HS6ST2 and myopia: In a mouse model, abnormally low sulfation of HS allows normal retinal neurogenesis and optic fissure closure; however, it leads to defective optic disc and stalk development.24 Adult mutant animals develop optic nerve aplasia/hypoplasia and exhibit retinal degeneration.24 Although myopia is not directly related to optic nerve aplasia/hypoplasia, but rather occurs if the eyeball is too long or the cornea is too curved, a link may exist between the mutation detected in the HS6ST2 gene and the severe myopia observed in the affected children.