Abstract Body: Introduction:
Brain arteriovenous malformations (bAVMs) are vascular anomalies resulting from defective morphogenesis of blood vessels in the brain. Kirsten rat sarcoma virus (KRAS) somatic activating gene mutations have been identified in the majority of bAVMs using digital droplet PCR-based assays (ddPCR). Currently, bAVM somatic mutation genetic characterization requires sequencing surgically excised lesion DNA, but recent advancements have overcome some conventional biopsy limitations through sequencing cell-free DNA (cfDNA) which is directly released into the blood circulation from cell breakdown and turnover at the site of the lesion. Therefore, cfDNA released from the mutated bAVM tissue cells may be detectable in a peripheral blood sample, providing a non-invasive approach for somatic mutation screening. Hypothesis: We hypothesize that somatic KRAS G12D mutations in bAVM patients can be detected using non-invasive cfDNA screening.

Methods:
We selected six bAVM patients whose surgically-resected bAVM lesions screened positive for somatic KRAS G12D mutation using ddPCR and had contributed a peripheral blood sample for research within 2 months prior to surgery. For each patient, cfDNA was isolated from 1.0 mL of banked plasma using the Circulating cfDNA/RNA Isolation Kit (Qiagen). We used the ddPCR KRAS G12D assay (Bio-Rad) to screen cfDNA samples for presence of the mutation. Samples were screened in duplicate using 8 uL and 4 uL of cfDNA eluate and assays included both positive controls (synthetic KRAS G12D oligo sequence (Integrated DNA Technologies)) and negative controls (no template and water). The variant allele frequency was estimated for each sample as the (target concentration)/(target + reference concentration).

Results:
Of the six bAVM cases, five screened positive for KRAS G12D mutation in the cfDNA sample. The KRAS G12D cfDNA variant allele frequency ranged from 0.20 - 0.54% for the five positive samples.

Conclusions:
We detected somatic KRAS G12D mutations in bAVM patients using non-invasive cfDNA screening. While further studies are needed to validate these findings, these exciting results suggest that we may be able to perform non-invasive KRAS somatic mutation screening using cfDNA in a greater number of bAVM cases (e.g., not just those undergoing surgery), which may be useful to clinically stratify bAVM patients and provide targeted therapies based on specific genetic defect.