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More recently, genome-wide association studies (GWAS) have identified susceptibility loci at 11q13. A recent meta-analysis of GWAS studies in European populations identified SNPs rs479844 near OVOL1, rs2164983 near ACTL9, and rs2897442 in intron 8 of KIF3A. Many of these loci contain genes that encode proteins involved in epidermal proliferation and differentiation or inflammatory cytokines. The skin of patients with AD is colonized by S aureus. Clinical infection with S aureus often causes a flare of AD, and S aureus has been proposed as a cause of AD by acting as a superantigen.
Similarly, superinfection with herpes simplex virus can also lead to a flare of disease and a condition referred to as eczema herpeticum. The hygiene hypothesis is touted as a cause for the increase in AD.
This attributes the rise in AD to reduced exposure to various childhood infections and bacterial endotoxins. Heat is poorly tolerated, as is extreme cold. A dry atmosphere increases xerosis. Sun exposure improves lesions, but sweating increases pruritus. These external factors act as irritants or allergens, ultimately setting up an inflammatory cascade.
The role of food antigens in the pathogenesis of AD is controversial, both in the prevention of AD and by the withdrawal of foods in persons with established disease.
Because of the controversy regarding the role of food in AD, most physicians do not withdraw food from the diet. Nevertheless, acute food reactions (urticaria and anaphylaxis) are commonly encountered in children with AD.
More recent information examining physician visits for AD in the United States from 1997-2004 estimates a large increase in office visits for AD occurred. In addition, blacks and Asians visit more frequently for AD than whites. Note that this increase involves all disease under the umbrella of AD and it has not been possible to allocate which type has increased so rapidly. This figure estimates the prevalence in developed countries. The frequency is increased in patients who immigrate to developed countries from underdeveloped countries.
Immigrants from developing countries living in developed countries have a higher incidence of AD than the indigenous population, and the incidence is rapidly rising in developed countries.
The incidence of AD is highest in early infancy and childhood. The disease may have periods of complete remission, particularly in adolescence, and may then recur in early adult life.
One third of patients develop allergic rhinitis. One third of patients develop asthma. In a longitudinal study of 7157 children and adolescents with AD from the Pediatric Eczema Elective Registry, researchers found that symptoms of mild to moderate AD are likely to persist into the teen years or beyond.
By age 20, approximately half of the patients had experienced at least one 6-month symptom- and medication-free period. A number of studies have reported that the financial burden to families and government is similar to that of asthma, arthritis, and diabetes mellitus.
In children, the disease causes enormous psychological burden to families and loss of school days. Sleep disturbance is common in AD patients, owing to the incessant pruritus. Sleep disturbances can significantly impact quality of life. Mortality due to AD is unusual. Kaposi varicelliform eruption (eczema herpeticum) is a well-recognized complication of AD. It usually occurs with a primary herpes simplex infection, but it may also be seen with recurrent infection.