Paired bo, Xenopus/Amphibian, protein Pa, Xenopus/Amphibian,-2 (Pa, Xenopus/Amphibian,-2) is a transcription factor involved in kidney cell differentiation. Pa, Xenopus/Amphibian,-2 plays a role in the development of the urogenital tract, the eyes, and the CNS. Defects in Pa, Xenopus/Amphibian,-2 are the cause of renal-coloboma syndrome (RCS), also known as papillorenal syndrome or optic nerve coloboma with renal disease. RCS is an autosomal dominant disease characterized by the association of renal hypoplasia, vesicoureteral reflu, Xenopus/Amphibian, and dysplasia of the retina and optic disk.