Genetic variation plays a greater role in the phenotype of cutaneous psoriasis, compared with psoriatic arthritis or psoriasis vulgaris, according to a study published in Scientific Reports.

Psoriatic disease is known to have a strong genetic basis, but understanding variations in the heritability of different forms of psoriasis is important for research into new genes, risk factors, and potential treatments, wrote Quan Li, PhD, of the faculty of medicine at Memorial University, St. John’s, Nfld., and coauthors.

“Heritability essentially refers to how much variation in a trait is due to variation in genetic factors,” the authors wrote. “Better approximation of the heritability of PsC [cutaneous psoriasis], PsV [psoriasis vulgaris], and PsA [psoriatic arthritis] will culminate in more efficient genetic profiling of psoriatic disease and facilitate gene identification studies by providing more accurate estimates of sample sizes needed based on the heritability of different subsets of psoriatic disease.”

The analysis used data from a previous genome-wide association study that looked at single nucleotide polymorphisms – a variation in the DNA sequence of a particular gene – in 2,938 people with PsV, 1,155 with PsC, 715 with PsA, and 3,117 unaffected controls.

The authors used two different modeling approaches to estimate the contribution these genetic variations made to each condition. These both revealed that PsC had a greater heritability than both PsV and PsA.

“This is the first study to quantify the additive heritability of three subsets of psoriatic disease that is attributable to common susceptibility [single nucleotide polymorphisms] from large-scale genotyping arrays,” the authors wrote.

The authors wrote that this finding differed from other population-based genetic epidemiologic studies, which had pointed to much greater heritability for PsA than for PsV. However, these earlier results could be attributed to common environmental factors.

Given these heritability estimates previously made for PsA, the authors commented on the surprising absence of PsA-specific genes that reach significance in genome-wide association studies.

“This is partly explained by the much larger number of patients in the PsC or PsV [genome-wide association] studies to date, compared with PsA,” they wrote, also suggesting that this may be because of the greater disease heterogeneity seen with PsA, compared with psoriasis.

“Considerably increasing the number of PsA patients in [genome-wide association] studies will help clarify the heritability estimate question for PsA,” they wrote, but acknowledged that lower heritability or greater environmental influence could also be an explanation for this finding.

The study was supported by the Atlantic Innovation Fund. The authors reported having no conflicts of interest.

SOURCE: Li Q et al. Sci Rep. 2020 Mar 18. doi: 10.1038/s41598-020-61981-5