Cancer risk to children of having older parents
Older parents are at significantly increased risk of having a child with the most common form of leukaemia, Cancer Research UK reveals.
A study of over 3,000 cases of acute lymphoblastic leukaemia (ALL) - which accounts for around a quarter of all childhood cancers - suggests children born to older mothers and fathers have an increased risk of developing the disease.
In a separate finding, researchers also confirmed that first-born children have a higher risk of ALL than later siblings.
Scientists at the Government-funded Childhood Cancer Research Group in Oxford identified over 10,000 cases of children's cancer from the British National Registry of Childhood Tumours. The registry is maintained in collaboration with the UK Children's Cancer Study Group (UKCCSG), which is funded mainly by Cancer Research UK.
Researchers compared the children on the registry with a similar sample of healthy children, in order to analyse factors which might have contributed to their cancer risk.
Children with ALL were more often born of older parents than would be expected, even when researchers took into account the fact that older mothers are more likely to have a child with Down Syndrome, a condition which is associated with increased risk of leukaemia. A mother between the ages of 35 and 39 was 30 per cent more likely to have a child with the disease than one aged 25 to 29, with the additional risk rising to 88 per cent for mothers of 40 or over.
Researchers observed a similar pattern in fathers, though they tended to be a little older, reflecting the pattern of parental ages in the general population. Since the age of one partner is related to the age of the other, researchers were unable to say whether the increased leukaemia risk was linked to maternal or paternal age, or to both.
Dr Gerald Draper, Honorary Senior Research Fellow at the Childhood Cancer Research Group, says: "We know that some rare inherited genetic conditions can increase the risk of developing leukaemia and our research suggests the risk of inheriting such conditions is higher when parents are older. Presumably, genetic damage is more likely to be found in the eggs and the sperm-forming cells as they age."
Researchers also made a second, equally interesting finding. In their study, a family's first born was significantly more likely to develop ALL than later children, with each subsequent child at lower risk of the disease. This result was statistically strong and separate from the effect produced by increasing parental age.
Firstborns may be less likely to be exposed to infections in early life. Some scientists believe that such early exposure can prime the immune system against the possibility that later infections, in a very small number of cases, may lead to leukaemia. Firstborn children may miss out on this protective effect.
Dr Draper again: "Second and third children often catch various infections from their older brothers and sisters - and in some ways this may do them good. We think our study highlighted two separate effects on the risk of leukaemia, one perhaps related to the ageing of sperm and eggs and the other related to exposure to infection."
Sir Paul Nurse, Chief Executive of Cancer Research UK, says: "Learning about the causes of childhood cancer is vital if we're to make progress towards new ways of prevention or treatment.
"By providing new insights into the most common form of childhood leukaemia, this research has taken us a step closer to a comprehensive understanding of the disease."