Father’s age linked to risks of autism and schizophrenia

Victoria Pease runs the rule over new research linking autism and schizophrenia in children to the father’s age.

New research published in the journal Nature (August 2012) suggests a link between paternal age and an increased risk of psychological mutations such as autism and schizophrenia to develop in their children. Although the findings deriving from this study are previously known, and hence do not prove that increased paternal age alone imparts the development of a mutation such as autism in a child, it emphasises a contributing risk factor linked to such diseases, and is the largest study providing this form of evidence thus far.

deCODE Genetics, the company that ran the study in Reyjavik, Iceland, analyse the human genome to discover genetic risk factors in common diseases that range from cardiovascular disease to cancer.

In better understanding the cause of new hereditary mutations, the study compared entire genome sequences of 78 trios of mother, father and child. Analysing the complete genome is integral to finding de novo mutations, i.e. spontaneous mutations that develop during gametogenesis that are not inherited by parent sperm of egg cells. Analysing complete genome sequences singles out new mutations by distinguishing inherited ones from both parental sides, while available family information allows for understanding any environmental effects that may have an effect on the development of brain disorders. To provide effective evidence with a large enough population sample, additional 1,859 Icelanders were involved in the study in the comparison of genome sequences.

Furthermore, by narrowing study participants down to the Icelandic population, confounding factors are limited.

Study results showed that fathers passed on nearly four times as many new mutations as mothers (55 versus 14), with random mutation numbers rising exponentially with age. Narrowing their data down further, researchers at deCODE Genetics found a two mutation per year increase in offspring with each one-year increase in the age of the father. In comparison, the number of mutations passed on by the maternal side was 15 at any age, while a child with a 20-year-old father had an average of 35 mutations passed on and a child of a 40-year-old father an average of 65 found mutations. For disorders such as autism and schizophrenia, the study emphasises the mother’s age as no contributing risk factor, as it is for chromosomal abnormalities such as Down’s syndrome.

Dr. Kari Stefánsson, CEO of deCODE Genetics, says de novo mutations would unsurprisingly play a significant role in brain disorders, as at least 50 percent of active genes play a role in neural development, making it less likely to affect organs that are not as exposed to such. Aside from this fact, the greater amount of random mutations, however, do not result in consequential brain disorders, just as an older paternal age is only one of many contributing factors that may lead to a child being born with autism. Around 20-30 percent of random mutations are thought to account for the case of autism, while the remaining percentage is defined by genetically inherited mutations as well as environmental factors.

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