A new study into autism has found a link between the disorder in children and their grandparents' age. The research, published in PLoS ONE last week, is the first of its kind to look at grandparents' as opposed to parents' ages.
The study used information from the Avon Longitudinal Study of Parents and Children (ALSPAC, also known as Children of the Nineties). The ALSPAC study has followed the development of 14,000 children for about 20 years from their mothers' pregnancy. 86 of these children were diagnosed with autism by age 11 and the parents of these children tended to be older on average. Specifically, mothers aged 30 or more at birth were about 50 per cent more likely to have an autistic child compared to younger mothers.
Maternal grandmothers were nearly twice as likely to have an autistic grandchild if they were over 30 when they had the child's mother, and three times as likely if they were over 35. The researchers found the mother's age had no additional effect when they accounted for mothers who have children later tending to have older mothers themselves.
The research was led by Professor Jean Golding, Professor Emeritus at the University of Bristol, who is also the founder of ALSPAC, and Professor Marcus Pembrey, Professor Emeritus of Paediatric Genetics at University College London's Institute of Child Health. Professor Pembrey is also the Progress Educational Trust's Founding Chair of Trustees.
Professor Golding said: 'No other study, to my knowledge, has considered the grandparents' ages in relation to autism, and other studies are needed to test against these findings'.
In the paper, Professor Pembrey introduces a theory explaining the process by which a grandchild could inherit both copies of autism risk genes from their mother due to genetic processes in her ovaries during fetal development. This 3M (meiotic mismatch methylation) hypothesis, although highly speculative, could be easily tested in the study families.
Professor Pembrey said: 'if these findings are replicated in other studies, they challenge the way we think about genetic and developmental influences in autistic spectrum disorders. They point to factors operating at the time when the mother was in the womb, which may influence her developing ovaries and thus the genomes of her future children'.