Wisconsin Twin Panel

Wisconsin Twin Project Overview: Temperament and Affective Neuroscience

The Wisconsin Twin Project encompasses nearly 30 years of longitudinal research that spans infancy to early adulthood. The twin sample was recruited from statewide birth records for birth cohorts 1989-2004. We summarize early recruitment, assessment, retention and recently completed twin neuroimaging studies. In addition to the focal twins, longitudinal data were also collected from two parents and nontwin siblings. Our adolescent and young adult neuroimaging sample (N = 600) completed several previous behavioral and environmental assessments, beginning shortly after birth. The extensive phenotyping is meant to support a range of empirical investigations with potentially differing theoretical perspectives.

Genetic and environmental influences on socio-emotional behavior in toddlers: an initial twin study of the infant-toddler social and emotional assessment

BACKGROUND

Relatively little is known about the genetic architecture of childhood behavioral disorders in very young children.

METHOD

In this study, parents completed the Infant-Toddler Social and Emotional Assessment, a questionnaire that assesses symptoms of childhood disorders, as well as socio-emotional competencies, for 822 twin pairs (49.3% female; age 17-48 months) participating in the Wisconsin Twin Project. Psychometric, rater bias, and sex-limitation models explored the role of genetic and environmental influences on (1) externalizing and internalizing behavior; (2) less commonly assessed behaviors pertaining to physical and emotional dysregulation, general competencies, social relatedness; and (3) infrequent behaviors such as those associated with pervasive developmental delays.

RESULTS

Heritable influences accounted for the majority (56% or more) of variation in behavior that was commonly observed by both parents. The remaining variance was associated with non-shared environmental factors, with the exception of competency and atypical behavior, which were also influenced by shared environmental factors. In contrast, for most behaviors, the variation unique to mother and father ratings was split between variation due to shared environment or rater biases and to measurement error. Little evidence emerged for sex differences in the underlying causes of variation.

Environmental influences on family similarity in afternoon cortisol levels: twin and parent-offspring designs

Modest genetic effects on morning, but not late-day, cortisol levels have been established. Environmental demands may influence basal cortisol levels later in the day. Thus, we anticipated that individuals in the same family would have similar afternoon cortisol levels to the extent that they share aspects of their environment. We examined afternoon basal cortisol levels measured across 3 consecutive days in mothers and fathers and in multiple offspring in two separate large and longitudinal studies. Study I involved 321 families with singletons while study II involved 233 families with twins. Modest family similarity was apparent for afternoon basal cortisol levels in both studies. Spouses' cortisol levels were also correlated. Data from study II demonstrated that family resemblance in afternoon cortisol was accounted for by underlying shared environmental factors, but not underlying genetic factors. Shared environment accounted for 62% of the variation in twin afternoon basal cortisol levels and 14% of the variation in parent afternoon basal cortisol levels. We used pooled data from the two studies to examine whether parental depression, socioeconomic status (SES), and offspring sex and age impacted cortisol levels. Female offspring had higher cortisol levels than males, and cortisol decreased with age until about 9 years of age, after which cortisol increased with age. Family similarity persisted after accounting for parental depression, SES, time of day, and offspring sex and age, which suggests that the shared family environment influences parent and offspring stress hormone levels throughout the childhood years.

A population-based twin study of parentally reported tactile and auditory defensiveness in young children

Some adults and children exhibit defensive behaviors to tactile or auditory stimulation. These symptoms occur not only in subsets of children with ADHD, autism, and Fragile X syndrome, but also in the apparent absence of accompanying disorders. Relatively little research explores the correlates and antecedents of sensory defensiveness. Using a population-based sample of 1,394 toddler-aged twins, mothers reported on tactile and auditory defensiveness, temperament, and behavior problems. The incidence of defensive symptoms was widely distributed, with some accumulation of cases in the extreme range. Girls were overrepresented in the extreme tactile defensiveness group. Both auditory and tactile defensiveness were modestly associated with fearful temperament and anxiety, but they were relatively distinct from other common dimensions of childhood behavioral dysfunction. Twin correlations for the full range of scores and concordance rates for the extremes suggested moderate genetic influences, with some indication that the tactile domain might be more heritable than the auditory domain.