TSPYL2 and Nystagmus: Although mutations of TSPYL2 have not been associated with a particular human phenotype, TSPYL2 interacts with CASK whose gene is mutated in mental retardation, with or without nystagmus, FG syndrome 4 [OMIM #300422] and mental retardation and microcephaly with pontine and cerebellar hypoplasia [OMIM #300749] [20–23].