Mutations in 3 genes (<i>MKS3</i>, <i>CC2D2A</i> and <i>RPGRIP1L</i>) cause COACH syndrome (Joubert syndrome with congenital hepatic fibrosis)

Mutations in MKS3 are responsible for the majority of COACH syndrome, with minor contributions from CC2D2A and RPGRIP1L; therefore, MKS3 should be the first gene tested in patients with JSRD plus liver disease and/or coloboma, followed by CC2D2A and RPGRIP1L.