The Phakomatoses

Abstract

In 1923 Van der Hoeve introduced the term “phakomatosis” (from the Greek phakos, meaning birthmark) to include a group of hereditary disorders characterized by hamartomas of the skin, eye, central nervous system (CNS), and other viscera. The phakomatoses later came to include other diseases, such as von Hippel-Lindau disease, Sturge-Weber syndrome, ataxia-telangiectasia (Louis-Bar syndrome), and Wyburn-Mason syndrome. Overlapping clinical features, such as pheochromocytoma in neurofibromatosis (NF) type 1 and von Hippel-Lindau disease, persuaded the medical world initially to unite these diseases. Other articles presented families with coincidental occurrence of more than one phakomatosis (eg, tuberous sclerosis with Sturge-Weber or von Hippel-Lindau with NF type 1), suggesting that these diseases were possibly derived from a single gene. Modern molecular genetics has correctly redivided them into distinct genetic disorders.The neurofibromatoses are a group of at least two genetically distinct diseases that have in common multiple tumor types, including neurofibromas, CNS tumors, and other dermatologic features. Developmental abnormalities such as hamartomas also occur, illustrating a need to define the role of the normal NF genes in development. Genetic mapping confirmed the separation of neurofibromatosis type 1 (NF1) from neurofibromatosis type 2 (NF2). The gene products for NF1 (neurofibromin) and NF2 (merlin or schwannomin) were isolated and characterized in the past 2 decades. This chapter looks in detail at both neurofibromatosis type 1 and neurofibromatosis type 2, before moving on to other forms of neurofibromatosis (Legius syndrome, Von Hippel-Lindau disease, Tuberous Sclerosis, and Sturge-Weber syndrome, and Cavernous Hemangioma Syndrome).