Finally, a recessive syndrome due to mutations in the gene coding for the ribonucleotide reductase-regulatory TP53-inducible subunit M2B (RRM2B) are associated with a clinical picture of ophthalmoplegia, ptosis, GI dysmotility, cachexia, and peripheral neuropathy, clinically overlapping MNGIE [31,59]. Here, RRM2B is linked to mitochondrial neurogastrointestinal encephalomyopathy.