Mutations in mitochondrial small subunit ribosomal proteins MRPS16 or MRPS22 cause severe, fatal respiratory chain dysfunction due to impaired translation of mitochondrial mRNAs. The loss of either MRPS16 or MRPS22 was accompanied by the loss of most of another small subunit protein MRPS11. However, MRPS2 was reduced only about 2-fold in patient fibroblasts. This observation suggests that the small ribosomal subunit is only partially able to assemble in these patients. Two large subunit ribosomal proteins, MRPL13 and MRPL15, were present in substantial amounts suggesting that the large ribosomal subunit is still present despite a non-functional small subunit.