Absence of association between asthma and high serum immunoglobulin E associated GPRA haplotypes and adult atopic dermatitis.

Atopic dermatitis (AD) is a chronic relapsing inflammatory skin disease that affects 10%–15% of children and 2%– 10% of adults (Williams, 1997). The skin in AD is typically dry and excoriated due in part to reduced ability of the epidermis to hold water. Immunological mechanisms are thought to play a critical pathogenic role with AD being associated with high immunoglobulin E (IgE) levels and the accumulation of T lymphocytes of the Th2 subtype in involved skin (Galli et al, 2003). AD is also associated with atopic diseases in other organs such as asthma and allergic rhinitis (Mortz et al, 2001). Atopy reflects a genetic predisposition for excessive IgE antibody production with 80% of children with AD generating serum concentrations of IgE typically five fold increased (Stone, 1973; Johansson et al, 2001). Whilst the pathogenesis of AD is unclear, family and twin studies support a significant genetic component underlying predisposition to the phenotype (Kuster et al, 1990). Furthermore, genome-wide scans for susceptibility loci have reported a number of chromosomal loci linked to the disease (Lee et al, 2000; Cookson et al, 2001; Bradley et al, 2002). Association studies provide a powerful method for isolating disease loci and a recent study of asthma patients and high serum IgE responders from isolated cohorts in Finland identified risk haplotypes from a 133 kb region on chromosome 7p (Laitinen et al, 2004). Located within this interval, a G protein-coupled receptor gene, GPRA, showed altered distribution patterns between bronchial biopsies from healthy and asthmatic individuals (Laitinen et al, 2004). This association has been further supported by two recent reports of asthma patients. These included a large German study (Kormann et al, 2005) and a cohort drawn from five Western European countries (Melén et al, 2005). Evidence of association was not observed in a Korean cohort (Shin et al, 2004), in which only a single-nucleotide polymorphism (SNP) was examined and as such may not have fully distinguished between the risk and non-risk haplotypes across the GPRA locus. The GPRA gene is also expressed in skin keratinocytes raising the possibility that variation in this gene may directly contribute to predisposition to AD (Laitinen et al, 2004). To investigate inherited susceptibility to AD we examined seven SNP that characterize or ‘‘tag’’ the seven haplotypes spanning GPRA identified by Laitinen et al (2004). These were genotyped in 188 adult patients of Northern European descent and in 221 ageand sex-matched controls. Ethical approval was given by the medical ethics committee of St Thomas’s Hospital and informed written consent was obtained from all participating subjects. The study was conducted according to Declaration of Helsinki Principles. All patients were diagnosed using standard clinical criteria of Hanifin and Rajka by experienced dermatologists (Hanifin, 1992). Minimum age at study was 18 y indicating that this cohort had persistence or recurrence into adulthood. Further these patients in general had increased disease activity compared with childhood AD. Taken together this suggests that this patient group represents a more severe phenotype. The positions of the SNP markers are listed in Table I with respect to genomic contig NT_000380. Genotyping of samples was performed by size assessment of primer extension products using the MALDI-TOF mass spectrometry Sequenom system (Jurinke et al, 2002). Genotype frequencies were found to be in Hardy–Weinberg equilibrium. Allele frequencies for each SNP were compared between patients and controls using w contingency tables. Haplotypes of the seven SNP were constructed separately for patients and controls using PHASE (Stephens et al, 2000). The allele frequencies for the seven markers in the patients and the controls are shown in Table I. No significant differences were observed in the allele frequencies between the patients and controls. Control allele frequencies were similar to those of the study by Laitinen et al (2004) and also to a German control population (Kormann et al, 2005). Haplotypes inferred using PHASE were used to assess whether specific haplotypes may harbor AD susceptibility alleles. These haplotypes were also compared with those observed in the asthma and high IgE cohorts (Laitinen et al, 2004). Similar haplotype frequencies were observed between the controls in this study and the controls reported in the asthma study and in those ascertained from Kormann et al (2005). An additional haplotype with a frequency greater than 2.5% was observed in this study by comparison with those reported in the asthma study (Hn, Table II). These haplotypes represented 96% of the haplotypes present in the cohort studied and no single haplotype accounted for more than 35% of the total. No overall statistical significant differences in haplotype frequencies were observed between AD patients and controls (Table II). These data imply Abbreviations: AD, atopic dermatitis; IgE, immunoglobulin E; SNP, single-nucleotide polymorphism