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. 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. 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. 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.
