Identification of a novel pathogenic deep intronic variant in PTEN resulting in pseudoexon inclusion in a patient with juvenile polyps.

Colorectal, hamartomatous juvenile polyps occur as part of different hereditary syndromes, including Juvenile polyposis syndrome and PTEN-hamartoma tumour syndrome. However, based on clinical manifestations alone, it is difficult to differentiate between the syndromes, and genetic analysis with an NGS-panel is often used to aid diagnostics. We report a 59-year-old male with colorectal juvenile polyps, who had been referred to genetic testing but had normal genetic analysis. He did not fulfil the clinical criteria of PTEN- hamartoma tumour syndrome, but the clinical criteria of Juvenile polyposis syndrome. With Whole Genome Sequencing we detected a novel intronic variant of unknown significance in PTEN (NC_000010.11:g.89687361 A > G(chr10, hg19), NM_000314.8:c.209 + 2047 A > G). RNA analysis classified the variant as likely pathogenic as it results in a pseudoexon inclusion introducing a frameshift and a premature stop codon. The patient was then diagnosed with PTEN-hamartoma Tumour syndrome. To our knowledge this is the first report of a variant resulting in pseudoexon inclusion in PTEN.