Dorret Boomsma, Andreas Busjahn and Leena Peltonen
Nature Reviews Genetics 2002;3:872-882

Twin studies have been a valuable source of information about the genetic basis of complex traits. To maximize the potential of twin studies, large, worldwide registers of data on twins and their relatives have been established. Here, we provide an overview of the current resources for twin research. These can be used to obtain insights into the genetic epidemiology of complex traits and diseases, to study the interaction of genotype with sex, age and lifestyle factors, and to study the causes of co-morbidity between traits and diseases. Because of their design, these registers offer unique opportunities for selected sampling for quantitative trait loci linkage and association studies.

Genetic Influences on Baroreflex Function in Normal Twins
Tank, J.; Jordan, J.; Diedrich, A.; Stoffels, M.; Franke, G.; Faulhaber, H. D.; Luft, F. C.; Busjahn, A.
Hypertension. 2001; 37 (3):907-910

Blood pressure and heart rate are strongly influenced by genetic factors; however, despite the pivotal role of genetics in short-term cardiovascular regulation, little is known about the genetic contribution to baroreflex function. We assessed genetic influence on baroreflex sensitivity (BRS) in 149 twin pairs (88 monozygotic of age 33+/-13 years and BMI 23+/-4 kg/m(2) and 61 dizygotic of age 33+/-11 years and BMI 24+/-4 kg/m(2)). ECG and finger arterial blood pressures were measured continuously under resting conditions. BRS values were calculated by use of cross-spectral analysis (baroreflex slope calculated as mean value of transfer function between systolic blood pressure and the R-R interval in the low-frequency band [BRSLF] and baroreflex slope calculated as the mean value of transfer function between systolic blood pressure and R-R interval in the respiratory frequency band [BRSHF]) and the sequence technique (BRS+, BRS-). Heritability (h(2)) was estimated with a path-modeling approach. BRS values did not differ significantly between groups (monozygotic, BRSLF, 17+/-13; BRSHF, 21+/-18; BRS+, 19+/-16; and BRS-, 21+/-15, and dizygotic, BRSLF, 16+/-9; BRSHF, 20+/-14; BRS+, 18+/-10; and BRS-, 20+/-11 ms/mm Hg), and were significantly correlated (P:<0.001). When variances and covariances for monozygotic and dizygotic twins were compared, significant correlations were found for BRS in monozygotic (range, r=0.38 to 0.48) but not in dizygotic twin pairs (r=-0.03 to 0.09). Thus, BRS is heritable; the variability can be explained by genetic influences (P:<0.01; h(2) range, 0.36 to 0.44). The genetic influence on BRS remained strong after correction for BMI and blood pressure. Therefore, BRS is strongly genetically determined, probably by different genes than are resting blood pressure and BMI.

beta-2 adrenergic receptor gene variations and blood pressure under stress in normal twins
Guo-Hua Li; Faulhaber H-D.; Rosenthal, M.; Schuster, H.; Jordan, J.; Timmermann B.; Hoehe M.R.; Luft F.C.; Busjahn, A.
Psychophysiology, 2001; 38 485-489

We tested the hypothesis that blood pressure (BP) responses to physical and mental stress are associated with polyphormisms in the beta-2 adrenergic receptor (AR) gene. We studied normotensive, young, monozygotic (MZ) and dizygotic (DZ) twins. The subjects underwent automated BP measurements at the brachial and digital arteries and were subjected to mental arithmetic and cold pressor stress. We used allele-specific PCR to genotype four single nucleotide polymorphisms in the beta-2 AR gene. The most functionallly relevant polymorphism in the beta-2 AR gene, Arg 16/Gly, was associated with systolic and diastolic BP under resting conditions, during mental arithmetic, and during the cold pressor test, as well as with the increase in diastolic BP during both forms of stress. These findings support a role for the beta-2 AR gene in BP regulation. They also indicate that the beta-2 AR gene influences the level of not only resting but also stress-related BP.