A faint and heterogeneous NDUFS4 staining was also observed in the II.4 tumor along with a generally positive but heterogeneous COXI staining (Figure 4A(b,f)), suggesting the MT-ND1 missense mutation m.3380G>A may have an effect on CI integrity, and that its mutation load reflects a population, not a cell, heteroplasmy. Here, MT-CO1 is linked to neoplasm.