HLA-C*18:01: A Rare Allele in the European Caucasian Population Coinciding with Difficult-to-Treat Plaque Psoriasis.

Background: Advances in knowledge about the metabolic pathways involved in the pathogenesis of psoriasis and related diseases have led to a search for new therapeutic targets and the development of new biological drugs. Several studies have focused on HLA-C*06 and investigated correlations between the genetic risk factors of psoriasis and clinical parameters such as the severity of the disease and the response to treatment.

Objective: Our objective is to share experience from our institution in the observation of two patients with severe chronic plaque psoriasis who were unresponsive to any anti-TNF-α treatment and only partially responsive to ustekinumab. The patients are carriers of a rare allele of HLA-C that occurs in Caucasians.

Methods: The patients with moderate-to-severe chronic plaque psoriasis, and candidates for biological therapy were typed for the HLA-C locus at high resolution via polymerase chain reaction sequence-specific oligonucleotide probes (PCR-SSOP) using a commercial kit (LAB(®)Type, One Lambda Inc., Canoga Park, CA, USA). The socio-demographic variables and clinical data were collected.

Results: In our cohort of 134 patients, only two showed the presence of the allele HLA-C*18:01. To our knowledge, a coincidence between HLA-C*18 and severe psoriasis in Caucasian patients has not previously been described. The fact that both of these patients showed the same clinical history (unresponsive to any anti-TNF-α treatment and partially responsive to ustekinumab) cannot be attributed to a random observation because HLA-C*18 is extremely rare in Europe. As a consequence, at this latitude, it probably indicates a severe disease for which the proper therapy has still not been identified.