Unborn babies can sow the seeds for rheumatoid arthritis in their mothers 鈥� and the dads might be to blame.
Rheumatoid arthritis is an autoimmune disease, meaning the body鈥檚 immune system turns on itself. In this case, . Women are three times as likely to develop the condition as men, and seem to be especially vulnerable soon after pregnancy.
A mother exchanges cells with the fetus while it is in the womb. 鈥淔or most women, shortly after you give birth, the fetal cells clear up,鈥� says Giovanna Cruz, an epidemiologist at the University of California at Berkeley. 鈥淏ut in a subset of women they actually persist for decades.鈥� In these women, the fetal cells are effectively incorporated into their bodies, a process known as .
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DNA swap
Women who develop autoimmune diseases seem to have a higher incidence of microchimerism than other women. Two small studies have shown that mothers who genetically have a low risk of developing arthritis but go on to develop the disease are more likely to show for rheumatoid arthritis. But these studies didn鈥檛 look directly at the genes of the father or the child.
In the largest study to date, Cruz and her colleagues analysed genes associated with arthritis in women with the condition and in family members. They did the same for healthy women who had given birth to at least one child, and unrelated men. In total, they looked at over 5000 individuals.
They found that regardless of the women鈥檚 own genetic risk, those with the disease were twice as likely to have given birth to children who had high-risk genes 鈥� most likely passed down from the father.
But how exactly this triggers arthritis remains a mystery. 鈥淲e still don鈥檛 know what these microchimeral cells are doing鈥�, says Cruz, who presented the study at the in San Diego this week. She speculates that it could be either maternal immune cells reacting to the presence of the fetal cells that triggers the response 鈥� in a similar way to a transplant patient鈥檚 body rejecting a donor organ 鈥� or it could be the stowaway fetal immune cells themselves launching the attack.
Dad鈥檚 fault?
鈥淚t is exciting to see work that has the potential to significantly advance our understanding,鈥� says at the University of Washington in Seattle, who carried out some of the initial work on arthritis and microchimerism.
Chris Deighton, medical adviser to the notes the peak age for the disease is around 70 and that it also affects men, as well as women who have never been pregnant. 鈥淚t may be that fetal microchimerism would only account for a small proportion of the aetiology of the disease鈥�. However, he adds that anything that helps us understand this 鈥渁stonishingly complicated鈥� disease is worth pursuing.
Future analysis of Cruz鈥檚 data will look at the genetic influence of the dads 鈥� to see if the partners of affected women are more likely to have high-risk genes than the partners of controls or unrelated men. They also plan to investigate whether having babies with genes known to decrease the risk of rheumatoid arthritis has any mitigating effect on mothers who already have the condition.
