Genetic analysis of motor milestones attainment in early childhood

Genetic confounding in the association of early motor development with childhood and adolescent exercise behavior

INTRODUCTION

Early motor development has been found to be a predictor of exercise behavior in children and adolescents, but whether this reflects a causal effect or confounding by genetic or shared environmental factors remains to be established.

METHODS

For 20,911 complete twin pairs from the Netherlands Twin Register a motor development score was obtained from maternal reports on the timing of five motor milestones. During a 12-year follow-up, subsamples of the mothers reported on the twins' ability to perform seven gross motor skills ability (N = 17,189 pairs), and weekly minutes of total metabolic equivalents of task (MET) spent on sports and exercise activities at age 7 (N = 3632 pairs), age 10 (N = 3735 pairs), age 12 (N = 7043 pairs), and age 14 (N = 3990 pairs). Multivariate phenotypic and genetic regression analyses were used to establish the predictive strength of the two motor development traits for future exercise behavior, the contribution of genetic and shared environmental factors to the variance in all traits, and the contribution of familial confounding to the phenotypic prediction.

RESULTS

Significant heritability (h2) and shared environmental (c2) effects were found for early motor development in boys and girls (h2 = 43-65%; c2 = 16-48%). For exercise behavior, genetic influences increased with age (boys: h2age7 = 22% to h2age14 = 51%; girls: h2age7 = 3% to h2age14 = 18%) paired to a parallel decrease in the influence of the shared environment (boys: c2age7 = 68% to c2age14 = 19%; girls: c2age7 = 80% to c2age14 = 48%). Early motor development explained 4.3% (p < 0.001) of the variance in future exercise behavior in boys but only 1.9% (p < 0.001) in girls. If the effect in boys was due to a causal effect of motor development on exercise behavior, all of the factors influencing motor development would, through the causal chain, also influence future exercise behavior. Instead, only the genetic parts of the regression of exercise behavior on motor development were significant. Shared and unique environmental parts of the regression were largely non-significant, which is at odds with the causal hypothesis.

CONCLUSION

No support was found for a direct causal effect in the association between rapid early motor development on future exercise behavior. In boys, early motor development appears to be an expression of the same genetic factors that underlie the heritability of childhood and early adolescent exercise behavior.

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

Importance

Although infancy is the most rapid period of postnatal growth and development, factors associated with variation in infant traits are not well understood.

Objective

To synthesize the large twin study literature partitioning phenotypic variance in psychological traits and developmental milestones in infancy into estimates of heritability and shared and nonshared environment.

Data Sources

PubMed, PsycINFO, and references of included publications were searched up to February 11, 2021.

Study Selection

Peer-reviewed publications using the classical twin design to study psychological traits and developmental milestones from birth to 2 years old were included.

Data Extraction and Synthesis

Data were extracted in line with Preferred Reporting Items for Systematic Reviews and Meta-Analyses and categorized using the International Classification of Functioning, Disability and Health: Children and Youth Version. Data were pooled in 3-level random effects models, incorporating within-cohort variance in outcome measurement and between-cohort variance. Data were analyzed from March 2021 through September 2021.

Main Outcomes and Measures

The primary outcomes were monozygotic and dizygotic twin correlations. These were used to calculate genetic and shared and nonshared environment estimates.

Results

Among 139 publications that were systematically retrieved, data were available on 79 044 twin pairs (31 053 monozygotic and 47 991 dizygotic pairs), 52 independent samples, and 21 countries. Meta-analyses were conducted on psychological traits and developmental milestones from 106 publications organized into 10 categories of functioning, disability, and health. Moderate to high genetic estimates for 8 categories were found, the highest of which was psychomotor functions (pooled h2, 0.59; 95% CI, 0.25-0.79; P < .001). Several categories of traits had substantial shared environment estimates, the highest being mental functions of language (pooled c2, 0.59; 95% CI, 0.24-0.86; P = .001). All examined categories of traits had moderate or high nonshared environment estimates, the highest of which were emotional functions (pooled e2, 0.42; 95% CI, 0.33-0.50; P < .001) and family relationships (pooled e2, 0.42; 95% CI, 0.30-0.55; P < .001).

Conclusions and Relevance

These findings may be an important source of information to guide future gene discovery research, public perspectives on nature and nurture, and clinical insights into the degree to which family history and environments may estimate major domains of infant functioning, disability, and health in psychological traits and developmental milestones.

Does idiopathic congenital talipes equinovarus have an impact on attainment of developmental milestones? A multicentre international study

PURPOSE

The Ponseti method is a well-established approach to treating clubfoot. Potentially, both the underlying pathology and adherence to post-correction bracing can affect lower limb function and age of independent standing and walking. This cohort study investigates the age at which infants with idiopathic clubfoot treated using the Ponseti method achieved three selected developmental milestones and whether or not this correlated with treatment compliance.

METHODS

A prospectively collected database from four centres was visited. Inclusion criteria were patients with idiopathic clubfoot with no comorbidities or prior treatment. Age at attainment of independent standing, walking, nocturnal continence was compared across three groups: I) congenital talipes equinovarus (CTEV) children compliant with treatment; II) CTEV children non-compliant with treatment; and III) typically-developed siblings. Minimum follow-up was five years.

RESULTS

In all, 130 patients (198 feet) fitted the inclusion criteria: 43:87 (F:M). Standing was achieved by a mean 12.0 months in group I (sd 2.50); 12.0 months (sd 2.0) in II and ten months (sd 3.0) in III. Walking was achieved by a mean 15 months (sd 4.0) in group I, 14 months (sd 1.75) in II and 12 months (sd 3) in III, respectively. Both the compliant and non-compliant CTEV children were significantly slower at achieving standing and walking compared to sibling controls (p < 0.0001). There was no significant difference between age of nocturnal continence between the three groups.

CONCLUSION

Infants with idiopathic clubfoot treated according to the Ponseti method achieve independent standing and walking approximately two months later than their typically-developed siblings. The delay is not related to the use of the foot abduction brace.

LEVEL OF EVIDENCE

III.

Genetic and Environmental Influences on Developmental Milestones and Movement: Results From the Gemini Cohort Study

PURPOSE

Variability in the timing of infant developmental milestones is poorly understood. We used a twin analysis to estimate genetic and environmental influences on motor development and activity levels in infancy.

METHOD

Data were from the Gemini Study, a twin birth cohort of 2,402 families with twins born in the United Kingdom in 2007. Parents reported motor activity level for each of the twins at age 3 months using the Revised Infant Behavior Rating Scale and reported the ages at which they first sat unsupported, crawled, and walked unaided.

RESULTS

Activity level at 3 months and ages when first sitting and crawling were about equally influenced by the shared family environment (45%-54%) and genes (45%-48%). Genetic influences dominated for age when children took their first independent steps (84%).

CONCLUSION

Aspects of the shared family environment appear to be important influences on motor activity levels and early milestones, although the timing of walking may have a stronger genetic influence. Further research to identify the specific environmental and genetic factors that promote early activity may be important for longer-term health outcomes.

Environmental rather than genetic factors determine the variation in the age of the infancy to childhood transition: a twins study

OBJECTIVE

Using a twins study, we sought to assess the contribution of genetic against environmental factor as they affect the age at transition from infancy to childhood (ICT).

STUDY DESIGN

The subjects were 56 pairs of monozygotic twins, 106 pairs of dizygotic twins, and 106 pairs of regular siblings (SBs), for a total of 536 children. Their ICT was determined, and a variance component analysis was implemented to estimate components of the familial variance, with simultaneous adjustment for potential covariates.

RESULTS

We found substantial contribution of the common environment shared by all types of SBs that explained 27.7% of the total variance in ICT, whereas the common twin environment explained 9.2% of the variance, gestational age 3.5%, and birth weight 1.8%. In addition, 8.7% was attributable to sex difference, but we found no detectable contribution of genetic factors to inter-individual variation in ICT age.

CONCLUSIONS

Developmental plasticity impacts much of human growth. Here we show that of the ∼50% of the variance provided to adult height by the ICT, 42.2% is attributable to adaptive cues represented by shared twin and SB environment, with no detectable genetic involvement.

Age for onset of walking and prewalking strategies

BACKGROUND

Age for onset of independent walking (AOW) is frequently used as an indicator of the progress of motor development in early life. Yet there is considerable uncertainty in the research literature about the age we should expect children to walk independently, and also whether prewalking strategies are of importance for this milestone. In clinical practice we commonly experience that children start walking at later ages than the standards presented in the Alberta Infant Motor Scale (AIMS), the most frequently used standardized instrument of gross motor development in Norway.

AIMS

To investigate the normal distribution of AOW among Norwegian children, which prewalking locomotor strategies (PLS) children used before AOW, and if children who crawled on hands and knees started to walk earlier than children with other strategies.

DESIGN AND METHODS

This cross-sectional study was based on parental self reports from two data sources, i.e. the Norwegian Mother and Child Cohort Study (MoBa, n = 47,515), and project specific regionally collected data (n = 636).

RESULTS

Half of the Norwegian children had started to walk at 13 months (median). Twenty-five percent walked at 12 months and 75% of the children walked at 14 months. Mean AOW, claiming at least 5 independent steps, was 13.1 (1.91)months. Children who used crawling on hands and knees (84.5%) as PLS started to walk unaided 0.9 months earlier (95% CI = 0.32-1.49, p < 0.05) than bottom shufflers (7.1%).

CONCLUSION

Norwegian children start to walk considerably later than standards reported in AIMS. Crawling on hands and knees is associated with an earlier onset of walking.

Motor development of Japanese twins in childhood as reported by mothers

OBJECTIVE

Twins tend to lag behind singletons in their motor development, though the causes of this appear to be complicated and are not yet fully understood. The present study was performed to clarify the factors associated with the motor development of twins.

METHODS

The twins in the first group consisted of school applicants, including 1131 twin pairs, and the second group consisted of children of members of several maternal associations, and included 951 pairs. All data were gathered by questionnaire survey, and six gross-motor development milestones were analyzed in individuals or pairs.

RESULTS

Relative to general population norms in Japan, twins tended to be delayed in reaching several motor development milestones. Stepwise regression analysis showed that of all the variables measured, gestational age was the most influential on all six milestones. Birthweight was also influential on most milestones. Other factors affecting motor development milestones were parity for 'sitting without support,' 'pulling up to a standing position,' and 'walking without support,' and zygosity for 'walking without support.' In these cases, longer gestational age, heavier birthweighf, primiparity, and dizygosity showed a tendency toward earlier attainment of development. Motor development within pairs was more similar in monozygotic pairs compared with dizygotic pairs regarding each item, suggesting genetic contributions.

CONCLUSION

The results of the present study showed specific and nonspecific factors that affect motor development of twins. These findings should prove useful in understanding the motor development of twin children and help clinicians to refine maternal and child health care for multiple-birth children.

Influences on Achieving Motor Milestones: A Twin–Singleton Study

In order to determine if twinning impacted achievement of motor milestones the attainment of early motor milestones in twins was examined and compared to published data from singletons of the same age from the same culture and birth years. We examined the influence of twinning, sex, zygosity and birth cohort (1987–2001) on the motor development of twins aged 0 to 24 months. Data on the attainment of motor milestones (turn, sit, crawl, stand and walk) of twins were collected from maternal reports. All data were corrected for gestational age. Data from the twin sample were compared to normative data from singletons, which were available from Child Health Clinics (CHC). Analyses across twin data and the CHC singleton data revealed no differences between twins and singletons in achievement of motor milestones. Girls were able to sit without support slightly earlier than boys, otherwise there were no other sex differences. Birth-order analyses revealed minimal but significant differences in turning over from back to belly and for sitting without support between the first- and second-born. Dizygotic (DZ) twins were faster than monozygotic (MZ) twins in achieving the moment of sit, crawl, stand and walk. Twins born in earlier cohorts were faster in reaching the moment of crawl, sit and walk. It is concluded that there are no differences in time of reaching motor milestones between twins and singletons within the normal range. Sex has minimal to no effect on motor development in early childhood. DZ twins achieve motor milestones sooner than MZ twins. Attainment of gross motor milestones (crawl, stand and walk) is delayed in later birth cohorts.

Motor development of triplets: a Japanese prospective cohort study

We analyzed whether motor development in early life is different between singletons and triplets in Japan. The motor development was reported by mothers by postal questionnaire for 1,121 triplet children and in regular health check-ups for 13,906 singleton children. Children who were suspected of having neurological abnormality or disability were excluded from the analysis. The ages of milestone achievements were significantly higher in triplets for each outcome compared to singletons. Further, after adjustment for gestational age, birthweight, and birth length, the differences were significant for maintaining head, sitting alone and standing holding on. In children with birthweight of 2 kg or more, the ages of milestone achievements were significantly higher in triplets for each outcome compared to singletons, except walking holding on. Moreover, after adjustment for the confounding factors, the differences were significant for sitting alone and walking independently. On the contrary, singletons attained motor development facilitating crawling, walking holding on, and walking independently slower than triplets among those children with birthweight of 2 kg or less after adjustment for gestational age. In conclusion, triplets are overall at higher risk for the delay of gross motor milestones as compared to singletons independently of birth-related factors. In contrast, among children with a birthweight of less than 2 kg, singletons showed slower motor development than triplets after adjusting for gestational age. There is an obvious need to apply developmental standards that consider at least both multiple birth status (singleton, twin or triplet) and birthweight.

Child and adolescent psychiatric genetics

The current status of child and adolescent psychiatric genetics appears promising in light of the initiation of genome-wide association studies (GWAS) for diverse polygenic disorders and the molecular elucidation of monogenic Rett syndrome, for which recent functional studies provide hope for pharmacological treatment strategies. Within the last 50 years, tremendous progress has been made in linking genetic variation to behavioral phenotypes and psychiatric disorders. We summarize the major findings of the Human Genome Project and dwell on largely unsuccessful candidate gene and linkage studies. GWAS for the first time offer the possibility to detect single nucleotide polymorphisms and copy number variants without a priori hypotheses as to their molecular etiology. At the same time it is becoming increasingly clear that very large sample sizes are required in order to enable genome wide significant findings, thus necessitating further large-scaled ascertainment schemes for the successful elucidation of the molecular genetics of childhood and adolescent psychiatric disorders. We conclude by reflecting on different scenarios for future research into the molecular basis of early onset psychiatric disorders. This review represents the introductory article of this special issue of the European Child and Adolescent Psychiatry.

Comparison of motor development between twins and singletons in Japan: a population-based study

This study was performed using population-based data to analyze whether motor development in early life is different between singletons and twins in Japan. For better comparison and investigation, we divided the 2 groups into a group with a birthweight of 2.5 kg or greater (subgroup A) and a group with a birthweight of less than 2.5 kg (subgroup B), respectively. We analyzed the database of medical check-ups for children aged 3 years between April 2001 and July 2004. They received medical checkups at 4 months, 1.5, and 3 years of age. Children who were suspected of having neurological abnormality or disability were referred to specialists and excluded from the database. The data of 14,132 children were analyzed. Among these, 13,040 (92.3%) children were singletons in subgroup A, 75 (0.5%) were twins in subgroup A, 866 (6.1%) were singletons in subgroup B and 151 (1.1%) were twins in subgroup B. The mean age at achieving milestones was slower in twins of subgroup A for each developmental outcome than singletons of subgroup A, and the difference between twins and singletons was significant after adjustment for rolling over. On the contrary, after adjusting for a confounding factor (gestational age), singletons of subgroup B attained motor development facilitating walking independently slower than twins of subgroup B. There were different tendencies in the results regarding the motor development of subjects of subgroup A and that of subjects of subgroup B.

Prognostic factors for walking attainment in very low-birthweight preterm infants

The purpose of this study was to compare the age of walking attainment between very low-birthweight (VLBW) preterm infants and normal term infants, and to determine the variables that affect the walking attainment in VLBW infants. Ninety-six VLBW preterm infants and 82 normal term infants were prospectively followed to determine their age of walking attainment and to monitor gross motor development with sequential clinic visits at 6, 9, 12 and 18 months corrected age. Perinatal and sociodemographic data were collected through review of medical records. The VLBW infants were significantly older at attainment of walking (median 14 months) than the term infants (median 12 months) after correction for prematurity. By the age of 18 months, all term infants had attained walking ability; while 11% of VLBW infants were still unable to walk. Multivariate proportional hazards regression analysis revealed that low gestational age was significantly associated with late attainment of walking in VLBW infants. With the adjustment for gestational age, prolonged ventilation (or oxygen therapy) and severe retinopathy of prematurity were significant predictors of late walking attainment. Our findings indicate that VLBW preterm infants have an increased risk of delayed attainment of walking. Furthermore, the contribution of low gestational age to the delayed walking attainment in VLBW infants may occur via the plausible pathways of neonatal respiratory distress and severe retinopathy of prematurity.