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At the time of writing (Oct 2009) the exact cause of Proteus syndrome is unknown. The cause of some overgrowth disorders have been established i.e. Simpson-Golabi-Behmel syndrome is caused by mutations in the glypican-3 gene. The gene is one of six that belong to the glypican family and are believed to play a role in cell growth, and in shaping tissues and organs. However, no genetic link has been made with Proteus syndrome.
It has been estimated that the chances of an individual contracting the disorder is less than one in a million, even if a family member has the condition. There are no cases that have been recorded of a parent passing on the Proteus syndrome disorder to their children.
Some researchers have identified mutations in a gene called PTEN. It codes for a protein called phosphatase and tensin homolog and it acts to suppress tumours. Mutations in the gene are also involved in many cancers - where the cell cycle goes out of control. However, there is some debate about the role of PTEN in Proteus syndrome as other scientists have found no PTEN mutations in individuals with Proteus syndrome.
Another gene that has been suspected of causing the condition is the GPC3 gene. It is a member of the glypican family of genes which are involved in cell proliferation and tissue growth. Though here too some researchers have cast doubt over its involvement. The conclusion of a 2004 paper titled "Mutation analysis of the tumor suppressor PTEN and the glypican 3 (GPC3) gene in patients diagnosed with Proteus syndrome" by WD Foulkes et al was that neither PTEN nor GPC3 are likely to have major roles in the development of Proteus syndrome.
