Transmissible and nontransmissible components of anthropometric variation in the Alexanderwohl Mennonites: I. Description and familial correlations

Influence of heritability on occlusal traits: a systematic review of studies in twins

BACKGROUND

The aim of this systematic review was to identify, evaluate, and provide a current literature about the influence of heritability on the determination of occlusal traits.

MATERIALS AND METHODS

MEDLINE, SCOPUS, Web of Science, LILACS, and Google Scholar were searched without restrictions up to March 2020. Studies with twin method were considered and the risk of bias assessment was performed using quality of genetic association studies checklist (Q-Genie). The coefficient of heritability (h²), model-fitting approaches, and coefficient correlation were used to estimate the genetic/environmental influence on occlusal traits. The GRADE tool was used to assess the quality of the evidence.

RESULTS

Ten studies met the eligibility criteria. Three studies presented good quality, five moderate quality, and two poor quality. Most studies have found that the intra-arch traits, mainly the maxillary arch morphology, such as width (h² 16-100%), length (h² 42-100%), and shape (h² 42-90%), and the crowding, mainly for mandibular arch (h² 35-81%), are under potential heritability influence. The traits concerning the inter-arch relationship, as overjet, overbite, posterior crossbite, and sagittal molar relation, seem not to be genetically determined. The certainty of the evidence was graded as low for all outcomes.

CONCLUSIONS

Although weak, the available evidence show that the heritability factors are determinant for the intra-arch traits, namely, arch morphology and crowding. Possibly due they are functionally related, the occlusal traits concerning the maxillary and mandibular relationship seem to have environmental factors as determinants. In this scenario, early preventive approaches can offer a more effective and efficient orthodontic treatment.

Heritability of Face Shape in Twins: A Preliminary Study using 3D Stereophotogrammetry and Geometric Morphometrics

INTRODUCTION

Previous research suggests that aspects of facial surface morphology are heritable. Traditionally, heritability studies have used a limited set of linear distances to quantify facial morphology and often employ statistical methods poorly designed to deal with biological shape. In this preliminary report, we use a combination of 3D photogrammetry and landmark-based morphometrics to explore which aspects of face shape show the strongest evidence of heritability in a sample of twins.

METHODS

3D surface images were obtained from 21 twin pairs (10 monozygotic, 11 same-sex dizygotic). Thirteen 3D landmarks were collected from each facial surface and their coordinates subjected to geometric morphometric analysis. This involved superimposing the individual landmark configurations and then subjecting the resulting shape coordinates to a principal components analysis. The resulting PC scores were then used to calculate rough narrow-sense heritability estimates.

RESULTS

Three principal components displayed evidence of moderate to high heritability and were associated with variation in the breadth of orbital and nasal structures, upper lip height and projection, and the vertical and forward projection of the root of the nose due to variation in the position of nasion.

CONCLUSIONS

Aspects of facial shape, primarily related to variation in length and breadth of central midfacial structures, were shown to demonstrate evidence of strong heritability. An improved understanding of which facial features are under strong genetic control is an important step in the identification of specific genes that underlie normal facial variation.

Maximum likelihood estimation of human craniometric heritabilities

This study presents univariate narrow-sense heritability estimates for 33 common craniometric dimensions, calculated using the maximum likelihood variance components method on a skeletal sample of 298 pedigreed individuals from Hallstatt, Austria. Quantitative genetic studies that use skeletal cranial measurements as a basis for inferring microevolutionary processes in human populations usually employ heritability estimates to represent the genetic variance of the population. The heritabilities used are often problematic: most come from studies of living humans, and/or they were calculated using statistical techniques or assumptions violated by human groups. Most bilateral breadth measures in the current study show low heritability estimates, while cranial length and height measures have heritability values ranging between 0.102-0.729. There appear to be differences between the heritabilities calculated from crania and those from anthropometric studies of living humans, suggesting that the use of the latter in quantitative genetic models of skeletal data may be inappropriate. The univariate skeletal heritability estimates seem to group into distinct regions of the cranium, based on their relative values. The most salient group of measurements is for the midfacial/orbital region, with a number of measures showing heritabilities less than 0.30. Several possible reasons behind this pattern are examined. Given the fact that heritabilities calculated on one population should not be applied to others, suggestions are made for the use of the data presented.

Biological aging and Cox hazard analysis of mortality trends in a Mennonite community from south-central Kansas

This study investigated mortality in 568 individuals from the Goessel Mennonite community in rural central Kansas. There were three main objectives to this research: 1) characterize mortality trends within a biologically well-defined Mennonite community; 2) determine what biochemical, morphological, and physiological risk factors could be related to all-cause mortality, stratified by age and sex; and 3) compare these results to previously described variables that were associated with both biological age and mortality in this population. Mortality data were obtained from three sources: Kansas Vital Records, the Social Security death index, and church records. In total, 221 (39%) individuals were found to have died in this population between January 1980-June 2002. Analogous to the larger US population, the three leading causes of death in this community were heart disease, cancer, and stroke, accounting for 60% of all deaths. Besides advancing age, the greatest biological risk factor in this population was decreased amounts of albumin in men (relative risk, 2.47), potentially indicating underreported cases of either chronic kidney disease or frailty syndrome for males. Cox proportional hazard models demonstrated that increased amounts of total cholesterol may provide a protective effect for elderly individuals. We conclude, based on the previously described heritability of both albumin (h(2) = 0.40) and total cholesterol (h(2) = 0.50) in this population, that underlying genetic factors associated with both chronic degenerative diseases and biological aging may have important implications for understanding mortality patterns in this community.

South Amerindian craniofacial morphology: Diversity and implications for Amerindian evolution

The most compelling models concerning the peopling of the Americas consider that modern Amerindians share a common biological pattern, showing affinities with populations of the Asian Northeast. The aim of the present study was to assess the degree of variation of craniofacial morphology of South American Amerindians in a worldwide context. Forty-three linear variables were analyzed on crania derived from American, Asian, Australo-Melanesian, European, South-Saharan African, and Polynesian regions. South America was represented by seven Amerindian samples. In order to understand morphologic diversity among Amerindians of South America, variation was estimated using regions and local populations as units of analysis. Variances and F(ST) values were calculated for each unit, respectively. Both analyses indicated that morphologic variation in Southern Amerindians is extremely high: an F(ST) of 0.01531 was obtained for Southern Amerindians, and values from 0.0371-0.1205 for other world regions. Some aspects linked to the time and mode of the peopling of the Americas and various microevolutionary processes undergone by Amerindians are discussed. Some of the alternatives proposed to explain this high variation include: a greater antiquity of the peopling than what is mostly accepted, a peopling by several highly differentiated waves, an important effect of genetic drift, and gene flow with Paleoamericans. A combination of some of these alternatives explains at least some of the variation.

Cranial variation in the Marquesas Islands

The Marquesas Islands have traditionally been divided into a northwestern and a southeastern group, a division which reflects language dialect differences. Additionally, archaeological studies have also suggested that differences in material culture existed between the northwestern and southeastern islands. This study examines Marquesan cranial discrete and metric traits to evaluate the level of intra-archipelago heterogeneity, and to determine if a northwest/southeast division is evident cranially. The data consist of 28 cranial discrete traits and 49 craniofacial measurements of prehistoric Marquesans. Male and female data are pooled for discrete trait and metric data, following a Z-score standardization technique adjustment. The data represent three island samples: Nuku Hiva (northwest), Fatuiva (southeast), and a combined Tahuata/Hiva 'Oa (southeast). Of the 28 discrete traits, 16 are utilized in a mean measure of divergence analysis that provides scores of 0.259 for Fatuiva-Tahuata/Hiva 'Oa, 1.850 for Nuku Hiva-Fatuiva, and 1.491 for Nuku Hiva-Tahuata/Hiva 'Oa. Of the 49 craniofacial measurements, 46 are utilized in RMET/NORM analyses, providing unbiased D(2) values of 0.0433 for Fatuiva-Tahuata/Hiva 'Oa, 0.1328 for Nuku Hiva-Fatuiva, and 0.0813 for Nuku Hiva-Tahuata/Hiva 'Oa. The islands of the southeastern group are closer to each other than either was to the island of the northwestern group. When a sample from 'Ua Huka is included in the craniometric analysis, the unbiased D(2) values of 0.0829, 0.1175, and 0.0431 are calculated for 'Ua Huka and Nuku Hiva, and Fatuiva and Tahuata/Hiva 'Oa pairings, respectively, indicating a close similarity of 'Ua Huka to the southeastern islands. Mean measure of divergence analysis of cranial discrete traits as well as RMET/NORM analyses of craniometric variables reveal that differences exist between the islands of the northwestern and southeastern Marquesas Islands. These results support previous research that documented linguistic and cultural differences between these regions of the archipelago. However, the results indicate that 'Ua Huka, an island traditionally included in the northwestern Marquesas Islands, has an affinity to the southeastern Marquesas Islands, possibly due to its pivotal position as a waypoint in the Marquesas Island interaction sphere.

A reassessment of human cranial plasticity: Boas revisited

In 1912, Franz Boas published a study demonstrating the plastic nature of the human body in response to changes in the environment. The results of this study have been cited for the past 90 years as evidence of cranial plasticity. These findings, however, have never been critiqued thoroughly for their statistical and biological validity. This study presents a reassessment of Boas' data within a modern statistical and quantitative genetic framework. The data used here consist of head and face measurements on over 8,000 individuals of various European ethnic groups. By using pedigree information contained in Boas' data, narrow sense heritabilities are estimated by the method of maximum likelihood. In addition, a series of t tests and regression analyses are performed to determine the statistical validity of Boas' original findings on differentiation between American and European-born children and the prolonged effect of the environment on cranial form. Results indicate the relatively high genetic component of the head and face diameters despite the environmental differences during development. Results point to very small and insignificant differences between European- and American-born offspring, and no effect of exposure to the American environment on the cranial index in children. These results contradict Boas' original findings and demonstrate that they may no longer be used to support arguments of plasticity in cranial morphology.

Genetic determination of biological age in the Mennonites of the Midwestern United States

Numerous studies have shown that longevity is moderately heritable in human populations. Longevity, however, contains limited information on functional status, since individuals may exhibit differential survival patterns. In this study, we employed a stepwise multiple regression approach to estimate biological aging in a Mennonite population, using chronological age as a dependent variable and various predictors of chronological age including subphenotypes related to diabetes, coronary heart disease, hypertension, renal function, and markers of functional ability. The residual (the difference between chronological and predicted ages) is considered a marker of biological age. In fact, two different data sets were used to obtain residuals due to the availability of data. In each analysis, chronological age was regressed on predictor variables in a stepwise manner, retaining the variables significant at the 5% level. The first analysis (N=729) included 6 significant predictors (R(2)=44.3%): glucose, blood urea nitrogen (BUN), cholesterol, albumin, systolic blood pressure (SBP), and ln potassium, and the second analysis (N=232) included 9 significant predictors (R(2)=71.5%): BUN, albumin, SBP, low-density lipoprotein cholesterol, forced expiratory volume in 1 sec (FEV1), grip strength, trunk flexibility, reaction time, and FEV1xsex. Using a variance components approach, we found that the data set-specific residuals were significantly heritable (h(2)+/-SE): first analysis=0.265+/-0.106, and second analysis=0.469+/-0.180. The residuals from the second data set appear to be more informative for biological aging, perhaps due to the inclusion of functional ability-related phenotypes in addition to the blood chemistry variables. In summary, we have shown that markers of biological aging in Mennonites are under substantial additive genetic influences.

Soft tissue facial resemblance in families and syndrome-affected individuals

We investigated soft tissue facial resemblance among relatives with or without syndromes and among related and unrelated individuals diagnosed with the same syndrome. Using correlation coefficients, we compared facial landmark (i.e., three-dimensional coordinate) positions and measurements gained by photogrammetry in various combinations of normal and syndrome-affected individuals. There were fewer significant correlations for the three-dimensional coordinates and measurements between the normal parent-normal child pairs than for the normal sib pairs. There was no discernible pattern for the single measurements in the parent-child pairs, whereas all of the midline vertical measurements were significantly positively correlated in the normal sib pairs. Significant correlations were always positive in all sib comparisons, but ranged from negative to positive in all parent-child correlations. The shared environment of sibs was a possible explanation for their greater resemblance in comparison with parent-child pairs. We also had measurements from 11 subjects (related and unrelated) diagnosed with one of four syndromes, and we used these to compare individuals with the same syndrome by calculating correlation coefficients based on all available pairs of measurements. The highest significant positive correlations were found for related individuals with the same syndrome (0.72 to 0.83). Unrelated individuals with the same syndrome also had significant positive correlations, but they were lower (0.35 to 0.65). We therefore inferred that the genetic similarities between unrelated individuals with syndromes played a role in the resemblance between them, and that common genes and environment in related individuals further contributed to the high correlations found for them.

Genetics of human body size and shape: complex segregation analysis

The genetic component in a mixed heritability model, including major gene, multifactorial and sibling environment transmissible components, was studied for some 20 anthropometric traits in two ethnically different samples. The first sample comprised 305 Mexican nuclear families, and the second comprised 83 Ashkenazi Jewish nuclear families living in Israel. All variables, after adjustment for age and sex, were subjected to principal-components analysis (PCA) in each sample separately. The mixed model of inheritance as implemented in the computer program POINTER was used in the present study. An attempt was made to evaluate genetic effects in the variation of the first principal components (PCs). PCA showed a clear separation of variables and was easily interpretable. The PC1 was a credibly general size factor. This factor alone accounted for about 30% of the total variance. Other components are rather shape factors for various combinations of traits. The testing of several genetic hypothesis showed the following: (1) For all factor scores the genetic component was high and statistically significant. (2) In a Mexican sample, for PC1 and PC2, both major gene and polygenes contributed significantly to the total variation of these variables; in the major locus the alleles were most probably codominant. (3) For all other PCs the major gene effect hypothesis was rejected, with more than 50% of the variation attributable to the polygenes contribution. (4) No evidence was found for sibling environmental resemblance in either sample.

Transmissible and nontransmissible components of anthropometric variation in the Alexanderwohl Mennonites: II. Resolution by path analysis

A study of the intergenerational transmissibilities of 34 anthropometric measures from the Alexanderwohl Mennonite congregations of Kansas and Nebraska is presented. Results presented tend to confirm the suggestion made previously by us (Devor et al., 1985) that patterns of transmissibility conform to a concept of "functional multifactorial complexes" operating in the body in a way analogous to the "field" concept of dental morphology.