Genetic susceptibility to temporomandibular joint involvement in juvenile idiopathic arthritis.

BACKGROUND: Juvenile idiopathic arthritis (JIA) is the most common chronic rheumatic condition of childhood. Temporomandibular joint (TMJ) is among the most commonly affected joints in JIA patients. When JIA involves the TMJ, it may affect condylar growth in the joint; therefore, JIA patients are at risk of unfavourable long-term outcomes from associated joint damage. If undetected, TMJ involvement can lead to various functional disabilities such as reduced mandibular mobility and disorders of the mastication muscles. Limitations in sagittal and vertical mandibular growth can result in micrognathia and anterior open bite with aesthetic and functional restrictions. OBJECTIVE: Genetic factors may play a role in determining which individuals are more prone to develop TMJ disorders or in predicting the severity of the disease process. Therefore, we applied a GWAS approach to identify loci associated with TMJ involvement in a sample of Estonian patients with JIA. Our aim was to address the potential role of genetic susceptibility factors in TMJ-JIA, a condition not previously studied in this context. METHODS: The case group consisted of 55 JIA patients with TMJ involvement and 208 patients without TMJ involvement comprised the control group. The entire cohort was genotyped using the Illumina HumanOmniExpress BeadChip arrays. Imputation was performed using a nationwide reference panel obtained of 2240 individuals whose data were obtained from the Estonian Biobank. RESULTS: We identified six loci as being associated with the risk of TMJ-JIA in Estonian JIA patients. The strongest associations were identified at CD6 rs3019551 (P = 3.80 × 10-6), SLC26A8/MAPK14 rs9470191 (P = 6.15 × 10-6), NLRP3 rs2056795 (P = 8.91 × 10-6) and MAP2K4 rs7225328 (P = 1.64 × 10-5). CONCLUSION: This study provides first insights into the risk-associated loci between JIA and its manifestation in the TMJ. The reported loci are involved in molecular pathways of immunological relevance and likely represent genomic regions that render the TMJ susceptible to involvement by JIA in Estonian patients.

Prevalence and short-term outcome of juvenile idiopathic arthritis: a population-based study in Estonia.

OBJECTIVES: To study the point prevalence of juvenile idiopathic arthritis (JIA) in children in Estonia on December 31, 2000. To examine the short-term clinical outcome of the disease. METHOD: Identification of patients diagnosed with JIA between 1995-2000. Prospective follow-up of new cases diagnosed between 1998-2000 for two years. Retrospective analysis of the medical records of patients diagnosed between 1995-1997. The study was population-based. RESULT: One hundred and ninety-seven (197) patients fulfilled the study criteria. On December 31, 2000, the point prevalence of JIA was 83.7 (95% CI: 72.4; 95.8) per 100 000 children aged 0-15 years, 90.7 (95% CI: 74.1; 108.9) for girls and 77.1 (95% CI: 62.2; 93.5) for boys. Prevalence was the highest among 11-15 year-old girls (132; 95% CI: 100.7; 167.4) and the lowest in 0-3 year-old girls (9.6; 95% CI: 1.2; 26.7). For 44 patients (22.3%), the disease was inactive after 2 years since the onset of the disease. For 76 patients (38.6%). the disease was active or stable after 2 years. CONCLUSION: This is the first population-based study on the prevalence and outcome of JIA in Estonia in which the new ILAR criteria have been used. A longer follow-up of JIA patients is needed to have a better overview of the course of the disease. Good cooperation between family doctors and specialists is crucial for diagnosing JIA as early as possible.

Incidence of juvenile idiopathic arthritis in children in Estonia: a prospective population-based study.

OBJECTIVE: To study the incidence rate of juvenile idiopathic arthritis (JIA) and its clinical subtypes in Estonia, to follow the course of the disease in newly diagnosed patients for 2 years, and to find the frequency of human leucocyte antigens (HLA) B27, DR1 and DR4 in JIA patients. METHOD: A population-based study involving prospective registration of new cases of JIA in 1998-2000 and their clinical follow-up for 2 years. RESULTS: In 1998-2000, 162 new cases of JIA were diagnosed. The mean annual incidence rate of JIA was 21.7 per 100 000 children aged 0-15 years (22.9 in girls and 19.3 in boys). During the investigation period, the incidence rate rose 3.5-fold. Oligoarthritis was the most frequent subtype (mean annual incidence rate of 11.7 per 100 000), followed by seronegative polyarthritis (4.4 per 100 000). HLA-DR1, B27 and DR4 were found respectively in 44.4, 28.6 and 11.1% of cases in which the analysis was performed. In HLA-B27-positive patients, inflammation markers of blood remained at a high level for a longer period compared with HLA-B27-negative patients. CONCLUSIONS: This is the first population-based study on the epidemiology of juvenile arthritis in Estonia in which the new classification criteria defined by the International League of Associations for Rheumatology (ILAR) have been used. In addition to environmental factors, an increase in awareness among family doctors is a probable reason for the rise in incidence during the study period. HLA-B27 might have predictive value as a marker of chronicity of inflammation.