This finding comes from a research article title "Rate of de novo mutations and the importance
of father's age to disease risk".
it was published in August 2012 in Nature by Stefansson's group at the university of
iceland in reykjavik.
This finding deals with our DNA and how our DNA differs from our parent's DNA.
Let's examine this a little closer by looking at HOW DNA is transmitted from parents to
children.
We inherit half of our DNA from our mother and half of our DNA from our father.
The DNA from our mother is provided in the egg and the DNA from our father is provided
in the sperm which together with the egg makes the embryo.
This is simple to understand but the story of how we get our DNA sequence gets a little
more complicated.
We know that as women age, the egg can, by mistake, give to the child a different DNA
sequence than that of the mother.
This is called a "mutation" which is a change in the DNA sequence.
Mutations in the egg provided by the mother as the mother ages is the reason women over
35 are at increased risk of having a child with Down Syndrome.
Mutations in eggs or sperm can cause a child to inherit a piece of DNA sequence that is
found in neither the mother nor the father.
We call this a "de novo" mutation.
As of now, it was not known precisely if the father also provided DNA with de novo mutations
to the child or if all of the de novo mutations came from the mother.
In this finding, the scientists were interested in seeing if fathers also contributed de novo
mutations to the child and if age at time of conception had any effect on the number
of mutations the father passed on to his child.
To do this, the scientists used 78 trios which include two parents and a child from the Icelandic
population.
Iceland is a great place to perform genetic studies because there has been very little
migration into and out of Iceland so individuals in Iceland all have very similar DNA.
This makes it easier for scientists to find mutations or differences in the DNA sequence.
So the scientists took the DNA of these 78 trios and sequenced all of the DNA looking
for specific changes in the DNA sequence at single bases.
And what they found was very interesting!
The scientists found that the children had mutations that were not present in either
one of the parents.
This meant that one of the two parents had transmitted DNA that was mutated to the child
and this happened either in the egg or in the sperm.
By looking at the DNA sequence around the mutation, the scientists were able to say
that fathers were transmitting to their children 4 times as many mutations as the mothers were.
PAUSE But that's not all!
When the scientists took into account father's age at the time of conception, they found
that the older the father, the more mutations were passed onto the child: (pause) two mutations
were passed on to the child for every year of the father's age at the time of conception.
So if the father was 22 years old when the child was conceived then he passed on about
44 mutations to his child, and the mother only passed on about 10 mutations (or 4 times
fewer than the father).
The data also indicated that the older the father at the time of conception, the higher
the mutation rate at ages above 40.
So if the father was 40 at the age of the conception, then he would pass on more than
2 mutations per year of his life ( more than 80 mutations)! so the mutation rate per year
of the father's life seemed to increase EXPONENTIALLY as the father ages.
Some of the older fathers that were studied here had passed on more than 100 mutations
to their child!!
So what do all of these mutations mean when it comes to the health of the child?
Are they good or are they bad?
Mutations are often thought of as being detrimental and they in fact can cause disease and this
happens most often BUT mutations can also be beneficial by protecting you from illness.
So are these de novo mutations transmitted by the father detrimental to the child's health?
Or are they beneficial?
Population studies in Iceland have shown that schizophrenia and autism increase significantly
with father's age at conception.
This is in line with the results of this finding showing that fathers transmit more mutations
to their children with increasing age at the time of conception.
So this suggests that at least some of the mutations that are transmitted from father
to child may be detrimental and increase the risk of autism and schizophrenia.
This does not mean that all of the mutations are detrimental.
it's definitely possible that some of the mutations may be beneficial to the child but
this remains an open question.
So what did this study show?
Thanks to new and affordable techniques for sequencing DNA, this study was able to show
that :
fathers transmit a considerable number of SINGLE BASE mutations to their child, about
4 times more than mothers.
In addition, this study also showed that the number of mutations transmitted by the father
increases as the father ages at a rate of about 2 mutations per year of the father's
age at time of conception and this may be increase exponentially at above 40 years of
age.
It is very surprising that father's transmit so many mutations to their child and that
the number of mutations transmitted increases with father's age!
Before this finding, it was known that father's transmitted SOME mutations to their child
but it was thought that those mutations transmitted by the father were insignificant compared
to the mutations transmitted by the mother.
But this study clearly shows that this is NOT the case!!
It still remains to be seen exactly HOW those mutations transmitted by the father affect
the child's health and how this might shape the population's genetic pool.
As our population ages and men conceive children later in life, it is interesting to think
about this study in the context of the population as a whole to try to predict or anticipate
if certain diseases will be more prevalent due to these mutations.
On the other hand, these de novo mutations may provide an advantage and allow us to continuously
adapt to our ever-changing environment by providing more genetic variation.