Heritability of Psychological Traits and Developmental Milestones in Infancy: A Systematic Review and Meta-analysis

Genome-wide association meta-analysis of age at onset of walking in over 70,000 infants of European ancestry

Age at onset of walking is an important early childhood milestone which is used clinically and in public health screening. In this genome-wide association study meta-analysis of age at onset of walking (N = 70,560 European-ancestry infants), we identified 11 independent genome-wide significant loci. SNP-based heritability was 24.13% (95% confidence intervals = 21.86-26.40) with ~11,900 variants accounting for about 90% of it, suggesting high polygenicity. One of these loci, in gene RBL2, co-localized with an expression quantitative trait locus (eQTL) in the brain. Age at onset of walking (in months) was negatively genetically correlated with ADHD and body-mass index, and positively genetically correlated with brain gyrification in both infant and adult brains. The polygenic score showed out-of-sample prediction of 3-5.6%, confirmed as largely due to direct effects in sib-pair analyses, and was separately associated with volume of neonatal brain structures involved in motor control. This study offers biological insights into a key behavioural marker of neurodevelopment.

Parent-child interaction at age 5 months: genetic and environmental contributions and associations with later socio-communicative development

BACKGROUND

Characteristics of parent-child interaction (PCI) early in life have been associated with later development in the child. Twin studies can help to disentangle child contributions to parent-child interaction, for example, by assessing the influence of the child's genetics on his/her social environment, which includes parental behaviour.

METHODS

Infant twins from a community sample [354 monozygotic (MZ), 268 same-sex dizygotic (DZ)] were assessed in terms of PCI at age 5 months. We used the classical twin design to map the aetiology of several parent and child PCI scales and their covariation. We investigated the relations between PCI and later parent-rated child's social communication, language, and autistic traits at ages 2 and 3.

RESULTS

Heritability was below 20% for all the included PCI traits. Unique (nonshared) environmental influences substantially overlapped across several PCI scales, suggesting that idiosyncrasies linked to each session shaped the scoring of several traits in a systematic way. Factor analysis revealed three uncorrelated latent factors, which were conceptualized as 'child negative affect', 'positive affective interaction', and 'parent's supportive strategies'. Parents who were rated highly on 'sensitive responsiveness' at 5 months tended to rate their offspring higher in terms of socio-communicative and language development and lower in terms of autistic traits in the second and third years of life.

CONCLUSIONS

This study maps the phenotypic and aetiological structure of PCI in early infancy and supports the view that parents' sensitive responsiveness towards their infant is associated with later developmental gains in several domains. We did not find strong evidence of any so-called evocative genetic effects on parents' behaviour. We discuss the results considering the general challenge for lab-based observational PCI measures to capture the richness of parent-child interaction.

Genetic and environmental contributions to individual differences in visual attention and oculomotor control in early infancy

Infants differ in their level of eye movement control, which at the extreme could be linked to autism. We assessed eye movements in 450 twins (225 pairs, 57% monozygotic, 46% female, aged 5-6 months) using the gap-overlap eye-tracking task. Shorter latency in the gap condition was associated with having more parent-rated autistic traits at 2 years. Latency across the task's three conditions was primarily explained by one highly heritable latent factor likely representing individual differences in basic oculomotor efficiency and/or in visual information processing. Additionally, disengagement of attention was linked to unique genetic factors, suggesting that genetic factors involved in visual attention are different from those involved in basic visual information processing and oculomotor efficiency.

Editorial: Parenting as an influence on the course of neurodevelopmental conditions - still a taboo topic?

Since the debate surrounding controversial theories, such as the refrigerator mother theory, the influence of parenting on the course of neurodevelopmental conditions has been a taboo topic for many years. However, recent research analyzing the complex interplay between genetics and the environment has introduced new approaches to examining the role of parenting. Several articles in this issue examine the new directions in the field of parenting and parent-child interactions. A key shift in perspective is the recognition that the relationship between parenting and child development is not unidirectional. Instead, the child's characteristics may also influence parental responses (evocative gene-environment), which in turn can shape the child's developmental trajectory. Moreover, parent-child interactions are not restricted to mother-child dyads, but also involve fathers and triadic interactions between both parents and the child. Experiences within these interactions are likely to transfer to other contexts, contributing to the child's language and social development. A better understanding of the time course and the mechanisms underlying parent-child interactions will enhance the design of interventions targeting parenting behavior. Although caregiver-mediated interventions have proven effective, they must take caregivers' skills into account and may need to incorporate alternative support systems beyond primary caregivers.

A systematic review and meta-analysis of the associations between motor milestone timing and motor development in neurodevelopmental conditions

Early motor skills may be important early markers of neurodevelopmental conditions or predictors of their later onset. To explore this, we conducted a systematic review and meta-analysis of infant motor skill assessments in those who go on to gain a clinical diagnosis of autism, attention deficit hyperactivity disorder (ADHD), schizophrenia, language conditions, tic disorders, or developmental coordination disorder (DCD). In total, 63 articles met inclusion criteria. Three three-level meta-analyses were run. Meta-analysis of milestone achievement in N= 21205 individuals revealed gross motor milestones were significantly delayed compared to controls (g= 0.53, p< 0.001). Subgroup analyses revealed autism (g= 0.63) and DCD (g= 0.53) had the highest magnitude delays. Specific delays were revealed for holding the head up (g= 0.21), sitting (g= 0.28), standing (g= 0.35), crawling (g= 0.19), and walking (g= 0.71). Meta-analyses of standardised motor skill measurements in N= 1976 individuals revealed reduced performance compared to controls in autism and language conditions (g= -0.54, p< 0.001). Together, these findings demonstrate delayed milestone attainment and motor impairments in early childhood in neurodevelopmental conditions.

Twenty-four-month effortful control predicts emerging autism characteristics

Longitudinal research can assess how diverging development of multiple cognitive skills during infancy, as well as familial background, are related to the emergence of neurodevelopmental conditions. Sensorimotor and effortful control difficulties are seen in infants later diagnosed with autism; this study explored the relationships between these skills and autism characteristics in 340 infants (240 with elevated familial autism likelihood) assessed at 4-7, 8-10, 12-15, 24, and 36 months. We tested: (1) the relationship between parent-reported effortful control (Rothbart's temperament questionnaires) and sensorimotor skills (Mullen Scales of Early Learning), using random intercept cross-lagged panel modelling; (2) whether household income and maternal education predicted stable individual differences in cognition; (3) sensorimotor and effortful control skills as individual and interactive predictors of parent-reported autism characteristics (Social Responsiveness Scale) at 3 years, using multiple regression; and (4) moderation of interactions by familial likelihood. Sensorimotor skills were longitudinally associated with effortful control at the subsequent measurement point from 12-15 months. Socioeconomic status indicators did not predict stable between-infant differences in sensorimotor or effortful control skills. Effortful control skills were longitudinally related to 3-year autism characteristics from the first year of life, with evidence for an interaction with sensorimotor skills at 24 months. Effects of effortful control increased with age and were particularly important for infants with family histories of autism. Results are discussed in relation to different theoretical frameworks: Developmental Cascades and Anterior Modifiers in the Emergence of Neurodevelopmental Disorders. We suggest a role for 24-month effortful control in explaining the emergent autism phenotype. RESEARCH HIGHLIGHTS: Sensorimotor skills longitudinally predicted effortful control from 12-15 months onward but effortful control did not longitudinally predict sensorimotor skills during infancy. Measures of effortful control skills taken before the age of 1 predicted continuous variation in autism characteristics at 36 months, with associations increasing in strength with age. Effortful control (measured at 12-15 and 24 months) was a stronger predictor of 36-month autism characteristics in infants with elevated familial likelihood for autism. The relationship between 24-month sensorimotor skills and 36-month autism characteristics was stronger in infants with weaker effortful control skills.

Evocative effects on the early caregiving environment of genetic factors underlying the development of intellectual and academic ability

This study examined gene-environment correlation (rGE) in intellectual and academic development in 561 U.S.-based adoptees (57% male; 56% non-Latinx White, 19% multiracial, 13% Black or African American, 11% Latinx) and their birth and adoptive parents between 2003 and 2017. Birth mother intellectual and academic performance predicted adoptive mother warmth at child age 6 (β = .14, p = .038) and 7 (β = .12, p = .040) but not 4.5 years, and adoptive father warmth at 7 (β = .18, p = .007) but not 4.5 or 6 years. These rGE effects were not mediated by children's language. Contrary to theory that rGE accounts for increasing heritability of intellectual ability, parenting did not mediate genetic effects on children's language or academic performance.

Pourcain B, Robinson EB, Bourgeron T, Baron-Cohen S, Børglum AD, Martin HC, Warrier V. An axis of genetic heterogeneity in autism is indexed by age at diagnosis and is associated with varying developmental and mental health profiles

There is growing recognition that earliest signs of autism need not clearly manifest in the first three years of life. To what extent is this variation in developmental trajectories associated with age at autism diagnosis? Does the genetic profile of autism vary with age at autism diagnosis? Using longitudinal data from four birth cohorts, we demonstrate that two different trajectories of socio-emotional behaviours are associated with age at diagnosis. We further demonstrate that the age at autism diagnosis is partly heritable (h2 SNP = 0.12, s.e.m = 0.01), and is associated with two moderately correlated (rg = 0.38, s.e.m = 0.07) autism polygenic factors. One of these factors is associated with earlier diagnosis of autism, lower social and communication abilities in early childhood. The second factor is associated with later autism diagnosis, increased socio-emotional difficulties in adolescence, and has moderate to high positive genetic correlations with Attention-Deficit/Hyperactivity Disorder, mental health conditions, and trauma. Overall, our research identifies an axis of heterogeneity in autism, indexed by age at diagnosis, which partly explains heterogeneity in autism and the profiles of co-occurring neurodevelopmental and mental health profiles. Our findings have important implications for how we conceptualise autism and provide one model to explain some of the diversity within autism.

The potential and translational application of infant genetic research

In the current genomic revolution, the infancy life stage is the most neglected. Although clinical genetics recognizes the value of early identification in infancy of rare genetic causes of disorders and delay, common genetic variation is almost completely ignored in research on infant behavioral and neurodevelopmental traits. In this Perspective, we argue for a much-needed surge in research on common genetic variation influencing infant neurodevelopment and behavior, findings that would be relevant for all children. We now see convincing evidence from different research designs to suggest that developmental milestones, skills and behaviors of infants are heritable and thus are suitable candidates for gene-discovery research. We highlight the resources available to the field, including genotyped infant cohorts, and we outline, with recommendations, special considerations needed for infant data. Therefore, infant genetic research has the potential to impact basic science and to affect educational policy, public health and clinical practice.

Disentangling genetic and environmental influences on early language development: The interplay of genetic propensity for negative emotionality and surgency, and parenting behavior effects on early language skills in an adoption study

Parenting and children's temperament are important influences on language development. However, temperament may reflect prior parenting, and parenting effects may reflect genes common to parents and children. In 561 U.S. adoptees (57% male) and their birth and rearing parents (70% and 92% White, 13% and 4% African American, and 7% and 2% Latinx, respectively), this study demonstrated how genetic propensity for temperament affects language development, and how this relates to parenting. Genetic propensity for negative emotionality inversely predicted language at 27 months (β = -.15) and evoked greater maternal warmth (β = .12), whereas propensity for surgency positively predicted language at 4.5 years (β = .20), especially when warmth was low. Parental warmth (β = .15) and sensitivity (β = .19) further contributed to language development, controlling for common gene effects.

Phenotypic and Genetic Associations Between Preschool Fine Motor Skills and Later Neurodevelopment, Psychopathology, and Educational Achievement

BACKGROUND

Fine motor skills are heritable and comprise important milestones in development, and some evidence suggests that impairments in fine motor skills are associated with neurodevelopmental conditions, psychiatric disorders, and poor educational outcomes.

METHODS

In a preregistered study of 9625 preschool children from TEDS (Twins Early Development Study), fine motor assessments (drawing, block building, folding, and questionnaires) were conducted at 2, 3, and 4 years of age. A cross-age fine motor score was derived using principal component analysis. Multivariate regression analysis was used to examine the relationships between the fine motor score and neurodevelopmental traits, psychopathology, and educational outcomes at 3 later ages (7-8, 12, and 16 years) and cross-age psychopathology composite scores. Polygenic scores (PGSs) were created for attention-deficit/hyperactivity disorder (ADHD), autism, schizophrenia, anxiety, major depressive disorder, obsessive-compulsive disorder, and years of education. We ran single-PGS models and a multi-PGS model.

RESULTS

Fine motor skills were negatively associated with neurodevelopmental traits and psychopathology across childhood and adolescence and positively associated with educational achievement in adolescence (β = 0.25, p < .001). Superior fine motor skills were associated with a higher years-of-education PGS (β = 0.07, p < .001), a lower ADHD PGS (β = -0.04, p = .011), and a higher anxiety PGS (β = 0.03, p = .040). Similarly, the multi-PGS model retained the PGSs for years of education (β = 0.07), ADHD (β = -0.03), and anxiety (β = 0.01). A non-preregistered analysis in an independent preschool sample replicated the ADHD PGS association, but not the years of education or anxiety PGS associations.

CONCLUSIONS

Fine motor skills are linked genetically and phenotypically to later neurodevelopment, psychopathology, and educational outcomes. Future work should investigate the mechanisms that underlie the role of fine motor development in later outcomes.

Editorial: Are government early years learning and development frameworks evidence-based? A scientist's perspective

Not all young children attend nurseries, childminders or other group settings before they start school, but many do. It is common for countries to set out a framework to guide practice for early years providers (such as nurseries) to follow. The conundrum regarding these frameworks for young children is that proving evidence of a causal link between early environments and later outcomes is very challenging scientifically. So how do governments choose what learning and development practices and goals to make mandatory for childcare providers? And is it realistic to expect early years providers to meet the legal requirements that these frameworks impose? We do not know which learning and development practices impact positively on later outcomes, and we certainly do not know if there is a one-size-fits-all approach for an early years framework that is guaranteed to work.

Brazilian Twin Studies: A Scoping Review

The current study was motivated by an interest in deepening understanding of Brazilian twin research, which is underrepresented internationally, in an effort to rectify this situation. Our aim was threefold: (1) to carry out a comprehensive investigation of Brazilian research on twins according to the area of knowledge; (2) to evaluate the representation of research in the field of psychology in comparison with other areas; (3) to evaluate characteristics of the research that may have contributed to its exclusion from the comprehensive meta-analysis of 50 years of twin research. A scoping review was performed according to PRISMA guidelines. Titles and abstracts were searched up to 2022 in six databases: CAPES, BDLTD, PePSIC, PubMed, Google Scholar, and SciELO, using selected keywords both in Portuguese and in English (e.g., 'twins' and 'Brazil'; 'twinning' and 'Brazil'; 'gemelaridade' [twinning], and 'gêmeos' [twins]). Three hundred and forty publications were included in the review. Approximately half (53.8‰) used the classic twin design to investigate the heritability of several traits, and the other half (46.2%) used other research designs. The scoping review showed that the number of publications doubled approximately every 10 years. Most publications were from the health area, with medicine accounting for approximately half of the studies, followed by psychology, odontology, and biology. We found that the interest in studying twins among Brazilian scientists is increasing over the years and there are reasons to be enthusiastic about the potential impact of this trend in the global scenario.

Maximizing the value of twin studies in health and behaviour

In the classical twin design, researchers compare trait resemblance in cohorts of identical and non-identical twins to understand how genetic and environmental factors correlate with resemblance in behaviour and other phenotypes. The twin design is also a valuable tool for studying causality, intergenerational transmission, and gene-environment correlation and interaction. Here we review recent developments in twin studies, recent results from twin studies of new phenotypes and recent insights into twinning. We ask whether the results of existing twin studies are representative of the general population and of global diversity, and we conclude that stronger efforts to increase representativeness are needed. We provide an updated overview of twin concordance and discordance for major diseases and mental disorders, which conveys a crucial message: genetic influences are not as deterministic as many believe. This has important implications for public understanding of genetic risk prediction tools, as the accuracy of genetic predictions can never exceed identical twin concordance rates.