It has been shown that there is a higher incidence of alopecia areata in genetically related individuals. This suggests that at least some people are genetically predisposed to develop alopecia areata.
The triggers for the onset of alopecia areata may be environmental, but the resistance of the alopecia areata lesion to treatment, its persistence and regression, and its extent over the body may be influenced by the presence and interaction of multiple genes.
Several studies suggest alopecia areata may have a genetic basis (Colombe 1995, Van der Steen 1992). Alopecia areata with similar times of onset or similar hair loss patterns has been reported in monozygotic twins (identical twins) (Alsaleh 1995, Scerri 1992, Bonjean 1968, Cole 1984, Hendren 1949, Weidman 1956, Stankler 1979) and dizygotic twins (Traub 1935, Anderson 1937, Bereston 1951, Barsky 1961, Wolf 1984, Insler 1989). Families with several generations of alopecia areata affected individuals also suggest AA may be a genetically determined disease (Shelton 1942, Gol’dshtein 1978, Dawn 1996, Hordinsky 1984, Valsecchi 1985, Van der Steen 1992).
Epidemiological studies provide basic evidence for involvement of alopecia areata susceptibility genes. Numerous studies suggest alopecia areata may be more frequently expressed in genetically related individuals. Typically 10 to 20% and in one study up to 42% of patients with alopecia areata indicated at least one other affected family member. In contrast, the lifetime risk of alopecia areata expression in the general population has been suggested to be 1.7% (Safavi 1995). Familial incidence is probably significantly higher than reported in the studies as there is a tendency not to discuss hair loss, particularly in previous generations where patchy alopecia areata hair loss was sometimes mistaken for the socially unacceptable disease, syphilis (Ormsby 1948). Even today the marked psycho-social consequences of hair loss inhibit some individuals from seeking diagnosis and treatment. Some may not be aware of their hair loss if it is limited or develops in an area not immediately visible to the individual.
A strong association has been observed between alopecia areata and Down’s syndrome. From 1000 patients and 1000 control subjects, Du Vivier and Munro observed 60 cases of Down’s syndrome individuals with alopecia areata verses 1 control (Du Vivier 1975). Carter and Jegasothy identified 19 cases in 214 Down’s patients and the statistical relationship is further supported in other studies (Carter 1976, Wunderlich 1965). The genetic mutation for autoimmune polyendocrinopathy syndrome type 1 (AIRE, autoimmune regulator gene, Finnish-German APECED Consortium 1997) is also associated with a 29 to 37% prevalence of alopecia areata (Betterle 1998). These studies suggest that candidate gene loci for alopecia areata susceptibility may be present on human Chromosome 21.
Associations of alopecia areata with other autoimmune diseases have also been reported. Between 7% and 27% of AA affected patients may also express a thyroid disease phenotype, including goiter presence, myxedema and Hashimoto’s thyroiditis (Cunliffe 1969, Milgraum 1987, Shellow 1992, Pualvilai 1994). Co-expression of vitiligo and alopecia areata has also been reported at between 4% and 9% (Muller 1963, Main 1975). However, the statistical significance of these disease associations when compared to appropriate control populations has been disputed elsewhere (Salamon 1971, Gollnick 1992, Schallreuter 1994). Numerous case reports detail concordant presence of AA with other autoimmune diseases, such as diabetes and myasthenia gravis, although the statistical significance is unknown (McElwee 1998).