Genetic ancestry of participants in the National Children’s Study

Background

The National Children’s Study (NCS) is a prospective epidemiological study in the USA tasked with identifying a nationally representative sample of 100,000 children, and following them from their gestation until they are 21 years of age. The objective of the study is to measure environmental and genetic influences on growth, development, and health. Determination of the ancestry of these NCS participants is important for assessing the diversity of study participants and for examining the effect of ancestry on various health outcomes.

Results

We estimated the genetic ancestry of a convenience sample of 641 parents enrolled at the 7 original NCS Vanguard sites, by analyzing 30,000 markers on exome arrays, using the 1000 Genomes Project superpopulations as reference populations, and compared this with the measures of self-reported ethnicity and race. For 99% of the individuals, self-reported ethnicity and race agreed with the predicted superpopulation. NCS individuals self-reporting as Asian had genetic ancestry of either South Asian or East Asian groups, while those reporting as either Hispanic White or Hispanic Other had similar genetic ancestry. Of the 33 individuals who self-reported as Multiracial or Non-Hispanic Other, 33% matched the South Asian or East Asian groups, while these groups represented only 4.4% of the other reported categories.

Conclusions

Our data suggest that self-reported ethnicity and race have some limitations in accurately capturing Hispanic and South Asian populations. Overall, however, our data indicate that despite the complexity of the US population, individuals know their ancestral origins, and that self-reported ethnicity and race is a reliable indicator of genetic ancestry.     

Effects of Androgen Deprivation on Cerebral Morphometry in Prostate Cancer Patients – An Exploratory Study

Background

Androgen deprivation therapy (ADT) is a common treatment for non-metastatic, low-risk prostate cancer, but a potential side effect of ADT is impaired brain functioning. Previous work with functional magnetic resonance imaging (MRI) demonstrated altered prefrontal cortical activations in cognitive control, with undetectable changes in behavioral performance. Given the utility of brain imaging in identifying the potentially deleterious effects of ADT on brain functions, the current study examined the effects of ADT on cerebral structures using high resolution MRI and voxel-based morphometry (VBM).

Methods

High resolution T1 weighted image of the whole brain were acquired at baseline and six months after ADT for 12 prostate cancer patients and 12 demographically matched non-exposed control participants imaged at the same time points. Brain images were segmented into gray matter, white matter and cerebral ventricles using the VBM toolbox as implemented in Statistical Parametric Mapping 8.

Results

Compared to baseline scan, prostate cancer patients undergoing ADT showed decreased gray matter volume in frontopolar cortex, dorsolateral prefrontal cortex and primary motor cortex, whereas the non-exposed control participants did not show such changes. In addition, the decrease in gray matter volume of the primary motor cortex showed a significant correlation with longer reaction time to target detection in a working memory task.

Conclusions

ADT can affect cerebral gray matter volumes in prostate cancer patients. If replicated, these results may facilitate future studies of cognitive function and quality of life in men receiving ADT, and can also help clinicians weigh the benefits and risks of hormonal therapy in the treatment of prostate cancer.     

An Exploratory Study of Domestic Violence: Perpetrators’ Reports of Violence Against Animals

The goal of the current exploratory study was to examine associations between animal cruelty (AC), intimate partner violence (IPV), and antisocial personality disorder (ASPD) among incarcerated adult males. Forty-two men incarcerated in a state prison participated in the study; all participants were incarcerated for IPV and/or admitted to committing IPV in a past relationship. They completed measures on childhood animal cruelty (CAC), lifetime prevalence of AC, and IPV. It was hypothesized that men with ASPD diagnoses would report greater exposure to, and perpetration of, AC, as well as more severe IPV behaviors. It was also expected that lifetime exposure to, and perpetration of, AC would be associated with greater animal abuse in the context of IPV. Lastly, it was hypothesized that participants who reported exposure to, and perpetration of, AC would also report higher rates of IPV behaviors. Rates of animal cruelty were high in this sample. Approximately 36% of participants endorsed CAC, 81% reported animal cruelty perpetration in their lifetime, 85.7% reported being exposed to animal cruelty during their lifetime, 38% endorsed using threats against animals during a relationship conflict, and 52% reported abusing and/or killing a pet during a relationship conflict. CAC was significantly related to increased use of psychological abuse and sexual coercion in the context of intimate relationships. ASPD was not related to animal cruelty in the context of IPV. CAC was significantly associated with both threats to, and actual perpetration of, animal abuse during relationship conflicts. The limitations and implications of our findings are discussed in relation to future research.     

Parkinson’s Disease in Saudi Patients: A Genetic Study

Parkinson’s disease (PD) is one of the major causes of parkinsonism syndrome. Its characteristic motor symptoms are attributable to dopaminergic neurons loss in the midbrain. Genetic advances have highlighted underlying molecular mechanisms and provided clues to potential therapies. However, most of the studies focusing on the genetic component of PD have been performed on American, European and Asian populations, whereas Arab populations (excluding North African Arabs), particularly Saudis remain to be explored. Here we investigated the genetic causes of PD in Saudis by recruiting 98 PD-cases (sporadic and familial) and screening them for potential pathogenic mutations in PD-established genes; SNCA, PARKIN, PINK1, PARK7/DJ1, LRRK2 and other PD-associated genes using direct sequencing. To our surprise, the screening revealed only three pathogenic point mutations; two in PINK1 and one in PARKIN. In addition to mutational analysis, CNV and cDNA analysis was performed on a subset of patients. Exon/intron dosage alterations in PARKIN were detected and confirmed in 2 cases. Our study suggests that mutations in the ORF of the screened genes are not a common cause of PD in Saudi population; however, these findings by no means exclude the possibility that other genetic events such as gene expression/dosage alteration may be more common nor does it eliminate the possibility of the involvement of novel genes.     

Rate of Primary Refractory Disease in B and T-Cell Non-Hodgkin’s Lymphoma: Correlation with Long-Term Survival

Background

Primary refractory disease is a main challenge in the management of non-Hodgkin’s Lymphoma (NHL). This survey was performed to define the rate of refractory disease to first-line therapy in B and T-cell NHL subtypes and the long-term survival of primary refractory compared to primary responsive patients.

Methods

Medical records were reviewed of 3,106 patients who had undergone primary treatment for NHL between 1982 and 2012, at the Hematology Centers of Torino and Bergamo, Italy. Primary treatment included CHOP or CHOP-like regimens (63.2%), intensive therapy with autograft (16.9%), or other therapies (19.9%). Among B-cell NHL, 1,356 (47.8%) received first-line chemotherapy with rituximab. Refractory disease was defined as stable/progressive disease, or transient response with disease progression within six months.

Results

Overall, 690 (22.2%) patients showed primary refractory disease, with a higher incidence amongst T-cell compared to B-cell NHL (41.9% vs. 20.5%, respectively, p<0.001). Several other clinico-pathological factors at presentation were variably associated with refractory disease, including histological aggressive disease, unfavorable clinical presentation, Bone Marrow involvement, low lymphocyte/monocyte ration and male gender. Amongst B-cell NHL, the addition of rituximab was associated with a marked reduction of refractory disease (13.6% vs. 26.7% for non-supplemented chemotherapy, p<0.001). Overall, primary responsive patients had a median survival of 19.8 years, compared to 1.3 yr. for refractory patients. A prolonged survival was consistently observed in all primary responsive patients regardless of the histology. The long life expectancy of primary responsive patients was documented in both series managed before and after 2.000. Response to first line therapy resulted by far the most predictive factor for long-term outcome (HR for primary refractory disease: 16.52, p<0.001).

Conclusion

Chemosensitivity to primary treatment is crucial for the long-term survival in NHL. This supports the necessity of studies aimed to early identify refractory disease and to develop different treatment strategies for responsive and refractory patients.     

Genetic Variations of GAK in Two Chinese Parkinson’s Disease Populations: A Case-Control Study

Cyclin G-associated kinase (GAK) modifies α–synuclein expression levels and affects the susceptibility of Parkinson’s disease (PD). The single-nucleotide polymorphism (SNP) rs1564282 of GAK gene has a significant association to the risk of PD among Caucasian populations. To date there is only one data with regards to ethnic Chinese from Mainland China. Here, we conducted a case-control study in two independent cohorts of Han Chinese populations from Taiwan and Singapore to validate this association. A total of 1,755 subjects (871 PD patients and 884 controls) were recruited. The results showed that neither the CT, TT genotypes nor the minor allele T of SNP rs1564282 were associated with PD among the subjects from Taiwan and Singapore as well as in the pooled analysis. Differences in our study population with regards to published literature may be due to epigenetic factors and gene-gene or gene-environmental interactions. Further studies in other Chinese populations will be of interest to validate these findings.     

An Exploratory Study of Human–Dog Co-sleeping Using Actigraphy: Do Dogs Disrupt Their Owner’s Sleep?

ABSTRACT

This exploratory study aimed to contribute to the limited research on human–animal co-sleeping by investigating the extent to which human sleep is disturbed by co-sleeping with a dog. Five female Australian dog owners and their dogs were fitted with activity monitors for seven nights. Raw activity of the dog and human for each sleep episode were matched and then compared using a time series correlation. Dog movement was a significant leading indicator of human movement, with dog activity positively indicating human activity up to 2.5 minutes in advance. Dogs were active for about 20% of the night, with humans 4.3 times more likely to be awake during dog activity than during dog inactivity (10.55%/2.45%). Co-sleeping appears to cause sleep disturbances (both arousals and wake ups), which is reinforced by poor scores on validated sleep measures. There also appears to be disparity between these objective measures and subjective evaluations of sleep quality and number of disturbances. At least in the small sample considered in the present study, co-sleeping with a dog appears to result in measurable, but relatively mild, reductions in overall sleep quality. This detrimental impact must be weighed against the benefits of co-sleeping.     

Development and Validation of Nomograms for Predicting Overall and Breast Cancer–Specific Survival in Young Women with Breast Cancer: A Population-Based Study

INTRODUCTION: The objective of current study was to develop and validate comprehensive nomograms for predicting the survival of young women with breast cancer. METHODS: Women aged <40 years diagnosed with invasive breast cancer between 1990 and 2010 were selected from the Surveillance, Epidemiology, and End Results database and randomly divided into training (n = 12,465) and validation (n = 12,424) cohorts. A competing-risks model was used to estimate the probability of breast cancer–specific survival (BCSS). We identified and integrated significant prognostic factors for overall survival (OS) and BCSS to construct nomograms. The performance of the nomograms was assessed with respect to calibration, discrimination, and risk group stratification. RESULTS: The entire cohort comprised 24,889 patients. The 5- and 10-year probabilities of breast cancer–specific mortality were 11.6% and 20.5%, respectively. Eight independent prognostic factors for both OS and BCSS were identified and integrated for the construction of the nomograms. The calibration curves showed optimal agreement between the predicted and observed probabilities. The C-indexes of the nomograms in the training cohort were higher than those of the TNM staging system for predicting OS (0.724 vs 0.694; P < .001) and BCSS (0.733 vs 0.702; P < .001). Additionally, significant differences in survival were observed in patients stratified into different risk groups within respective TNM categories. CONCLUSIONS: We developed and validated novel nomograms that can accurately predict OS and BCSS in young women with breast cancer. These nomograms may help clinicians in making decisions on an individualized basis.     

Correction to: Genetic characterization of Addison’s disease in Bearded Collies

Diversity of the CRISPR locus of Mycobacterium tuberculosis complex has been studied since 1997 for molecular epidemiology purposes. By targeting solely the 43 spacers present in the two first sequenced genomes (H37Rv and BCG), it gave a biased idea of CRISPR diversity and ignored diversity in the neighbouring cas-genes. We set up tailored pipelines to explore the diversity of CRISPR-cas locus in Short Reads. We analyzed data from a representative set of 198 clinical isolates as evidenced by well-characterized SNPs. We found a relatively low diversity in terms of spacers: we recovered only the 68 spacers that had been described in 2000. We found no partial or global inversions in the sequences, letting always the Direct Variant Repeats (DVR) in the same order. In contrast, we found an unexpected diversity in the form of: SNPs in spacers and in Direct Repeats, duplications of various length, and insertions at various locations of the IS6110 insertion sequence, as well as blocks of DVR deletions. The diversity was in part specific to lineages. When reconstructing evolutionary steps of the locus, we found no evidence for SNP reversal. DVR deletions were linked to recombination between IS6110 insertions or between Direct Repeats. This work definitively shows that CRISPR locus of M. tuberculosis did not evolve by classical CRISPR adaptation (incorporation of new spacers) since the last most recent common ancestor of virulent lineages. The evolutionary mechanisms that we discovered could be involved in bacterial adaptation but in a way that remains to be identified.     

Innate Immunity and Non-Hodgkin’s Lymphoma (NHL) Related Genes in a Nested Case-Control Study for Gastric Cancer Risk

Objective

Genetic variants regulating the host immune system may contribute to the susceptibility for the development of gastric cancer. Little is known about the role of the innate immunity- and non-Hodgkin’s lymphoma (NHL)-related genes for gastric cancer risk. This nested case-control study was conducted to identify candidate genes for gastric cancer risk for future studies.

Methods

In the Discovery phase, 3,072 SNPs in 203 innate immunity- and 264 NHL-related genes using the Illumine GoldenGateTM OPA Panel were analyzed in 42 matched case-control sets selected from the Korean Multi-center Cancer Cohort (KMCC). Six significant SNPs in four innate immunity (DEFA6, DEFB1, JAK3, and ACAA1) and 11 SNPs in nine NHL-related genes (INSL3, CHMP7, BCL2L11, TNFRSF8, RAD50, CASP7, CHUK, CD79B, and CLDN9) with a permutated p-value <0.01 were re-genotyped in the Replication phase among 386 cases and 348 controls. Odds ratios (ORs) for gastric cancer risk were estimated adjusting for age, smoking status, and H. pylori and CagA sero-positivity. Summarized ORs in the total study population (428 cases and 390 controls) are presented using pooled- and meta-analyses.

Results

Four SNPs had no heterogeneity across the phases: in the meta-analysis, DEFA6 rs13275170 and DEFB1 rs2738169 had both a 1.3-fold increased odds ratio (OR) for gastric cancer (95% CIs = 1.1–1.6; and 1.1–1.5, respectively). INSL3 rs10421916 and rs11088680 had both a 0.8-fold decreased OR for gastric cancer (95% CIs = 0.7–0.97; and 0.7–0.9, respectively).

Conclusions

Our findings suggest that certain variants in the innate immunity and NHL-related genes affect the gastric cancer risk, perhaps by modulating infection-inflammation-immunity mechanisms that remain to be defined.     

Innate Immunity Pathways and Breast Cancer Risk in African American and European-American Women in the Women’s Circle of Health Study (WCHS)

African American (AA) women are more likely than European American (EA) women to be diagnosed with early, aggressive breast cancer. Possible differences in innate immune pathways (e.g., inflammatory responses) have received little attention as potential mechanisms underlying this disparity. We evaluated distributions of selected genetic variants in innate immune pathways in AA and EA women, and examined their associations with breast cancer risk within the Women’s Circle of Health Study (WCHS). In stage I of the study (864 AA and 650 EA women) we found that genotype frequencies for 35 of 42 tested SNPs (18 candidate genes) differed between AAs and EAs (corroborated by ancestry informative markers). Among premenopausal AA women, comparing variant allele carriers to non-carriers, reduced breast cancer risk was associated with CXCL5-rs425535 (OR=0.61, P=0.02), while among EA women, there were associations with TNFA-rs1799724 (OR =2.31, P =0.002) and CRP-rs1205 (OR=0.54, P=0.01). For postmenopausal women, IL1B-rs1143627 (OR=1.80, P=0.02) and IL1B-rs16944 (OR=1.85, P =0.02) were associated with risk among EA women, with significant associations for TNFA-rs1799724 limited to estrogen receptor (ER) positive cancers (OR=2.0, P =0.001). However, none of the SNPs retained significance after Bonferroni adjustment for multiple testing at the level of P0.0012 (0.05/42) except for TNFA-rs1799724 in ER positive cancers. In a stage II validation (1,365 AA and 1,307 EA women), we extended evaluations for four SNPs (CCL2-rs4586, CRP-rs1205, CXCL5-rs425535, and IL1RN-rs4251961), which yielded similar results. In summary, distributions of variants in genes involved in innate immune pathways were found to differ between AA and EA populations, and showed differential associations with breast cancer according to menopausal or ER status. These results suggest that immune adaptations suited to ancestral environments may differentially influence breast cancer risk among EA and AA women.     

Default-Mode Network Changes in Huntington’s Disease: An Integrated MRI Study of Functional Connectivity and Morphometry

Previous MRI studies of functional connectivity in pre-symptomatic mutation carriers of Huntington’s disease (HD) have shown dysfunction of the Default-Mode Network (DMN). No data however are currently available on the DMN alterations in the symptomatic stages of the disease, which are characterized by cortical atrophy involving several DMN nodes. We assessed DMN integrity and its possible correlations with motor and cognitive symptoms in 26 symptomatic HD patients as compared to 22 normal volunteers, by analyzing resting state functional MRI data, using the Precuneal Cortex/Posterior Cingulate Cortices (PC/PCC) as seed, controlling at voxel level for the effect of atrophy by co-varying for gray matter volume. Direct correlation with PC/PCC was decreased, without correlation with atrophy, in the ventral medial prefrontal cortex (including anterior cingulate and subgenual cortex), right dorso-medial prefrontal cortex, and in the right inferior parietal cortex (mainly involving the angular gyrus). Negative correlations with PC/PCC were decreased bilaterally in the inferior parietal cortices, while a cluster in the right middle occipital gyrus presented increased correlation with PC/PCC. DMN changes in the ventral medial prefrontal cortex significantly correlated with the performance at the Stroop test (p = .0002). Widespread DMN changes, not correlating with the atrophy of the involved nodes, are present in symptomatic HD patients, and correlate with cognitive disturbances.     

Lipid Integration in Neurodegeneration: An Overview of Alzheimer’s Disease

Various types of lipids and their metabolic products associated with the biological membrane play a crucial role in signal transduction, modulation, and activation of receptors and as precursors of bioactive lipid mediators. Dysfunction in the lipid homeostasis in the brain could be a risk factor for the many types of neurodegenerative disorders, including Alzheimer’s disease, Huntington’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis. These neurodegenerative disorders are marked by extensive neuronal apoptosis, gliosis, and alteration in the differentiation, proliferation, and development of neurons. Sphingomyelin, a constituent of plasma membrane, as well as its primary metabolite ceramide acts as a potential lipid second messenger molecule linked with the modulation of various cellular signaling pathways. Excessive production of reactive oxygen species associated with enhanced oxidative stress has been implicated with these molecules and involved in the regulation of a variety of different neurodegenerative and neuroinflammatory disorders. Studies have shown that alterations in the levels of plasma lipid/cholesterol concentration may result to neurodegenerative diseases. Alteration in the levels of inflammatory cytokines and mediators in the brain has also been found to be implicated in the pathophysiology of neurodegenerative diseases. Although several mechanisms involved in neuronal apoptosis have been described, the molecular mechanisms underlying the correlation between lipid metabolism and the neurological deficits are not clearly understood. In the present review, an attempt has been made to provide detailed information about the association of lipids in neurodegeneration especially in Alzheimer’s disease.     

Analysis of an Advisor–Advisee Relationship: An Exploratory Study of the Area of Exact and Earth Sciences in Brazil

Scientific collaboration has been studied by researchers for decades. Several approaches have been adopted to address the question of how collaboration has evolved in terms of publication output, numbers of coauthors, and multidisciplinary trends. One particular type of collaboration that has received very little attention concerns advisor and advisee relationships. In this paper, we examine this relationship for the researchers who are involved in the area of Exact and Earth Sciences in Brazil and its eight subareas. These pairs are registered in the Lattes Platform that manages the individual curricula vitae of Brazilian researchers. The individual features of these academic researchers and their coauthoring relationships were investigated. We have found evidence that there exists positive correlation between time of advisor–advisee relationship with the advisee’s productivity. Additionally, there has been a gradual decline in advisor–advisee coauthoring over a number of years as measured by the Kulczynski index, which could be interpreted as decline of the dependence.     

First-Year Evaluation of Mexico’s Tax on Nonessential Energy-Dense Foods: An Observational Study

BackgroundIn an effort to prevent continued increases in obesity and diabetes, in January 2014, the Mexican government implemented an 8% tax on nonessential foods with energy density ≥275 kcal/100 g and a peso-per-liter tax on sugar-sweetened beverages (SSBs). Limited rigorous evaluations of food taxes exist worldwide. The objective of this study was to examine changes in volume of taxed and untaxed packaged food purchases in response to these taxes in the entire sample and stratified by socioeconomic status (SES).ConclusionsHousehold purchases of nonessential energy-dense foods declined in the first year after the implementation of Mexico’s SSB and nonessential foods taxes. Future studies should evaluate the impact of the taxes on overall energy intake, dietary quality, and food purchase patterns (see S1 Abstract in Spanish).     

An Atomic Force Microscope Study Revealed Two Mechanisms in the Effect of Anticancer Drugs on Rate-Dependent Young’s Modulus of Human Prostate Cancer Cells

Mechanical properties of cells have been recognized as a biomarker for cellular cytoskeletal organization. As chemical treatments lead to cell cytoskeletal rearrangements, thereby, modifications of cellular mechanical properties, investigating cellular mechanical property variations provides insightful knowledge to effects of chemical treatments on cancer cells. In this study, the effects of eight different anticancer drugs on the mechanical properties of human prostate cancer cell (PC-3) are investigated using a recently developed control-based nanoindentation measurement (CNM) protocol on atomic force microscope (AFM). The CNM protocol overcomes the limits of other existing methods to in-liquid nanoindentation measurement of live cells on AFM, particularly for measuring mechanical properties of live cells. The Young’s modulus of PC-3 cells treated by the eight drugs was measured by varying force loading rates over three orders of magnitude, and compared to the values of the control. The results showed that the Young’s modulus of the PC-3 cells increased substantially by the eight drugs tested, and became much more pronounced as the force load rate increased. Moreover, two distinct trends were clearly expressed, where under the treatment of Disulfiram, paclitaxel, and MK-2206, the exponent coefficient of the frequency- modulus function remained almost unchanged, while with Celebrex, BAY, Totamine, TPA, and Vaproic acid, the exponential rate was significantly increased.     

Freezing of Gait in Parkinson’s Disease: An Overload Problem?

Freezing of gait (FOG) is arguably the most severe symptom associated with Parkinson’s disease (PD), and often occurs while performing dual tasks or approaching narrowed and cluttered spaces. While it is well known that visual cues alleviate FOG, it is not clear if this effect may be the result of cognitive or sensorimotor mechanisms. Nevertheless, the role of vision may be a critical link that might allow us to disentangle this question. Gaze behaviour has yet to be carefully investigated while freezers approach narrow spaces, thus the overall objective of this study was to explore the interaction between cognitive and sensory-perceptual influences on FOG. In experiment #1, if cognitive load is the underlying factor leading to FOG, then one might expect that a dual-task would elicit FOG episodes even in the presence of visual cues, since the load on attention would interfere with utilization of visual cues. Alternatively, if visual cues alleviate gait despite performance of a dual-task, then it may be more probable that sensory mechanisms are at play. In compliment to this, the aim of experiment#2 was to further challenge the sensory systems, by removing vision of the lower-limbs and thereby forcing participants to rely on other forms of sensory feedback rather than vision while walking toward the narrow space. Spatiotemporal aspects of gait, percentage of gaze fixation frequency and duration, as well as skin conductance levels were measured in freezers and non-freezers across both experiments. Results from experiment#1 indicated that although freezers and non-freezers both walked with worse gait while performing the dual-task, in freezers, gait was relieved by visual cues regardless of whether the cognitive demands of the dual-task were present. At baseline and while dual-tasking, freezers demonstrated a gaze behaviour that neglected the doorway and instead focused primarily on the pathway, a strategy that non-freezers adopted only when performing the dual-task. Interestingly, with the combination of visual cues and dual-task, freezers increased the frequency and duration of fixations toward the doorway, compared to non-freezers. These results suggest that although increasing demand on attention does significantly deteriorate gait in freezers, an increase in cognitive demand is not exclusively responsible for freezing (since visual cues were able to overcome any interference elicited by the dual-task). When vision of the lower limbs was removed in experiment#2, only the freezers’ gait was affected. However, when visual cues were present, freezers’ gait improved regardless of the dual-task. This gait behaviour was accompanied by greater amount of time spent looking at the visual cues irrespective of the dual-task. Since removing vision of the lower-limbs hindered gait even under low attentional demand, restricted sensory feedback may be an important factor to the mechanisms underlying FOG.     

The Interplay of Landscape Features and Social System on the Genetic Structure of a Primate Population: An Agent-Based Simulation Study Using “Tamarins”

Tamarins are small-bodied, forest-dwelling, callitrichines that live in groups containing one to a few adult individuals of each sex. Within these groups, reproduction is usually heavily skewed toward a single dominant male and dominant female, females commonly give birth to cooperatively reared twin offspring, and individuals of both sexes disperse, most often to adjacent groups. Throughout their geographic range, tamarin species are being subject to habitat loss and fragmentation, which may influence their ability to survive and disperse successfully. Here, we use a spatially explicit agent-based population genetics simulation toolkit (GENESYS) to explore the potential effects of social structure and landscape features on the population genetic structure of tamarin primates. We first model the population genetic consequences of tamarin social organization in a homogeneous landscape unconstrained by any barriers to gene flow. We then repeat our analyses using the same social system parameters but in different landscapes that either introduce a barrier to gene flow that restricts dispersal from one half of the model world to the other or divide the world into regions with differing “permeabilities” to dispersal. Our results demonstrate that, in our simulated populations, the social system of tamarins results in the clear and rapid genetic differentiation of social groups within a very short time frame. Over time, the limited dispersal of both males and females leads to a pattern of isolation by distance, as expected from a stepping-stone model of gene flow among groups. Introducing a barrier results in a somewhat more complex pattern: isolation by distance still obtains among social groups within regions on each side of the barrier, but the barrier has a much more significant effect on the structuring of genetic variation, leading to strong genetic differentiation among groups on opposite sides that becomes more pronounced over time. Introducing a region of limited dispersal permeability also results in strong differentiation of groups across that region, even though gene flow throughout the landscape is still possible. Our study demonstrates the utility of the GENESYS toolkit for modeling, in silico, the genetic consequences of many features of the social systems of primates and other group-living animals and for simultaneously exploring the effects of landscape features on spatial genetic structure.