While it is known that the immune system plays a role in the development of the disease, what causes the immune system to function abnormally is unknown. It is speculated that environmental factors play a role, but the data have not consistently supported this theory.12,13 There is, however, evidence to suggest that genetic components play a role. Several immunologic gene abnormalities (eg, interferon regulatory factor 5, protein tyrosine phosphatase nonreceptor type 22, and integrin alpha M) have been identified. Additionally, research in homozygous twins has shown a higher incidence of SLE in families where the prevalence of the disease in other family members was low.2,14 Furthermore, those with infantile-onset SLE occurring within the first year of life have a high incidence of having family members with a history of autoimmune diseases.15
There is also some evidence that hormone abnormalities are associated with SLE. Estrogen and androgen metabolism have been found to differ in men and women with SLE compared with healthy controls.16 For example, women with SLE metabolize estrogen to a more potent form, 16a-hydroxyestrone, instead of 2-hydroxyestrone, and can have irregular menstruation cycles and increased risk of miscarriage. Prolactin levels can also be elevated in patients with SLE.16 Use of hormone replacement therapy has also been shown to increase the risk of developing SLE.17 Infection with the Epstein-Barr virus has been associated with the production of autoantibodies that are present in up to 38% of patients with SLE.18 However, it is