Identification of CARD9 mutations by gene panel sequencing and characterization of the cellular phenotype by quantitative PCR, immunoblot, luciferase reporter, and cytometric bead array assays were performed.
Gene panel sequencing identified compound heterozygous CARD9 variants, c.1118G>C (p.R373P) and c.586A>G (p.K196E), in a 4-year-old patient with multiple cerebral lesions and systemic lymphadenopathy due to Exophiala dermatitidis. The p.R373P is a known disease-causing variant, whereas the p.K196E is a private variant. Although the patient\'s siblings, a 10-year-old brother and an 8-year-old sister, were also compound heterozygous, they have been asymptomatic to date. Normal CARD9 mRNA and protein expression were found in the patient\'s CD14+ monocytes. However, these cells exhibited markedly impaired pro-inflammatory cytokine production in response to fungal stimulation. Monocytes from both asymptomatic siblings displayed the same cellular phenotype.
CARD9 deficiency should be considered in previously healthy patients with invasive Exophiala dermatitidis disease. Asymptomatic relatives of all ages should be tested for CARD9 deficiency. Detecting cellular defects in asymptomatic individuals is useful for diagnosing CARD9 deficiency.