Simon P. Lee

Common loss-of-function variants of the epidermal barrier protein filaggrin are a major predisposing factor for atopic dermatitis

Atopic disease, including atopic dermatitis (eczema), allergy and asthma, has increased in frequency in recent decades and now affects ∼20% of the population in the developed world. Twin and family studies have shown that predisposition to atopic disease is highly heritable. Although most genetic studies have focused on immunological mechanisms, a primary epithelial barrier defect has been anticipated. Filaggrin is a key protein that facilitates terminal differentiation of the epidermis and formation of the skin barrier. Here we show that two independent loss-of-function genetic variants (R510X and 2282del4) in the gene encoding filaggrin (FLG) are very strong predisposing factors for atopic dermatitis. These variants are carried by ∼9% of people of European origin. These variants also show highly significant association with asthma occurring in the context of atopic dermatitis. This work establishes a key role for impaired skin barrier function in the development of atopic disease.

Arginine‐16 β2 adrenoceptor genotype predisposes to exacerbations in young asthmatics taking regular salmeterol

Background: The homozygous presence of the arginine-16 variant of the β2 adrenoceptor gene ADRB2 reverses the benefits from the regular use of short acting β2 agonists in asthmatic adults compared with the homozygous glycine-16 genotype. We studied the effect of this polymorphic variation on asthma exacerbations in children and young adults and its relation to long acting β2 agonists. Methods: A cross-sectional survey was undertaken using electronic records, direct interviews, and genotype determination of position 16 and 27 of the ADRB2 gene in DNA from mouthwash samples of 546 children and young asthmatics attending paediatric and young adult asthma clinics in Tayside, Scotland during 2004–5. The primary outcome measure was asthma exacerbations over the previous 6 months. Results: There was an increased hazard of asthma exacerbations across all treatment steps of the British Thoracic Society (BTS) asthma guidelines when the homozygous genotypes Arg/Arg and Gly/Gly were compared (OR 2.05, 95% CI 1.19 to 3.53, p = 0.010), particularly in patients treated with salmeterol (OR 3.40, 95% CI 1.19 to 9.40, p = 0.022). The Glu27Gln polymorphism had no significant effect on asthma exacerbations in any treatment group. Conclusions: The arginine-16 genotype of ADRB2 predisposes to exacerbations in asthmatic children and young adults, particularly in those exposed to regular salmeterol. This may be explained by genotype selective salmeterol induced downregulation and impaired receptor coupling, and associated subsensitivity of the response.

Increased cardiovascular morbidity and mortality in type 2 diabetes is associated with the glutathione S transferase theta-null genotype : a Go-DARTS study

Background—Glutathione S-transferases (GSTs) modulate oxidative stress, and variation in GST genes has been associated with cardiovascular disease risk. We prospectively determined smoking-related cardiovascular morbidity by GST genotype in a large cohort of individuals with type 2 diabetes using a population-based diabetes research database (DARTS). Methods and Results—We performed a cohort study of 2015 individuals with type 2 diabetes. Individuals were genotyped for the Ile105Val variant of GSTP1 and the deleted variants of GSTT1 and GSTM1. Clinical characteristics, smoking status, and incidence of subsequent cardiovascular events were obtained by examining the DARTS databases. Variation in the GSTP1 and GSTM1 genes was not associated with smoking-related risk of death or cardiovascular events. There was an increase in the rate of cardiovascular events in smokers lacking the GSTT1 gene compared with smokers with the GSTT1 gene intact (hazard ratio [HR], 1.96; P=0.001). This excess of cardiovascular events was due to both strokes (HR, 2.7; P=0.008) and myocardial infarctions (HR, 1.9; P=0.006). The rate of death as a result of a cardiovascular event was even more markedly increased in the GSTT1-null smokers (HR, 2.7; P=0.001), with a 2-fold increase in myocardial infarction fatality ratio. These effects translated into an increase in overall death and a decrease in age at death. We also found that the GSTT1− genotype was associated with progression of both diabetic retinopathy and nephropathy (P=0.005 and P=0.01, respectively), although we found little evidence for an interaction with smoking. Conclusions—Genetic absence of the GSTT1 enzyme is an independent and powerful predictor of premature vascular morbidity and death in individuals with type 2 diabetes.

Glutathione S-Transferase M1 and P1 Genotype, Passive Smoking, and Peak Expiratory Flow in Asthma

OBJECTIVES. Our purpose with this work was to assess the contribution of glutathione S-transferase gene variants to asthma susceptibility and pulmonary function in relation to tobacco smoke exposure in the home. METHODS. Young individuals with asthma (age: 3–21 years; n = 504) were recruited through primary and secondary care throughout Tayside, Scotland (BREATHE Study). Spirometry was obtained on 407 individuals. Binary logistic regression and general linear modeling were used to explore phenotypic characteristics by genotype and tobacco smoke exposure status in younger children (3–12 years; n = 384) and teenagers and young adults (13–21 years; n = 120). RESULTS. Three- to 12-year-olds with asthma, null for the GSTM1 gene or homozygous for the GSTP1Val105 allele, were overrepresented in the group exposed to environmental tobacco smoke. No differences in lung function values could be detected in this group. In contrast, 13- to 21-year-olds with the GSTM1-null genotype or homozygous for the GSTP1Val105 allele from smoking households were more likely to have a substantially lower percentage of predicted peak expiratory flow rates than those from nonsmoking households (83% vs 98%). CONCLUSIONS. Three- to 12-year-olds who are null for GSTM1 or homozygous for the GSTP1Val105 allele are more susceptible to asthma associated with environmental tobacco smoke exposure than those with more intact glutathione S-transferase status. In the 13- to 21-year-olds, GSTM1-null status interacts with environmental tobacco smoke exposure to substantially reduce peak expiratory flow rate. The environmental tobacco smoke effect in GSTM1-null children with asthma could be cumulative over time, resulting in detrimental effects on peak expiratory flow rate in 13- to 21-year-olds with asthma.

Loss-of-function variants of the filaggrin gene are associated with atopic eczema and associated phenotypes in Swedish families.

Recent studies have identified 2 loss-of-function variants, R501X and 2282del4, in the filaggrin gene as predisposing factors in the development of eczema. In this study, representing the first analysis of the variants in a Swedish population, we analysed transmission in 406 multiplex eczema families with mainly adult patients. In accordance with previous studies we found association between the filaggrin gene variants and atopic eczema (p=9.5 x 10(-8)). The highest odds ratio for the combined allele, 4.73 (1.98-11.29), p=3.6 x 10(-8), was found for the subgroup with a severe eczema phenotype, and association was also found with raised allergen-specific IgE, allergic asthma and allergic rhinoconjunctivitis occurring in the context of eczema. Our results support an important role for the filaggrin gene variants R501X and 2282del4 in the development and severity of atopic eczema and indicate a possible role for the subsequent progression into eczema-associated phenotypes.

Association of common variation in the PPARA gene with incident myocardial infarction in individuals with type 2 diabetes: A Go-DARTS study

BackgroundCommon variants of the PPARA gene have been found to associate with ischaemic heart disease in non diabetic men. The L162V variant was found to be protective while the C2528G variant increased risk. L162V has also been associated with altered lipid measures. We therefore sought to determine the effect of PPARA gene variation on susceptibility to myocardial infarction in patients with type 2 diabetes. 1810 subjects with type 2 diabetes from the prospective Go-DARTS study were genotyped for the L162V and C2528G variants in the PPARA gene and the association of the variants with incident non-fatal myocardial infarction was examined. Coxs proportional hazards was used to interrogate time to event from recruitment, and linear regression for analysing association of genotype with quantitative clinical traits.ResultsThe V162 allele was associated with decreased risk of non-fatal myocardial infarction (HR = 0.31, 95%CI 0.10–0.93 p = 0.037) whereas the C2528 allele was associated with increased risk (HR = 2.77 95%CI 1.34–5.75 p = 0.006). Similarly V162 was associated with a later mean age of diagnosis with type 2 diabetes and C2582 an earlier age of diagnosis. C2528 was also associated with increased total cholesterol and LDL cholesterol, which did not account for the observed increased risk. Haplotype analysis demonstrated that when both rare variants occurred on the same haplotype the effect of each was abrogated.ConclusionGenetic variation at the PPARA locus is important in determining cardiovascular risk in both male and female patients with diabetes. This genotype associated risk appears to be independent of the effect of these genotypes on lipid profiles and age of diagnosis with diabetes.

PPARG Locus Haplotype Variation and Exacerbations in Asthma

The peroxisome proliferator‐activated receptor gamma (PPARγ) regulates inflammation and may play a role in asthma. Using mouthwash‐derived DNA and clinical interviews and measurements, we investigated the association of previously characterized single‐nucleotide polymorphisms in the PPARG gene (Pro12Ala, C1431T, and C‐681G) with asthma exacerbations in patients aged 3–22 years (n=569). The common homozygous haplotype combination of the Pro12 and C1431 alleles was associated with increased risk for asthma exacerbations (ProC, odds ratio (OR) 1.87, 95% confidence interval 1.25–2.79; P=0.002). The ProC genotype was associated with increased school absences (OR 1.82, 95% confidence interval 1.21–2.76; P=0.004) and hospital admissions (OR 2.32, 95% confidence interval 1.18–4.58; P=0.015) over the preceding 6 months. The population‐attributable risk of this genotype was 33%. Common genetic variation at the PPARG locus may play an important role in modulating the long‐term control of asthma in children and young adults.

Cornulin, a marker of late epidermal differentiation, is down-regulated in eczema.

Background:  Eczema is a common chronic inflammatory skin disorder which shows strong genetic predisposition. To identify new potential molecular determinants of the disease pathogenesis, we performed a gene expression study in an eczema mouse model. This analysis identified a marked down regulation of the cornulin gene (CRNN), a member of the epidermal differentiation complex, in the eczema‐like skin. We then investigated CRNN as an eczema candidate gene and studied its polymorphism and the expression in the skin of eczema patients.

Filaggrin mutations are a major predisposing factor in childhood-onset adult-persistent atopic dermatitis

The transfer of normal genes into somatic cells is one strategy to treat patients with genetic diseases. However, this strategy has still encounters technical problems including effi cacy of gene transfer rate and practical clinical safety. Thus, other strategies including pharmacological therapy or gene correction, are receiving increasing attention. Dystrophic epidermolysis bullosa (DEB) is caused by mutations in the COL7A1 encoding type VII collagen. This study examined the feasibility of antisense oligoribonucleotide (AON) therapy for DEB. AON was designed to induce skipping of a targeted exon containing a premature termination codon mutation, resulting in restoration of the open reading frame. We targeted exon 70 of COL7A1 since a recurrent mutation 5818delC was localized to exon 70 in Japanese DEB patients. We initially designed and synthesized two AONs to modulate splicing of exon 70 and found that one AON induced effective skipping of normal exon 70 containing the 16 amino acids. Attachment and migration analyses showed that recombinant collagen without contribution of exon 70 had similar effect to normal type VII collagen. Next, we synthesized mutation-specifi c AON by deleting cytosine at 5818. Introduction of this AON into DEB keratinocytes harboring 5818delC without expression of type VII collagen showed that the AON induced skipping of exon 70 in the abnormal 5818delC allele. Furthermore, 6.2 % of the DEB keratinocytes started to express type VII collagen in vitro after application of the mutation-specifi c AON. Injection of the AON into rat model grafted the DEB keratinocytes and fi broblasts induced detectable of type VII collagen expression at the basement membrane zone. We conclude that skipping of targeted exons using mutation-specifi c AON may show potential for future gene therapy for DEB patients.We recently reported that ABCA12 works as an epidermal keratinocyte lipid transporter, and that defective ABCA12 results in a loss of the skin lipid barrier, leading to harlequin ichthyosis (HI), one of the most devastating genodermatoses. In the present study, precise expression pattern of ABCA12 was studied in human embryonic and fetal skin of 7-22 weeks estimated gestational age (EGA) and newborn skin samples. For controls, we also studied the expression of transglutaminase 1 (TGase1) that is known to cross-link several precursor proteins in the formation of the cornifi ed cell envelope during keratinocyte terminal differentiation. In twolayered epidermis (about 6-9 weeks EGA), both ABCA12 and TGase1 were only expressed in periderm cells. In three-layered epidermis (10-13 weeks EGA), ABCA12 staining was seen not only in periderm, but also throughout the entire epidermis, while TGase1 staining was restricted to the periderm. A similar pattern was observed during four- or more-layered epidermal development (14-22 weeks EGA). In newborn skin, ABCA12 and TGase1 were seen only in the upper epidermal layers, mainly the granular layer. These staining patterns were similar to those in normal adult skin. Next, we studied ABCA12 mRNA expression in extracts of the fetal skin (at 10, 14, 15 weeks EGA). In 15 weeks EGA, the expression level of ABCA12 mRNA was signifi cantly increased compared with that in the early development (10 and 14 weeks EGA). This increasing pattern of ABCA12 mRNA expression is consistent with ABCA12 immunofl uorescent staining during human epidermal development. The unique pattern of ABCA12 expression during human epidermal development might imply severe symptoms of HI patients with ABCA12 mutations around the birth. 2006 ESDR ABSTRACTS www.Mutations in ABCA12 lead to harlequin ichthyosis and lamellar ichthyosis. The keratinocyte lipid transporter ABCA12 is a member of the ATP-binding cassette transporter family, and members of the ABCA subfamily have closely related functions as lipid transporters. Previously, we reported that the pathomechanism of harlequin ichthyosis involves the defective function of the lipid transporter ABCA12.To further elucidate the precise distribution pattern and function of ABCA12, we performed double-labeling immunofl uorescence staining for ABCA12 and for Golgi-associated or lamellar granule-associated molecules both on normal human epidermis and cultured normal human keratinocytes. We studied the precise localization of ABCA12 and other molecules using confocal laser scanning microscope. In normal human epidermis, ABCA12 was observed mainly in the granular layers with glucosylceramide (one of the major lamellar granule contents) and transglutaminase 1 (a cornifi ed cell envelope-associated keratinization marker), but not always colocalized with GM130 and TGN46 (Golgi-related molecules) that were expressed from the lower epidermis. In normal human keratinocytes cultured in high Ca++ concentration medium, ABCA12 colocalized with GM130 (a cis-Golgi- associated molecule), TGN46 (a trans-Golgi-associated molecule) and glucosylceramide. Transglutaminase 1 was restricted to the cell membrane and ABCA12 localization was within the cytoplasm distinct from transglutaminase 1 localization. The present results suggest that ABCA12 is mainly expressed in differentiated, granular layer keratinocytes with glucosylceramide and transglutaminase 1, and, at the subcellular level, ABCA12 is distributed from the cisside of the Golgi apparatus to trans-Golgi network, lamellar granules at the cell periphery. Our results suggest that ABCA12 may play an important role in lipid transport from the cis-side of the Golgi apparatus through the trans-Golgi network, to the cell periphery via lamellar granules in human epidermal granular layer keratinocytesHarlequin ichthyosis (HI) is a devastating genodermatosis that is often fatal during the neonatal period. Until the identifi cation of ABCA12-encoding a keratinocyte lipid transporter, as the causative gene for HI, prenatal diagnosis (PNDx) had been performed for more than 20 years by electron microscopic examination of fetal skin biopsy samples. We report here the fi rst case of DNA-based PNDx for HI. The proband, the fi rst child of healthy non-consanguineous French parents, showed a typical HI phenotype and died soon after birth. ABCA12 immunostaining was markedly reduced in the proband’s skin. Direct sequence analysis of ABCA12 revealed that the proband was a compound heterozygote for two novel mutations: a maternal nonsense mutation p.Ser1249X in exon 26 and a paternal missense mutation p.Arg2479Lys occurring at the last codon of exon 50. p.Ser1249X leads to an approximate 52 % truncation of the ABCA12 protein losing both ATP-binding cassette active sites. p.Arg2479Lys involves a highly conserved codon among diverse species in the second ABCA12 ATP-binding cassette. For their third pregnancy, the parents requested PNDx. Direct sequence analysis using fetal genomic DNA from amniotic fl uid cells at 17 weeks of pregnancy revealed that the fetus was a compound heterozygote for both mutations. The fetus was predicted to be affected and the parents requested the pregnancy to be terminated. The aborted fetus showed typical signs of HI. Analysis of ABCA12 transcripts of cultured keratinocytes from the abortus showed the presence of six abnormally spliced products arising from the allele carrying the missense mutation. Four of them lead to premature termination codons while the two others produced deleted proteins missing 21 and 31 amino acids in the second ATP-binding cassette. These results indicated residual expression of ABCA12. The present report paves the way for molecular PNDx of HI in the earlier stages of pregnancy