McFadden J P
Department of Dermatology, St Mary's Hospital, London, UK.
Clin Exp Dermatol. 1990 Jan;15(1):39-43. doi: 10.1111/j.1365-2230.1990.tb02017.x.
The high genetic frequency of some inherited disorders may in part be related to a survival advantage conferred against an environmental hazard. Psoriasis is an inherited disorder which is common amongst populations of northern latitudes. Cutaneous delayed-type hypersensitivity response to streptococcal antigen is altered in such patients with a decrease in induration and erythema. Scarlet fever has until recently been associated with a high childhood mortality, the pathogenesis of which is related to interdependent primary toxicity and secondary toxicity (including delayed-type hypersensitivity) to streptococcal antigen (erythrogenic toxin), leading to cellular damage and potentially lethal shock. Streptococcal infection, usually presenting as pharyngitis, is a classical trigger for both scarlet fever and psoriasis. Individual susceptibility to scarlet fever has been clinically assessed in the past by the Dick test--an intradermal injection of the filtrate of a broth culture of scarlatina-producing strains of Streptococcus giving an erythematous reaction at 24-48 h (Dick-positive). The degree of reaction is directly related to susceptibility to scarlet fever. The severity of and mortality from scarlet fever may be ameliorated by immunological mechanisms also found in psoriatic patients. The high prevalence of psoriasis amongst some populations today may be related to such a protective factor.
某些遗传性疾病的高基因频率可能部分与针对环境危害所赋予的生存优势有关。银屑病是一种遗传性疾病，在北纬地区的人群中很常见。这类患者对链球菌抗原的皮肤迟发型超敏反应会发生改变，硬结和红斑减少。直到最近，猩红热仍与儿童高死亡率相关，其发病机制与对链球菌抗原（红疹毒素）的相互依存的原发性毒性和继发性毒性（包括迟发型超敏反应）有关，导致细胞损伤并可能引发致命性休克。链球菌感染通常表现为咽炎，是猩红热和银屑病的典型触发因素。过去临床上通过狄克试验评估个体对猩红热的易感性——皮内注射产猩红热链球菌肉汤培养滤液，在24 - 48小时出现红斑反应（狄克阳性）。反应程度与对猩红热的易感性直接相关。银屑病患者中也存在的免疫机制可能会减轻猩红热的严重程度和死亡率。如今某些人群中银屑病的高患病率可能与此类保护因素有关。
