Conference: 2008 International PHA Conference and Scientific Sessions
Release Date: 06.20.2008
Presentation Type: Abstracts
Zellner C.1, 2, Liao W. 2,3, Pullinger C.R.2, Chan S.2,3, Poon A.2,3, Kwok P.2,3, Malloy M.J.2, Kane J.P. 2, McGlothlin D.1, Chatterjee K.1, DeMarco T.D.1
1. Division of Cardiology, University of California San Francisco, CA, USA
2. Cardiovascular Research Institute, University of California San Francisco, CA, USA
3. Institute of Human Genetics, University of California San Francisco, CA, USA
BACKGROUND: Idiopathic pulmonary arterial hypertension (IPAH) is a rare disease predominately affecting women and characterized by pulmonary hypertension and progressive right heart failure. IPAH is typically identified in advanced stages and treatment options are limited. Although IPAH has been associated with mutations in BMPR2 in a small number of affected families, the genetic factors predisposing to IPAH in the majority of patients are poorly understood. We hypothesized that gene variants in caveolin-1 (CAV-1) and caveolin-2 (CAV-2) could contribute to the development of IPAH. These two genes, expressed in endothelial cells and pneumocytes, encode structural proteins in caveolae, membrane invaginations that play a critical role in protein trafficking and in many signal transduction pathways. Phenotypes of CAV-1 (-/-) and CAV-2 (-/-) mice closely resemble IPAH with CAV-2 (-/-) strictly limited to a pulmonary phenotype. Both genes were studied to identify informative mutations and single nucleotide polymorphisms (SNPs).
METHODS: We screened coding, promoter and splice-sites of CAV-1 and CAV-2 using DNA from the UCSF Genomic Resource in Pulmonary Hypertension for cases and matched controls using denaturing gradient gel electrophoresis (DGGE) and direct sequencing. Cases were Caucasian patients clinically diagnosed with IPAH who underwent left and right heart catheterization, chest CT, echocardiography, and serologic testing to exclude other etiologies of pulmonary hypertension. Controls consisted of healthy Caucasian subjects from the San Francisco Bay Area without pulmonary hypertension, inflammatory autoimmune disease, or cancer. Differences in CAV-1 and CAV-2 gene allele frequency between cases and controls were analyzed using the chi-square test.
RESULTS: For CAV-1, 62 patients with IPAH and 600 unrelated controls were screened using DGGE and sequencing. Four intronic SNPs and three coding region synonymous SNPs were identified. Non-synonymous coding region or frameshift mutations were absent. Statistical analysis of CAV-1 showed no significant difference in SNP frequency between cases and controls. For CAV-2, 35 cases with IPAH and 92 controls were sequenced to identify CAV-2 SNPs. A total of 14 SNPs were identified, 12 previously identified in dbSNP and two novel SNPs. Analysis of SNP allele frequencies in cases versus controls showed that one SNP located in the 5’ UTR of exon 1 was enriched for the homozygous TT genotype (p=0.05).
COMMENTS AND CONCLUSIONS: We did not find any coding mutations in CAV-1 or CAV-2 that correlated with the IPAH phenotype. However, we identified a SNP in the 5’ UTR of CAV-2 that was nominally associated with IPAH (p=0.05). Because this polymorphism could affect transcriptional regulation, the significance of this SNP will be tested in a larger independent cohort of patients with IPAH. Correlation of this SNP with clinical data such as invasive hemodynamics and cardiac imaging will be done to identify possible mechanisms by which this gene variant may contribute to the PAH phenotype.