Increased genetic modification in teenage fathers

Sperm of adolescents have significantly more mutations

The large oval structures are cross sections of the seminiferous tubules. © CeRA, WWU Münster
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Paternity in the teen age carries risks: sperm from very young men show a surprising number of genetic alterations, as researchers have found. They also found more mutations in the male teenagers than in the ova of the same age women. These results could explain why babies of very young parents are relatively often affected by birth defects, say scientists in the British journal Proceedings of the Royal Society B.

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It has long been known that especially children of very young parents are particularly often born with autism, schizophrenia, spina bifida (vertebral column) and other birth defects. Why, but so far remained unclear. The risk of mutations actually increases the more frequently the precursors of the egg and sperm cells have already shared.

The more divisions, the higher the risk of error

This increases the risk of false copies, especially in men during their lifetime. Because the production of Urkeimzellen runs in the sexes differently: In women, all Urkeimzellen are fully formed shortly after birth. The mature egg in the monthly cycle of the adult woman arises from this pool of primordial germ cells. The spermatozoa, on the other hand, are always produced anew during the sexual maturity of the male. In the course of his life, the number of divisions for the sperm-producing cells therefore increases - and thus increases the risk of mutation.

The extent to which the risk of such mutations in men and women changes with age is examined by Heidi Pfeiffer from the Münster University Hospital and her colleagues in 24, 097 parents and their children. They analyzed blood samples from the subjects and compared certain sections of their DNA, the so-called microsatellites. display

These are very short, repetitive DNA sequences that do not code for genes. Only with cell divisions mutations arise here, on them therefore cell division and mutation rate can be measured particularly well.

Mutation rate slower in men

The evaluation provided several surprises: First, the mutation rate in men does not seem to increase linearly with age. Instead, the number of mutations in their first few decades after puberty increases much more slowly than previously expected: for 50-year-old fathers, it is only 30 percent higher than for teenagers.

This slow rate of mutation is explained by a reservoir of special stem cells in the testes. After puberty, these remain virtually in the background as a silent reserve and at first hardly share. In middle age, spermatozoa then develop via intermediates, which then receive correspondingly fewer mutations.

Riddling fault with teenagers

And one more thing was amazing: In sperm from teenage fathers, the researchers found unexpectedly many mutations. There were more than the 20-year-old men and seven times more than in the ova of the same age girls. This is surprising because it was previously thought that the germ cells of a boy from birth to puberty only complete about 30 divisions and thus have little opportunity to accumulate mutations.

But to explain the now measured mutation rate, sperm precursor cells should have shared around 150 times by the end of puberty. And that does not explain why teenage sperm seem to be even more susceptible to DNA errors than men just a few years older.

"Perhaps the DNA replication mechanism at the beginning of male puberty is particularly prone to error, " says Pfeiffer. She speculates that this may be the reason that teenage parents give birth to children with birth defects more often. (The Royal Society Proceedings B, 2015; doi: 10.1098 / rspb.2014.2898)

(Westf lische Wilhelms-Universit t M nster, 19.02.2015 - MAH)