Mondo Description X-linked neurodegenerative syndrome, Hamel type is an X-linked neurodegenerative disorder characterised by intellectual deficit, blindness, convulsions, spasticity, mild hypomyelination and early death. It has been described in about ten male members from two generations of one family. The genetic defect responsible for the disorder is located in the pericentromeric region of the X chromosome, Xp11.3-q12.