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sChromosomal abnormalities like Down’s syndrome are common in children born to mothers who have conceived at a late age.
Generalizing this condition, all of us tend to believe that it is the mother’s age which is responsible for the development of most of the genetically linked disorders in children. However, in a new study, which turns conventional wisdom on its head, researchers have found that:
It is the father’s age which plays an important role in deciding a child’s risk of developing genetic disorders like autism and schizophrenia.
The study, which was carried out by a private firm deCODE Genetics based in Reykjavik, and has been published in a recent issue of the journal Nature, sequenced the entire genomes of 78 families from Iceland. The children from these families had been diagnosed with autism (in 44 cases) or schizophrenia (in 21 cases). The whole genome sequences of the father, the mother and the child were compared. The entire genome sequence of 1,859 other people from Iceland was also done in order to compare the results.
In the largest study of its kind, the researchers tried to look for those mutations in the child which were not present in the genome sequence of either of the parent. These mutations could have developed spontaneously in the sperm, the egg, or the embryo. In such cases, although there will be no family history of a particular disease, all the cells in the child would be carrying the genetic mutation linked to the disease.
Mutations increase with father's age
The researchers observed that for every one year of increase in the father’s age, an average of two new mutations appeared in the offspring. In other words, the number of new mutations in an offspring for which the father can be held accountable doubles every 16.5 years after the onset of puberty. Even women are responsible for transmitting some of the mutations.
But the number of mutations passed from a father to his child far exceeds the number of mutations passed from the mother.
Two defective genes –EPHB2 and CUL3, transmitted from the fathers, were found in children suffering from autism related disorders.
According to Kari Stefansson, the chief executive of deCODE Genetics, one can safely conclude from the recent study that as the fathers age, there are more mutations taking place inside their sperms, which are then getting transmitted to their children. Sperms are more likely to show mutations in comparison to eggs because, unlike eggs, they are constantly produced by dividing precursor cells, and begin to show error as the man ages.