Mutation screening at the RNA level of the STK11/LKB1 gene in Peutz-Jeghers syndrome reveals complex splicing abnormalities and a novel mRNA isoform (STK11 c.597(insertion mark)598insIVS4).

This study was intended to evaluate a diagnostic reverse transcriptase polymerase chain reaction based protein-truncation test for the identification of germline mutations in the serine/threonine protein kinase 11 (STK11, also designated LKB1) gene in Peutz-Jeghers syndrome (PJS). Our data exemplify that the inactivation of STK11 can be due to unusual disturbances in splicing regulation which result in truncations of the protein. However, nonsense mediated mRNA decay must be blocked with puromycin to detect shortened STK11 gene products contained in the leucocytic mRNA pool of PJS patients. Interestingly, two mutations escaped from detection by exon sequencing techniques with usual flanking PCR primers, since alterations were located right in the middle of intronic sequences. We describe a compound heterozygous PJS patient who carried two different mutations in intron 1 on separate alleles. Each of the two mutations was transmitted individually to one of his two children. In the course of our RNA based analyses we detected high level expression of a novel STK11/LKB1 mRNA variant retaining intron 4 (STK11 c.597(insertion mark)598insIVS4) in various tissues. This mRNA isoform was initiated from an alternative transcription regulatory region as revealed by primer extension analyses even in cell lines with complete methylation of the normal promoter. As a consequence of novel mutational mechanisms identified we discuss the impact of RNA based strategies for the detection of germinal STK11 mutations in PJS.