Epidemiology of Autoimmune Disease
There are nearly 100 different forms of auto-immune disease, making these disorders a major cause of chronic illness, affect-ing up to 3 percent of the general population. Nearly any organ can be affected by either systemic or organ-specific autoim-mune disease (Table 6.1). Women make up nearly 75 percent of all individuals afflicted by autoimmune disease, making these disorders one of the ten leading causes of death in women less than sixty-five years old. However, the female-to-male ratio var-ies widely among different diseases, being as high as 9:1 in SLE, Sjögren’s syndrome, and autoimmune thyroiditis and as low as 1:1 in TID, Goodpasture’s syndrome, and vitiligo (Table 6.1). The mean age of onset also varies widely, with some disorders typically occurring early in childhood (e.g., TID, juvenile rheumatoid arthritis), oth-ers in the childbearing years (ages 15–45, e.g., SLE), and still others in later life (e.g., Sjögren’s syndrome). There may be strik-ing ethnic/racial predispositions to auto-immune disease. For example, SLE is about three times more prevalent in individuals of African, Asian, or Latin ancestry than in individuals of European ancestry, whereas Sjögren’s syndrome and multiple sclerosis are more prevalent in those of European ancestry. The racial/ethnic differences are likely to reflect differences in the frequen-cies of disease susceptibility genes. The costs of these disorders to society are enor-mous. Rheumatoid arthritis (RA) affects 2.1 million Americans (1.5 million women and 600,000 men) at an annual cost of about $6,000 per patient (direct medical costs and indirect costs such as absence from work). Lupus affects 500,000 Americans at an esti-mated annual cost of $13,000 per patient, a total $6.5 billion per year.