PITX2 and Axenfeld-Rieger syndrome: 5 Variants in these two genes account for approximately 70% of ARS cases, although it is unclear whether the remaining 30% are caused by undetected variants at these same loci, or others.6 Furthermore, the presence of microdontia/hypodontia and umbilical anomalies is highly specific for PITX2-associated ARS: in one case series these were observed in 91% and 94% of cases with PITX2-associated ARS (n=59), as compared to 0% and 11% of FOXC1-associated ARS (n=69).6