Dana L. Duren

Body Composition Methods: Comparisons and Interpretation

The incidence of obesity in the United States and other developed countries is epidemic. Because the prevalence of comorbidities to obesity, such as type 2 diabetes, has also increased, it is clear there is a great need to monitor and treat obesity and its comorbidities. Body composition assessments vary in precision and in the target tissue of interest. The most common assessments are anthropometric and include weight, stature, abdominal circumference, and skinfold measurements. More complex methods include bioelectrical impedance, dual-energy X-ray absorptiometry, body density, and total body water estimates. There is no single universally recommended method for body composition assessment in the obese, but each modality has benefits and drawbacks. We present here the most common methods and provide guidelines by way of examples to assist the clinician/researcher in choosing methods appropriate to their situation.

Quantitative genetics of modern human cranial variation

The anatomy and biology of the basicranial complex and its relationships to the other cranial complexes has long played a central role in functional and phylogenetic interpretations of the hominin fossil record. Cranial traits frequently populate character lists in phylogenetic analyses and are commonly described as comprising an anatomical or functional complex. Most often these traits are treated as individual independent characters of equal phyletic value. Implicit in such considerations, however, is the assumption that the genetic contribution to morphological variation is high and equivalent across traits, and that phenotypic and genetic correlations between traits, irrespective of their magnitude, introduce negligible confounding effects in phylogenetic reconstruction (Hlusko, 2004). While the ability to quantify and assess phenotypic variation in craniofacial variables has seen significant advances in recent years, the extent to which genetic and nongenetic factors influence this variation is typically not addressed. A key component to understanding the influences environmental and genetic factors have on the evolution of the craniofacial complex is a solid foundation of detailed knowledge of the genetic components underlying the development of normal craniofacial variation in modern populations. The aim of the present study is to elucidate fundamental aspects of the genetic architecture of normal variation in the human craniofacial complex. In the current context, genetic architecture refers to the characterization of: (1) the extent to which variation in a trait is under genetic control, and (2) the degree to which two traits are controlled by the same genes or set of genes. The first of these is the heritability (h2) of a trait, and the second is the genetic correlation (ρG) between traits. Heritability estimates provide important information regarding the potential evolutionary response of traits to selective forces—the rate of evolutionary change being determined by the product of the heritability and the selection coefficient (Lynch and Walsh, 1998). Genetic correlations provide a means for quantifying the shared effects of genes on two or more traits. Genetic correlations have become critical in understanding the phenotypic heterogeneity observed in many craniofacial syndromes (Cohen, 2002), and have significant implications for the evolution of the hominin craniofacial complex. Human cranial variation: evidence from family-based studies Craniofacial morphometrics of archaeological or museum osteological collections have provided the field of human evolution with a broad perspective of craniofacial variation. These studies, however, cannot address issues of the genetic influence on trait variation, or covariation between traits. In order to adequately approach such issues, a large number of individuals of known biological relatedness is necessary. One such population is the Fels Longitudinal Study, which includes over 3,000 individuals belonging to ~250 families. Participants of the Fels Longitudinal Study have been the focus of numerous research articles including many that have had significant anthropological and human evolutionary significance, such as several papers detailing the growth and development of cranial structures (Young, 1956, 1957; Garn et al., 1963; Lewis and Roche, 1972, 1974; Roche and Lewis, 1974, 1976; Roche et al., 1977; Lewis et al., 1982, 1985; Ohtsuki et al., 1982a,b) and a classic paper investigating ontogenetic changes in basicranial flexion (i.e., the saddle angle; Lewis and Roche, 1977). In this report we seek to continue and extend the analysis of the Fels Longitudinal Study cranial data by presenting the first quantitative genetic analysis of the cranial data available in the archives.

Bayesian longitudinal plateau model of adult grip strength

This article illustrates the use of applied Bayesian statistical methods in modeling the trajectory of adult grip strength and in evaluating potential risk factors that may influence that trajectory.

A Genomewide Linkage Scan for Quantitative Trait Loci Influencing the Craniofacial Complex in Baboons (Papio hamadryas spp.)

Numerous studies have detected significant contributions of genes to variation in development, size, and shape of craniofacial traits in a number of vertebrate taxa. This study examines 43 quantitative traits derived from lateral cephalographs of 830 baboons (Papio hamadryas) from the pedigreed population housed at the Southwest National Primate Research Center. Quantitative genetic analyses were conducted using the SOLAR analytic platform, a maximum-likelihood variance components method that incorporates all familial information for parameter estimation. Heritability estimates were significant and of moderate to high magnitude for all craniofacial traits. Additionally, 14 significant quantitative trait loci (QTL) were identified for 12 traits from the three developmental components (basicranium, splanchnocranium, and neurocranium) of the craniofacial complex. These QTL were found on baboon chromosomes (and human orthologs) PHA1 (HSA1), PHA 2 (HSA3), PHA4 (HSA6), PHA11 (HSA12), PHA13 (HSA2), PHA16 (HSA17), and PHA17 (HSA13) (PHA, P. hamadryas; HSA, Homo sapiens). This study of the genetic architecture of the craniofacial complex in baboons provides the groundwork needed to establish the baboon as an animal model for the study of genetic and nongenetic influences on craniofacial variation.

Musculoskeletal function following bariatric surgery

Bariatric surgery is an effective method for acute weight loss. While the impact of bariatric surgery on general medical conditions (e.g., type 2 diabetes) is well documented, few studies focus on physical functional outcomes following weight‐loss induced by bariatric surgery.

Rapid Infant Weight Gain and Advanced Skeletal Maturation in Childhood

OBJECTIVE To test the hypothesis that rapid infant weight gain is associated with advanced skeletal maturity in children from the United States and South Africa. STUDY DESIGN Longitudinal data from 467 appropriate-for-gestational-age infants in the Fels Longitudinal Growth Study (Dayton, Ohio) and 196 appropriate-for-gestational-age infants in the Birth to Twenty birth cohort study (Johannesburg, South Africa) were used. Multiple linear regression models tested the association between internal SD score change in weight from 0 to 2 years and relative skeletal age at 9 years, adjusting for body mass index, stature, and other covariates. RESULTS In both studies, faster infant weight gain was associated with more advanced skeletal maturity (approximately 0.2 years or 2.4 months per SD score) at age 9 years (P <.0001-.005), even when adjusting for the positive associations of both birth weight and body mass index at age 9 years. This effect appeared to be accounted for by the greater childhood stature of subjects with more rapid infant weight gain. CONCLUSIONS Relatively rapid infant weight-gain is associated with advanced skeletal development in late childhood, perhaps via effects on stature.

Mandibular Symphysis of Large-Bodied Hominoids

The hominoid mandibular symphysis has received a great deal of attention from anatomists, human biologists, and paleontologists. Much of this research has focused on functional interpretations of symphyseal shape variation. Here, we examine the two-dimensional cross-sectional shape of the adult mandibular symphysis for 45 humans, 42 chimpanzees, 37 gorillas, and 51 orangutans using eigenshape analysis, an outline-based morphometric approach. Our results demonstrate that a large proportion of the variation described by the first eigenshape correlates with proposed functional adaptations to counteract stresses at the mandibular midline during mastication. Subsequent eigenshapes describe subtle aspects of shape variation in the mandibular symphysis. The morphology associated with these eigenshapes does not conform with functional predictions, nor does it show a relationship with sexual dimorphism. However, eigenshapes provide for considerable taxonomic discrimination between the four taxa studied and may consequently prove useful in the analysis of fossil material. Comparison with elliptical Fourier analysis of the mandibular symphysis identifies eigenshape analysis as providing superior taxonomic discrimination. The results presented here demonstrate that the cross-sectional shape of the mandibular symphysis results from a complex interplay of functional and nonfunctional influences and for the first time identifies and quantifies the specific aspects of variation attributable to these factors.

Skeletal growth and the changing genetic landscape during childhood and adulthood

Growth, development, and decline of the human skeleton are of central importance to physical anthropology. All processes of skeletal growth (longitudinal growth as well as gains and losses of bone mass) are subjected to environmental and genetic influences. These influences, and their relative contributions to the phenotype, can be asserted at any stage of life. We present here the gross phenotypic and genetic landscapes of four skeletal traits, and show how they vary across the life span. Phenotypic sex differences are found in bone diameter and cortical index (a ratio of cortical thickness over bone diameter) at a very early age and continue throughout most of life. Sexual dimorphism in summed cortical thickness and bone length, however, is not evident until shortly after the pubertal growth spurt. Genetic contributions (heritability) to these skeletal phenotypes are generally moderate to high. Bone length and bone diameter (which both scale with body size) tend to have the highest heritability, with heritability of bone length fairly stable across ages (with a notable dip in early childhood) and that of bone diameter peaking in early childhood. The bone traits summed cortical thickness and cortical index that may better reflect bone mass, a more plastic phenomenon, have slightly lower genetic influences, on average. Results from our phenotypic and genetic landscapes serve three key purposes: 1) demonstration of the integrated nature of the genetic and environmental underpinnings of skeletal form, 2) identification of periods of bones relative sensitivity to genetic and environmental influences, 3) and stimulation of hypotheses predicting the effects of exposure to environmental variables on the skeleton, given variation in the underlying genetic architecture.

A Genome-Wide Linkage Scan for Quantitative Trait Loci Influencing the Craniofacial Complex in Humans (Homo sapiens sapiens)

The genetic architecture of the craniofacial complex has been the subject of intense scrutiny because of the high frequency of congenital malformations. Numerous animal models have been used to document the early development of the craniofacial complex, but few studies have focused directly on the genetic underpinnings of normal variation in the human craniofacial complex. This study examines 80 quantitative traits derived from lateral cephalographs of 981 participants in the Fels Longitudinal Study, Wright State University, Dayton, Ohio. Quantitative genetic analyses were conducted using the Sequential Oligogenic Linkage Analysis Routines analytic platform, a maximum‐likelihood variance components method that incorporates all familial information for parameter estimation. Heritability estimates were significant and of moderate to high magnitude for all craniofacial traits. Additionally, significant quantitative trait loci (QTL) were identified for 10 traits from the three developmental components (basicranium, splanchnocranium, and neurocranium) of the craniofacial complex. These QTL were found on chromosomes 3, 6, 11, 12, and 14. This study of the genetic architecture of the craniofacial complex elucidates fundamental information of the genetic architecture of the craniofacial complex in humans. Anat Rec, 2011.

Heritability of the Human Craniofacial Complex

Quantifying normal variation and the genetic underpinnings of anatomical structures is one of the main goals of modern morphological studies. However, the extent of genetic contributions to normal variation in craniofacial morphology in humans is still unclear. The current study addresses this gap by investigating the genetic underpinnings of normal craniofacial morphology. The sample under investigation consists of 75 linear and angular measurements spanning the entire craniofacial complex, recorded from lateral cephalographs of 1,379 participants in the Fels Longitudinal Study. Heritabilities for each trait were estimated using SOLAR, a maximum‐likelihood variance components approach utilizing all pedigree information for parameter estimation. Trait means and mean effects of the covariates age, sex, age2, sex × age, and sex × age2 were simultaneously estimated in the analytic models. All traits of the craniofacial complex were significantly heritable. Heritability estimates ranged from 0.10 to 0.60, with the majority being moderate. It is important to note that we found similar ranges of heritability occurring across the different functional/developmental components of the craniofacial complex, the splanchnocranium, the basicranium, and the neurocranium. This suggests that traits from different regions of the craniofacial complex are of comparable utility for the purposes of population history and phylogeny reconstruction. At the same time, this genetic influence on craniofacial morphology signals a caution to researchers of nongenetic studies to consider the implications of this finding when selecting samples for study given their project design and goals. Anat Rec, 298:1535–1547, 2015.