01661nas a2200253   4500000000100000008004100001260001600042653001200058653001600070653002700086653001100113653001100124653000900135653001400144653002100158100001700179700001400196245005300210300001200263490000800275050001900283520109100302022001401393       2007                            d  c2007 Jul 2110aAnimals10aComorbidity10aDisease Models, Animal10aFemale10aHumans10aMale10aPsoriasis10aSocial Isolation1 aGriffiths CE1 aBarker JN00aPathogenesis and clinical features of psoriasis.  a263-2710 v370  aGRIFFITHS 20073 a<p>Psoriasis, a papulosquamous skin disease, was originally thought of as a disorder primarily of epidermal keratinocytes, but is now recognised as one of the commonest immune-mediated disorders. Tumour necrosis factor alpha, dendritic cells, and T-cells all contribute substantially to its pathogenesis. In early-onset psoriasis (beginning before age 40 years), carriage of HLA-Cw6 and environmental triggers, such as beta-haemolytic streptococcal infections, are major determinants of disease expression. Moreover, at least nine chromosomal psoriasis susceptibility loci have been identified. Several clinical phenotypes of psoriasis are recognised, with chronic plaque (psoriasis vulgaris) accounting for 90% of cases. Comorbidities of psoriasis are attracting interest, and include impairment of quality of life and associated depressive illness, cardiovascular disease, and a seronegative arthritis known as psoriatic arthritis. A more complete understanding of underlying pathomechanisms is leading to new treatments, which will be discussed in the second part of this Series.</p>  a1474-547X