Geostatistical Fisher discriminant analysis

A geostatistical version of the classical Fisher rule (linear discriminant analysis) is presented.This method is applicable when a large dataset of multivariate observations is available within a domain split in several known subdomains, and it assumes that the variograms (or covariance functions) are comparable between subdomains, which only differ in the mean values of the available variables. The method consists on finding the eigen-decomposition of the matrix W-1B, where W is the matrix of sills of all direct- and cross-variograms, and B is the covariance matrix of the vectors of weighted means within each subdomain, obtained by generalized least squares. The method is used to map peat blanket occurrence in Northern Ireland, with data from the Tellus
survey, which requires a minimal change to the general recipe: to use compositionally-compliant variogram tools and models, and work with log-ratio transformed data.

Myeloperoxidase G-463A polymorphism and Alzheimer's disease in the ApoEurope study

Alzheimer's disease (AD) is the most common cause of dementia in the elderly. Epidemiological and molecular genetic studies have shown the existence of several genes associated with increased risk of AD, the major genetic susceptibility locus coding for apolipoprotein E (apoE). A polymorphism in the myeloperoxidase gene (MPO) has previously been associated with AD susceptibility. However, results in the literature are controversial and seem to be dependent on several factors such as gender, apoE polymorphism or the genetic structure of the population. We investigated MPO G-463A and apoE polymorphism in 265 cases and 246 controls from the ApoEurope Study. In females, we found a significant association between MPO genotype and AD (P=0.034), GG genotype frequency being lower in cases (52.4%) as compared to controls (64.2%). In men, there was no significant effect of MPO polymorphism. No interaction was found between MPO polymorphism and apoE epsilon 4 allele. In conclusion, the G-463A polymorphism of MPO was statistically associated with AD in a gender-specific manner. However, given the low significance of P value we suggest no causal effect of the MPO gene in AD, as also evidenced in a recent meta-analysis. Our results support the hypothesis of a possible linkage disequilibrium between the MPO G-463A gene polymorphism and another functional variant involved in AD.