As scientists strive to decipher the complex melding of genetic and environmental factors that cause certain kids to get juvenile idiopathic arthritis (JIA), a multitude of questions arise.
For parents who have one child with JIA, a major concern may be the likelihood of siblings getting the disease. Adults who had JIA in their youth may wonder if it will affect their kids.
In answer to the first question, various population studies have looked at the frequencies with which twins, siblings and even cousins of those with JIA get the disease themselves. The basis for comparison is the accepted statistic that one in 1,000 children under the age of 16 has JIA.
The Case With Twins
Starting with identical twins, the closest genetic matchup, “it’s generally reported that 25 percent to 40 percent of identical twins of somebody with JIA also develop the disease,” says Sampath Prahalad, MD, associate professor of Pediatrics and Human Genetics at Emory University in Atlanta. Using the conservative number of 25 percent, that means that one in four identical twins whose twin has JIA will also get it.
Will Siblings Get JIA?
A study conducted by Dr. Prahalad shows that siblings have a 12-times greater risk of getting JIA. “With the population prevalence of JIA at one in 1,000, a 12-times greater risk may sound like a lot but it’s only equal to 1.2 percent,” he says. “So there’s a 98 percent chance that the family would not have another child with arthritis.”
Between first cousins, Dr. Prahalad found the risk drops to six times greater than the general population.
One Family’s Experience
Though these numbers are reassuring, they belie the angst that many families experience. Addisen Ogden of South Jordan, Utah, is a vibrant 4-year-old who, except for infrequent flares, moves without pain or joint swelling on a well-tolerated regimen of methotrexate. But her parents, Staci and Jeremy, remember all too well when she was diagnosed at 18 months old with polyarticular JIA. When considering adding to their family they conferred with their rheumatologist about the risk of having another child with JIA.
“We talked quite bit with our doctor and we understood the risk was elevated but there was a less than 2 percent chance of having another child with JIA,” says Staci.
Baby Elli is now a bit older than Addisen was when she was diagnosed with the disease. “Elli’s fine so far, but any time she complains about a joint, falls or says ‘owie’ that’s the first thing that comes to my mind,” admits Staci. “I think because we’ve been through it once, we tend to think the worst right off the bat.”
Marta Moroldo of the University of Cincinnati found that siblings with JIA tend to develop the disease around the same age. For example, in a family with a 10- and 6-year-old, the 10-year-old got JIA when he was 5, and so did the 6-year-old. Moroldo also found that siblings are more likely to have the same subtype of arthritis.
Will My Kids Inherit JIA?
When Addisen Ogden is grown up, will she have to worry about having kids with JIA? Researchers don't yet know.
“At this point we know of more sibling pairs than parent-child pairs with JIA,” says Dr. Prahalad.
Constructing accurate family histories for studies of parents of kids with JIA is sometimes difficult since pediatric rheumatology as a specialty is very young. A formal classification system for juvenile arthritis was proposed in the U.S. only in the 1970s.
In the meantime, the pace of genetic research into the causes of arthritis continues to accelerate, as does the development of new drugs to treat JIA.
“As scared as parents are of JIA, if properly diagnosed and managed, children have really good quality of life and really good outcome these days,” says Dr. Prahalad.