Arginine methyltransferase involved in the assembly or stability of mitochondrial NADH:ubiquinone oxidoreductase complex (complex I) (PubMed:20406883, PubMed:24089531, PubMed:24838397). Acts by mediating symmetric dimethylation of 'Arg-118' of NDUFS2 after it assembles into the complex I, stabilizing the early intermediate complex (PubMed:24089531). L-arginyl-[protein] + 2 S-adenosyl-L-methionine = 2 H(+) + N(omega),N(omega)'-dimethyl-L-arginyl-[protein] + 2 S-adenosyl-L-homocysteine Interacts with NDUFS2 (PubMed:20406883, PubMed:24089531). Defects in NDUFAF7 may be a cause of susceptibility to pathologic myopia, a genetically heterogeneous disorder characterized by extreme, familial, early-onset vision loss and described as myopia accompanied by severe deformation of the eye besides excessive elongation of the eye. Belongs to the NDUFAF7 family. Stoichiometry of the protein is unclear. According to a report, it forms a homodimer (PubMed:20406883). According to another publication, it is mainly monomeric (PubMed:24838397).