PTEN and Lhermitte-Duclos disease: Mutations of the TSG phosphatase tensin homology (PTEN) on chromosome 10q23, also called MMAC1 and TEP1, occur frequently in familial developmental and cancer syndromes such as Cowden-Bannayan syndrome and Lhermitte-Duclos disease.80,81 Many of these syndromes include GBM as part of the clinical spectrum.