Gaussian graphical models have been widely used to construct gene regulatory networks from gene expression data. Most existing methods for Gaussian graphical models are designed to model homogeneous data, assuming a single Gaussian distribution. In practice, however, data may consist of gene expression studies with unknown confounding factors, such as study cohort, microarray platforms, experimental batches, which produce heterogeneous data, and hence lead to false positive edges or low detection power in resulting network, due to those unknown factors. To overcome this problem and improve the performance in constructing gene networks, we propose a two-stage approach to construct a gene network from heterogeneous data. The first stage is to perform a clustering analysis in order to assign samples to a few clusters where the samples in each cluster are approximately homogeneous, and the second stage is to conduct an integrative analysis of networks from each cluster. In particular, we first apply a model-based clustering method using the singular value decomposition for high-dimensional data, and then integrate the networks from each cluster using the integrative |$\psi$|-learning method. The proposed method is based on an equivalent measure of partial correlation coefficients in Gaussian graphical models, which is computed with a reduced conditional set and thus it is useful for high-dimensional data. We compare the proposed two-stage learning approach with some existing methods in various simulation settings, and demonstrate the robustness of the proposed method. Finally, it is applied to integrate multiple gene expression studies of lung adenocarcinoma to identify potential therapeutic targets and treatment biomarkers.

Interethnic differences in genetic polymorphism in genes encoding drug-metabolizing enzymes and transporters are one of the major factors that cause ethnic differences in drug response. This study aimed to investigate genetic polymorphisms in genes involved in drug metabolism, transport, and excretion among Korean, Japanese, and Chinese populations, the three major East Asian ethnic groups. The frequencies of 1936 variants representing 225 genes encoding drug-metabolizing enzymes and transporters were determined from 786 healthy participants (448 Korean, 208 Japanese, and 130 Chinese) using the Affymetrix Drug-Metabolizing Enzymes and Transporters Plus microarray. To compare allele or genotype frequencies in the high-dimensional data among the three East Asian ethnic groups, multiple testing, principal component analysis (PCA), and regularized multinomial logit model through least absolute shrinkage and selection operator were used. On microarray analysis, 1071 of 1936 variants (>50% of markers) were found to be monomorphic. In a large number of genetic variants, the fixation index and Pearson's correlation coefficient of minor allele frequencies were less than 0.034 and greater than 0.95, respectively, among the three ethnic groups. PCA identified 47 genetic variants with multiple testing, but was unable to discriminate ethnic groups by the first three components. Multinomial least absolute shrinkage and selection operator analysis identified 269 genetic variants that showed different frequencies among the three ethnic groups. However, none of those variants distinguished between the three ethnic groups during subsequent PCA. Korean, Japanese, and Chinese populations are not pharmacogenetically distant from one another, at least with regard to drug disposition, metabolism, and elimination.