Sequential Oligogenic Linkage Analysis Routines Research Articles

Genome-wide QTL analysis for anxiety trait in bipolar disorder type I

BackgroundGenetic studies have been consistent that bipolar disorder type I (BPI) runs in families and that this familial aggregation is strongly influenced by genes. In a preliminary study, we proved that anxiety trait meets endophenotype criteria for BPI. MethodsWe assessed 619 individuals from the Central Valley of Costa Rica (CVCR) who have received evaluation for anxiety following the same methodological procedure used for the initial pilot study. Our goal was to conduct a multipoint quantitative trait linkage analysis to identify quantitative trait loci (QTLs) related to anxiety trait in subjects with BPI. We conducted the statistical analyses using Quantitative Trait Loci method (Variance-components models), implemented in Sequential Oligogenic Linkage Analysis Routines (SOLAR), using 5606 single nucleotide polymorphism (SNPs). ResultsWe identified a suggestive linkage signal with a LOD score of 2.01 at chromosome 2 (2q13-q14). LimitationsSince confounding factors such as substance abuse, medical illness and medication history were not assessed in our study, these conclusions should be taken as preliminary. ConclusionsWe conclude that region 2q13-q14 may harbor a candidate gene(s) with an important role in the pathophysiology of BPI and anxiety.

Genetic correlations between intraocular pressure, blood pressure and primary open-angle glaucoma: a multi-cohort analysis.

Primary open-angle glaucoma (POAG) is the most common chronic optic neuropathy worldwide. Epidemiological studies show a robust positive relation between intraocular pressure (IOP) and POAG and modest positive association between IOP and blood pressure (BP), while the relation between BP and POAG is controversial. The International Glaucoma Genetics Consortium (n=27 558), the International Consortium on Blood Pressure (n=69 395), and the National Eye Institute Glaucoma Human Genetics Collaboration Heritable Overall Operational Database (n=37 333), represent genome-wide data sets for IOP, BP traits and POAG, respectively. We formed genome-wide significant variant panels for IOP and diastolic BP and found a strong relation with POAG (odds ratio and 95% confidence interval: 1.18 (1.14-1.21), P=1.8 × 10-27) for the former trait but no association for the latter (P=0.93). Next, we used linkage disequilibrium (LD) score regression, to provide genome-wide estimates of correlation between traits without the need for additional phenotyping. We also compared our genome-wide estimate of heritability between IOP and BP to an estimate based solely on direct measures of these traits in the Erasmus Rucphen Family (ERF; n=2519) study using Sequential Oligogenic Linkage Analysis Routines (SOLAR). LD score regression revealed high genetic correlation between IOP and POAG (48.5%, P=2.1 × 10-5); however, genetic correlation between IOP and diastolic BP (P=0.86) and between diastolic BP and POAG (P=0.42) were negligible. Using SOLAR in the ERF study, we confirmed the minimal heritability between IOP and diastolic BP (P=0.63). Overall, IOP shares genetic basis with POAG, whereas BP has limited shared genetic correlation with IOP or POAG.

Heritability and genetic correlation between GERD symptoms severity, metabolic syndrome, and inflammation markers in families living in Mexico City.

ObjectiveThe aim of this study was to estimate the heritability (h2) and genetic correlation (ρG) between GERD symptoms severity, metabolic syndrome components, and inflammation markers in Mexican families.MethodsCross-sectional study which included 32 extended families resident in Mexico City. GERD symptoms severity was assessed by the ReQuest in Practice questionnaire. Heritability and genetic correlation were determined using the Sequential Oligogenic Linkage Analysis Routines software.Results585 subjects were included, the mean age was 42 (±16.7) years, 57% were women. The heritability of the severity of some GERD symptoms was h2 = 0.27, 0.27, 0.37, and 0.34 (p-value <1.0x10-5) for acidity complaints, lower abdominal complaints, sleep disturbances, and total ReQuest score, respectively. Heritability of metabolic syndrome components ranged from 0.40 for fasting plasma glucose to 0.61 for body mass index and diabetes mellitus. The heritability for fibrinogen and C-reactive protein was 0.64 and 0.38, respectively. Statistically significant genetic correlations were found between acidity complaints and fasting plasma glucose (ρG = 0.40); sleep disturbances and fasting plasma glucose (ρG = 0.36); acidity complaints and diabetes mellitus (ρG = 0.49) and between total ReQuest score and fasting plasma glucose (ρG = 0.43). The rest of metabolic syndrome components did not correlate with GERD symptoms.ConclusionGenetic factors substantially explain the phenotypic variance of the severity of some GERD symptoms, metabolic syndrome components and inflammation markers. Observed genetic correlations suggest that these phenotypes share common genes. These findings suggest conducting further investigation, as the determination of a linkage analysis in order to identify regions of susceptibility for developing of GERD and metabolic syndrome.

A genome-wide quantitative trait locus (QTL) linkage scan of NEO personality factors in Latino families segregating bipolar disorder.

Personality traits have been suggested as potential endophenotypes for Bipolar Disorder (BP), as they can be quantitatively measured and show correlations with BP. The present study utilized data from 2,745 individuals from 686 extended pedigrees originally ascertained for having multiplex cases of BP (963 cases of BPI or schizoaffective BP). Subjects were assessed with the NEO Personality Inventory, Revised (NEO PI-R) and genotyped using the Illumina HumanLinkage-24 Bead Chip, with an average genetic coverage of 0.67 cM. Two point linkage scores were calculated for each trait as a quantitative variable using SOLAR (Sequential Oligogenic Linkage Analysis Routines). Suggestive evidence for linkage was found for neuroticism at 1q32.1 (LOD = 2.52), 6q23.3 (2.32), 16p12 (2.79), extraversion at 4p15.3 (2.33), agreeableness at 4q31.1 (2.37), 5q34 (2.80), 7q31.1 (2.56), 16q22 (2.52), and conscientiousness at 4q31.1 (2.50). Each of the above traits have been shown to be correlated with the broad BP phenotype in this same sample. In addition, for the trait of openness, we found significant evidence of linkage to chromosome 3p24.3 (rs336610, LOD = 4.75) and suggestive evidence at 1q43 (2.74), 5q35.1 (3.03), 11q14.3 (2.61), 11q21 (2.30), and 19q13.1 (2.52). These findings support previous linkage findings of the openness trait to chromosome 19q13 and the agreeableness trait to 4q31 and identify a number of new loci for personality endophenotypes related to bipolar disorder.

Heritability of the Severity of the Metabolic Syndrome in Whites and Blacks in 3 Large Cohorts.

Although dichotomous criteria for the metabolic syndrome (MetS) appear heritable, it is not known whether MetS severity as assessed by a continuous MetS score is heritable and whether this varies by race. We used SOLAR (Sequential Oligogenic Linkage Analysis Routines) to evaluate heritability of Adult Treatment Panel-III MetS and a sex- and race-specific MetS severity Z score among 3 large familial cohorts: the JHS (Jackson Heart Study, 1404 black participants), TOPS (Take Off Pounds Sensibly, 1947 white participants), and PLRS (Princeton Lipid Research Study, 229 black and 527 white participants). Heritability estimates were larger for Adult Treatment Panel-III MetS among black compared with white cohort members (JHS 0.48; 95% confidence interval [CI], 0.28-0.68 and PLRS blacks 0.93 [95% CI, 0.73-1.13] versus TOPS 0.21 [95% CI, -0.18 to 0.60] and PLRS whites 0.27 [95% CI, -0.04 to 0.58]). The difference by race narrowed when assessing heritability of the MetS severity score (JHS 0.52 [95% CI, 0.38, 0.66] and PLRS blacks 0.64 [95% CI, 0.13-1.15] versus TOPS 0.23 [95% CI, 0.15-0.31] and PLRS whites 0.60 [95% CI, 0.33-0.87]). There was a high degree of genetic and phenotypic correlation between MetS severity and the individual components of MetS among all groups, although the genetic correlations failed to reach statistical significance among PLRS blacks. Meta-analyses revealed a combined heritability estimate for Adult Treatment Panel-III MetS of 0.24 (95% CI, 0.11-0.36) and for the MetS severity score of 0.50 (95% CI, -0.05 to 0.99). MetS severity seems highly heritable among whites and blacks. This continuous MetS severity Z score may provide a more useful means of characterizing phenotypic MetS in genetic studies by minimizing racial differences.

Heritability of Vascular Structure and Function: A Parent-Child Study.

BackgroundUnderstanding the heritable contribution of vascular measures, from parent to offspring, may aid in risk stratification and atherosclerosis prevention efforts. We hypothesized that measures of vascular structure and function would be heritable in this cohort of parents and their adolescent offspring.Methods and ResultsHigh‐resolution ultrasound scans of the brachial and carotid arteries were obtained in parents (n=558) and their offspring (n=369). Lumen diameter and flow‐mediated dilation were measured in the brachial artery. Intima‐media thickness, lumen diameter, incremental elastic modulus, diameter distensibility, and cross‐sectional distensibility were measured, and carotid cross‐sectional compliance was measured in the carotid artery. Carotid–radial pulse wave velocity was obtained using SphygmoCor®. Heritability analysis (h2, expressed as %) using Sequential Oligogenic Linkage Analysis Routines was performed on the entire cohort and adjusted for age, sex, race, body–mass index, smoking, and mean arterial pressure. Data are presented as mean±SE. Measures of brachial artery diameter (h2=25±9%, P=0.001), lumen diameter (h2=55±9%, P<0.001), intima‐media thickness (h2=29±13%, P=0.014), diameter distensibility (h2=28±7%, P<0.001), cross‐sectional distensibility (h2=27±7%, P<0.001), and pulse wave velocity (h2=26±9%, P<0.001) were significantly heritable. Flow‐mediated dilation and incremental elastic modulus were not significantly heritable. Similar associations were observed in analysis restricted to siblings and complete Trios (mother, father, and child).ConclusionsThese data show that the majority of noninvasive measures of vascular structure and function are heritable, suggesting that measurement of these subclinical risk factors in parents may be helpful in assessing childhood risk for future cardiovascular disease.

The heritable basis of gene\u2013environment interactions in cardiometabolic traits

Aims/hypothesisLittle is known about the heritable basis of gene–environment interactions in humans. We therefore screened multiple cardiometabolic traits to assess the probability that they are influenced by genotype–environment interactions.MethodsFourteen established environmental risk exposures and 11 cardiometabolic traits were analysed in the VIKING study, a cohort of 16,430 Swedish adults from 1682 extended pedigrees with available detailed genealogical, phenotypic and demographic information, using a maximum likelihood variance decomposition method in Sequential Oligogenic Linkage Analysis Routines software.ResultsAll cardiometabolic traits had statistically significant heritability estimates, with narrow-sense heritabilities (h2) ranging from 24% to 47%. Genotype–environment interactions were detected for age and sex (for the majority of traits), physical activity (for triacylglycerols, 2 h glucose and diastolic BP), smoking (for weight), alcohol intake (for weight, BMI and 2 h glucose) and diet pattern (for weight, BMI, glycaemic traits and systolic BP). Genotype–age interactions for weight and systolic BP, genotype–sex interactions for BMI and triacylglycerols and genotype–alcohol intake interactions for weight remained significant after multiple test correction.Conclusions/interpretationAge, sex and alcohol intake are likely to be major modifiers of genetic effects for a range of cardiometabolic traits. This information may prove valuable for studies that seek to identify specific loci that modify the effects of lifestyle in cardiometabolic disease.

A combined linkage and association strategy identifies a variant near the GSTP1 gene associated with BMI in the Mexican population.

Obesity is a major public health concern in Mexico and worldwide. Although the estimated heritability is high, common variants identified by genome-wide association studies explain only a small proportion of this heritability. A combination of linkage and association strategies could be a more robust and powerful approach to identify other obesity-susceptibility variants. We thus sought to identify novel genetic variants associated with obesity-related traits in the Mexican population by combining these methods. We performed a genome-wide linkage scan for body mass index (BMI) and other obesity-related phenotypes in 16 Mexican families using the Sequential Oligogenic Linkage Analysis Routines Program. Associated single-nucleotide polymorphisms (SNPs) were tested for associations in an independent cohort. Two suggestive BMI-linkage peaks (logarithm of odds ⩾1.5) were observed at chromosomal regions 11q13 and 13q22. Only rs614080 in the 11q13 region was significantly associated with BMI and related traits in these families. This association was also significant in an independent cohort of Mexican adults. Moreover, this variant was significantly associated with GSTP1 gene expression levels in adipose tissue. In conclusion, the rs614080 SNP near the GSTP1 gene was significantly associated with BMI and GSTP1 expression levels in the Mexican population.

Genetic complexity at expression quantitative trait loci.

BackgroundIdentifying variants that regulate gene expression and delineating their genetic architecture is a critical next step in our endeavors to better understand the genetic etiology of complex diseases. The appropriate genomic tools are in place, and preliminary analytic strategies have been developed.MethodsHere we used Genetic Analysis Workshop (GAW) 19 data to investigate the genetic complexity of expression quantitative trait loci (eQTL), chromosomal regions likely to harbor regulatory elements responsible for gene expression. For this investigation, we analyzed the lymphocyte expression profiles of 653 individuals in 20 pedigrees who were also genotyped by single nucleotide polymorphism (SNP) arrays, followed by sequencing and imputation. We used these data to examine the degree of allelic heterogeneity, a contributor to genetic complexity at eQTL, by sequentially conditioning on the most significantly associated SNPs.ResultSOLAR (Sequential Oligogenic Linkage Analysis Routines)-MGA (measured genotype approach) and FaST-LMM (Factored Spectrally Transformed Linear Mixed Model) software allowed us to analyze pedigree data. The power and Type 1 error rates for single SNP association testing and multiple SNP sequential association testing were consistent for these programs. Sequential conditioning of the real expression data revealed substantial levels of allelic heterogeneity at the 2 eQTL examined, illustrating this feature of genetic complexity.ConclusionseQTL exhibit substantial genetic complexity among and within pedigrees.

Heritability and Familiality of Temperament and Character Dimensions in Korean Families with Schizophrenic Linkage Disequilibrium.

ObjectiveCategorical syndromes such as schizophrenia may represent complexes of many continuous psychological structural phenotypes along several dimensions of personality development/degeneration. The present study investigated the heritability and familiality of personality dimensions in Korean families with schizophrenic linkage disequilibrium (LD).MethodsWe recruited 179 probands (with schizophrenia) as well as, whenever possible, their parents and siblings. We used the Temperament and Character Inventory (TCI) to measure personality and symptomatic dimensions. The heritability of personality dimensions in a total of 472 family members was estimated using Sequential Oligogenic Linkage Analysis Routines (SOLAR). To measure familiality, we compared the personality dimensions of family members with those of 336 healthy unrelated controls using analysis of variance (ANOVA) analysis.ResultsThree of the seven TCI variables were significantly heritable and were included in subsequent analyses. The three groups (control, unaffected first-degree relative, case) were found to significantly differ from one another, with the expected order of average group scores, for all heritable dimensions.ConclusionDespite several study limitations with respect to family recruitment and phenotyping, our results show that aberrations in several personality dimensions related to genetic-environment coactions or interactions may underlie the complexity of the schizophrenic syndrome.

Gene expression in large pedigrees: analytic approaches

BackgroundWe currently have the ability to quantify transcript abundance of messenger RNA (mRNA), genome-wide, using microarray technologies. Analyzing genotype, phenotype and expression data from 20 pedigrees, the members of our Genetic Analysis Workshop (GAW) 19 gene expression group published 9 papers, tackling some timely and important problems and questions. To study the complexity and interrelationships of genetics and gene expression, we used established statistical tools, developed newer statistical tools, and developed and applied extensions to these tools.MethodsTo study gene expression correlations in the pedigree members (without incorporating genotype or trait data into the analysis), 2 papers used principal components analysis, weighted gene coexpression network analysis, meta-analyses, gene enrichment analyses, and linear mixed models. To explore the relationship between genetics and gene expression, 2 papers studied expression quantitative trait locus allelic heterogeneity through conditional association analyses, and epistasis through interaction analyses. A third paper assessed the feasibility of applying allele-specific binding to filter potential regulatory single-nucleotide polymorphisms (SNPs). Analytic approaches included linear mixed models based on measured genotypes in pedigrees, permutation tests, and covariance kernels. To incorporate both genotype and phenotype data with gene expression, 4 groups employed linear mixed models, nonparametric weighted U statistics, structural equation modeling, Bayesian unified frameworks, and multiple regression.Results and discussionRegarding the analysis of pedigree data, we found that gene expression is familial, indicating that at least 1 factor for pedigree membership or multiple factors for the degree of relationship should be included in analyses, and we developed a method to adjust for familiality prior to conducting weighted co-expression gene network analysis. For SNP association and conditional analyses, we found FaST-LMM (Factored Spectrally Transformed Linear Mixed Model) and SOLAR-MGA (Sequential Oligogenic Linkage Analysis Routines –Major Gene Analysis) have similar type 1 and type 2 errors and can be used almost interchangeably. To improve the power and precision of association tests, prior knowledge of DNase-I hypersensitivity sites or other relevant biological annotations can be incorporated into the analyses. On a biological level, eQTL (expression quantitative trait loci) are genetically complex, exhibiting both allelic heterogeneity and epistasis. Including both genotype and phenotype data together with measurements of gene expression was found to be generally advantageous in terms of generating improved levels of significance and in providing more interpretable biological models.ConclusionsPedigrees can be used to conduct analyses of and enhance gene expression studies.

Heritabilities, proportions of heritabilities explained by GWAS findings, and implications of cross-phenotype effects on PR interval.

Electrocardiogram (ECG) measurements are a powerful tool for evaluating cardiac function and are widely used for the diagnosis and prediction of a variety of conditions, including myocardial infarction, cardiac arrhythmias, and sudden cardiac death. Recently, genome-wide association studies (GWASs) identified a large number of genes related to ECG parameter variability, specifically for the QT, QRS, and PR intervals. The aims of this study were to establish the heritability of ECG traits, including indices of left ventricular hypertrophy, and to directly assess the proportion of those heritabilities explained by GWAS variants. These analyses were conducted in a large, Dutch family-based cohort study, the Erasmus Rucphen Family study using variance component methods implemented in the SOLAR (Sequential Oligogenic Linkage Analysis Routines) software package. Heritability estimates ranged from 34 % for QRS and Cornell voltage product to 49 % for 12-lead sum. Trait-specific GWAS findings for each trait explained a fraction of their heritability (17 % for QRS, 4 % for QT, 2 % for PR, 3 % for Sokolow–Lyon index, and 4 % for 12-lead sum). The inclusion of all ECG-associated single nucleotide polymorphisms explained an additional 6 % of the heritability of PR. In conclusion, this study shows that, although GWAS explain a portion of ECG trait variability, a large amount of heritability remains to be explained. In addition, larger GWAS for PR are likely to detect loci already identified, particularly those observed for QRS and 12-lead sum.Electronic supplementary materialThe online version of this article (doi:10.1007/s00439-015-1595-9) contains supplementary material, which is available to authorized users.

Impact of family structure and common environment on heritability estimation for neuroimaging genetics studies using Sequential Oligogenic Linkage Analysis Routines.

Imaging genetics is an emerging methodological field that combines genetic information with medical imaging-derived metrics to understand how genetic factors impact observable phenotypes. In order for a trait to be a reasonable phenotype in an imaging genetics study, it must be heritable: at least some proportion of its variance must be due to genetic influences. The Sequential Oligogenic Linkage Analysis Routines (SOLAR) imaging genetics software can estimate the heritability of a trait in complex pedigrees. We investigate the ability of SOLAR to accurately estimate heritability and common environmental effects on simulated imaging phenotypes in various family structures. We found that heritability is reliably estimated with small family-based studies of 40 to 80 individuals, though subtle differences remain between the family structures. In an imaging application analysis, we found that with 80 subjects in any of the family structures, estimated heritability of white matter fractional anisotropy was biased by <10% for every region of interest. Results from these studies can be used when investigators are evaluating power in planning genetic analyzes.

Plasma lipidome is independently associated with variability in metabolic syndrome in Mexican American families

Plasma lipidome is now increasingly recognized as a potentially important marker of chronic diseases, but the exact extent of its contribution to the interindividual phenotypic variability in family studies is unknown. Here, we used the rich data from the ongoing San Antonio Family Heart Study (SAFHS) and developed a novel statistical approach to quantify the independent and additive value of the plasma lipidome in explaining metabolic syndrome (MS) variability in Mexican American families recruited in the SAFHS. Our analytical approach included two preprocessing steps: principal components analysis of the high-resolution plasma lipidomics data and construction of a subject-subject lipidomic similarity matrix. We then used the Sequential Oligogenic Linkage Analysis Routines software to model the complex family relationships, lipidomic similarities, and other important covariates in a variance components framework. Our results suggested that even after accounting for the shared genetic influences, indicators of lipemic status (total serum cholesterol, TGs, and HDL cholesterol), and obesity, the plasma lipidome independently explained 22% of variability in the homeostatic model of assessment-insulin resistance trait and 16% to 22% variability in glucose, insulin, and waist circumference. Our results demonstrate that plasma lipidomic studies can additively contribute to an understanding of the interindividual variability in MS.

Genetic influences of sports participation in Portuguese families

To estimate familial aggregation and quantify the genetic and environmental contribution to the phenotypic variation on sports participation (SP) among Portuguese families. The sample consisted of 2375 nuclear families (parents and two offspring each) from different regions of Portugal with a total of 9500 subjects. SP assessment was based on a psychometrically established questionnaire. Phenotypes used were based on the participation in sports (yes/no), intensity of sport, weekly amount of time in SP and the proportion of the year in which a sport was regularly played. Familial correlations were calculated using family correlations (FCOR) in the SAGE software. Heritability was estimated using variance-components methods implemented in Sequential Oligogenic Linkage Analysis Routines (SOLAR) software. Subjects of the same generation tend to be more similar in their SP habits than the subjects of different generations. In all SP phenotypes studied, adjusted for the effects of multiple covariates, the proportion of phenotypic variance due to additive genetic factors ranged between 40% and 50%. The proportion of variance attributable to environmental factors ranged from 50% for the participation in sports to 60% for intensity of sport. In this large population-based family study, there was significant familial aggregation on SP. These results highlight that the variation on SP phenotypes have a significant genetic contribution although environmental factors are also important in the familial resemblance of SP.

High Heritability of Hallux Valgus and Lesser Toe Deformities in Adult Men and Women

To estimate the heritability of 3 common disorders affecting the forefoot, i.e., hallux valgus, lesser toe deformities, and plantar forefoot soft tissue atrophy, in white adult men and women. Between 2002 and 2008, a trained examiner used a validated foot examination to document the presence of hallux valgus, lesser toe deformities, and plantar soft tissue atrophy in 2,446 adults from the Framingham Foot Study. Among these, 1,370 participants with an available pedigree structure were included. Heritability was estimated using pedigree structures by the Sequential Oligogenic Linkage Analysis Routines package. Results were adjusted for age, sex, and body mass index. The mean age of the participants was 66 years (range 39-99 years) and 57% were women. The prevalence of hallux valgus, lesser toe deformities, and plantar soft tissue atrophy was 31%, 29.6%, and 28.4%, respectively. Significant heritability was found for hallux valgus (range 0.29-0.89, depending on age and sex) and lesser toe deformity (range 0.49-0.90, depending on age and sex). The heritability for lesser toe deformity in men and women ages >70 years was 0.65 (P = 9 × 10(-7)). Significant heritability was found for plantar soft tissue atrophy in men and women ages >70 years (H(2) = 0.37, P = 3.8 × 10(-3)). To our knowledge, these are the first findings of heritability of foot disorders in humans, and they confirm the widely-held view that hallux valgus and lesser toe deformities are highly heritable in white men and women of European descent, underscoring the importance of future work to identify genetic determinants of the underlying genetic susceptibility to these common foot disorders.

Heritability Analysis Suggests Comparable Genetic Component of Mechanical Pain Threshold and Tolerance: Table 1

Genetic basis of pain sensation became one of the hot topics in pain medicine over the past several years. Although numerous studies have suggested the existence of the genetic component of pain threshold, majority of these findings were based on a candidate-gene approach and remained un-replicated, and thus of limited importance (1). Commonly used approach to investigate genetic basis of any trait is to initially estimate heritability, which is defined as the proportion of the total variance of the measured trait attributable to genes. We performed a heritability analysis of the mechanical pain threshold and tolerance in a large-scale pedigree, based on the isolated population of the island of Vis in Croatia, within 10, 001 Dalmatians project (2). A total of 349 subjects were involved in the measurement of mechanical pain threshold and pain tolerance using Algometer Wagner ForceOne. After initial training measurement, subjects were exposed to the actual pain threshold measurement. Three consecutive pain threshold measurements on the dorsal side of the middle phalange of the index finger (on both hands) were performed by a single trained measurer. Additionally, we performed two consecutive measurements of pain tolerance on the same site of both hands. Mixed model analysis was performed using Sequential Oligogenic Linkage Analysis Routines – SOLAR (3), with age and gender as the predictor variables. The results indicated intermediate level of heritability of pain threshold (0.508 for right hand and 0.362 for left hand) and pain tolerance (0.542 for right hand and 0.307 for left hand, notably, the last heritability estimate was not significant ; Table 1). A strong gender and age effects were recorded in all models, with the exception of age in the pain threshold models (Table 1). These results suggest that gene mapping efforts are likely to have similar success both in pain threshold and pain tolerance, despite some previous suggestions that pain threshold is more a physiological function, while tolerance is influenced by stronger modifying effects of different environmental and psychological confounders (4). Furthermore, it should be noted that we detected difference in handedness - the heritability for pain tolerance in left hand was insignificant, with very large standard errors. This could arise from the overall small sample size or it could be pointing to differential mechanisms of pain tolerance in left vs. right, that is dominant, vs. non-dominant hand, which was implied before (5). Regardless of these results, high heritability does not warrant productive gene mapping. Heritability of height was commonly reported as one of the highest ones, generally in the range of 0.92-0.97. However, only creation of a mega-consortium of studies, which consisted of over 180, 000 measured subjects and used genome-wide approach, surpassed previous nearly futile efforts and yielded 180 loci involved in determination of the adult height, and showed a highly polygenic genetic architecture of height (6). If the same is applicable to pain, then we might be expecting a rather complex and lengthy search for genetic architecture of pain. However, the use of hypothesis-free approach, such as genome-wide association study, promises wider and deeper understanding of pain sensation, which is interesting not only for better understanding, but also for the development of new approaches to pain diagnosis and treatment.

Genetic Contributions to the Midsagittal Area of the Corpus Callosum

The degree to which genes and environment determine variations in brain structure and function is fundamentally important to understanding normal and disease-related patterns of neural organization and activity. We studied genetic contributions to the midsagittal area of the corpus callosum (CC) in pedigreed baboons (68 males, 112 females) to replicate findings of high genetic contribution to that area of the CC reported in humans, and to determine if the heritability of the CC midsagittal area in adults was modulated by fetal development rate. Measurements of callosal area were obtained from high-resolution MRI scans. Heritability was estimated from pedigree-based maximum likelihood estimation of genetic and non-genetic variance components as implemented in Sequential Oligogenic Linkage Analysis Routines (SOLAR). Our analyses revealed significant heritability for the total area of the CC and all of its subdivisions, with h2 = .46 for the total CC, and h2 = .54, .37, .62, .56, and .29 for genu, anterior midbody, medial midbody, posterior midbody and splenium, respectively. Genetic correlation analysis demonstrated that the individual subdivisions shared between 41% and 98% of genetic variability. Combined with previous research reporting high heritability of other brain structures in baboons, these results reveal a consistent pattern of high heritability for brain morphometric measures in baboons.

Genetic analyses of smoking initiation, persistence, quantity, and age-at-onset of regular cigarette use in Brazilian families: the Baependi Heart Study.

BackgroundThe purpose of this study was to estimate the genetic influences on the initiation of cigarette smoking, the persistence, quantity and age-at-onset of regular cigarette use in Brazilian families.MethodsThe data set consisted of 1,694 individuals enrolled in the Baependi Heart Study. The heritability and the heterogeneity in genetic and environmental variance components by gender were estimated from variance components approaches, using the SOLAR (Sequential Oligogenic Linkage Analysis Routines) computer package. The mixed-effects Cox model was used for the genetic analysis of the age-at onset of regular cigarette use.ResultsThe heritability estimates were high (> 50%) for smoking initiation and were intermediate, ranging from 23.4 to 31.9%, for smoking persistence and quantity. Significant evidence for heterogeneity in variance components by gender was observed for smoking initiation and age-at-onset of regular cigarette use. Genetic factors play an important role in the interindividual variation of these phenotypes in females, while in males there is a predominant environmental component, which could be explained by greater social influences in the initiation of tobacco use.ConclusionsSignificant heritabilities were observed in smoking phenotypes for both males and females from the Brazilian population. These data add to the literature and are concordant with the notion of significant biological determination in smoking behavior. Samples from the Baependi Heart Study may be valuable for the mapping of genetic loci that modulate this complex biological trait.

Heritability of Level of Response and Association with Recent Drinking History in Nonalcohol‐Dependent Drinkers

Level of response (LR) to alcohol has been shown to be associated with the risk of developing alcohol dependence and can be measured using the self-rating of the effects of alcohol (SRE) questionnaire. This study examined the heritability of the SRE-measured LR and the relationship between LR and recent alcohol drinking history (RDH) in a predominantly African American nonalcohol-dependent population. This was a sibling study of 101 social drinkers aged 21 to 35 years recruited from the Washington, DC metropolitan area. Participants were administered the SRE to assess LR and the timeline followback (TLFB) to assess RDH. The indices of SRE used were total SRE score (SRTT), early drinking SRE score (SRED), regular drinking SRE score (SRRD), and heavy drinking SRE score (SRHD). Pearson's product-moment correlation and linear regression were used to analyze SRE indices and RDH variables (quantity and drinks per drinking occasion). Heritability analysis was conducted using Sequential Oligogenic Linkage Analysis Routines (SOLAR) software with SRE indices as traits of interest. There was a significant relationship between SRE and RDH measures. Drinks per drinking day, maximum drinks, and quantity of drinks were significantly associated with SRTT, SRHD, and SRRD (all p < 0.05). SRTT showed significant heritability (h(2) = 0.67, p = 0.025), however, the SRE subindices (SRED, SRRD, SRHD) were not significantly heritable. Analysis performed in the subset consisting of only African Americans (n = 86) showed similar trends. LR, as measured by the SRE, is associated with RDH. The high level of heritability of the SRE total score suggests that genetics accounts for a significant proportion of the variation in the LR to alcohol in social drinkers.