Ke Won Kang

Genetic Factors in Determining Bone Mass

This investigation was undertaken to evaluate possible genetic determinants of bone mass with the premise that inheritance of bone mass could be of etiologic importance in osteoporosis. Bone mass and width measurements were made with the photon absorption technique on the right radius of 71 juvenile and 80 adult twin paris. The variance of intrapair differences of bone mass in monozygotic (MZ) juvenile twins was 0.0013 g(2)/cm(2) compared to 0.0052 g(2)/cm(2) in the dizygotic (DZ) twins. For the adult twins the variance of intrapair differences in bone mass was 0.0069 for MZ and 0.0137 for DZ twins. Similar results were obtained for bone width. The significantly larger variation in intrapair differences in DZ twins indicates that these traits have significant genetic determinants. These intrapair differences were found to increase with age, suggesting that genetic-environmental interaction also contributes to the observed variation in bone mass. These data provide evidence that bone mass does have significant genetic factors, which alone or in conjunction with environmental factors may predispose persons to the development of osteoporosis.

Genetic Analysis of Dermatoglyphic Patterns in Twins

Analysis of variance was performed on 71 dermatoglyphic variables in 424 twin sets. Using a method of twin analysis estimates of genetic variance were obtained. 54 of the variables were quantitated using a scoring system with modifications of arch or no pattern = 0, loops = 1, whorl = 2. The results indicated a significant genetic influence in most pattern areas. Patterning was more genetically controlled in the hand than in the foot. The hallucal area had the most significant genetic component of the foot while the patterns in the thumb had nonsignificant components of genetic variance. The thumb deviated from patterning in the rest of the fingers and may be more closely related to big-toe patterning.

Dominance and environmental variances: their effect on heritabilities estimated from twin data.

A method for partitioning genetic variance estimated from twin data into additive and dominance variances was presented using Falconers variance component model. The effects of dominance and environmental variances on a number of heritability estimates were also reviewed. A heritability estimate, based on the analysis of variance and the genetic variance estimates presented by HASEMAN and ELSTON and CHRISTIAN et al. which utilizes all available information from twin data, was proposed and discussed. This estimate seems to be the least affected by fluctuations in the magnitudes of dominance and environmental variances.

Efficiency of human monozygotic twins in studies of blood lipids

Abstract The cost of human experimentation often severely limits the size of experimental groups in studies of human metabolism. In animal studies workers have found that monozygotic (MZ) twins are efficient experimental subjects, because small, within twin-pair differences allow experiments to be done with fewer animals. This communication presents a method of using uniformity trials (all experimental subjects treated alike) to estimate the efficiency of MZ twins relative to unrelated experimental subjects. Fasting blood lipids were measured in 44 sets of MZ twins. The within twin-pair variation was used to estimate the experimental error for studies using twins, while the between twin-pair variation estimated experimental error for unrelated subjects. A total of 18 blood lipid parameters were measured, and there was evidence that 17 could be studied more efficiently with MZ twins than with unrelated subjects. For example, it was estimated that an experiment requiring 24 individuals to test the effects of two treatments on plasma cholesterol could be done with three sets of MZ twins.

Genetic variability of human plasma and erythrocyte lipids

Genetic variation of fasting plasma lipids, lipoproteins and erythrocyte membrane lipids was studied in 67 sets of like-sexed twins and 3 sets of triplets. All of the plasma lipids were more variable in dizygotic twins than monozygotic twins with the exception of phosphatidyl ethanolamine, but only cholesteryl esters, lecithin, phosphatidyl inositol and β-lipoprotein showed significant genetic variation. In contrast, no significant genetic variability was found in any of the erythrocyte membrane lipids and erythrocyte phosphatidyl ethanolamine had significantly greater variation in monozygotic twins. Two sets of twins had an extra lipoprotein band (slow α1); in one family the variant appeared to be segregating as a dominant trait.

Genetic variance of erythrocyte parameters in adult male twins

Erythrocyte count, hematocrit, mean corpuscular volume and reticulocyte counts were measured in 59 pairs of monozygotic (MZ) and 69 pairs of dizygotic (DZ) adult, Caucasian male twins. The means of MZ and DZ twins were not significantly different for any of the traits measured. Erythrocyte count and mean corpuscular volume had significant estimates of genetic variance (P < 0.05).

Sampling variances in twin and sibling studies of man.

The sampling variances in twin and sibling studies of man for estimation of intraclass correlation coefficients and their relation to heritabilities are evaluated. For twins and full-sibs the higher the estimated heritability of a trait the smaller the sampling variance. With increase in the number of twin sets or of full-sibships studied, the sampling variances decrease by their proportions. Twin and full-sib studies with lower heritabilities (h2

Fatty acid variability of plasma lipids and cholesteryl esters in adult male twins and their brothers

Variation in the fatty acid composition of fasting plasma lipids and of cholesteryl esters was studied in 69 sets of adult male twins and 25 of their brothers. Genetic variances were estimated using the twin model. In general, monozygotic (MZ) twins were characterized by the smallest within-pair variance, and brothers of twins by the largest. Variation within dizygotic pairs fell intermediate to that of MZ twins and brothers. The present study did not reveal consistent significant (P<0.05) genetic variation in plasma fatty acids from total plasma lipids or cholesteryl esters.

A search for stratification-free association between plasma lipids and HLA using dizygotic twins.

A total of 71 pairs of like-sexed dizygotic twins were studied, comparing within-pair differences for plasma total, free and esterified cholesterol, and triglyceride with the number of HLA haplotypes the twins had in common. If associations are present between HLA and the blood lipids studied, the twins with no haplotypes in common would be expected to have the largest within-pair mean square, those with two in common the smallest, and those with one in common an intermediate value. No significant differences were found comparing within- pair mean squares for the variables studied.

Simulation of twin data controlling population mean, variance, skewness and kurtosis.

A computer system for simulation of quantitative twin data is being developed. The capability is being built in a simulate distributions with known means, standard deviations, skewness and kurtosis.