PAX9 and tooth agenesis: Over the past two decades, continuous scientific efforts have led to the decoding of a cluster of genes that encode key proteins of major developmental pathways that are currently accepted to be the etiologies for 90% of tooth agenesis; these genes include Paired box 9 (PAX9), Msh homeobox 1 (MSX1), Wnt family member 10A (WNT10A), ectodysplasin A (EDA), Wnt family member 10 B (WNT10B), LDL receptor related protein 6 (LRP6), and Axin 2 (AXIN2) [7,8,9,10,11,12,13,14,15,16,17,18,19].