Heritability of Venous Function in Humans
Marina Brinsuk, Jens Tank, Friedrich C. Luft, Andreas Busjahn, Jens Jordan
Arterioscler Thromb Vasc Biol. 2004;24:207-211

OBJECTIVE: Venous function contributes to the pathogenesis of thrombophlebitis, venous thrombosis, and possibly to arterial hypertension. Venous disease is presumably heritable; however, the genetic variance of venous function is unknown.
METHODS AND RESULTS: We determined the heritability of venous function in 46 twin pairs (24 monozygotic, age 35+/-11 years, 14 men, 34 women; 22 dizygotic, age 30+/-8 years, 19 men, 25 women). After a resting phase in the supine position, we determined venous function in both legs by impedance plethysmography. Venous capacity was determined by a standardized protocol. In addition, we obtained venous pressure volume curves by slowly deflating a thigh cuff from 60 to 0 mm Hg. Venous compliance was determined as the steepest part of the venous pressure volume curve. Heritability was estimated using a path modeling approach. Unadjusted heritability was 0.6 (P<0.05) for venous capacity and 0.9 (P<0.05) for venous compliance. The heritability estimate for venous capacity decreased to 0.3 after adjustment for age, body mass index, and body fat. The heritability estimate for venous compliance remained essentially unchanged after adjustment for sex and age.
CONCLUSIONS: We conclude that venous function is strongly influenced by genetic factors. The genes involved may influence venous disease states.

Association of the serum and glucocorticoid regulated kinase (sgk1) gene with QT interval
Busjahn A, Seebohm G, Maier G, Toliat MR, Nurnberg P, Aydin A, Luft FC, Lang F.
Cell Physiol Biochem. 2004;14(3):135-42.

The serum and glucocorticoid inducible kinase (SGK1) is well known to up-regulate the renal epithelial Na(+) channel ENaC. Excessive SGK1 activity would be expected to cause renal Na(+) retention and blood pressure increase. Certain polymorphisms of the SGK1 gene (E8CC/CT;I6CC) are indeed associated with moderately enhanced blood pressure. We have recently disclosed another function of SGK1, i.e. the stimulation of the slowly activating K(+) channel KCNE1/KCNQ1. Among the functions of this channel is the repolarisation of cardiac myocytes. Accordingly, defective KCNE1 and/or KCNQ1 lead to long QT syndrome, a disorder causing fainting and sudden cardiac death. In the present study we demonstrate that coexpression of SGK1 in Xenopus oocytes increases KCNQ1/KCNE1 induced current without significantly altering voltage dependence, activation and deactivation kinetics. To test for the relevance of SGK1 in human cardiac repolarization, we analysed the ECG of monozygotic (MZ) (126 pairs) and dizygotic (DZ) (70 pairs) twin subjects and parents of DZ twins. The E8CC/CT;I6CC polymorphism was indeed significantly (p<0.025) associated with shortened age and gender corrected QT interval. No significant differences were observed in any other ECG parameter, including heart rate, P, PQ and QRS. We conclude that the regulation of KCNE1/KCNQ1 by SGK1 is similarly relevant for the repolarization of cardiac myocytes as for regulation of renal ENaC activity and blood pressure control.

A common polymorphism in KCNH2 (HERG) hastens cardiac repolarization
Bezzina CR, Verkerk AO, Busjahn A, Jeron A, Erdmann J, Koopmann TT, Bhuiyan ZA, Wilders R, Mannens MM, Tan HL, Luft FC, Schunkert H, Wilde AA.
Cardiovasc Res. 2003 Jul 1;59(1):27-36.

OBJECTIVE: Genetic variants of cardiac ion channels may influence cardiac repolarization. Thereby such variants may modulate the penetrance of primary electrical disorders, contribute to differences in susceptibility to drug-induced QT-prolongation between individuals, or contribute to rhythm disturbances in the context of structural heart disease. Since the current encoded by KCNH2 (HERG; I(Kr)) is a primary determinant of repolarization, we conducted association studies between the respective alleles of the common amino acid-changing polymorphism at codon 897 (2690A>C; K897T) within HERG and rate-corrected QT interval (QTc).
METHODS AND RESULTS: Association analysis in Caucasian subjects (n=1030) revealed a significant association of this polymorphism with QTc (P=0.0025) with CC homozygotes having a significantly shorter QTc (388.5+/-2.9 ms) compared to AA homozygotes (398.5+/-0.9) and heterozygotes (AC, 397.2+/-1.2). The latter two genotypes were associated with comparable mean QTc's, suggesting that the 2690C-allele is recessive. After stratification by sex, the polymorphism was more predictive of QTc in females (P=0.0021), a finding that was replicated in a second population sample (n=352) from the same ethnic background (P=0.044). To assess whether this polymorphism could represent a 'functional' polymorphism, we compared the biophysical properties of K897- and T897-HERG channels by whole-cell voltage clamp. Compared to the K897 channel, the T897 channel displayed a shift of -7 mV in voltage dependence of activation and increased rates of current activation and deactivation.
CONCLUSION: As confirmed in modeling studies, these changes are expected to shorten action potential duration by an increase in I(Kr). This recapitulates the shorter QTc in females homozygous for the 2690C-allele.