New aQTL SNPs for the CYP2D6 identified by a novel mediation analysis of genome-wide SNP arrays, gene expression arrays, and CYP2D6 activity.
BACKGROUND
The genome-wide association studies (GWAS) have been successful during the last few years. A key challenge is that the interpretation of the results is not straightforward, especially for transacting SNPs. Integration of transcriptome data into GWAS may provide clues elucidating the mechanisms by which a genetic variant leads to a disease.


METHODS
Here, we developed a novel mediation analysis approach to identify new expression quantitative trait loci (eQTL) driving CYP2D6 activity by combining genotype, gene expression, and enzyme activity data.


RESULTS
389,573 and 1,214,416 SNP-transcript-CYP2D6 activity trios are found strongly associated (P < 10⁻⁵, FDR = 16.6% and 11.7%) for two different genotype platforms, namely, Affymetrix and Illumina, respectively. The majority of eQTLs are trans-SNPs. A single polymorphism leads to widespread downstream changes in the expression of distant genes by affecting major regulators or transcription factors (TFs), which would be visible as an eQTL hotspot and can lead to large and consistent biological effects. Overlapped eQTL hotspots with the mediators lead to the discovery of 64 TFs.


CONCLUSIONS
Our mediation analysis is a powerful approach in identifying the trans-QTL-phenotype associations. It improves our understanding of the functional genetic variations for the liver metabolism mechanisms.
Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, IN 46202, USA ; Center for Computational Biology and Bioinformatics, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
Guanglong
G
Jiang
Arindom
A
Chakraborty
Zhiping
Z
Wang
Malaz
M
Boustani
Yunlong
Y
Liu
Todd
T
Skaar
Lang
L
Li
D015331:Cohort Studies; D019389:Cytochrome P-450 CYP2D6 / Q000235:genetics* / Q000378:metabolism; D020869:Gene Expression Profiling; D015971:Gene Expression Regulation, Enzymologic; D055106:Genome-Wide Association Study; D005838:Genotype; D006801:Humans; D008099:Liver / Q000378:metabolism*; D010641:Phenotype; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D040641:Quantitative Trait Loci / Q000235:genetics*; D059467:Transcriptome / Q000235:genetics
D019389:Cytochrome P-450 CYP2D6