PHOX2A and fibrosis: For the recessive forms of these disorders, genetic studies of affected consanguineous families have allowed successful identification of novel genes involved in ocular motility such as paired-like homeobox 2a (PHOX2A; recessive congenital fibrosis of the extraocular muscles) [10] and roundabout homolog 3 (ROBO3; recessive horizontal gaze palsy with progressive scoliosis) [11].