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Introduction

Autoimmune diseases are conditions in which the human immune system attacks healthy human tissues within the body. The self-inflicted damage to tissues in the body is a consequence of abnormal behaviours in the human immune system. Autoimmune disorders occur when the immune system incorrectly identifies certain tissues in the body as foreign entities. The immune system produces antibodies in response to the mis-identified human cells which results in destruction of healthy tissues.

A variety of autoimmune disorders have been identified. More than 80 chronic diseases are classified as being autoimmune diseases. Disorders are broadly grouped into two categories: systemic and localized. Systemic diseases are those in which several organs are damaged, and localized diseases involve damage to one organ. Rheumatoid arthritis is an example of a systemic autoimmune disorder in which skin, joints, lungs, and blood vessels may be affected. Localized diseases are immune system attacks on single organs as seen in Crohn’s disease in which the gastrointestinal tract is damaged.

Both environment and genes play an expected role in the causation of autoimmune disorders. Although it is not known what exactly causes these diseases, several environmental and genetic factors have been observed to influence disease conditions.

Genetics

Autoimmune diseases are conditions in which the human immune system attacks healthy human tissues within the body. The exact genes responsible for causing each autoimmune disease have not been completely isolated. However, several experimental methods such as the genome-wide association scans have been used to identify certain genetic risk variants. Research focusing on both genome scanning and family trait inheritance analysis has enabled scientists to further understand the etiology of autoimmune diseases such as Type 1 diabetes and Rheumatoid arthritis.


 * Type 1 Diabetes: Type 1 Diabetes (T1D) is a condition in which pancreatic β-cells are targeted and destroyed by the immune system .  Approximately 5% of the U.S. population are recorded to have T1D . The condition is a result of neo-natal mutations to the insulin gene (INS) which is responsible for mediating the production of the insulin in the pancreas .  The INS gene is located on the short arm of chromosome 11p15.5 in between the genes for tyrosine hydroxylase and insulin-like growth factor II .  The loci for this gene was determined using human-mouse somatic cell hybridization as well as In Situ hybridization .  In addition to chromosome 11, a significant genetic determinant of type 1 diabetes is a locus called the major histocompatibility complex (MHC) located on chromosome 6p21 .  The two genetic variables that influence susceptibility to T1D are the INS gene on chromosome 11 and the MHC loci on chromosome 6.


 * Rheumatoid arthritis: Rheumatoid arthritis (RA) is an autoimmune disorder that affects approximately 0.6% of the population in the U.S. .  The disease is an inflammatory condition that typically affects the joints, but is also known to cause tissue damage to other organs of the body.  Although there is no complete genetic mapping for this condition, several genes are thought to play a role in causing RA. The genes that influence the human immune system contain a TNF receptor associated factor 1(TRAF1).  This TRAF1 is located on chromosome 9q33-34 .  In addition, B1 genes in the human genome contain an increased concentration of HLA-DRB1 alleles that are most commonly seen in RA patients .  RA can range from mildly dangerous to life threatening in different individuals suffering from the condition as a consequence of varying polymorphisms within the genome .  As a result, the nature and severity of RA is heavily influenced by the human genome and the mutations or chemical abnormalities within it.