NAIL INVOLVEMENT:

 seen in up to 50% of psoriasis patients, more common in patients with psoriatic arthropathy
 histopath -> psoriasiform onychitis with spongiform pustulation, negative fungal special stains (see photos)
 differential -> onychomycosis, eczematous onychitis, Reiter syndrome

Susceptibility loci

 PSORS1 locus at 6p21 (#12148091#)

References

 Gottlieb AB. Psoriasis: emerging therapeutic strategies. Nat Rev Drug Discov. 2005 Jan;4(1):19-34. PMID: #15688070#

 Bowcock AM, Cookson WO. The genetics of psoriasis, psoriatic arthritis and atopic dermatitis. Hum Mol Genet. 2004 Apr 1;13 Spec No 1:R43-55. PMID: #14996755#

 Bhalerao J, Bowcock AM. The genetics of psoriasis: a complex disorder of the skin and immune system. Hum Mol Genet. 1998;7(10):1537-45. PMID: #9735374#