Furthermore, nDNA mutations in RRM2B, which encodes the ribonucleotide reductase p53R2 subunit, can lead to multiple mtDNA deletions in Kearns-Sayre syndrome through defective ribonucleotide reductase assembly.337 This defective assembly disrupts deoxynucleotide provision and the maintenance of dNTP pools.338. The gene discussed is RRM2B; the disease is Kearns-Sayre syndrome.