Genetics Suggest Adult & Child Arthritis Aren’t So Different

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There has long been a wall separating adult rheumatologists from pediatric rheumatologists. A recent review article published in the January edition of Arthritis & Rheumatology (A&R) suggests that genetics, rather than age, may be a better way to categorize forms of primary inflammatory arthritis across the lifespan.¹

“Pediatric and adult rheumatologists don’t generally interact that much,” says Peter A. Nigrovic, MD, an adult and pediatric rheumatologist who directs the Center for Adults with Pediatric Rheumatic Illness (CAPRI) at the Brigham and Women’s Hospital, Boston. “We have a tendency to stay within our own groups and to classify our diseases separately.”

In other areas of medicine if two diseases have different names, it is often because there are clinical differences. This does not always hold true in arthritis.

“Historically, arthritic diseases have been categorized depending on whether they presented before or after the 16th birthday,” said Dr. Nigrovic. “There is no disease in arthritis that has the same name on both sides of this age wall. If you think about it, that is sort of absurd.”

Nomenclature Important

Dr. Nigrovic

Nomenclature is important. It determines who can enroll in studies, plays an integral part in the development and implementation of treatment algorithms, and is used by insurance companies to define what claims they will pay. It also limits the ability to track diseases longitudinally, such as when those with juvenile idiopathic arthritis (JIA) grow up.

“In fact, the clinical and genetic evidence is pretty clear that most subtypes of arthritis cross the adult/pediatric boundary,” said Dr. Nigrovic. “So are divisions in our arthritis nomenclature really based on biology? Or should we be try to be more like the rest of medicine, where pneumococcal pneumonia is pneumococcal pneumonia no matter the patient’s age?”

New Ways of Identifying Disease Patterns

The study of genetics has pointed toward new ways of identifying disease patterns. Genetics has the added advantage in this context of being stable across the age groups. After all, the genes expressing proteins that result in inflammatory arthritis do not suddenly change when a person hits 16 years of age.

“If genetics reflects mechanism, then shared genetics is strong prima facie evidence of a common pathology,” wrote Dr. Nigrovic in the A&R article. “This principle can help define disease clusters.”

Clusters by Genetics, Not Age

Dr. Nigrovic suggests four broad clusters of immune-mediated arthritis. They include:

• Seropositive RA;
• Seronegative RA;
• Spondyloarthritis; and
• Systemic arthritis.

He argues that changing the nomenclature will also enable better exploration of how age fits into the equation.