Two-Gene Test Differentiates Psoriasis from Eczema

Previous attempts to gain insight into the pathogenesis of psoriasis and eczema by comparing their molecular signatures were hampered by the high inter-individual variability of those complex diseases.

Although it is possible to distinguish classical plaque-type psoriasis from typical atopic eczema, in daily clinical practice, discrimination is often challenging because psoriasis and eczema phenotypes might overlap or mimic each other.

Scientists at the Helmholtz Zentrum München (Munich, Germany) and their colleagues investigated the molecular signature of psoriasis and eczema, using psoriasis and eczema tissue samples from 24 patients who had both diseases. The cohort for the validation of the disease classifier consisted of 25 patients with psoriasis, with a mean age of 47 ± 13 years and 60% were female and 28 patients with eczema with a mean age 35 ± 15 years and 64% were female. Skin punch biopsies were obtained under local anesthesia from either one eczema lesion or one psoriasis plaque, and clinically noninvolved skin of all patients.

Biopsies were divided for routine histologic evaluation and isolation of total ribonucleic acid (RNA). The RNA yield and quality were determined with a NanoDrop ND1000 UV-Vis Spectrophotometer and the 2100 Bioanalyzer (Agilent Technologies, Santa Clara, CA, USA). Whole-genome expression array fluorescence signals were detected by reading the arrays in the Agilent Technology microarray scanner system iScan. Real-time polymerase chain reactions (PCRs) were performed in 384-well plates and analyzed on the ViiA 7 Real Time PCR machine (Applied Biosystems; Foster City, CA, USA).

Among other differences that the investigators found, for example, 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—nitric oxide synthase 2 (NOS2) and Chemokine (C-C Motif) Ligand 27 (CCL27)—that they considered would make a reliable classifier of disease. They then showed, with the validation 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, with the two-gene test producing results within a day.

The authors concluded that the two-gene classifier identifies the correct diagnosis with a high accuracy, and their initial results suggest that it might be superior to gold standard techniques such as clinical evaluation and histology, and will 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 are expensive. Therapeutic strategies for psoriasis and eczema are distinct and sometimes opposing, so this diagnostic tool could be valuable to set the correct diagnosis in special cases. The study was published on July 9, 2014, in the journal Science Translational Medicine.

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