A BIOMETRICAL STUDY OF THE RELATIONSHIP BETWEEN SODIUM-LITHIUM COUNTERTRANSPORT AND TRIGLYCERIDES

We addressed the question: Is there evidence that allelic variation in a single unmeasured gene that has a large effect on maximal activity of erythrocyte sodium-lithium countertransport (Na-Li CNT) also has pl eiotropic effects on variation in plasma triglyceride levels? Complex segregation analysis models that included plasma triglyceride levels a s a covariate were considered as explanations for interindividual vari ation in Na-Li CNT. A sample of 711 healthy adults from 254 pedigrees enrolled in the Rochester Family Heart Study was selected for this stu dy. The majority of the pedigrees supported the hypothesis that variat ions in a single unmeasured non-transmitted environmental factor have large effects on the Na-Li CNT distribution. Only gender-specific firs t-order covariate parameters were necessary in the complex segregation models suggesting that the form of the relationship between Na-Li CNT and plasma triglyceride level was not influenced by variation in the inferred environmental factor with large effects. Stratification of th e sample by this inferred environmental factor resulted in three class es of individuals with significant differences in the distributions of coronary heart disease risk factor traits, as well as interindividual variation in both Na-Li CNT and plasma triglyceride levels. These res ults, along with other observations from the Rochester Family Heart St udy sample, emphasize the complex and multifactorial nature of the cau ses of interindividual variation in Na-Li CNT. Our study further sugge sts that new research strategies are needed for studying the relations hips between genetic ic and environmental variation and variation in q uantitative traits such as Na-Li CNT that have been identified as risk factors for hypertension.