In the past three decades, scientists have had immense success in identifying genes and their variants that contribute to an array of diseases. While the identification of such genetic variants has informed our knowledge of the etiologic bases of diseases, there continues to be a substantial gap in our understanding of the factors that modify disease severity. Monogenic diseases provide an opportunity to identify modifiers as they have uniform etiology, detailed phenotyping of affected individuals, and familial clustering. Cystic fibrosis (CF) is among the more common life-shortening recessive disorders that displays wide variability in clinical features and survival. Considerable progress has been made in elucidating the contribution of genetic and nongenetic factors to CF. Allelic variation in CFTR, the gene responsible for CF, correlates with some aspects of the disease. However, lung function, neonatal intestinal obstruction, diabetes, and anthropometry display strong genetic control independent of CFTR, and candidate gene studies have revealed genetic modifiers underlying these traits. The application of genome-wide techniques holds great promise for the identification of novel genetic variants responsible for the heritable features and complications of CF. Since the genetic modifiers are known to alter the course of disease, their protein products become immediate targets for therapeutic intervention.

The cystic fibrosis transmembrane conductance regulator (CFTR) and Calcium-activated Chloride Conductance (CaCC) each play critical roles in maintaining normal hydration of epithelial surfaces including the airways and colon. TGF-beta is a genetic modifier of cystic fibrosis (CF), but how it influences the CF phenotype is not understood.

Recently, genetic pathways that modify the clinical severity of Duchenne muscular dystrophy (DMD) have been identified. The pathways uncovered as modifiers are useful to predict prognosis and also elucidate molecular signatures that can be manipulated therapeutically.

Liver disease is increasingly common in cystic fibrosis (CF). As new therapeutic options emerge, life expectancy increases and common hepatobiliary manifestations impact on quality of life and survival of CF patients. Hepatobiliary abnormalities in CF vary in nature and range from defects attributable to the underlying CFTR gene defect to those related to systemic disease and malnutrition. Today complications of liver disease represent the third most frequent cause of disease-related death in patients with CF. Here we review molecular and clinical genetics of CF, including genetic modifiers of CF-associated liver disease, and provide practical recommendations for genetic testing, diagnosis and treatment of hepatobiliary manifestations in CF.

Cystic fibrosis (CF) is usually considered a rare disease in the Indian population. Two studies have reported on the frequency of cystic fibrosis transmembrane conductance regulator (CFTR) gene mutations in Indian males with congenital absence of the vas deferens (CAVD), however, data on the spectrum of CFTR gene mutations are still lacking. Therefore, the present study was designed to identify the spectrum of CFTR gene mutations as well as to investigate an association of CF genetic modifiers in the penetrance of CAVD in infertile Indian men. A total of 60 consecutive infertile males with a diagnosis of CAVD were subjected to CFTR gene analysis which revealed 13 different CFTR gene mutations and 1 intronic variant that led to aberrant splicing. p.Phe508del (n = 16) and p.Arg117His (n = 4) were among the most common severe forms of CFTR mutations identified. The IVS8-T5 allele, which is considered as a mild form of CFTR mutation, was found with an allelic frequency of 28.3%. Eight novel mutations were also identified in the CFTR gene from our patient cohort. It is noteworthy that the spectrum of CFTR gene mutation is heterogeneous, with exon 4 and exon 11 as hot spot regions. Moreover, we also found an association of the CF genetic modifiers, viz., transforming growth factor (TGF)-β1 and endothelial receptor type-A (EDNRA) genes with the CAVD phenotype. The findings are of considerable clinical significance because men suffering from infertility due to CAVD can decide to use artificial reproduction technology. The children of men with CAVD are at risk of carrying CFTR mutations; therefore, genetic counseling is a crucial step for such patients. With special reference to developing countries, such as India, where whole gene sequencing is not feasible, the outcome of our study will make the screening procedure for CFTR gene simpler and more cost-effective as we have identified hot spot regions of the CFTR gene which are more prone to mutation in Indian males with CAVD. Moreover, this is the first study from the Indian population to investigate the association of CF genetic modifiers with penetrance of the CAVD phenotype. The observed association of the genetic modifiers TGF-β1 and EDNRA in the penetrance of CAVD further supports their involvement in genesis of the vas deferens.

The mechanisms responsible for the determination of phenotypes are still not well understood; however, it has become apparent that modifier genes must play a considerable role in the phenotypic heterogeneity of Mendelian disorders. Significant advances in genetic technologies and molecular medicine allow huge amounts of information to be generated from individual samples within a reasonable time frame. This review focuses on the role of modifier genes using the example of cystic fibrosis, the most common lethal autosomal recessive disorder in the white population, and discusses the advantages and limitations of candidate gene approaches versus genome-wide association studies. Moreover, the implications of modifier gene research for other monogenic disorders, as well as its significance for diagnostic, prognostic, and therapeutic approaches are summarized. Increasing insight into modifying mechanisms opens up new perspectives, dispelling the idea of genetic disorders being caused by one single gene.

The clinical course of cystic fibrosis (CF) varies considerably among patients carrying the same CF-causing gene mutation. Additional genetic modifiers may contribute to this variability. As airway inflammation is a key component of CF pathophysiology, we investigated whether major cytokine variants represent such modifiers in young CF patients. We tested 13 polymorphisms in 8 genes that play a key role in the inflammatory response: tumor necrosis factor, lymphotoxin alpha, interleukin (IL) 1B, IL1 receptor antagonist, IL6, IL8, IL10 and transforming growth factor beta 1 (TGFB1), for an association with lung disease progression and nutritional status in 329 CF patients. Variants in the TGFB1 gene at position +869T/C demonstrated a significant association with lung function decline. A less pronounced rate of decline in forced expiratory volume in 1 sec (FEV(1)) and forced vital capacity (FVC) were observed in patients heterozygous for TGFB1 +869 (+869CT), when compared to patients carrying either TGFB1 +869TT or +869CC genotypes. These findings support the concept that TGFB1 gene variants appear to be important genetic modifiers of lung disease progression in CF.

OBJECTIVE:To identify associations between genetic polymorphisms (in the MBL2, TGF-beta1 and CD14 genes) and the severity of the lung disease in patients with cystic fibrosis (CF), as well as between the presence of DeltaF508 alleles and lung disease severity in such patients. METHODS:This was a cross-sectional cohort study, based on clinical and laboratory data, involving 105 patients with CF treated at a university hospital in the 2005-2006 period. We included 202 healthy blood donors as controls for the determination of TGF-beta1 and CD14 gene polymorphisms. Polymorphisms in the MBL2 and TGF-beta1 genes at codon 10, position +869, were genotyped using the allele-specific PCR technique. The C-159T polymorphism in the CD14 gene was genotyped using PCR and enzymatic digestion. RESULTS:Of the 105 CF patients evaluated, 67 presented with severe lung disease according to the Shwachman score. The MBL2 gene polymorphisms were not associated with disease severity in the CF patients. Analysis of the T869C polymorphism in the TGF-beta1 gene showed an association only between TC heterozygotes and mild pulmonary disease. Although patients presenting the TT genotype of the C159T polymorphism in the CD14 gene predominated, there was no significant difference regarding lung disease severity. CONCLUSIONS:There was an association between the TC genotype of the T869C polymorphism (TGF-beta1) and mild pulmonary disease in CF patients. In the CD14 gene, the TT genotype seems to be a risk factor for pulmonary disease but is not a modulator of severity. We found no association between being a DeltaF508 homozygote and presenting severe lung disease.

Cystic fibrosis (CF) is the most common lethal autosomal recessive disorder in the Caucasian population, affecting about 30,000 individuals in the United States. The gene responsible for CF, the CF transmembrane conductance regulator (CFTR), was identified 15 years ago. Substantial variation in the many aspects of the CF phenotype among individuals with the same CFTR genotype demonstrates that factors independent of CFTR exert considerable influence on outcome in CF. To date, the majority of published studies investigating the cause of disease variability in CF report associations between candidate genes and some aspect of the CF phenotype. However, a definitive modifier gene for CF remains to be identified. Despite the challenges posed by searches for modifier effects, studies of affected twins and siblings indicate that genetic factors play a substantial role in intestinal manifestations. Identifying the factors contributing to variation in pulmonary disease, the primary cause of mortality, remains a challenge for CF research.

Cystic fibrosis (CF), the most common lethal single gene disorder in Caucasians, is due to mutations in the CFTR gene. Twin and sibling analysis indicates that modifier genes, rather than allelic variation in CFTR, are responsible for most of the variability in severity of lung disease, the major cause of mortality in CF patients. We used a family-based approach to test for association between lung function and two functional SNPs (rs1800469, '-509' and rs1982073, 'codon 10') in the 5' region of transforming growth factor-beta1 (TGFB1), a putative CF modifier gene. Quantitative transmission disequilibrium testing of 472 CF patient-parent-parent trios revealed that both TGFB1 SNPs showed significant transmission distortion when patients were stratified by CFTR genotype. Although lung function and nutritional status are correlated in CF patients, there was no evidence of association between the TGFB1 SNPs and variation in nutritional status. Additional tagging SNPs (rs8179181, rs2278422, rs8110090, rs4803455 and rs1982072) that capture most of the diversity in TGFB1 were also typed but none showed association with variation in lung function. However, a haplotype composed of the -509 C and codon 10 T alleles along with the C allele of the 3' SNP rs8179181 was highly associated with increased lung function in patients grouped by CFTR genotype. These results demonstrate that TGFB1 is a modifier of CF lung disease and reveal a previously unrecognized beneficial effect of TGFB1 variants upon the pulmonary phenotype.

Polymorphisms in genes other than the cystic fibrosis transmembrane conductance regulator (CFTR) gene may modify the severity of pulmonary disease in patients with cystic fibrosis.

Polymorphisms in transforming growth factor (TGF)-beta(1) associated with variations in cytokine levels are linked to fibrosis in a number of tissues. However, the contribution of this cytokine to organ fibrosis in patients with cystic fibrosis is presently unclear. This study was undertaken to examine the association between TGF-beta(1) gene polymorphisms and the development of pulmonary dysfunction in patients with cystic fibrosis.

Previously, several polymorphisms in TGFB1 have been identified in non-small-cell lung cancer (NSCLC), and the variants, C-509T, T869C, and G915C, have been demonstrated to associate with higher circulating levels of TGF-β1. However, little is known about the prognostic value of TGF-β1 polymorphisms in cancers. In this study, by genotyping the TGF-β1 T869C polymorphism in a total of 261 patients with NSCLC using DNA from blood lymphocytes, we first found that NSCLC patients, especially those with allele C carriers, had significantly higher serum TGF-β1 levels than healthy individuals. By using chi-square (χ2) test and Fisher's exact test, we noticed that TC/CC genotypes were positively correlated with smoking, clinical TNM stage, lymph node, and distant metastasis in NSCLC patients. Kaplan-Meier analysis showed that patients with TT genotype had a better overall survival than the allele C carriers (TC + CC). Finally, multivariate analysis confirmed histology, lymph node, and distant metastasis but not T869C polymorphism as independent prognostic factors for NSCLC. Taken together, our data, as a proof of principle, suggest that T869C polymorphism in TGFB1 may act as a genetic modifier in NSCLC progression and a promising prognostic marker of survival in NSCLC patients.

Multiple investigators have undertaken genetic studies in idiopathic pulmonary fibrosis populations in attempts to define genetic links to disease in hopes that this would improve understanding of disease pathogenesis and target pathways for therapy. Multiple genes have been evaluated using a candidate gene approach with limited success, with results suggesting a disease modifier effect rather than a disease causing effect. Using this approach, associations have been observed between idiopathic pulmonary fibrosis and specific polymorphisms in genes encoding interleukin-1 receptor antagonist, tumor necrosis factor-alpha, and complement receptor 1. Recently investigators have used familial pulmonary fibrosis cohorts to evaluate for genetic mutations associated with idiopathic pulmonary fibrosis. Using one pulmonary fibrosis kindred, a mutation in the gene encoding surfactant protein C was identified as the cause of pulmonary fibrosis in this family. Subsequently, another individual with idiopathic pulmonary fibrosis was identified with a different mutation in surfactant protein C. Though rarely found in patients with idiopathic pulmonary fibrosis, these surfactant protein C mutations highlight the importance of the alveolar epithelium in disease pathogenesis. A recent collaboration between investigators at three major centers has resulted in the largest collection of families with pulmonary fibrosis to date, with hopes that this effort will identify genetic mutations associated with idiopathic pulmonary fibrosis. If genetic links to idiopathic pulmonary fibrosis are defined in this study, then the pathways involved with these genes and gene products can be targeted by investigators to help identify potential treatment options for this disease.

Cystic fibrosis (CF), the most common lethal single gene disorder in Caucasians, is due to mutations in the CFTR gene. Twin and sibling analysis indicates that modifier genes, rather than allelic variation in CFTR, are responsible for most of the variability in severity of lung disease, the major cause of mortality in CF patients. We used a family-based approach to test for association between lung function and two functional SNPs (rs1800469, '-509' and rs1982073, 'codon 10') in the 5' region of transforming growth factor-beta1 (TGFB1), a putative CF modifier gene. Quantitative transmission disequilibrium testing of 472 CF patient-parent-parent trios revealed that both TGFB1 SNPs showed significant transmission distortion when patients were stratified by CFTR genotype. Although lung function and nutritional status are correlated in CF patients, there was no evidence of association between the TGFB1 SNPs and variation in nutritional status. Additional tagging SNPs (rs8179181, rs2278422, rs8110090, rs4803455 and rs1982072) that capture most of the diversity in TGFB1 were also typed but none showed association with variation in lung function. However, a haplotype composed of the -509 C and codon 10 T alleles along with the C allele of the 3' SNP rs8179181 was highly associated with increased lung function in patients grouped by CFTR genotype. These results demonstrate that TGFB1 is a modifier of CF lung disease and reveal a previously unrecognized beneficial effect of TGFB1 variants upon the pulmonary phenotype.

Polymorphisms in transforming growth factor (TGF)-beta(1) associated with variations in cytokine levels are linked to fibrosis in a number of tissues. However, the contribution of this cytokine to organ fibrosis in patients with cystic fibrosis is presently unclear. This study was undertaken to examine the association between TGF-beta(1) gene polymorphisms and the development of pulmonary dysfunction in patients with cystic fibrosis.

Liver disease is increasingly common in cystic fibrosis (CF). As new therapeutic options emerge, life expectancy increases and common hepatobiliary manifestations impact on quality of life and survival of CF patients. Hepatobiliary abnormalities in CF vary in nature and range from defects attributable to the underlying CFTR gene defect to those related to systemic disease and malnutrition. Today complications of liver disease represent the third most frequent cause of disease-related death in patients with CF. Here we review molecular and clinical genetics of CF, including genetic modifiers of CF-associated liver disease, and provide practical recommendations for genetic testing, diagnosis and treatment of hepatobiliary manifestations in CF.

Cystic fibrosis (CF) is usually considered a rare disease in the Indian population. Two studies have reported on the frequency of cystic fibrosis transmembrane conductance regulator (CFTR) gene mutations in Indian males with congenital absence of the vas deferens (CAVD), however, data on the spectrum of CFTR gene mutations are still lacking. Therefore, the present study was designed to identify the spectrum of CFTR gene mutations as well as to investigate an association of CF genetic modifiers in the penetrance of CAVD in infertile Indian men. A total of 60 consecutive infertile males with a diagnosis of CAVD were subjected to CFTR gene analysis which revealed 13 different CFTR gene mutations and 1 intronic variant that led to aberrant splicing. p.Phe508del (n = 16) and p.Arg117His (n = 4) were among the most common severe forms of CFTR mutations identified. The IVS8-T5 allele, which is considered as a mild form of CFTR mutation, was found with an allelic frequency of 28.3%. Eight novel mutations were also identified in the CFTR gene from our patient cohort. It is noteworthy that the spectrum of CFTR gene mutation is heterogeneous, with exon 4 and exon 11 as hot spot regions. Moreover, we also found an association of the CF genetic modifiers, viz., transforming growth factor (TGF)-β1 and endothelial receptor type-A (EDNRA) genes with the CAVD phenotype. The findings are of considerable clinical significance because men suffering from infertility due to CAVD can decide to use artificial reproduction technology. The children of men with CAVD are at risk of carrying CFTR mutations; therefore, genetic counseling is a crucial step for such patients. With special reference to developing countries, such as India, where whole gene sequencing is not feasible, the outcome of our study will make the screening procedure for CFTR gene simpler and more cost-effective as we have identified hot spot regions of the CFTR gene which are more prone to mutation in Indian males with CAVD. Moreover, this is the first study from the Indian population to investigate the association of CF genetic modifiers with penetrance of the CAVD phenotype. The observed association of the genetic modifiers TGF-β1 and EDNRA in the penetrance of CAVD further supports their involvement in genesis of the vas deferens.

Cystic fibrosis (CF) is the most common lethal autosomal recessive disorder in the Caucasian population, affecting about 30,000 individuals in the United States. The gene responsible for CF, the CF transmembrane conductance regulator (CFTR), was identified 15 years ago. Substantial variation in the many aspects of the CF phenotype among individuals with the same CFTR genotype demonstrates that factors independent of CFTR exert considerable influence on outcome in CF. To date, the majority of published studies investigating the cause of disease variability in CF report associations between candidate genes and some aspect of the CF phenotype. However, a definitive modifier gene for CF remains to be identified. Despite the challenges posed by searches for modifier effects, studies of affected twins and siblings indicate that genetic factors play a substantial role in intestinal manifestations. Identifying the factors contributing to variation in pulmonary disease, the primary cause of mortality, remains a challenge for CF research.

Epidemiological evidence has shown two polymorphisms (namely RS#1800468G>A and RS#1800471G>C) of transforming growth factor-beta 1 (TGF-β1) gene may be involved in the cancer development. However, their role in the carcinogenic process of esophageal squamous cell carcinoma (ESCC) has been less well elaborated. We conducted a hospital-based case-control study including 391 ESCC cases and 508 controls without any evidence of tumors to evaluate the association between these two polymorphisms and ESCC risk and prognosis for Zhuangese population by means of polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and amplification refractory mutation system (ARMS)-PCR techniques. We found that individuals with the genotypes with RS#1800471 C allele (namely RS#1800471-GC or -CC) had an increased risk of ESCC than those without above genotypes (namely RS#1800471-GG, adjusted odds ratio 3.26 and 5.65, respectively). Further stratification analysis showed that this polymorphism was correlated with tumor histological grades and TNM (tumor, node, and metastasis) stage, and modified the serum levels of TGF-β1. Additionally, RS#1800471 polymorphism affected ESCC prognosis (hazard ratio, 3.40), especially under high serum levels of TGF-β1 conditions. However, RS#1800468 polymorphism was not significantly related to ESCC risk. These findings indicated that TGF-β1 RS#1800471G>C polymorphism may be a genetic modifier for developing ESCC in Zhuangese population.

Cystic fibrosis (CF), the most common lethal single gene disorder in Caucasians, is due to mutations in the CFTR gene. Twin and sibling analysis indicates that modifier genes, rather than allelic variation in CFTR, are responsible for most of the variability in severity of lung disease, the major cause of mortality in CF patients. We used a family-based approach to test for association between lung function and two functional SNPs (rs1800469, '-509' and rs1982073, 'codon 10') in the 5' region of transforming growth factor-beta1 (TGFB1), a putative CF modifier gene. Quantitative transmission disequilibrium testing of 472 CF patient-parent-parent trios revealed that both TGFB1 SNPs showed significant transmission distortion when patients were stratified by CFTR genotype. Although lung function and nutritional status are correlated in CF patients, there was no evidence of association between the TGFB1 SNPs and variation in nutritional status. Additional tagging SNPs (rs8179181, rs2278422, rs8110090, rs4803455 and rs1982072) that capture most of the diversity in TGFB1 were also typed but none showed association with variation in lung function. However, a haplotype composed of the -509 C and codon 10 T alleles along with the C allele of the 3' SNP rs8179181 was highly associated with increased lung function in patients grouped by CFTR genotype. These results demonstrate that TGFB1 is a modifier of CF lung disease and reveal a previously unrecognized beneficial effect of TGFB1 variants upon the pulmonary phenotype.

Polymorphisms in genes other than the cystic fibrosis transmembrane conductance regulator (CFTR) gene may modify the severity of pulmonary disease in patients with cystic fibrosis.

Liver disease is increasingly common in cystic fibrosis (CF). As new therapeutic options emerge, life expectancy increases and common hepatobiliary manifestations impact on quality of life and survival of CF patients. Hepatobiliary abnormalities in CF vary in nature and range from defects attributable to the underlying CFTR gene defect to those related to systemic disease and malnutrition. Today complications of liver disease represent the third most frequent cause of disease-related death in patients with CF. Here we review molecular and clinical genetics of CF, including genetic modifiers of CF-associated liver disease, and provide practical recommendations for genetic testing, diagnosis and treatment of hepatobiliary manifestations in CF.

In this work, we are interested to study the implication of -509C/T polymorphism, located in the promoter region of TGFB1 (transforming growth factor β1), in the phenotypic variability of CF patients.

The mechanisms responsible for the determination of phenotypes are still not well understood; however, it has become apparent that modifier genes must play a considerable role in the phenotypic heterogeneity of Mendelian disorders. Significant advances in genetic technologies and molecular medicine allow huge amounts of information to be generated from individual samples within a reasonable time frame. This review focuses on the role of modifier genes using the example of cystic fibrosis, the most common lethal autosomal recessive disorder in the white population, and discusses the advantages and limitations of candidate gene approaches versus genome-wide association studies. Moreover, the implications of modifier gene research for other monogenic disorders, as well as its significance for diagnostic, prognostic, and therapeutic approaches are summarized. Increasing insight into modifying mechanisms opens up new perspectives, dispelling the idea of genetic disorders being caused by one single gene.