Heritability Index Research Articles

Lithium accumulation in erythrocytes of manic-depressive patients: an in vivo twin study.

Genetic factors play an important role in drug metabolism and drug response. In order to investigate genetic variables in lithium prophylaxis and lithium distribution across the erythrocyte in manic-depression, we have examined forty-two pairs of twins monozygotic (n = 25) and dizygotic (n = 17) with manic-depression. Concordant twins as a group show better lithium prophylaxis than do discordant twins. These results are consistent with previously published family studies of affective illness suggesting a positive relationship between genetic background and success of lithium prophylaxis. Lithium distribution across the red blood cell (RBC) was assessed by estimating lithium RBC/plasma ratios. The lithium ratio's intrapair differences in both groups of twins were minimal with a high heritability index suggesting that genetic factors play a role in lithium ion distribution. A high linear correlation was found between lithium ratio and plasma lithium and there was no difference in lithium ratios according to sex, affective state and response to lithium. The distribution of lithium ratios was homogenous in the lithium responders' population but this was not the case in the non-responders, suggesting biological heterogeneity of lithium distribution in lithium failures. The implications of these results are discussed as they relate to the genetic determinates of lithium prophylaxis in manic-depressive illness. These results indicate that lithium ratios are of limited value in lithium maintenance therapy. Our lithium kinetic data, however, are consistent with the concept of a lithium extrusion mechanism from red blood cells.

Genetic control of interindividual variations in racemic warfarin binding to plasma and albumin of twins.

Warfarin binding to plasma as well as to charcoal‐treated purified albumin was studied in monozygotic (MZ) and dizygotic (DZ) twins by equilibrium dialysis. The association constants of warfarin binding and the number of warfarin binding sites per molecule were more similar within MZ than within DZ twins. These data indicate that genetic factors control interindividual variations in warfarin‐albumin association constants and in the number of warfarin binding sites per albumin molecule. A heritability index of a .87 was obtained for the association constant of warfarin binding to plasma and of 0.89 for warfarin binding to albumin. Heritability indices of 0.80 and 0.85 were obtained for the number of warfarin sites per albumin molecule in plasma and albumin, respectively. When the values of Ka and n for warfarin binding to albumin are plotted for the 44 individuals in this study, the distribution of Ka as well as n appears to be trimodal. The distribution of n falls into three classes, with 19 having an average binding site of 0.9, 14 having an average binding site of 1.4, and 3 having an average binding site of 2.1. Since this distribution conforms to a Hardy‐Weinberg equilibrium with gene frequencies of 0.72 and 0.28 and since the average number of binding sites is close to integral numbers of 1 and 2, it is tempting to speculate that these data disclose for the first time a common polymorphism of the albumin molecule affecting both nand Ka such that the phenotypic variations are controlled by two alleles at a single genetic locus. Since the number of subjects is too small for this distribution analysis to be completely secure, family studies will be required to determine whether such a polymorphism exists. Ka and n, though significantly correlated, have r values that are not very high (for isolated albumin, r = 0.63 for Ka vs n in MZ twins, p < O.Ol;r = 0.34 for Ka vs n in DZ twins, p = 0.05; for whole plasma, r = 0.78 for n vs Ka in MZ twins, p < 0.01; r = 0.57 for n vs Ka in DZ twins, p < 0.0 1). With respect to avidity of warfarin binding and number of warfarin sites per albumin molecule, these results suggest that inherited structural differences in the albumin molecule may affect the transport of certain drugs within the body of

Heritability of “sinking” pre‐beta lipoprotein level: a twin study

In a twin series at the Toronto Twin Register, University of Toronto, the “sinking” pre‐beta lipoprotein fraction (sp β), quantitatively determined, was found to have a heritability index of 0.98. If confirmed, this warrants use of spβ concentration as a genetic marker. Its importance may lie in its association with angina of effort and myocardial infarction.

Language development in young twins: biological, genetic and social aspects.

The present study has confirmed previous evidence that young twins show a marked delay in language development. This delay averaged six months at the age of 48 months, compared to a control group of singletons; it was evenly reflected in all nine subtests of the Illinois Test of Psycholinguistic Abilities, and was shown equally in MZ and DZ twins. Biological variables such as birth weight, gestational age and reproductive complications were only weakly associated with language scores at four years. The twins were not significantly retarded on non-verbal tests of general intelligence, compared with population norms or with the singleton controls. Environmental factors, particularly social class and family size were strongly correlated with language scores, though the association was stronger in singletons than in twins. Middle class twins were relatively much more retarded in language development compared with middle class singletons than working class twins compared with working class singletons. Comparison of intra-class correlations between 28 MZ and 64 DZ pairs yielded a heritability index of 44% for the test as a whole, with considerable variations in h2over the nine subtests. Heritabilities were highest for tests sampling the visual motor channel, and lowest for tests on the auditory-vocal channel. In confirmation of this finding, an examination of the test profiles of the singleton controls suggested that social class differences were most marked on tests of the auditory-vocal channel. It is suggested that the latter are more susceptible to environmental variables.

Size of the physiologic cup of the optic nerve head. hereditary and environmental factors.

This study provides a quantitative assessment of heritability of size of the normal physiologic cup when estimated as a continuous variable. A horizontal cup-disc ratio was estimated clinically among a sample of 37 pairs of monozygotic (MZ) and 26 pairs of like-sexed dizygotic (DZ) twins. Differences in intrapair variance and intraclass correlation coefficient between the MZ and the DZ samples were large and highly significant, and suggest that inheritance plays a major role in determining diameter of the normal physiologic cup. Values of heritability index (Hl, an estimate of the proportion of variance within pairs explained by genetic factors) ranged from 0.60 to 0.80 by various computational methods employed.

Genetic determinant of lithium ion distribution. I. An in vitro monozygotic-dizygotic twin study.

Research in pharmacogenetics has provided evidence that individual variation in rate of metabolism of various drugs is genetically controlled. To evaluate the possibility of a genetic determinant of lithium ion distribution, a monozygotic (MZ)-dizygotic (DZ) twin study method was used. Red blood cell (RBC) lithium ion concentrations were assessed for ten MZ and seven DZ twin pairs following a 24-hour incubation in vitro. The distributions of intrapair difference scores of MZ twin pairs and DZ twin pairs were relatively nonoverlapping, with MZ intrapair difference scores being smaller on the average. A heritability index of 0.85, calculated as a function of intrapair difference scores, indicated that a substantial genetic factor is operative in RBC uptake of lithium ion.

Genetics of dermatoglyphic patterns on palms.

SUMMARYGenetics of palmar dermatoglyphics have been investigated on the basis of a topological classification of dermal ridge patterns. A study was undertaken in a sample of 201 Polish families, comprising 187 pairs of parents and 666 children. Correlational analysis was performed using an IBM computer.The first step was to establish frequencies of dermatoglyphic characters in the sample and anatomical correlations between various patterns on palms and finger tips. Then, correlation coefficients between relatives were calculated for eighteen dermatoglyphic characters. Further genetical analysis of the data was performed, including estimates of heritability index (h2), dominance‐recessivity index (dr)2 and search for the possible influence of sex‐linked genes. The results obtained show that the dermatoglyphic characters on palms vary considerably with respect to the proportions of genetical and environmental components; some of them, like hypothenar H loop, interdigital loop II and triradius t and some quantitative characters, like pattern intensity, have high heritability indices, while the others, like hypothenar distal loop H, radial hypothenar loop Hr or z triradii, are almost entirely determined by environmental influences.It was further possible to examine the mode of inheritance of some of the pattern elements.It can be assumed, on a basis of results so far obtained, that some dermatoglyphic characters like loops Ĥ and II and presence of triradius t may be determined mainly by single genes those for the loops being in homozygous recessive form.

Some Problems in Psychology of Musical Ability

How FAR ANY ABILIN shown by an individual is innate and how far it is acquired from the environment is difficult to decide. Yet the question is not a purely academic one. It underlies the difference between what Ralph Smith (10) called the "aristocratic" and the "democratic" attitudes to music education. Even the democrat who believes that every child can profit from instruction in music has to admit that pupils vary markedly in motivation and capacity to learn. If musical aptitude is largely innate, ought the schools to spend too much time on the unmusical? So long as the supply of good music teachers remains inadequate, shouldn't their efforts be mainly directed toward discovering and fostering the talents of the gifted? Most earlier studies of the heritability of musical talent have been based on the family trees of musicians or on the assessment of musical ability from questionnaire data. These include the interesting inquiry by Scheinfeld (7) into the incidence of musical talent among the relatives of professional musicians and music students. Some use has also been made of the Seashore and Kwalwasser-Dykema tests in genetic studies, but the results obtained by different investigators have been inconsistent and difficult to interpret. For an investigation of hereditary and environmental factors in musical ability I compared identical with fraternal twins and parents with their children. Of the standardized tests available in 1956, the Wing battery appeared to be the most comprehensive and best validated. Though my subjects took all seven tests, in the case of the twins brought up together many were so unmusical that it seemed advisable to use the scores from the first three tests only. The age range of the 50 pairs of child twins who were tested was from 9 to 16. I classified them as identical or fraternal by general impression and careful inspection. Scores from 11 adult pairs were also obtained. Intrapair correlations (8) are shown in Table 1. These figures give a "heritability index" for the child pairs showing that heredity contributed 42 percent to their musical ability. The extent of the contrast between the two types of twins was less than that reported in the literature on intelligence perhaps partly due to the low ability level of most of the twins. In the case of the boys considered separately, 62 percent of their ability was attributable to heredity. This sex difference did not seem tc be related to differences in ability level, interest in music, or oppor-