Finding Needles in Genomic Haystacks with “Wide” Random Forest

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Recent advances in genome sequencing technologies and bioinformatics have enabled whole-genomes to be studied at population-level rather then for small number of individuals. This provides new power to whole genome association studies (WGAS), which now seek to identify the multi-gene causes of common complex diseases like diabetes or cancer.

As WGAS involve studying thousands of genomes, they pose both technological and methodological challenges. The volume of data is significant, for example the dataset from 1000 Genomes project with genomes of 2504 individuals includes nearly 85M genomic variants with raw data size of 0.8 TB. The number of features is enormous and greatly exceeds the number of samples, which makes it challenging to apply traditional statistical approaches.

Random forest is one of the methods that was found to be useful in this context, both because of its potential for parallelization and its robustness. Although there is a number of big data implementations available (including Spark ML) they are tuned for typical dataset with large number of samples and relatively small number of variables, and either fail or are inefficient in the GWAS context especially, that a costly data preprocessing is usually required.

To address these problems, we have developed the RandomForestHD – a Spark based implementation optimized for highly dimensional data sets. We have successfully RandomForestHD applied it to datasets beyond the reach of other tools and for smaller datasets found its performance superior. We are currently applying RandomForestHD, released as part of the VariantSpark toolkit, to a number of WGAS studies.

In the presentation we will introduce the domain of WGAS and related challenges, present RandomForestHD with its design principles and implementation details with regards to Spark, compare its performance with other tools, and finally showcase the results of a few WGAS applications.