how to perform QTL analysis and how to integrate multi-omit datasets

Question

[Bioinfonext]

Hi,

I can understand that we can identified SNPs (genetic variants) associated with disease condition by using GWAS analysis. But not sure how do we identify eQTL/mQTL associated with particular disease condition?

For eQTL identification should we use raw SNPs data with differentially expressed gene expression dataset between heathy control and patient samples. And similarly significant EWAS data for control and patient samples linked with raw SNPs data for mQTL identification.

And then should we use SMR & HEIDI approach to link GWAS significant SNPs with eQTL or mQTL.Could you please help me to understand how SMR & HEIDI approach is different from two step MR