SIX6 and coloboma of optic nerve: PAX2 malformations have been associated with optic nerve coloboma [4,5,32], SIX6 mutations with bilateral anophthalmia and pituitary abnormalities [33] as well as microphthalmia [34], CHX10 mutations with microphthalmia [3], and SHH mutations with human microphthalmia and coloboma [35].