Juvenile idiopathic arthritis is a complex autoimmune disease—its exact cause is not fully known, but researchers believe several factors contribute to its development.

• Environmental triggers : In children who are genetically predisposed, external factors such as infections or other environmental influences may trigger the immune system to start attacking joint tissues, though no specific trigger has been definitively proven.
• Genetic predisposition : Certain genes may increase a child’s likelihood of developing JIA. Children with family members who have autoimmune or rheumatic conditions are more likely to be affected, and specific genetic markers (like HLA types) have been linked to susceptibility.
• Autoimmune response : The child’s immune system mistakenly attacks healthy joint tissues, causing inflammation, pain, swelling, and stiffness. This abnormal immune activity is the central mechanism behind JIA.
• Complex interaction of factors : Most experts believe JIA arises from a combination of genetic susceptibility plus environmental influences, rather than a single clear cause, which is why the term “idiopathic” (meaning unknown cause) is used.

What are the juvenile idiopathic arthritis risk factors?

The main risk factors for juvenile idiopathic arthritis (JIA) are explained below.

• Gender: Girls are more likely than boys to develop many forms of JIA, especially the oligoarticular and polyarticular types.
• Genetics and family history: Certain genes and inherited traits may make a child more susceptible to JIA. A family history of autoimmune or rheumatic diseases suggests a higher risk, although JIA can still occur in children with no family history.
• Age: JIA most often occurs in children under 16, with many cases beginning between about 2 and 3 years old. This age range is when the condition is most likely to develop.
• Immune system abnormalities : Since JIA is an autoimmune disease, children whose immune systems are more likely to attack their own tissues may be at higher risk. This includes genetic factors that influence immune response.
• Environmental exposures : Some studies suggest that exposure to cigarette smoke before birth or in early life and certain air pollutants may be linked with a higher chance of developing JIA, though more research is needed to confirm these associations.

Diagnosing juvenile idiopathic arthritis can be hard because there is no single test that proves it. Instead, doctors make the diagnosis by carefully reviewing symptoms, performing physical examinations, and using blood and imaging tests to rule out other causes and support the diagnosis.

• Medical History and Physical Exam: The doctor begins by asking about the child’s symptoms, when they started, and how they affect movement and daily activities. During the physical exam, the doctor checks the joints for swelling, tenderness, warmth, or limited range of motion, which are signs of inflammation.
• Erythrocyte Sedimentation Rate (ESR): This test measures how quickly red blood cells fall to the bottom of a tube of blood. A higher rate means there is more inflammation in the body. It helps show whether the immune system is active, but by itself it does not confirm JIA.
• C‑Reactive Protein (CRP): CRP is a protein made by the liver when the body has inflammation. A higher CRP level suggests the presence of inflammation. Like ESR, it shows inflammation but does not specifically prove JIA.
• Rheumatoid Factor (RF): ​RF is an antibody that is sometimes found in the blood of children with a subtype of JIA that resembles adult rheumatoid arthritis. A positive RF test may suggest a form of arthritis that can be more persistent, but many children with JIA are RF‑negative.
• Anti‑Cyclic Citrullinated Peptide (anti‑CCP): This test looks for antibodies that are less common in children but, when present, may be linked with a more severe or aggressive form of arthritis. It helps doctors understand the likely course of the disease.​
• HLA‑B27: HLA‑B27 is a genetic marker rather than a sign of inflammation. If a child tests positive, it suggests they may have a subtype of JIA called enthesitis‑related arthritis. However, having this marker does not by itself confirm JIA.
• Antinuclear Antibodies (ANA): ANA are proteins the immune system produces that sometimes attack the body’s own cells. A positive ANA test can be seen in many children with JIA, and these children are more likely to develop inflammation of the eye, so regular eye exams are often recommended.