Acne is an inflammatory dermatosis, the genetics of which have not been well studied. Acne is characterized by the development of inflammatory papules, comedones and pustules, leading on to possible disfiguring scarring. At a minimal level of severity, acne is ubiquitous in adolescence, and only a minority of cases will develop scarring or have a clinical course running into the second quarter of life.
Three etiological factors are known: sebum excretion from sebaceous glands, infection, and hair follicle duct obstruction (most sebaceous glands empty into the hair follicle duct). The main determinant of sebum excretion rate is hormonal, principally androgens. Therapies rely on targeting each of the etiological factors: reducing sebum excretion (retinoids, estrogens), infection (antibiotics) and duct obstruction (keratolytics).
No secular trends or geographical differences in incidence for the principal clinical variants of acne are known. Family studies of acne are difficult to interpret because the peak prevalence of the disease is in adolescence, recall of disease imperfect, and the disease course is altered by widely available and effective therapies.
Goulden and colleagues in a UK population provided evidence of clustering of acne within families with a fourfold increase in the chance of a relative of a proband case having acne compared with the relative of a control subject (Goulden et al., 1999). Three twin studies have been reported (one in abstract form only). Bataille in a UK population-based twin survey of middle-aged females (based on recall of earlier disease) reported polychoric correlations of 0.82 and 0.40 for MZ and DZ twins respectively, with a quoted heritability of 81% (Bataille et al., 2002). The result are in keeping with preliminary results (in abstract) from Kirk and colleagues in Australia (Kirk et al., 2004) and the earlier findings of Friedman in the US (Friedman, 1984).
Sebum excretion could be considered an intermediate phenotype and its endocrine physiology is well understood. There is only one study looking at the genetics of sebum excretion. Forty pairs of twins were examined, and differences in sebum excretion rates were greater between DZ than MZ twin pairs, but the statistical analysis was superficial (Walton et al., 1988).
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