Sibling recurrence risk ratio analysis of the metabolic syndrome and its components over time

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Abstract
Background: The purpose of this study was to estimate both cross-sectional sibling recurrence risk ratio (λ s ) and lifetime λ s for the metabolic syndrome and its individual components over time among sibships in the prospectively followed-up cohorts provided by the Genetic Analysis Workshop 13. Five measures included in the operational criteria of the metabolic syndrome by the Adult Treatment Panel III were examined. A method for estimating sibling recurrence risk with correction for complete ascertainment was used to estimate the numerator, and the prevalence in the whole cohort was used as the denominator of λ s . Results: Considerable variability in the λ s was found in terms of different time-points for the cross-sectional definition, the times of fulfilling the criterion for lifetime definition, and different components. Obesity and hyperglycemia had the highest cross-sectional λ s of the five components. Both components also had the largest slopes in the linear trend of the lifetime λ s . However, the magnitudes of the lifetime λ s were similar to that of the mean cross-sectional λ s , which were s of the metabolic syndrome and its components varies substantially across time, and the λ s of lifetime diagnosis was not necessarily larger than that of a cross-sectional diagnosis. The magnitude of λ s does not predict well the maximum LOD score of linkage analysis.