Human
epidemiology suggests genes affect alopecia areata
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 (non-identical) 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).
This apparent asociation with other autoimmune diseases further
supports the idea that alopecia areata is also an autoimmune disease.
It may be that genes involved in one form of autoimmune disease
can also contribute to the development of other autoimmune disease
forms.
Overall then, many epidemiological studies support the notion
that alopecia areata susceptibility is determined in part by genetics,
at for a least some of those affected by the disease. Probably
genetics contributes to alopecia areata in everyone who has it,
but the contribution may be bigger and strogner in some while
for others the environment plays a bigger role.
Human
epidemiology suggests genes affect alopecia areata references
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