The natural history of infantile mitochondrial DNA depletion syndrome due to RRM2B deficiency

Genet Med. 2020 Jan;22(1):199-209. doi: 10.1038/s41436-019-0613-z. Epub 2019 Aug 29.

Abstract

Purpose: Mitochondrial DNA (mtDNA) depletion syndrome (MDDS) encompasses a group of genetic disorders of mtDNA maintenance. Mutation of RRM2B is an uncommon cause of infantile-onset encephalomyopathic MDDS. Here we describe the natural history of this disease.

Methods: Multinational series of new genetically confirmed cases from six pediatric centers.

Results: Nine new cases of infantile-onset RRM2B deficiency, and 22 previously published cases comprised a total cohort of 31 patients. Infants presented at a mean of 1.95 months with truncal hypotonia, generalized weakness, and faltering growth. Seizures evolved in 39% at a mean of 3.1 months. Non-neurological manifestations included respiratory distress/failure (58%), renal tubulopathy (55%), sensorineural hearing loss (36%), gastrointestinal disturbance (32%), eye abnormalities (13%), and anemia (13%). Laboratory features included elevated lactate (blood, cerebrospinal fluid (CSF), urine, magnetic resonance (MR), spectroscopy), ragged-red and cytochrome c oxidase-deficient fibers, lipid myopathy, and multiple oxidative phosphorylation enzyme deficiencies in skeletal muscle. Eight new RRM2B variants were identified. Patients with biallelic truncating variants had the worst survival. Overall survival was 29% at 6 months and 16% at 1 year.

Conclusions: Infantile-onset MDDS due to RRM2B deficiency is a severe disorder with characteristic clinical features and extremely poor prognosis. Presently management is supportive as there is no effective treatment. Novel treatments are urgently needed.

Keywords: mitochondrial disease; mtDNA depletion; outcomes; ribonucleotide reductase; treatment.

Publication types

  • Multicenter Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Cycle Proteins / chemistry
  • Cell Cycle Proteins / genetics*
  • Female
  • Humans
  • Infant
  • Infant, Newborn
  • Intestinal Pseudo-Obstruction / genetics*
  • Intestinal Pseudo-Obstruction / mortality
  • Male
  • Models, Molecular
  • Muscular Dystrophy, Oculopharyngeal / genetics*
  • Muscular Dystrophy, Oculopharyngeal / mortality
  • Mutation, Missense*
  • Ophthalmoplegia / congenital
  • Prognosis
  • Protein Conformation
  • Ribonucleotide Reductases / chemistry
  • Ribonucleotide Reductases / genetics*
  • Survival Analysis

Substances

  • Cell Cycle Proteins
  • RRM2B protein, human
  • Ribonucleotide Reductases

Supplementary concepts

  • Visceral myopathy familial external ophthalmoplegia