Transcriptome analysis of Generalized Pustular Psoriasis (GPP) versus Palmoplantar Pustular Psoriasis (PPP) uncovers raised potential markers of severity, atopy and anxiety in GPP

Background. Generalized pustular psoriasis (GPP), palmoplantar pustular psoriasis (PPP) and Acrodermatitis continua suppurativa Hallopeau (ACH) are 3 prototypes of pustular psoriasis. Treating them with the established psoriasis armamentarium of immunomodulating therapies is more or less a trial-and-error game because pathophysiology has not been uncovered in detail yet. Objectives. To promote the decoding of immunological pathways in GPP as the maximal variant of pustular psoriasis. Methods. Focusing on transcriptomic differences in GPP versus PPP, bulk RNA sequencing of affected skin and healthy skin of 3 GPP and 3 PPP patients was performed, and results were compared to each other and to matching healthy skin samples. Results. Analysis of heatmaps confirmed the expected up-regulation of Interleukin (IL-) 17, IL-23 and IL-36 pathways, especially in GPP. Interestingly, in our GPP patients we detected an unexpected marked atopic-like milieu with an upregulated T-helper cell (Th) type 2 profile. This raises the bar concerning personalized medicine as recently introduced IL-36 blockage will probably not be able to succeed as a monotherapy in GPP. In PPP-patients the ‚typical‘ immune signatures, although differentially regulated, struck with a notable heterogeneity. The atopic markers were not as overregulated as in GPP. Further findings might elucidate clinical features of GPP: Severity of symptoms was accompanied by up-regulated SERPIN B4 and L-selectin. And, an overexpression of KYNU and TDO2 as a sign for imbalance in tryptophan metabolism could deliver an explanation for psychological findings like anxiety and depression during an acute flare of GPP. Conclusions. GPP has an atopic component next to notorious drivers of classical psoriasis and IL-36. Key factors for aggressiveness of disease and psychological distress during flares could be overexpression of SERPIN B4/L-selectin respectively KYNU/TDO2. Trials with a greater number of patients and even more meticulous transcriptome analysis possibly supported by artificial intelligence should be considered.