Psoriasis and PsA are immune-mediated diseases with a strong genetic component. More than 20 new loci have been recently linked to these diseases. However, interactions between these genes and the phenotypic traits of both diseases are poorly understood at present. Stratification of psoriatic disease according to the sex of the patients, genetic factors or age at onset has allowed in the last few years a better understanding of the principles governing the onset and progression of these processes. The age of onset of psoriasis has been used for decades as an appropriate descriptor to define two subpopulations of psoriatic patients (types I and II) whose clinical and immunogenetic characteristics have been very well differentiated. Moreover, in patients with PsA this distinction between type I and II psoriasis also seems equally operative. In patients with PsA expressing the HLA-C*06 antigen, the latency between the onset of psoriasis and onset of joint symptoms is longer than in those without this marker. It is also known that PsA tends to appear earlier in patients with HLA-B*27 positivity, and that these patients also show a shorter interval of time between the onset of cutaneous lesions and the onset of joint disease. This review highlights the growing importance of age at disease onset as a key stratification factor in worldwide clinical and genetic studies of psoriatic disease.

It has been shown that males with spondyloarthritis tend to suffer from more severe spinal disease while females are more likely to have peripheral joint involvement. Nevertheless, gender-related differences have not been thoroughly explored in psoriatic arthritis (PsA). In PsA, males accumulate more peripheral and axial joint damage compared to women. However, it is not clear whether these findings are secondary to differences in occupational physical activity, hormonal changes, or other factors. The present study analyzed the differences in clinical expression of PsA between men and women. We have also evaluated the possible existence of gender-linked differences in the distribution of genes and polymorphisms within the major histocompatibility complex and whether patients' age at the onset of psoriasis established any differences in these aspects. Women suffered more polyarthritis, greater functional impairment, and a larger number of swollen joints during followup. We appreciated a differential expression of certain MHC genes according to gender and age at onset of psoriasis. Our results point to the need to include patient's age at the onset of psoriasis and gender as key stratification elements in future studies of genetic associations in PsA.

Obesity is a common cardiovascular risk factor in psoriatic disease. Although the prevalence of obesity is high, the factors associated with it in patients with psoriatic arthritis (PsA) are poorly understood. We aimed to analyze the frequency and obesity-associated factors in a cohort of PsA. This retrospective cross-sectional study included 290 consecutive patients with PsA according to CASPAR criteria. Three-hundred ten psoriatic patients without arthritis and 600 outpatients without inflammatory conditions were used as comparison populations. The factors associated with obesity were analyzed first using conditional logistic regression. The significant factors in this first model were introduced in a multivariate model using a backward step approach. This series included 159 men (54.8%) and 131 women (45.2%), with an average age of 54 ± 12 years. Obesity was more common both in psoriasis (36.5% vs 22%, OR 2.1 [95%CI: 1.5–2.8), P < .01]) and PsA (27.6% vs 22%, OR 1.4 [95%CI: 1.0–1.9], P < .05) than in the non-inflammatory population. Obesity was more frequent in psoriasis (36.5%) than in PsA (27.6%), OR 1.5 95% CI: 1.1 to 2.1, P < .05. After correcting for age, sex, disease duration, and other confounders, independent associations with obesity ( P < .05) were: PsA family history (OR 3.6, 95%CI: 1.1–12.4), evolution as axial disease (OR 4.4, 95%CI: 1.0–15.4), and dyslipidemia (OR 3.5, 95%CI: 1.5–8.6). Obesity is common in psoriatic disease, but much more frequent among patients with cutaneous than joint disease. Patients who present with spondylitis during evolution are more prone to this comorbidity, and therefore, should be closely monitored to correct this eventuality in a timely manner.

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AL is an uncommon finding in axial PsA and its appearance at disease onset is exceptional. MRI is a key tool in its early recognition.