Increased arterial stiffness is a main determinant in the pathogenesis of hypertension and is a strong, independent predictor of cardiovascular events and mortality. Arterial stiffness is defined by a reduction in arterial distensibility and influences the speed of travel of the cardiac pulse wave. Carotid -femoral pulse wave velocity (PWV) is used clinically as a non-invasive measurement of arterial stiffness. Several studies have shown a substantial heritability of blood-pressure and arterial-stiffness, what suggests important genetic contributions (4, 5). Recently, genome wide association studies investigated the genetic component of pulse wave velocity.

There is limited information on the development of arterial stiffness and pulse wave velocity in healthy, community-based children. There is increased interest not only in the conventional environmental factors influencing the early vascular phenotype, but also in genetic influences. This study proposes a genome wide association study on pulse wave velocity in children ages 5 -10 years.

In two large population-based cohort studies, ALSPAC and Generation R, pulse wave velocity is measured in children at the ages of 5 years and 9 years. Both studies will genotype several SNP's and perform genome wide association studies on this phenotype, adjusted for gender and age at visit. Because ALSPAC and Generation R are the only cohorts with these data, combined analysis will be conducted to increase the number of available samples. Analysis will be performed as part of the EAGLE consortium.

Analysis Plan

Traits of interest

* Pulse Wave Velocity at the age of 5 years (range 60.9 - 87.1 months)

* Pulse Wave Velocity at the age of 9 years (range ...-... months)

Participating studies

* ALSPAC

* Generation R

Projected number of subjects

* PWV5: ~ 522

* PWV9: ~ #?

Genotyping + Imputation

* Genotyped SNPs (Affymetrix, Illumina, Perlegen)

* Imputation HapMap Phase II CEU SNPs. Preferred release 22 of HapMap, build 36. Predefined marker filters to apply before imputation (HWEPgreater than 10-6, MAFgreater than 0.01, SNP-callgreater than 95%). Suggestion left open to cohorts to apply specific filters but should be reported.

* Analyse all SNPs, no filtering on call rate/HWE/MAF/imputation quality (QC metrics to be reported, and filtering will be done at meta-analysis stage)

Model of association

* Additive model (SNP coded as allele dose from 0 to 2), which accounts for genotype imputation uncertainty by use of linear regression onto estimated dose (as included in MACHQTL, ProbABEL, SNPTEST), adjusting for population structure and covariates.

Data exchange

* See separate RESULTS_FORMAT file for details of results file formatting and file naming.

* Summary statistics to be uploaded to common server.

* Only summary statistics will be transferred, not individual level genotype or phenotype data.