X-linked recessive CGD (X-CGD) accounts for approximately 70% of CGD cases (Jirapongsananuruk et al., 2002) due to a variant in the CYBB gene that results in an abnormal gp91phox protein in the encoded NADPH oxidase complex (Köker et al., 2013). The gene discussed is CYBB; the disease is chronic granulomatous disease.