![]() If feather growth resumes in these birds, the feathers dry up, cease to grow, and often break off. The alopecia universalis is rarely seen until adulthood and is characterized by short (<0.5 cm), undeveloped feathers. ![]() It is hypothesized, but as yet unproven, that a feather development defect interacts with the SL melanization and immunologic defects to initiate the partial (areata) and complete (universalis) alopecias. Inheritance of the vitiligo is polygenic with an additional genetic component for the alopecia trait. ![]() The incidence of alopecia, however, is significantly lower in the SL101 subline than in the other two. Of the three sublines (SL101, SL102, and SL103) the vitiligo has a significantly earlier onset and severity in the SL101 than in the other two lines. Three different MHC haplotypes were identified in the original line that was selected for vitiligo, and from these, three sublines were developed, each homozygous for a different haplotype. Quadrichrome vitiligo has additional marginal or perifollicular hyperpigmentation. Trichrome vitiligo has a hypopigmented zone between normal and depigmented skin. The major histocompatibility haplotype (MHC) has a major effect on the incidence and expression of the vitiligo, as well as the alopecia that occurs within vitiliginous birds. In vitiligo universalis >80 of the body surface area is depigmented.1 Clinical variants include: Inflammatory vitiligo describes erythema and raised borders at lesion margins. Both the vitiligo and the alopecia have an autoimmune component, as shown by histologic and immunologic studies, including the correctional influences of corticosterone and cyclosporine-A. Although human vitiligo patients are known to have a four times greater chance of having alopecia areata than do people without vitiligo, in the SL model, feather loss is limited to birds that show some degree of amelanosis of feather and skin tissue. The Smyth line (SL) chicken model for spontaneous, postnatal expression of vitiligo may also show varying incidences and degrees of severity ranging from alopecia areata-like to universalis-like integumental changes. ![]()
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