Identification of a germline deep intronic PTEN-deletion leading to exonization through whole genome and targeted RNA sequencing

Abstract

PTEN Hamartoma Tumor Syndrome (PHTS) is an autosomal dominant disorder characterized by high penetrance and significant phenotypic variability. In most patients, targeted high-throughput sequencing (HTS) approaches enable the detection of loss-of-function pathogenic variants in PTEN, a tumor suppressor gene acting as a negative regulator of the PI3K-AKT pathway. We describe a patient exhibiting a clinical phenotype strongly indicative of PHTS, yet lacking a molecular diagnosis through PTEN-targeted HTS. After several years of diagnostic uncertainty, trio whole genome sequencing (WGS) ultimately identified a de novo germline deep intronic 98 bp deletion in PTEN intron 5 (c.492 + 1671_492 + 1768del). Targeted RNA sequencing revealed the inclusion of a pseudoexon, resulting in a frameshift and predicted protein truncation at codon 171 (p.Val166Asnfs*6). These data underline the importance of WGS approaches in detecting deep intronic structural variants, that may be overlooked by conventional methods.

Keywords: Deep intronic variants; PTEN; PTEN Hemartoma Tumor Syndrome; Whole genome sequencing.