The researchers, from the Helmholtz Zentrum München and the Technical University of Munich (TUM), report their work in the journal Science Translational Medicine.
In their introduction, the researchers behind this latest study explain how the complex appearance that both psoriasis and eczema present often varies widely among different patients - and the genes involved in each disease can differ between patients - which is probably why previous attempts to compare the molecular signatures of the two diseases have failed.
The study looked at patients with both psoriasis and eczema
So for their study, the team took a different approach - they looked at patients who had both disorders.
Both psoriasis and eczema are non-contagious, inflammatory skin reactions that can appear as itchy red patches.
Using psoriasis and eczema tissue samples from 24 patients who had both diseases, they identified genes and signaling pathways that were shared and unique for each disease across all patients.
Co-author Fabian Theis, a professor in the Institute of Computational Biology at the Helmholtz Zentrum, says they were "able to drastically reduce random genetic or environmental influences and gain a detailed picture of the development of these two diseases."
Among other differences, they found for example, that genes specific to psoriasis were important regulators of glucose and lipid metabolism, while genes specific to eczema related to epidermal barrier and reduced innate immunity.
From further analysis they selected two genes - NOS2 and CCL27 - that they considered would make a reliable classifier of disease. Then they showed, with a new group of patients, that a test using the two genes was able to diagnose all 28 eczema and 25 psoriasis cases correctly.
The test also "identified initially misdiagnosed or clinically undifferentiated patients," they note.
Two-gene test should produce results within a day
The hope is that a test based on the two-gene disease classifier will not only save the distress that a misdiagnosis brings, but also save time and money. In recent years many new specific treatments have been developed for psoriasis and eczema, but they are only effective for the target disease, and they cost a lot of money. Each treatment typically costs several tens of thousands of dollars per patient per year.
The researchers see a test that compares samples of diseased and healthy skin producing results within a day. They have already applied for a patent for a test based on the two-gene disease classifier.
They note that the discovery marks a first step toward personalized medicine for chronic inflammatory skin diseases, similar to what is already happening in oncology, where mutation analyses are becoming more common and forming the basis of individual-specific cancer treatment.
In 2013, dermatologists at the University of Pennsylvania reported a major study that found people with psoriasis are more likely to have other diseases. When they investigated about 100,000 patient medical records, they found people with the skin condition were more likely to develop diabetes and cardiovascular disease, and other conditions.