Mitochondrial DNA (mtDNA) is used to assign traits in human evolution: for example it was claimed that the Ur-mother of modern humans lived in Africa. mtDNA may harbor fatal mutations which cannot be treated. If there occurs a mutation during the life of an individual this mutation is rarely fatal since it is well diluted. However, if a women during oogenesis transfers these mutation to the oocyte, the problem is multiplied since there are only some mtDNA molecules transferred and therefore one mutation might result in diseases like diabetes, cancer, male infertility, Parkinson, or Alzheimer. The male mtDNA does not reach the progeny.
In an article in PNAS Rebolledo-Jaramillo and colleagues have analyzed in detail mutation rates, disease accumulation and dependency of the age of the mother on the frequency of mutations in the child. They show that on average 9 mtDNA molecules are transferred to the oocyte. The mutation rate is 1.3 × 108 /year (10 times higher than for genomic DNA) which means a mutation in about every 78 th mitochondium (mitochondium has 16.5 kB). They found also, and that is easily comprehensible, that the older the mother the higher the risk of a defect mitochondrium for the child. Ten years older means a tenfold higher risk.
This risk is independent of fathers since only the maternal mtDNA is inherited. There might be other risks due to age in man but they have to be analysed.
Nice and careful article! Recommended!