐G allele and MAPT rs1052553 (H1 haplotype) were both associated with an increased risk of PD, whilst contrary to previous reports, GSK3B variants were not. No pair‐wise interaction was observed between SNCA, MAPT, and GSK3B; the risk effects of SNCA rs356219‐G and MAPT rs1052553‐H1 were seen in a similar manner across genotypes of other variants, with no evidence suggesting synergistic, antagonistic, or deferential effects. Conclusions: In the Caucasian patient–control series examined, risk for PD was influenced by variation in SNCA and MAPT but not GSK3B. Additionally, those three genes did not interact in determining disease risk.     

Clinical subtypes in Parkinson’s disease: the impact of MAPT haplotypes

The H1 haplotype of the MAPT gene influences the risk of PD and has been related to the development of PDD. We evaluated the influence of MAPT haplotypes on the expression of motor features in PD patients. We genotyped, for the MAPT haplotypes H1 and H2, a sample of 181 PD patients with distinct clinical subtypes: tremor dominant and non-tremor dominant (NTD). Our results indicate that the MAPT haplotypes contribute to the expression of motor features of PD. H1 homozygous PD patients are significantly more likely to present a NTD phenotype, a clinical subtype characterized by widespread pathological degeneration, than H2 carriers.     

Replication of MAPT and SNCA,but not PARK16‐18, as susceptibility genes for Parkinson's disease

Recent genome‐wide association studies of Parkinson's disease have nominated 3 new susceptibility loci (PARK16‐18) and confirmed 2 known risk genes (MAPT and SNCA) in populations of European ancestry. We sought to replicate these findings. We genotyped single‐nucleotide polymorphisms in each of these genes/loci in 1445 Parkinson's disease patients and 1161 controls from northern Spain. Logistic regression was used to test for association between genotype and Parkinson's disease under an additive model, adjusting for sex, age, and site. We also performed analyses stratified by age at onset. Single‐nucleotide polymorphisms in MAPT (rs1800547; P = 3.1 × 10^?4) and SNCA (rs356219; P = 5.5 × 10^?4) were significantly associated with Parkinson's disease. However, none of the markers in PARK16‐18 associated with Parkinson's disease in the overall sample, or in any age stratum, with P values ranging from .09 to .88. Although our data further validate MAPT and SNCA as Parkinson's disease susceptibility genes, we failed to replicate PARK16, PARK17, and PARK18. Potential reasons for the discordance between our study and previous genome‐wide association studies include effects of population structure, power, and population‐specific environmental interactions. Our findings suggest that additional studies of PARK16‐18 are necessary to establish the role of these loci in modifying risk for Parkinson's disease in European‐derived populations. © 2011 Movement Disorder Society     

Alpha-synuclein in blood and brain from familial Parkinson disease with SNCA locus triplication

The authors recently demonstrated that genetic triplication of the SNCA locus causes Parkinson disease. Here it is shown that SNCA triplication results in a doubling in the amount of alpha-synuclein protein in blood. Examination of brain tissue showed a doubling in the level of SNCA message. However, at the protein level in brain, there was a greater effect on deposition of aggregated forms into insoluble fractions than on net expression of soluble alpha-synuclein.     

SNPs in neurotrophin system genes and Alzheimer's disease in an Italian population

Increasing evidence suggests a role for nerve growth factor (NGFB), brain-derived neurotrophic factor (BDNF), and their receptors, nerve growth factor receptor (NGFR), and neurotrophin tyrosine kinase receptors 1 and 2 (NTRK1 and NTRK2), in Alzheimer's disease (AD). However, genetic association between the neurotrophin system genes and AD has been poorly investigated. We genotyped 21 single nucleotide polymorphisms (SNPs) within these genes in a population of Italian AD patients and healthy controls. We found an allele-wise association of rs2072446 on NGFR with familial AD (fAD, p = 0.047), and a genotype-wise association of rs2289656 on NTRK2 with sporadic AD (sAD, p = 0.0036). rs6336 on NTRK1 resulted associated to early-onset sAD in both allele-wise (p = 0.028) and genotype-wise (p = 0.014) analysis, while rs1048218 on BDNF showed allele-wise association with late-onset sAD (p = 0.047). A trend to association with sAD and/or fAD was observed for other SNPs. Our results suggest that genetic variants of neurotrophin system genes might confer susceptibility to AD.     

Diagnosing mild cognitive impairment in Parkinson’s disease: which tests perform best in the Italian population?

Mild cognitive impairment (MCI) is common in patients with Parkinson’s disease (PD) and should be recognized early because it represents a predictor of PD-related dementia and worse disease course. Diagnostic criteria for PD-related MCI (PD-MCI) have recently been defined by a Movement Disorders Society (MDS) task force. The present study explored which neuropsychological tests perform best for a level II (i.e., comprehensive neuropsychological assessment) diagnosis of PD-MCI according to the MDS task force criteria in Italian-speaking PD patients. To this aim, we assessed a comprehensive 23-item neuropsychological battery, derived the best-performing 10-test battery (i.e., two tests per domain for each of the five cognitive domains), and explored its accuracy for diagnosing PD-MCI in comparison to the full battery in a group of PD patients. A secondary aim was to explore the role of this battery for subtyping PD-MCI according to single-domain vs. multiple-domain involvement. The 10-test battery showed 73% sensitivity and 100% specificity for diagnosing PD-MCI, and 69% sensitivity and 100% specificity for PD-MCI subtyping. In patients older than 70 years, we derived a slightly different 10-test battery with 84% sensitivity and 100% specificity for PD-MCI diagnosis, and 86% sensitivity and 100% specificity for PD-MCI subtyping. These 10-item neuropsychological batteries might represent a good trade-off between diagnostic accuracy and time of application, and their role in PD-MCI diagnosis and subtyping should be further explored in future prospective studies.     

Glucocerebrosidase gene mutations and Parkinson disease in the Norwegian population

An association between mutations in the glucocerebrosidase (GBA) gene and Parkinson disease (PD) was recently reported in Ashkenazi Jews. The authors screened a series of 311 Norwegian patients with PD and 474 controls for 2 common functional mutations of the GBA protein, N370S and L444P. Seven patients (2.3%) and 8 controls (1.7%) carried a mutant GBA allele (p = 0.58). This study does not indicate increased susceptibility to PD in GBA mutations carriers in Norway.     

Friedreich's disease: survival analysis in an Italian population

This investigation is the first population-based study of survival in Friedreich's disease (FD). All cases of FD diagnosed between 1945 through 1984 among residents of a defined area of northwestern Italy were ascertained (N = 58). These patients were followed to death or to December 31, 1984 (whichever came first) to determine the patterns of survival. The 10-, 20-, and 30-year survival rates were respectively 96%, 80%, and 61%, suggesting a better prognosis than previously reported. Survival of FD patients was poorer than expected from the general population. Survival for males was poorer than for females even after adjustment for expected survival. Age of onset was not a significant prognostic factor. Survival for patients diagnosed in 1960 or later was better than for those diagnosed before 1960; however, the difference was not statistically significant.