number of tandem repeats) is specialized and may entail unique requirements as most commercial arrays and custom genotyping platforms may not include this. Nonetheless, if only a few SNPs can be genotyped, tagging a gene may be preferable to simply pursuing the “usual suspects”. Tagging refers to identifying all variation, regardless of function, that captures variation across the gene. This includes important regulatory regions, such as promoters and enhancers which are increasingly recognized as key contributors (Zannas & Binder, 2014). Reliance on simple annotation of “function” (i.e., typically, a nonsynonymous exonic variant, meaning that the location is known to be in a part of the gene that produces an alteration in the gene’s protein product) is short-sighted as modern annotations available via the identification of epigenetic marks along the genome suggest that even intronic variants can have a profound impact on genomic action (e.g., Ziller et al., 2013). An exciting and upcoming possibility is a highly cost efficient chip being designed by the Psychiatric Genomics Consortium (PGC) that will include custom common and rare variation and will be based on SNPs nominated by expert consensus and validated via meta-analytic methods.
