Pets and Our Mental Health: The Why,the What and the How

ABSTRACT

There is growing evidence that pet ownership and human–animal interaction (HAI) have benefits for human physical and psychological well-being. However, there may be pre-existing characteristics related to patterns of pet ownership and interactions with pets that could potentially bias results of research on HAI. The present study uses a behavioral genetic design to estimate the degree to which genetic and environmental factors contribute to individual differences in frequency of play with pets among adult men. Participants were from the ongoing longitudinal Vietnam Era Twin Study of Aging (VETSA), a population-based sample of 1,237 monozygotic (MZ) and dizygotic (DZ) twins aged 51–60 years. Results demonstrate that MZ twins have higher correlations than DZ twins on frequency of pet play, suggesting that genetic factors play a role in individual differences in interactions with pets. Structural equation modeling revealed that, according to the best model, genetic factors accounted for as much as 37% of the variance in pet play, although the majority of variance (63–71%) was due to environmental factors that are unique to each twin. Shared environmental factors, which would include childhood exposure to pets, overall accounted for <10% of the variance in adult frequency of pet play, and were not statistically significant. These results suggest that the effects of childhood exposure to pets on pet ownership and interaction patterns in adulthood may be mediated primarily by genetically-influenced characteristics.     

Latent activity rhythm disturbance sub-groups and longitudinal change in depression symptoms among older men

Activity rhythm disturbances and depression often co-occur among older adults. However, little is known about how activity rhythm disturbances themselves co-occur, or how disturbances to multiple aspects of the activity rhythm relate to depression over time. In this study, we performed a Latent Class Analysis to derive sub-groups of older men [total n?=?2933, mean age?=?76.28, standard deviation (SD)?=?5.48] who shared similar patterns of activity rhythm disturbances (defined as extreme values of modeled activity rhythm parameters). We found eight sub-groups with distinct combinations of activity rhythm disturbances: one had all normative activity rhythm parameters (32.09%), one had only lower activity (10.06%), three had earlier activity (totaling 26.96%) and three had later activity (totaling 30.89%). Groups with similar timing were distinguished depending on whether the relative length of the active period was shorter and/or if the activity rhythm had lesser amplitude/robustness. We next examined whether the derived activity rhythm sub-groups were associated with different rates of change in depression symptom levels over an average of 5.5 (0.52 SD) follow-up years. The sub-group with lower activity only had faster increases in depressive symptoms over time (compared with the group with normative rhythm parameters), but this association was accounted for by adjustments for concurrently assessed health status covariates. Independent of these covariates, we found that four activity rhythm disturbance sub-groups experienced faster depressive symptom increases (compared with the normative sub-group): These included all three sub-groups that had later activity timing and one sub-group that had earlier activity timing plus a shorter active period and a dampened rhythm. Low activity rhythm height/robustness with normal timing therefore may mark depression risk that is attributable to co-occurring disease processes; in contrast, having late or combined early/compressed/dampened activity rhythms may independently contribute to depression symptom development. Our findings suggest that activity rhythm-related depression risk is heterogeneous, and may be detected when multiple aspects of rhythm timing are delayed or when early timing is accompanied by compressed/dampened activity rhythms. Future studies should consider how distinct combinations of altered activity rhythm timing and height/robustness develop and conjointly determine health risks. Further research is also needed to determine whether/how activity rhythms can be modified to improve depression outcomes.     

Genetic and environmental contributions to prosocial behaviour in 2- to 9-year-old South Korean twins

Although over 50 twin and adoption studies have been performed on the genetic architecture of antisocial behaviour, far fewer studies have investigated prosocial behaviour, and none have done so on a non-western population. The present study examined mothers' ratings of prosocial behaviour in 514 pairs of 2- to 9-year-old South Korean monozygotic and dizygotic twins. Correlational analyses showed a tendency of increasing genetic effects and decreasing shared environmental effects with age although shared family environment effects and the moderating effects of age did not attain statistical significance in model-fitting analyses. The best-fitting model indicated that 55% (95% CI: 45-64%) of the variance in the 2- to 9-year-olds' prosocial behaviour was due to genetic factors and 45% (95% CI: 36-55%) was due to non-shared environmental factors. It is concluded that genetic and environmental influences on prosocial behaviour in young South Koreans are mostly similar to those in western samples.     

Genetic and environmental contributions to population group differences on the Raven's Progressive Matrices estimated from twins reared together and apart

We carried out two studies to test the hypothesis that genetic and environmental influences explain population group differences in general mental ability just as they do individual differences within a group. We estimated the heritability and environmentality of scores on the diagrammatic puzzles of the Raven's Coloured and/or Standard Progressive Matrices (CPM/SPM) from two independent twin samples and correlated these estimates with group differences on the same items. In Study 1, 199 pairs of 5- to 7-year-old monozygotic (MZ) and dizygotic (DZ) twins reared together provided estimates of heritability and environmentality for 36 puzzles from the CPM. These estimates correlated with the differences between the twins and 94 Serbian Roma (both rs=0.32; Ns=36; ps<0.05). In Study 2, 152 pairs of adult MZ and DZ twins reared apart provided estimates of heritability and environmentality for 58 puzzles from the SPM. These estimates correlated with the differences among 11 diverse samples including (i) the reared-apart twins, (ii) another sample of Serbian Roma, and (iii) East Asian, White, South Asian, Coloured and Black high school and university students in South Africa. In 55 comparisons, group differences were more pronounced on the more heritable and on the more environmental items (mean rs=0.40 and 0.47, respectively; Ns=58; ps<0.05). After controlling for measurement reliability and variance in item pass rates, the heritabilities still correlated with the group differences, although the environmentalities did not. Puzzles found relatively difficult (or easy) by the twins were those found relatively difficult (or easy) by the others (mean r=0.87). These results suggest that population group differences are part of the normal variation expected within a universal human cognition.     

Genetic Influences on Changes in Body Mass Index: A Longitudinal Analysis of Women Twins

AUSTIN, MELISSA A, YECHIEL FRIEDLANDER, BETH NEWMAN, KAREN EDWARDS, ELIZABETH J MAYER-DAVIS, MARY-CLAIRE KING. Genetic influences on changes in body mass index: a longitudinal analysis of women twins. Numerous studies have demonstrated genetic influences on body fat, but there also may be genetic effects on its intraindividual variation over time. This study examined changes in body mass index (BMI) using longitudinal data from two examinations of the Kaiser Permanente Women Twins Study, performed a decade apart. The analysis included 630 women, 185 monozygotic and 130 dizygotic twin pairs, with average ages of 41 years and 51 years at the two examinations, respectively. Age adjusted heritability estimates for the change in BMI over the decade ranged from 0.57 to 0.86 (all ρ≤0.001) using three different statistical analysis approaches, indicating that at least half, and possibly as much as 85%, of the variance in the change in BMI is attributable to genetic influences under a polygenic model. These estimates remained statistically significant after adjusting for environmental factors (ranging from 0.57 to 0.78) and with additional adjustment for BMI at baseline (ranging from 0.41 to 0.79), although dizygotic intraclass correlations were low after these adjustments. Thus, in addition to known environmental and behavioral influences, these results provide evidence for genetic influences on changes in BMI over a decade in women.     

The interface between genetics and psychology: lessons from developmental dyslexia

Developmental dyslexia runs in families, and twin studies have confirmed that there is a substantial genetic contribution to poor reading. The way in which discoveries in molecular genetics are reported can be misleading, encouraging us to think that there are specific genes that might be used to screen for disorder. However, dyslexia is not a classic Mendelian disorder that is caused by a mutation in a single gene. Rather, like many other common disorders, it appears to involve combined effects of many genes and environmental factors, each of which has a small influence, possibly supplemented by rare variants that have larger effects but apply to only a minority of cases. Furthermore, to see clearer relationships between genotype and phenotype, we may need to move beyond the clinical category of dyslexia to look at underlying cognitive deficits that may be implicated in other neurodevelopmental disorders.     

Differentiating between monozygotic twins through DNA methylation-specific high-resolution melt curve analysis

Although short tandem repeat profiling is extremely powerful in identifying individuals from crime scene stains, it is unable to differentiate between monozygotic (MZ) twins. Efforts to address this include mutation analysis through whole genome sequencing and through DNA methylation studies. Methylation of DNA is affected by environmental factors; thus, as MZ twins age, their DNA methylation patterns change. This can be characterized by bisulfite treatment followed by pyrosequencing. However, this can be time-consuming and expensive; thus, it is unlikely to be widely used by investigators. If the sequences are different, then in theory the melting temperature should be different. Thus, the aim of this study was to assess whether high-resolution melt curve analysis can be used to differentiate between MZ twins. Five sets of MZ twins provided buccal swabs that underwent extraction, quantification, bisulfite treatment, polymerase chain reaction amplification and high-resolution melting curve analysis targeting two markers, Alu-E2F3 and Alu-SP. Significant differences were observed between all MZ twins targeting Alu-E2F3 and in four of five MZ twins targeting Alu-SP (P < 0.05). Thus, it has been demonstrated that bisulfite treatment followed by high-resolution melting curve analysis could be used to differentiate between MZ twins.     

A common heritable factor influences prosocial obligations across multiple domains

Although it has been shown that prosocial behaviour is heritable, it has not yet been established whether narrower aspects of prosociality are heritable, nor whether a common mechanism influences prosociality across its multiple domains. Here, we examine civic duty, work-place commitment and concern for the welfare of others with a study of prosocial obligations in 958 adult twin-pairs. Multivariate modelling indicated the existence of genetic factors underlying general prosocial obligations in females, with familial effects (genetic and shared-environment effects were indistinguishable) influencing this general mechanism in males. At the domain-specific level, modest genetic effects were observed in females for civic and work obligations, with shared-environment effects influencing welfare obligations. In males, genetic influences were observed for welfare obligation, with unique environments affecting work and civic duty.     

Circadian Rhythms in 6-Sulphatoxymelatonin and Nocturnal Sleep in Blind Children

This article describes the relationship between melatonin secretion and sleep quality and subjective complaints about sleep in totally blind children. Eleven boarding-school children (mean age 15.2 years) participated. The major urinary melatonin metabolite 6-sulphatoxymelatonin (aMT6s) was measured five times a day for 48 h. Sleep-wake cycles were recorded by continuous actigraphic recordings during the same time period. Results showed that delayed secretory peaks in aMT6s were significantly associated with disturbed nocturnal sleep and with complaints about morning fatigue.     

Circadian Rhythms in 6-Sulphatoxymelatonin and Nocturnal Sleep in Blind Children

This article describes the relationship between melatonin secretion and sleep quality and subjective complaints about sleep in totally blind children. Eleven boarding-school children (mean age 15.2 years) participated. The major urinary melatonin metabolite 6-sulphatoxymelatonin (aMT6s) was measured five times a day for 48 h. Sleep-wake cycles were recorded by continuous actigraphic recordings during the same time period. Results showed that delayed secretory peaks in aMT6s were significantly associated with disturbed nocturnal sleep and with complaints about morning fatigue.     

Differentiating between monozygotic twins through next-generation mitochondrial genome sequencing

Monozygotic (MZ) twins, considered to be genetically identical, cannot be distinguished from one another by standard forensic DNA testing. A recent study employed whole genome sequencing to identify extremely rare mutations and reported that mutation analysis could be used to differentiate between MZ twins. Compared with nuclear DNA, mitochondrial DNA (mtDNA) has higher mutation rates; therefore, minor differences theoretically exist in MZ twins' mitochondrial genome (mtGenome). However, conventional Sanger-type sequencing (STS) is neither amenable to, nor feasible for, the detection of low-level sequence variants. The recent introduction of massively parallel sequencing (MPS) has the capability to sequence many targeted regions of multiple samples simultaneously with desirable depth of coverage. Thus, the aim of this study was to assess whether full mtGenome sequencing analysis can be used to differentiate between MZ twins. Ten sets of MZ twins provided blood samples that underwent extraction, quantification, mtDNA enrichment, library preparation, and ultra-deep sequencing. Point heteroplasmies were observed in eight sets of MZ twins, and a single nucleotide variant (nt15301) was detected in five sets of MZ twins. Thus, this study demonstrates that ultra-deep mtGenome sequencing could be used to differentiate between MZ twins.     

Comparison of two different actigraphs with polysomnography in healthy young subjects

The present study aimed to compare two commercially available actigraphs, with a concurrent polysomnographic (PSG) recording. Twelve healthy volunteers (six women; age range 19-28 yrs) simultaneously wore the Basic Mini-Motionlogger^® and Actiwatch^® for seven overnight polysomnographic recordings. Comparisons of the following sleep measures were focused on: sleep onset latency (SOL), total sleep time, wake after sleep onset, and sleep efficiency. Both devices underestimated SOL in comparison to PSG, but they had similar performance compared to PSG for the other sleep measures. A limit of the study is that the results can be only generalized to healthy young subjects.