NEW YORK (Reuters Health) – Contrary to a recent study, a new study suggests that fathers with multiple sclerosis are no more likely than mothers with MS to transmit the genetic risk of the disease to their children.

The study team identified 3,088 Canadian families with one parent with MS. Of the 8,401 children in those families, 798 had MS. "We observed equal disease transmission to offspring from affected mothers (9.76%) and affected fathers (9.41%)," report Dr. George C. Ebers from the University of Oxford, UK and colleagues in the June 27 online issue of Neurology.

Moreover, they observed that equal numbers of daughters and sons inherited the genetic risk of the disease from their parents and there was no difference in sibling recurrence risk by gender of affected parent.

"It is widely believed," Dr. Ebers told Reuters Health, "that MS risk is determined by multiple genes with small effects plus an unknown environmental influence."

"Interestingly," he said, "when there are half siblings, both with MS, we found the mother is much more likely to be the single common parent, but here the parents are unaffected, implying the environmental factor may be operative at a maternal level even though this is an adult onset disease for the most part."

In a recent study involving 197 nuclear families, children of affected fathers were reported to be more likely to have MS than children of affected mothers. The phenomenon was attributed to the Carter effect, which predicts that because men are more resistant to MS, those who are affected carry a higher genetic load and are thus more likely to transmit the genetic risk to their offspring.

"In the case of MS where males are less affected, those affected males should have more affected offspring than affected females since they have more genes to pass on to daughters who are more likely to be affected," Dr. Ebers explained.

However, he told Reuters Health, "In a study 16 times as large, we found no such effect, implying that the model of many genes with small effect is not correct."