Genomewide association analysis of respiratory syncytial virus infection in mice.

Respiratory syncytial virus (RSV) is the major cause of lower respiratory tract infection in infants, with about half being infected in their first year of life. Yet only 2 to 3% of infants are hospitalized for RSV infection, suggesting that individual susceptibility contributes to disease severity. Previously, we determined that AKR/J (susceptible) mice developed high lung RSV titers and showed delayed weight recovery, whereas C57BL/6J (resistant) mice demonstrated low lung RSV titers and rapid weight recovery. In addition, we have reported that gene-targeted mice lacking the cystic fibrosis transmembrane conductance regulator (Cftr; ATP-binding cassette subfamily C, member 7) are susceptible to RSV infection. For this report, recombinant backcross and F2 progeny derived from C57BL/6J and AKR/J mice were infected with RSV, their lung titers were measured, and quantitative trait locus (QTL) analysis was performed. A major QTL, designated Rsvs1, was identified on proximal mouse chromosome 6 in both recombinant populations. Microarray analysis comparing lung transcripts of the parental strains during infection identified several candidate genes that mapped to the Rsvs1 interval, including Cftr. These findings add to our understanding of individual RSV susceptibility and strongly support a modifier role for CFTR in RSV infection, a significant cause of respiratory morbidity in infants with cystic fibrosis.

Joint influences of Acidic-Mammalian-Chitinase with Interleukin-4 and Toll-like receptor-10 with Interleukin-13 in the genetics of asthma.

In the genetics of asthma, single genetic polymorphisms confer only a small individual risk factor. Haplotype-based association analyses, including joint analyses of several candidate genes, might therefore yield more convincing results than single-region statistics. We set out to test for joint influences of asthma genes previously identified in our study population that is acidic mammalian chitinase (AMCase), Toll-like receptor (TLR)-10, and the interleukins IL-4, IL-13, IL-8, and IL-15. In particular, we investigated whether haplotypes at two or three genes show stronger association with the trait than at a single gene alone. We genotyped 26 polymorphisms in 321 asthmatic children and 270 controls. Haplotype-based association analyses were performed by the program FAMHAP. Single-, two-, and three-gene analyses were conducted as well as conditional analyses for pairs of genes. In the two-region analyses, best evidence was found for a joint effect on asthma for AMCase and IL-4 (p(raw) < 5 x 10(-7)) as well as AMCase and IL-13 (p(raw) = 5 x 10(-7)). Besides, IL-13 and TLR-10 showed a stronger two-gene result (p(raw) = 0.001607) than the respective single-gene analyses. Conditional analyses yielded similar results for these two-gene combinations and also revealed mutual additional effects for IL-13 and IL-4 (p(stratified) = 0.014831 and 0.001525, respectively). The most significant results demonstrate a joint effect of AMCase with IL-4 or IL-13 on the trait. Furthermore, additional mutual effects were seen for AMCase and IL-4 as well as for TLR-10 and IL-13. The corresponding pathways might therefore be of particular importance in the genetics of asthma. Further studies are needed to elucidate the functional importance of these gene-gene effects and their precise role in asthma pathogenesis.

Polymorphisms of toll like receptors in the genetics of severe RSV associated diseases.

Toll like receptors (TLRs) are an essential part of the innate immune response. So far, ten different TLRs were identified in humans. They recognize a wide range of microbial and viral pathogens. Infection by respiratory syncytial virus (RSV) is still a major health problem, about 2% of all children are hospitalised due to RSV bronchiolitis during their first 2 years of live. TLR4 has already been described in association with RSV associated diseases by us and others. Thus we were interested whether other TLRs are also involved in the genetics of severe RSV infection. We genotyped 19 polymorphisms in the autosomal TLRs, these are TLR1, 2, 3, 5, 6, 9 and 10. Association analyses by the Armitage's Trend test revealed weak association of one TLR9 promoter polymorphism with RSV infection (p = 0.013). In addition, association was found with TLR10 haplotypes (p = 0.024). We conclude from our data--that--although we can not rule out a minor involvement of TLR9 polymorphism and TLR10 haplotypes--TLRs other than TLR4 do not play a major role in the genetics of severe RSV associated diseases. Future studies should focus on additional genes of the innate immune response.

Polymorphisms of interferons and their receptors in the genetics of severe RSV-associated diseases.

Because of their important role in the pathophysiology of severe RSV infection, IFNs represent an ideal group of candidate genes for determining RSV disease severity. We studied 14 polymorphisms within 7 genes involved in IFNs signalling. Our study populations consisted of 156 infants with severe RSV infection and 296 healthy control children. None of the genes showed association with severe RSV infection in children. Thus, despite the involvement of different IFNs in the pathophysiology of RSV infection, genetic variants in IFNG and related genes might not alter the risk for the development of severe RSV-associated diseases.

Association study of mitochondrial genetic polymorphisms in asthmatic children.

It has been suggested that mitochondrial dysfunction plays a role in the pathogenesis of asthma. To test whether mitochondrial variants influence the risk of asthma, we analyzed 16,158 mtSNPs in a sample of 372 asthmatic children and 395 healthy children using the DNA pooling technique and genome wide association analysis. Stratified analysis by sex was performed to explain the differences observed between sexes in the etiology of asthma. Different variants were detected to be significant in the sample of girls and boys with the smallest adjusted p values being 1.4 × 10(-09) (mt5295) and 3.6 × 10(-12) (mt16158), respectively. Most of the significant locations found in boys are within the CYB gene and the non-coding region. For girls, most of the significant mtSNPs lie within NADH-dehydrogenase-subunits. The variants reported here have not previously been described in connection with asthma. Although further studies in other cohorts are needed to confirm these findings our study highlights the importance of the mitochondria among the factors that contribute to the risk of asthma.

Association of a FGFR-4 gene polymorphism with bronchopulmonary dysplasia and neonatal respiratory distress.

BACKGROUND: Bronchopulmonary dysplasia (BPD) is the most common chronic lung disease of premature birth, characterized by impaired alveolar development and inflammation. Pathomechanisms contributing to BPD are poorly understood. However, it is assumed that genetic factors predispose to BPD and other pulmonary diseases of preterm neonates, such as neonatal respiratory distress syndrome (RDS). For association studies, genes upregulated during alveolarization are major candidates for genetic analysis, for example, matrix metalloproteinases (MMPs) and fibroblast growth factors (FGFs) and their receptors (FGFR). OBJECTIVE: Determining genetic risk variants in a Caucasian population of premature neonates with BPD and RDS. Methods. We genotyped 27 polymorphisms within 14 candidate genes via restriction fragment length polymorphism (RFLP): MMP-1, -2, -9, and -12, -16, FGF receptors 2 and 4, FGF-2, -3, -4, -7, and -18, Signal-Regulatory Protein α (SIRPA) and Thyroid Transcription Factor-1 (TTF-1). RESULTS: Five single nucleotide polymorphisms (SNPs) in MMP-9, MMP-12, FGFR-4, FGF-3, and FGF-7 are associated (P < 0.05) with RDS, defined as surfactant application within the first 24 hours after birth. One of them, in FGFR-4 (rs1966265), is associated with both RDS (P = 0.003) and BPD (P = 0.023). CONCLUSION: rs1966265 in FGF receptor 4 is a possible genetic key variant in alveolar diseases of preterm newborns.

Genetic and epidemiological risk factors in the development of bronchopulmonary dysplasia.

Bronchopulmonary dysplasia (BPD) is the chronic lung disease of preterm infants and still represents a major burden of prematurity. Several clinical risk factors for the onset of the disease are already known. In addition, some candidate genes have recently been identified. We set out to determine clinical as well as genetic risk factors for the development of BPD in the German population. 155 infants born with a gestational age < or = 28 at the tertiary neonatal Centre, Freiburg, were recruited. Clinical data were recorded from hospital charts. 47 children developed moderate or severe BPD. For genetic analyses, 37 polymorphisms within sixteen genes were genotyped on all children. The strongest epidemiological risk factor for BPD was birth weight, followed by low gestational age. Genetic association was detected with single polymorphisms within Tumour necrosis factor alpha, Toll like receptor 10 and vascular endothelial growth factor. The former two genes showed also association with BPD in haplotype analyses. In conclusion, association of BPD was far more convincingly found with a few clinical factors than with genetic polymorphisms. This underscores the genetic complexity of the disease. Furthermore, the identification of predisposing genetic polymorphisms might be hampered by the complex interaction between clinical and genetic factors.

Respiratory syncytial virus bronchiolitis and asthma - insights from recent studies and implications for therapy.

Infection with respiratory syncytial virus (RSV) is a leading cause of upper and lower respiratory tract infection in infants. It is accompanied by a considerably disease burden and a hospitalisation rate of up to 3% in infected infants. Besides, it is still a matter of intensive discussion whether severe RSV infection in early infancy causes the development of asthma later in live or whether RSV bronchiolitis just chronologically precedes asthma in children who are susceptible to asthma. The latter could be due to a common genetic background of both diseases predisposing to an exaggerated inflammatory response of the lungs to allergens and pathogens. Genetic studies might help to elucidate the mechanisms leading to both diseases and to highlight common as well as diverse pathways. The results of such investigations will influence the current understanding of the diseases and might even change our therapeutical approaches to both disorders. This review summarizes current findings in the genetics of bronchial asthma and severe RSV bronchiolitis. The question whether a relationship exists between severe RSV bronchiolitis in infancy and childhood asthma will also be discussed by taking recent epidemiological studies in account. A special focus is laid on the implications of these findings for a targeted drug therapy of both diseases.

Association of interleukin-13/-4 and toll-like receptor 10 with preterm births.

BACKGROUND: Preterm birth (PTB) is accompanied by an increased neonatal morbidity. The cause of PTB is multifactorial and the interplay between environmental and genetic factors - of mothers and newborns - determines the risk. OBJECTIVES: We were interested to identify fetal genes predisposing to PTB in the German population. METHODS: We started our study by screening 31 polymorphisms within 15 genes of 121 preterm infants born below 32 gestational weeks and 270 healthy controls. Genotyping was performed by restriction fragment length polymorphism. Statistical analyses used Armitage's trend test for single polymorphisms and FAMHAP for calculation of haplotypes. RESULTS: No single polymorphism showed association with PTB; however, haplotypes of interleukin (IL)-13/IL-4 and Toll-like receptor (TLR)-10 were associated (p = 0.0001 and p = 0.0011, respectively). The association was further confirmed in an extended population of a total of 164 preterm infants. Furthermore, one polymorphism in IL-13 showed a weak association with PTB in this population (p = 0.031). Finally, we analyzed whether the cause of PTB, i.e. medically indicated cesarean section versus spontaneous PTB, affects association results and found evidence in favor of a separate analysis of both groups. CONCLUSIONS: IL-13/IL-4 and TLR-10 might be involved in the genetics of PTB. The dissection of the genetic background may provide a deeper understanding of the pathophysiology of PTB and help to identify new drug targets for its prevention.