Alopecia areata is a genetically determined, immune-mediated disorder of the hair follicle with an estimated lifetime risk of approximately 2%, making it one of the most common human autoimmune diseases (Gilhar and Kalish, 2006). It shows a spectrum ... Alopecia areata is a genetically determined, immune-mediated disorder of the hair follicle with an estimated lifetime risk of approximately 2%, making it one of the most common human autoimmune diseases (Gilhar and Kalish, 2006). It shows a spectrum of severity that ranges from patchy localized hair loss on the scalp to the complete absence of hair everywhere on the body.
Alopecia areata is characterized by patchy hair loss on the scalp, which can eventually involve the entire scalp (alopecia totalis) or the entire body (alopecia universalis) (Martinez-Mir et al., 2007). The onset of the disease can be sudden, ... Alopecia areata is characterized by patchy hair loss on the scalp, which can eventually involve the entire scalp (alopecia totalis) or the entire body (alopecia universalis) (Martinez-Mir et al., 2007). The onset of the disease can be sudden, its progression is unpredictable, and it can be recurrent throughout life. Alopecia areata is viewed as a tissue-specific autoimmune disease of the hair follicle (Martinez-Mir et al., 2007). The hair follicle is an immune-privileged site, with low levels of major histocompatibility complex (MHC) expression. It is thought that alopecia areata represents a breakdown in immune privilege with the subsequent destruction of the hair follicle by T lymphocytes. Reports of overnight whitening of the hair are thought to represent the abrupt onset of alopecia areata, since it preferentially targets pigmented hairs, leaving only white hairs behind (Goldenhersh, 1992; Barlag and Ruzicka, 1995). Alopecia areata has a deeply disturbing psychologic impact on affected individuals. Lubowe (1959) described a family with affected mother and affected daughter and son. Evidence suggested an autoimmune mechanism in this disorder. See autoimmune diseases (109100). Stankler (1979) observed onset in brother and sister at age 2, with regular and periodic synchronous exacerbation thereafter. One incidence of exacerbation was after mumps. In a white American family, Hordinsky et al. (1984) found alopecia universalis in 2 brothers and alopecia areata in the son of one of them. Martinez-Mir et al. (2007) suggested that alopecia areata fits the paradigm of a complex or multifactorial genetic trait based on several lines of evidence: its prevalence in the population of approximately 2%; concordance in twins of 55% (Jackow et al., 1998); a Gaussian distribution of severity; a 10-fold increased risk for first-degree relatives of affected individuals; and the aggregation of affected individuals in families with no clear mendelian pattern of inheritance.
Among first-degree relatives of 348 severely affected patients, van der Steen et al. (1992) found that one of the parents was affected in 7%. Among the sibs, 3% had developed alopecia areata (AA), while AA was present in ... Among first-degree relatives of 348 severely affected patients, van der Steen et al. (1992) found that one of the parents was affected in 7%. Among the sibs, 3% had developed alopecia areata (AA), while AA was present in 2% of the children. Taking into account the age of the children, they estimated that the lifetime risk approached 6%. They concluded that the degree of involvement observed in the probands did not influence the frequency and type of AA present in their first-degree relatives. Alopecia areata occurs in approximately 0.1% of the general population (Safavi, 1992), but in approximately 9% of patients with Down syndrome (Brown et al., 1977).