MT-CO3 and idiopathic pulmonary fibrosis: However, 8 (22%) IPF patients had in total 9 NS variants in the COX3 gene (coding for cytochrome c oxidase subunit 3 of the respiratory chain complex IV) (Figure 1), compared with 8 NS variants in the COX3 gene in 80 (10%) control subjects (22% vs. 10%, p = 0.148).