KIF21A and Duane retraction syndrome: Based on the current understanding of the genetics of DRS, at least six genes—spalt like transcription factor 4 (SALL4), chimerin 1 (CHN1), homeobox A1 (HOXA1), MAF bZIP transcription factor B (MAFB), kinesin family member 21A (KIF21A), and tubulin beta 3 class III (TUBB3)—have been identified to be associated with DRS4,5.