Enzyme gene mutations

• Cause increase of metabolite before
• Cause decrease of metabolite after
• Might also cause the production of another (toxic) metabolite

Genetic metabolic diseases

• are rare and heterogeneous
• Hielprik contains 17 metabolic diseases → early intervention might significantly increase quality of life.
• Diagnostics
  • Clinical suspicion
    • → metabolomics
      • → functional assays
    • → WES/WGS (newer)
      • → interpretation
      • → diagnosis

GOT2 deficiency

• Patient 1:

  • 1st month:
    • generalized hypotonia
    • abdominal spasms
  • 8th month
    • therapy resistant febrile seizures
  • 8th year
    • microcephaly
  • Low serine concentrations were found in plasma
    • serine biosynthesis by three enzymes → none were defect
  • WES
    • GOT2 was heterozygously mutated and has a metabolic function
    • GOT2 is mitochondrial, very low expression in patient

• Additional patients

  • four other childerens with this mutation with intellectual disabilities, epilepsy, congenital microcephaly.
  • fibroblast enzyme activity is low in all patients, carrier also have reduced enzyme activity.
  • GOT2 is important for the malate aspartate shuttle:
    • NADH production has to go from cytosol to mito for oxfos
    • NADH → NAD+ in mito

  

  • other patients did not have low serine plasma concentrations.

• link serine and GOT2:

  • first step from glucose to serine needs NAD+, which is not properly produced because of the GOT2 mutation

  

  • flux study → serine produced from glucose is decreased.
  • in vitro study KO of GOT2 shows a decrease in serine

• How to rescue?

  • Give serine agains epilepsy
  • Giving pyruvate to replenish NAD+ levels

Other defects in the malate aspartate shuttle:

• generally brain + muscle phenotype