90. TERT promoter mutation detection by ddPCR in glial atypia

Aly Abdelkareem

Alaa Koleilat

Alaa Koleilat is originally from Bismarck, ND. She attended UCLA for her undergraduate degree in Biology and then the University of Minnesota, Twin Cities for her masters in Biological Sciences. She obtained her Ph. D from the Mayo Clinic Graduate School of Biomedical sciences in the clinical and translational sciences track which takes an interdisciplinary approach to science with population-based, patient-based and laboratory-based concentrations. Her doctorate training working with Dr. Lisa Schimmenti and Dr. Stephen Ekker focused on developing novel therapies to treat genetic hearing loss, specifically Usher Syndrome and designing, validating, and testing a unique clinical hearing assessment tool that can broaden access to hearing testing. One of the goals of her doctoral training was to understand how to translate research to health care in order to accelerate medical discoveries and to impact patient care. She is continuing her patient-centered career path in the field of genetics and genomics and is in the last year of her training as a laboratory genetics and genomics fellow at Mayo Clinic. Dr. Koleilat continues her research involvement in both molecular genetics and cytogenetics projects. She has presented her work at conferences both nationally and internationally and invited as a seminar speaker and panelist. Dr. Koleilat has a personal interest in improving diversity, equity and inclusion and is involved in many initiatives in her department to help improve workplace diversity and increase awareness regarding minority experiences.


Alaa Koleilat, Dragana Milosevic, Cristiane Ida

Mayo Clinic, Rochester, MN, USA

Glial atypia is a frequent ‘non-diagnostic’ diagnosis in surgical neuropathology and may represent a neoplastic or reactive process. Detection of a TERT promoter (TERTp) mutation in this context would support the diagnosis of neoplasia. Droplet digital PCR (ddPCR) has emerged as a platform with increased sensitivity when compared to next-generation sequencing (NGS). We evaluated the diagnostic yield of TERTp C228T and C250T mutation testing by ddPCR for cases with provided histopathological diagnosis of glial atypia that tested negative by NGS. De-identified residual DNA extracted from formalin-fixed paraffin-embedded tissue (2018-2021; n=47) previously tested by a targeted amplicon-based TERTp C228T and C250T NGS assay with analytical sensitivity of 5% variant allele frequency was analyzed by BIO-RAD TERTp C228T and C250T expert design ddPCR assays. A valid result required a minimum of 10,000 acceptable droplets and 700 total copies (equivalent to 2.5ng DNA input) and was considered positive if at least 5 mutant copies were detected with a minimum of 0.5% fraction abundance. Of the 47 tested cases, 37 (79%) had valid results. A TERTp mutation was detected in 7 (of 37; 19%) cases: 5 C228T and 2 C250T. The average and median fraction abundance for the TERTp mutations were 4.0 and 4.4%, respectively (range, 0.7-6.7). All detected mutations had at least 300 total supporting sequencing reads with over 10,000X coverage upon manual review of NGS data. The increased sensitivity of ddPCR offers improved diagnostic yield for TERTp mutation detection in comparison to NGS for cases with histopathological diagnosis of glial atypia.