Common IL-31 gene haplotype associated with non-atopic eczema is not implicated in epidermolysis bullosa pruriginosa.

Epidermolysis bullosa pruriginosa (EBP; OMIM #604129) is an unusual variant of autosomal dominant (or occasionally recessive) dystrophic epidermolysis bullosa (DEB) in which intense itching and scratching impacts upon the phenotype (1, 2). Although trauma-induced blistering often occurs, and toenail dystrophy is almost universal, the skin lesions can often resemble nodular prurigo, lichen simplex chronicus, hypertrophic lichen planus, dermatitis artefacta or other acquired itchy dermatoses (1, 3, 4). EBP therefore can be difficult to diagnose clinically and its precise pathophysiology is not known. Of note, the nature of the underlying mutations in the type VII col-lagen gene, COL7A1, does not differ substantially from those delineated in other non-itchy cases of DEB (3–5). Moreover, parameters such as IgE levels, atopy, biochemical or endocrinological abnormalities, iron deficiency, filaggrin gene pathology, and matrix metalloproteinase-1 gene promoter polymorphisms, have all been excluded as potential disease-modifying factors (1, 3, 4, 6). Itch is a common, complex, and only partially understood clinical symptom (7). Nevertheless, recent data have demonstrated that interleukin-31 (IL-31), a cytokine belonging to the IL-6 family, may be relevant to some pruritic disorders (8–11). Notably, over-expression of IL-31 in transgenic mice (ubiquitous or lymphocyte-specific promoter) induces severe itching, normal IgE levels and a phenotype similar to non-atopic eczema (8). Expression of the IL-31 gene is also up-regulated in the skin in several itchy human skin disorders, including atopic dermatitis, allergic contact dermatitis, psoriasis and nodular prurigo (9–11). IL-31 signals via a receptor complex that is composed of IL-31 receptor A (IL-31RA) and oncostatin M receptor (OSMR) subunits (12), and naturally occurring mutations in both these receptor components may underlie familial primary localized cutaneous amyloidosis, a pruritic autosomal dominant disease (13). Polymorphisms in the IL-31 gene have also been linked to eczema susceptibility. Schulz et al. (14) have shown that a particular IL-31 gene haplotype may be associated with altered regulation of IL-31 gene expression, and that this can have functional consequences and be more common in subjects with non-atopic eczema. Schulz et al. (14) identified three principal IL-31 gene haplotypes, which they termed A, B and C, that are present in > 90% of the white Caucasian population. These could be distinguished by genotyping three single-nucleotide polymorphisms: IL-31 2057 G>A (rs6489188; chromosomal position 121226729), IL-31 1066 G>A (rs11608363; chromosomal position 121225738), and IL-31 IVS2+12 A>G (chromosomal position 121224332). The A, B and C haplotypes reflected the following combination of polymorphisms: GAA, AGA and GGG, …