One of the first discovered and most studied PDYN polymorphisms is rs35286281 a variable number nucleotide repeat (VNTR) of 1-5 copies of 68-bp tandem which contains a putative AP-1 transcription complex binding site, located 1250 bp upstream of exon 1. SNP rs61761346 was identified at the ninth nucleotide of each repeat (Rockman et al. 2005; Rouault et al. 2011). In vitro, PDYN expression studies using various constructs, different cell lines, and different species reported opposite effects (Babbitt et al. 2010; Rouault et al. 2011; Zimprich et al. 2000).
