Data Products » Genetics
Important note concerning flipped strand issues and associated correction method
In mid-2014, we became aware of an annotation issue with the Illumina HumanOmni2.5-v1_D manifest that caused strand flip errors in the annotation for approximately 20,000 SNPs genotyped in the Health and Retirement Study 2006/2008 samples. This manifest also served as the foundation for the 1000 Genomes imputation for those samples. We systematically investigated the problem and identified two issues with the Illumina HumanOmni2.5-v1_D manifest that led to the strand flip errors. The issues are described in detail in HRS1-2_dbGaPUserInfo_v3.pdf
In order to correct the flipped strand issue, users should take the following action. SNPs that are affected by the strand swap are flagged as problem.type2.SNP = TRUE in HRS1-2_HumanOnmi2.5v1_D_flaggedSNPs.zip. Users should switch the coded and non-coded allele annotation for the affected SNPs in the annotation files. For example, if coded_allele=A and noncoded_allele=T, then coded_allele should be T and noncoded _allele should be A.