Dear Jean,

Yes, HLA-typing can help to find PSORS1-positive psoriasis.

Fan X, Yang S, Huang W, Wang Z-M, Sun L-D, et al. (2008) Fine Mapping of the Psoriasis Susceptibility Locus PSORS1 Supports HLA-C as the Susceptibility Gene in the Han Chinese Population. PLoS Genet 4(3): e1000038. doi:10.1371/journal.pgen.1000038

HLA-Cw6 or HLA-C*06, not 'HLA-C06', could be located next to a mutated PSORS1C3 gene. The HLA-Cw and PSORS1 genes are both located on the short arm of chromosome 6 as neighbors . HLA-Cw6 is a surrogate marker for mutated PSORS1 genes, only. HLA-Cw6 is always associated with HLA-B13, B27 or B57 (linkage disequilibrium).

But there a lot of others genes which can cause psoriasis, too! I think a lot of different diseases are potted as 'psoriasis'.

Best regards,

Thomas

HLA-C*06 is the PSORS1 gene: correct?

My question is: does it take extra genes to develop psoriatic arthritis, or is the skin psoriasis genetic background enough?

Solving this question requires to compare patients with pure skin psoriasis with patients with psoriatic arthritis.

Usually, skin psoriasis cohorts are followed by dermatologists, not very aware of the subtleties of psoriatic arthritis. Similarly, rheumatologists may under diagnose skin psoriasis.

My experience suggests there is no such thing as purely cutaneous psoriasis.

But experience may be misleading......

No, the HLA-C*06 gene is located on short arm of chromosome 6 in the neighborhood of the PSORS1 gene, only. These are 2 different genes!

Yes, it takes extra genes to develop psoriatic arthritis and/or skin psoriasis, too.

Because there are different genes (not only PSORS1), which can cause psoriasis (and psoriatic arthritis), we can find HLA-C*06-positive and -negative diseases.

As I said before, HLA-C*06 is a surrogate marker for mutated PSORS1 genes, only.

Patients with psoriatic arthritis are frequently associated with HLA-B27 and HLA-B27 is frequently associated with HLA-Cw6!

Best regards,

Thomas

Quotation from: (Dtsch Arztebl 2006; 103(21): A 1455–61.) https://www.aerzteblatt.de/archiv/51551/Psoriasis-Arthritis-eine-interdisziplinaere-Herausforderung

Summary

Psoriatic arthritis – an interdisciplinary challenge

'Viewed by the dermatologist as a rare organ manifestation of psoriasis and the rheumatologist as the "little sister" of rheumatoid arthritis, psoriatic arthritis (PsA) has been relatively neglected when it comes to gathering data. Given the lack of specific therapeutic studies, PsA has often been treated similarly rheumatoid arthritis, often with unsatisfactory results. Several of the more widely used drugs are not even licensed for use in PsA. Recent data suggest about twice the previously assumed prevalence, and a more severe course than previously thought. Based on substantial progress in the pathophysiologic understanding of immune-mediated inflammatory disease, in particular, the role of tumour necrosis factor alpha (TNF-a) inhibitors have been introduced in the treatment of PsA which also prove effective in the therapy of psoriatic skin manifestations. Optimal management of patients with PsA has therefore become an interdisciplinary challenge, with primary care physicians playing a key role in early detection of psoriasis and prevention of PsA.'

Dear Jean,

A nice overview you could find here:

https://www.verywellhealth.com/the-genetics-of-psoriatic-arthritis-and-psoriasis-4061328

(HLA-B17 is the broad of the splits HLA-B57 and HLA-B58. MICA is a HLA-like molecule located next to HLA-B and HLA-C on chromosome 6.)

Best regards,

Thomas

I think the case for HLA-C being the PSORS1 gene is pretty much established ( see the classical Elder paper in Am J Human Genetics 2006Article Sequence and haplotype analysis supports HLA-C as the psoria...

or a very recent review from 2017 on the genetics of psoriasis Article The Genetic Basis of Psoriasis

But my question asks whether pure skin psoriasis and psoriatic arthritis are different diseases or just different perceptions of the same disease by dermatologists and rheumatologists.

Precisely, are there HLA markers of pure skin psoriasis and HLA-markers of arthritis involvement in psoriasis??

Look to my last reply!

Thomas