Older dads linked to lower IQ levels in their kids
OLDER fathers are the chief source of faulty genes linked to intellectual disability, a study has found.
The mental problem, characterised by low IQ, is associated with chromosomal abnormalities caused by missing, repeated or reshuffled DNA sequences.
The research shows the genetic defects mainly arise anew in fathers, especially those who are older. Sperm cells carrying the faults pass them onto a father's children.
Scientists believe the defects occur because of the way sperm cells continue to divide and renew themselves throughout a man's life, increasing the chances of genetic mistakes creeping in.
Female egg cells, on the other hand, stop replicating during foetal development in the womb after about 30 generations.
The findings were published online yesterday in the Journal of Medical Genetics.
Chromosomal abnormalities due to missing, repeated, inverted or misplaced DNA sequences are known as copy number variations (CNVs).
Scientists in the Netherlands investigated the prevalence of CNVs among almost 3,500 people with intellectual disabilities.
They found the group was twice as likely to have "new", or de novo, CNVs which had not been passed down through generations as people with autism. New CNVs were also three times more common in people with intellectual disability than in people with asthma.
Further analysis of CNV origin in 118 people for whom data were available showed that 90 had arisen in the father. Three quarters involved missing DNA sequences.
A significant increase in father's age was associated with CNVs occurring in non-repetitive DNA sequences, which account for most of the abnormalities.
The authors, led by Dr Jayne Hehir-Kwa, from the University of Nijmegen, the Netherlands, wrote: "In conclusion, our data provide for the first time convincing evidence that CNVs in ID (intellectual disability) are largely paternal in origin.
"Both the paternal bias as well as the age effect that we observed can be explained by the continuation of cell divisions of self-renewing spermatogonia in males.."