Tests on world's oldest woman reveal 'stem cell exhaustion' and hundreds of genetic mutations

Blood tests of a woman who lived to 115 have revealed that when she died the majority of the white blood cells in her body originated from just two stem cells.

The finding suggests that 'stem cell exhaustion' - where the stem cells that continually replenish tissues in the body gradually die out - may limit human lifespan.

'Is there a limit to the number of stem cell divisions, and does that imply that there's a limit to human life?' Dr Henne Holstege of the VU University Medical Centre in Amsterdam, the Netherlands, who led the research, asked New Scientist. 'Or can you get round that by replenishment with cells saved from earlier in your life?'

Humans are born with around 20,000 blood stem cells, Dr Holstege told the magazine, 'and at any one time, around 1,000 are simultaneously active to replenish blood'.

The blood was taken from the body of former world's oldest woman Hendrikje van Andel-Schipper on her death in 2005 after she bequeathed her body to science.

Further evidence of van Andel-Schipper's advanced years was found by looking at the blood cell telomeres — the repetitive sequences at the ends of chromosomes that protect the genetic code from corruption. Telomeres shorten each time a cell divides.

On average, the telomeres on van Andel-Schipper's white blood cells were 17 times shorter than those in her brain cells, which hardly ever replicate.

The researchers also detected over 400 genetic mutations in the blood cells, a finding which would seem to run counter to the fact of van Andel-Schipper's long, healthy life. Genetic mutations occurring in the body's cells — somatic mutations — are known to cause many diseases, including cancer.

The results suggest that a person can accumulate many mutations in their cells over a lifetime but if these occur in regions of the genome not associated with disease, as van Andel-Schipper's did, then there may be few consequences for health.

'When there is mutation, there's an opportunity for selection and some somatic mutations lead to cancer', Dr Chris Tyler-Smith of the Wellcome Trust Sanger Institute told New Scientist. 'Now we see the range of somatic mutations in normal, non-cancerous tissues like blood, so we can start to think about the health consequences'.

The study was published in the journal Genome Research.