Identification of a novel PTEN intronic deletion in Li-Fraumeni syndrome and its effect on RNA processing
Germline mutations of the TP53 tumor suppressor gene account for the predisposition to cancer observed in many Li-Fraumeni syndrome (LFS) families. A causative genetic factor in the remaining families that harbor no TP53 mutations remains to be elucidated. The PTEN phosphatase tumor suppressor gene is mutated in human cancers observed in LFS. There also exists some phenotypic overlap in the occurrence of cancers in LFS and Cowden's disease (CD), for which germline PTEN mutations are believed to be responsible. We hypothesized that PTEN may be altered in some TP53-wild-type LFS families. We examined LFS primary patient lymphocytes for PTEN alterations using SSCP and sequence analysis. A novel intronic deletion was found in two unrelated individuals, adjacent to the splice acceptor site of PTEN exon 4. Based on an in vitro mRNA processing assay this alteration is predicted to be a polymorphism. The in vivo effects of this proximal splice site deletion are unknown and a genetic cause for the cancers in these families remains to be elucidated. Germline mutations of PTEN were not detected in other families, suggesting that alterations of this tumor suppressor gene do not account for the cancers observed in the subset of LFS individuals with wild-type germline TP53.