Mutations in the MRPS28 gene encoding the small mitoribosomal subunit protein bS1m in a patient with intrauterine growth retardation, craniofacial dysmorphism and multisystemic involvement

Hum Mol Genet. 2019 May 1;28(9):1445-1462. doi: 10.1093/hmg/ddy441.

Abstract

Mitochondria contain a dedicated translation system, which is responsible for the intramitochondrial synthesis of 13 mitochondrial DNA (mtDNA)-encoded polypeptides essential for the biogenesis of oxidative phosphorylation (OXPHOS) complexes I and III-V. Mutations in nuclear genes encoding factors involved in mitochondrial translation result in isolated or multiple OXPHOS deficiencies and mitochondrial disease. Here, we report the identification of disease-causing variants in the MRPS28 gene, encoding the small mitoribosomal subunit (mtSSU) protein bS1m in a patient with intrauterine growth retardation, craniofacial dysmorphism and developmental delay. Whole exome sequencing helped identify a seemingly homozygous missense variant NM_014018.2:c.356A>G, p.(Lys119Arg) which affected a highly conserved lysine residue. The variant was present in the mother in a heterozygous state, but not in the father who likely carried a large deletion spanning exon 2 and parts of introns 1 and 2 that could account for the apparent homozygosity of the patient. Polymerase chain reaction (PCR) amplification and Sanger sequencing of MRPS28 cDNA from patient fibroblasts revealed the presence of a truncated MRPS28 transcript, which lacked exon 2. Molecular and biochemical characterization of patient fibroblasts revealed a decrease in the abundance of the bS1m protein, decreased abundance of assembled mtSSU and inhibited mitochondrial translation. Consequently, OXPHOS biogenesis and cellular respiration were compromised in these cells. Expression of wild-type MRPS28 restored mitoribosomal assembly, mitochondrial translation and OXPHOS biogenesis, thereby demonstrating the deleterious nature of the identified MRPS28 variants. Thus, MRPS28 joins the increasing number of nuclear genes encoding mitoribosomal structural proteins linked to mitochondrial disease.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Abnormalities, Multiple / diagnosis*
  • Abnormalities, Multiple / genetics*
  • Alleles
  • Amino Acid Sequence
  • Cell Respiration / genetics
  • Craniofacial Abnormalities / diagnosis
  • Craniofacial Abnormalities / genetics
  • DNA Mutational Analysis
  • Female
  • Fetal Growth Retardation / diagnosis*
  • Fetal Growth Retardation / genetics*
  • Fibroblasts / metabolism
  • Gene Expression
  • Genetic Association Studies
  • Genetic Predisposition to Disease
  • Genotype
  • Humans
  • Magnetic Resonance Imaging
  • Male
  • Mitochondria / genetics
  • Mitochondria / metabolism
  • Mitochondrial Proteins / chemistry
  • Mitochondrial Proteins / genetics*
  • Models, Molecular
  • Mutation*
  • Phenotype
  • Protein Biosynthesis
  • Protein Conformation
  • Protein Subunits / genetics*
  • Ribosomal Proteins / chemistry
  • Ribosomal Proteins / genetics*
  • Structure-Activity Relationship
  • Whole Exome Sequencing

Substances

  • Mitochondrial Proteins
  • Protein Subunits
  • Ribosomal Proteins