Phakomatoses (or "neurocutaneous syndromes") are diseases that are caused by neurological disorders, and primarily result in lesions on the skin and the retina.
This grouping is an artifact of an earlier time in medicine, before the distinct genetic basis of each of these diseases was understood.
Nevus Outreach, Inc. - Non-profit organization dedicated to education and research into giant congenital nevi and associated disorders, including neurocutaneous melanosis.