42. Common Population Variants Cause Susceptibility to Disseminated Coccidioidomycosis

Abstract

Background Coccidioides are endemic, dimorphic fungi found in soils of southwestern United States, Mexico and Central America. Infection occurs via inhalation of arthroconidia which swell, differentiate into spherules and rupture releasing endospores. While the majority of infected individuals will never report illness, roughly 1/3 seek medical attention for fungal pneumonia and ~1% of those present with disseminated coccidioidomycosis (DCM). IL12-IFNγ pathway mutations have been reported in DCM but are exceedingly rare and cannot account for the ~500–600 cases of DCM/year.MethodsWe performed whole exome sequencing on 66 individuals with DCM, retaining variants predicted damaging (CADD >15) with a population frequency < 10%.ResultsHomozygous CLEC7A c.714T >G; p.Y238* causing a truncated Dectin-1 receptor was overrepresented (OR=9.8449, 95% CI 3.0841 to 31.4260, P=0.0001). Dectin-1 signaling pathway variants included 3 homozygous and 11 heterozygous CLEC7A p.Y238* individuals, one each CLEC7A p.I223S and MALT1 p.R149Q and five PLCG2 p.R268W. Since Dectin-1 is the receptor for b-glucan, a major Coccidioides cell-wall component, we hypothesized that Dectin-1 pathway variants could affect fungal recognition and cellular response. Healthy control PBMCs stimulated with purified β-glucan or heat-killed Candida albicans induced 6-fold more TNFα than patients with homozygous or heterozygous CLEC7A, PLCG2 or MALT1 variants (P=0.0022, Ordinary one-way ANOVA). Additionally, one patient with a family history of DCM but lacking a defined mutation also failed to up-regulate TNFα after stimulation.Normalized TNF production from healthy control and DCM patient’s peripheral blood mononuclear cellsConclusion These data are consonant with increased dissemination in Clec7a-/- mice as well as in patients receiving anti-TNF biologics. These gene variants accounted for 31% of our DCM cohort (21/66 patients). This is the first demonstration of variants outside the IL12-IFNg pathway impairing fungal recognition and cellular response in coccidioidomycosis. Common heterozygous variants may be sufficient for disease susceptibility to highly pathogenic organisms.Disclosures Michail Lionakis, MD, ScD, Matinas BioPharma (Research Grant or Support)