Genetics of juvenile idiopathic arthritis: an update.

Juvenile idiopathic arthritis (JIA) refers to a collection of chronic arthritides in children, and the major subtypes of JIA are similar to the subtypes of juvenile rheumatoid arthritis (JRA). Several genetic variants influencing susceptibility to JIA have been identified, including genes encoding the HLA molecules, cytokines, and other modulators of immune responses. This review outlines the principles behind genetic studies and summarizes recent studies on the genetics of JIA. Recent studies confirm the association/linkage between JIA and the HLA region and provide evidence for additional loci involved in susceptibility to JIA. Several studies suggest that polymorphisms in other candidate genes also influence susceptibility to JIA. In addition, some genetic variants seem to influence the phenotype of JIA. A genome-wide scan for JRA in 121 affected sibling pair families confirms that gene(s) in the HLA region influence susceptibility to JRA and identifies other chromosomal regions that possibly influence susceptibility to JRA or subtypes of JRA. Functional studies suggest that biologic markers could be useful in defining the phenotype of individuals with JIA. Familial studies and gene expression profiling are useful tools in the dissection of the genetic basis of JIA. Although there are challenges to the identification of genetic factors underlying complex diseases such as JIA, considerable progress has been made in JIA genetics. Candidate gene studies remain important to identify genetic variants with small to moderate effects on the JIA phenotype.