Pharmacogenetics of asthma

Review on Pharmacogenetics and Pharmacogenomics Applied to the Study of Asthma

Nearly one-half of asthmatic patients do not respond to the most common therapies. Evidence suggests that genetic factors may be involved in the heterogeneity in therapeutic response and adverse events to asthma therapies. We focus on the three major classes of asthma medication: β-adrenergic receptor agonist, inhaled corticosteroids, and leukotriene modifiers. Pharmacogenetics and pharmacogenomics studies have identified several candidate genes associated with drug response.In this chapter, the main pharmacogenetic and pharmacogenomic studies in addition to the future perspectives in personalized medicine will be reviewed. The ideal treatment of asthma would be a tailored approach to health care in which adverse effects are minimized and the therapeutic benefit for an individual asthmatic is maximized leading to a more cost-effective care.

Pharmacogenetics of drugs used in the treatment of ocular inflammatory diseases

INTRODUCTION

Ocular inflammatory diseases comprise uveitis, scleritis, and inflammation of adjacent structures of the eye. Therapy may be challenging and often involves corticosteroids and immunomodulatory agents.

AREAS COVERED

This review describes the genes involved in noninfectious ocular inflammatory diseases and focuses on pharmacogenetic studies regarding different classes of anti-inflammatory drugs used in the management of uveitis, including corticosteroids, antimetabolites, calcineurin inhibitors, alkylating agents, and biological agents.

EXPERT OPINION

Pharmacogenetics holds the promise of a personalized medicine with potential to customize treatment that can achieve the best clinical response and avoid toxicity. Several polymorphisms in various genes involved in the metabolism of drugs commonly utilized in the treatment of ocular inflammatory diseases have been described. Most promising is the polymorphism in thiopurinemethyltransferase gene for which a genotype analysis can reveal slow metabolizers of azathioprine and help avoid serious drug toxicity. Although pharmacogenetic studies with specific focus on ocular inflammatory diseases are lacking, knowledge from studies in rheumatologic diseases and transplant medicine can provide a platform for future research. Prospective clinical studies are needed to determine the clinical significance of such polymorphisms and their true effect on drug metabolism and side effects.

Frequency of MDR1 single nucleotide polymorphisms in a Jordanian population, including a novel variant

The multidrug resistance gene (MDR1 or ABCB1) codes for P-glycoprotein, which plays an important role in regulating absorption, distribution, and elimination of drugs. We examined MDR1 gene variants in 100 unrelated subjects from various regions of Jordan. The MDR1 gene was scanned using direct sequencing. Six rare variants in MDR1 were detected, including a new variant, T3075A. This variant did not affect the protein sequence (synonym for threonine). Among the common SNPs, the frequencies of rs1128503 (C1236T) genotypes were: 0.23 (CC), 0.41 (CT) and 0.36 (TT). For the rs2032582 (G2677T) SNP, genotype frequencies were 0.38 for GG, 0.45 for GT, 0.13 for TT, 0.03 for GA, and 0.01 for TA, whereas for rs1045642 (C3435T), genotype frequencies were 0.17 for CC, 0.5 for CT and 0.33 for TT. The observed distribution of the common variants in the Jordanian population was within the range detected in other populations. These data on MDR1 gene variants in the Jordanian population will be useful for investigations on response to P-glycoprotein substrate drugs.

Acute adrenal crisis in an asthmatic child treated with inhaled fluticasone proprionate

Adrenal suppression secondary to prolonged inhaled corticosteroid use is usually limited to biochemical abnormalities, with no obvious clinical effects. Acute adrenal crisis is much rarer event but has been reported with increasing frequency. We report a case of a 7-year-old asthmatic child who presented with an acute history of lethargy after a respiratory infection. He was maintained on 220 mug/day of fluticasone propionate for several years. Initial evaluation revealed severe adrenal suppression, with undetectable cortisol levels and minimal response after stimulation with ACTH. After fluticasone was discontinued, a gradual recovery of the adrenal axis was seen. This case shows that acute adrenal crisis may be a consequence even at the usual prescribed doses, stressing the importance of using the lowest dose of inhaled steroids needed to control symptoms and having an increased awareness of this complication.

Functional polymorphism in CTLA4 gene influences the response to therapy with inhaled corticosteroids in Slovenian children with atopic asthma

We genotyped CTLA4 CT60 (rs3087243) functional single nucleotide polymorphism (SNP) in children with asthma and in healthy controls and correlated the genotype data with asthma clinical data, including treatment response with inhaled corticosteroids measured by forced expiratory volume in the first second (FEV(1)). FEV(1) increased by 21.7% after 4 weeks of therapy in atopic asthmatics with the A/A genotype compared with an 8.6% increase in heterozygotes and a 5.8% increase in G/G homozygotes (p <0.01). Genotype and allele frequencies in asthmatics did not differ significantly from those in the control group. SNP CT60 in the CTLA4 gene is significantly associated with the response to treatment with inhaled corticosteroids in children with atopic asthma and could be a useful biomarker for personalized therapy in asthmatic children. SNP CT60 in the CTLA4 gene plays only a minor role in genetic susceptibility to childhood asthma in the Caucasian population.

Gene-environment interactions in asthma

Asthma is a complex disease, and its incidence is determined by an intricate interplay of genetic and environmental factors. The identification of novel genes for asthma suggests that many genes with small effects rather than few genes with strong effects contribute to the development of asthma. These genetic effects may in part differ with respect to a subject's environmental exposures, although some genes may also exert their effect independently of the environment. Whereas the geneticist uses highly advanced, rapid, comprehensive technologies to assess even subtle changes in the human genome, the researcher interested in environmental exposures is often confronted with crude information obtained from questionnaires or interviews. There is thus substantial need to develop better tools for individual exposure assessment in all relevant environmental fields. Despite these limitations, a number of important gene-environment interactions have been identified. These interactions point to the biology of environmental exposures as the involved genetic variation is suggestive of certain underlying mechanisms. Furthermore, the identification of subjects who are particularly susceptible to environmental hazards through genetic analyses helps to estimate better the strength of effect of environmental exposures. Finally, the analysis of gene-environment interactions may result in a reconciliation of seemingly contradictory findings from studies not taking environmental exposures into account.

Update on gene modifiers in cystic fibrosis

PURPOSE OF REVIEW

Cystic fibrosis (CF) is a common, life-limiting monogenic disease, which typically manifests as progressive bronchiectasis, exocrine pancreatic dysfunction, and recurrent sinopulmonary infections. Although the gene responsible for CF (CFTR) was described in 1989, it has become increasingly evident that modifier genes and environmental factors play substantial roles in determining the severity of disease, particularly lung disease. Identifying these factors is crucial in devising therapies and other interventions to decrease the morbidity and mortality associated with this disorder.

RECENT FINDINGS

Although many genes have been proposed as potential modifiers of CF, only a handful have withstood the test of replication. Several of the replicated findings reveal that genes affecting inflammation and infection response play a key role in modifying CF lung disease severity. Interactions between CFTR genotype, modifier genes, and environmental factors have been documented to influence lung function measures and infection status in CF patients.

SUMMARY

Several genes have been demonstrated to affect disease severity in CF. Furthermore, it is likely that gene-gene and gene-environment interactions can explain a substantial portion of the variation of lung disease. Ongoing genome-wide studies are likely to identify novel genetic modifiers. Continued exploration of the role of genetic and nongenetic modifiers of CF is likely to yield new options for combating this debilitating disease.