Deleterious mis-splicing of STK11 caused by a novel single-nucleotide substitution in the 3' polypyrimidine tract of intron five.

BACKGROUND: Pathogenic variants in STK11, also designated as LKB1, cause Peutz-Jeghers syndrome, which is a rare autosomal dominant disorder characterized by mucocutaneous pigmentation changes, polyposis, and a high risk of cancer. METHODS: A male meeting the clinical diagnostic criteria for Peutz-Jeghers syndrome underwent next-generation sequencing. To validate the predicted splicing impact of a detected STK11 variant, we performed RNA-Seq on mRNA extracted from patient-derived Epstein-Barr virus-transformed lymphocytes treated with cycloheximide to inhibit nonsense-mediated decay ex vivo. RESULTS: Blood testing identified a novel single-nucleotide substitution, NM_000455.4:c.735-10C>A, at the end of the 3' polypyrimidine tract of intron five in STK11. RNA-Seq confirmed a predicted eight base pair insertion in the mRNA transcript. Following inhibition of nonsense-mediated decay, the out-of-frame insertion was detected in 50% of all RNA-Seq reads. This confirmed a strong, deleterious splicing impact of the variant. CONCLUSION: We characterized a novel likely pathogenic germline variant in intron five of STK11 associated with Peutz-Jeghers syndrome. The study highlights RNA-Seq as a useful supplement in hereditary cancer predisposition testing.