GENE-18. USE OF PRIMARY TEETH AND A TOOTH BRUSH AS SOURCES OF DNA IN AN ANAPLASTIC ASTROCYTOMA CASE

Abstract

BACKGROUND: Anaplastic astrocytomas (AA) are aggressive glial cancers with poor prognosis and high recurrence. Although a majority of astrocytomas are sporadic, recent studies have shown that up to 10% of patients with cancer may have an underlying cancer predisposition syndrome. Identification of germline mutations allows for proper management and screening for cancer in patients and their at-risk family members. In this study, we present a unique case of two siblings who developed AA within 8 years of each other. Clinical whole exome testing of our patient's germline DNA revealed a maternally inherited PTCH2 mutation of unknown significance. The PTCH2 gene is highly homologous to the PTCH1 gene, which is associated with increased risk for basal cell carcinoma, medulloblastoma, rhabdomyoma and ovarian fibroma. However, this has never been described in a glioma before. METHODS: Prior to extracting DNA, the teeth were fragmented in liquid nitrogen and de-calcified in 1.0mM EDTA. The toothbrush was processed for DNA extraction by removing the head from the handle and submerging in Tris base solution. DNA extraction was performed using QIAamp DNA Mini-kit. Genomic DNA from the teeth and toothbrush were pre-amplified using primers for specific genes (H3F3A and IDH1) and detected by digital polymerase chain reaction (dPCR). PTCH2 gene germline mutation in DNA isolated from teeth and toothbrush were examined by Sanger sequencing. RESULTS: In this study, by using germline DNA from primary teeth and tooth brush of the brother, we were able to determine whether the PTCH2 germline mutation played a role in the development of astrocytomas in the two siblings. This method can be applied in many clinical scenarios where classification of germline variants is important for the determination of cancer risk in surviving family members.