Alu-mediated genomic deletion of the serine/threonine protein kinase 11 (STK11) gene in Peutz-Jeghers syndrome.

Abstract. Background & Aims; Peutz-Jeghers syndrome (PJS) is an autosomal dominantly inherited syndrome characterized by mucocutanoeus pigmentation, multiple hamartomatous polyps in the gastrointestinal tract and an increased risk of cancer at a young age. Inactivating germ-line mutations in the tumor suppressor gene STK11/LKB1 have been detected in approximately 80% of patients. The aim of this work is to clarify the molecular basis of the disease in Italian PJS patients. Methods: We investigate the STK11/LKB1 gene mutations in a well-characterized series of 9 unrelated Italian PJS patients, by using a combination of PCR, RT-PCR, DNA sequencing, Southern blot analysis and real-time polymerase chain reaction techniques. Results: We have characterized the specific STK11 mutation in 6 probands, and identified 2 truncating mutations (1 novel and 1 known mutation), one missense known mutation in the exon four, and two novel small in-frame deletions in the exon six. Finally, we have found an intra-exonic in-frame deletion encompassing exons 2 and 4: the possible mechanism leading to this genomic rearrangement is most likely an Alu-Alu homologous recombination. Conclusions: In our study point mutations, small scale deletions/insertions and exonic STK11 deletions account for about 67% of PJS; mutations in other STK11 related genes examined have not be found. Other gene inactivating methods, such as chromosomal rearrangements mediated by Alu-Alu homologous recombination, which cannot be detected by routinely molecular biology screening methods, might be responsible for PJS in mutations negative population subset. However, the existence of genetic heterogeneity cannot be excluded.