CYBB and chronic granulomatous disease: Around 70% of CGD cases are due to mutations in the NOX2 coding gene, CYBB. NOX2 or gp91phox is the catalytic subunit of the complex and the founding member of the NADPH oxidase family, which is comprised of seven isoforms in mammals (NOX1-NOX5, DUOX1 and DUOX2) [3].