Juvenile idiopathic arthritis (JIA) – HLA-A, HLA-B, HLA-G, HLA-DPB1, HLA-DQA1, HLA-DQB1, HLA-DRB1, IL2RA, IL2RB, IL6, MIF, PTPN22, SLC11A1, STAT4, TNF, TNFAIP3, TRAF1, CCN6, ANKRD55, CD247, CTLA4, FAS, LACC1, PTPN2, RUNX1, TYK2, UBE2L3 and ZFP36L1 genes 

            Juvenile idiopathic arthritis (JIA) corresponds to a group of autoimmune disorders characterized by inflammation of the joints, which appears for the first time before age 16. Seven types of JIA have been described, and are distinguished from each other by their signs and symptoms, the number of joints affected, the results of laboratory tests, and family history:

• Systemic juvenile idiopathic arthritis (SJIA). This form of the disease causes inflammation in one or more joints. In this case, arthritis is accompanied by a high daily fever that can last at least 2 weeks, or it may precede arthritis. In addition, affected individuals may present rashes, lymphadenopathy (swollen lymph nodes), hepatomegaly or splenomegaly (enlarged liver and spleen, respectively).

• Oligoarticular juvenile idiopathic arthritis. This form of the disease is characterized by the appearance of arthritis in four or less joints during the first 6 months of the disease. It is divided into two subtypes depending on its evolution; If arthritis is limited to four or less joints after 6 months, it is classified as persistent oligoarthritis, while if there are more than four affected joints after 6 months, it is classified as extended oligoarthritis.

• Rheumatoid factor-positive polyarticular juvenile idiopathic arthritis (also known as rheumatoid factor-positive polyarthritis). In this case, the disease causes inflammation in five or more joints throughout the first 6 months of its course. In addition, people with this type of juvenile idiopathic arthritis have positive results of rheumatoid factors in the blood. This type of arthritis closely resembles rheumatoid arthritis seen in adults.

• Rheumatoid factor-negative polyarticular juvenile idiopathic arthritis (also known as rheumatoid factor-negative polyarthritis). It is characterized by arthritis in five or more joints in the first 6 months of the pathology. However, individuals with this type of condition show negative results for rheumatoid factor in blood.

• Psoriatic juvenile idiopathic arthritis (PsJIA) (also known as juvenile psoriatic arthritis -JPsA-). Generally, this type of arthritis occurs in combination with a skin disorder (psoriasis). Some affected individuals develop psoriasis before arthritis, while others first develop arthritis. Other features of juvenile psoriatic arthritis include abnormalities in the fingers and nails or eye disorders.

• Juvenile idiopathic arthritis related to enteritis. This form of the disease is characterized by enteritis that accompanies the inflammation of the joints. Enteritis-related arthritis can also involve inflammation in parts of the body other than the joints.

• Undifferentiated juvenile idiopathic arthritis. This type of juvenile idiopathic arthritis includes affected individuals who do not correspond to any of the above described types or who meet the criteria for more than one type of JIA.

            It is considered that juvenile idiopathic arthritis is the consequence of a combination of genetic and environmental factors. The term "idiopathic" indicates that the specific cause of the disease is unknown. Its signs and symptoms are due to excessive inflammation in and around the joints. Inflammation occurs when the immune system sends signaling molecules and leukocytes to a site of the lesion to fight microbial invaders and facilitate tissue repair. Normally, the body stops the inflammatory response when the healing process has been completed to prevent damage to its own cells and tissues. In people with JIA, the inflammatory response is prolonged, especially during joint movement. However, the reasons for this excessive inflammatory response are unclear.

            The risk of developing juvenile idiopathic arthritis has been associated with particular changes in certain genes. Many of these genes belong to a family of genes that encode a group of related proteins that form the human leukocyte antigen (HLA) complex. The HLA complex helps the immune system distinguish the body's own proteins from proteins produced by invading agents (such as viruses and bacteria). Each HLA gene has different normal variations, which allow each person's immune system to react to a wide range of foreign proteins. It has been described that certain normal variations of several HLA genes participate in the risk of developing juvenile idiopathic arthritis. In addition, variations in other genes have also been associated with JIA. It is likely that many of these genes play roles in immune system function. In addition, other unknown factors, both genetic and environmental, that affect the immune system, may also influence the chances of developing this disease.

            Most cases of juvenile idiopathic arthritis are sporadic, which means that they occur in people without a history of pathology in their family. It has been identified that a small percentage of cases are inherited, although the inheritance pattern of the disease is unknown.

Tests performed in IVAMI: in IVAMI we perform the detection of mutations associated with Juvenile idiopathic arthritis (JIA), by means of the complete PCR amplification of the exons of the HLA-A, HLA-B, HLA-G, HLA-DPB1, HLA-DQA1, HLA-DQB1, HLA-DRB1, IL2RA, IL2RB, IL6, MIF, PTPN22, SLC11A1, STAT4, TNF, TNFAIP3, TRAF1, CCN6, ANKRD55, CD247, CTLA4, FAS, LACC1, PTPN2, RUNX1, TYK2, UBE2L3 and ZFP36L1 genes, respectively, and their subsequent sequencing.

Recommended samples: non-coagulated blood obtained with EDTA for separation of blood leucocytes, or a card with a dried blood sample (IVAMI can mail the card to deposit the blood sample).