The Babytwins Study Sweden (BATSS): A Multi-Method Infant Twin Study of Genetic and Environmental Factors Influencing Infant Brain and Behavioral Development

Abstract

Twin studies can help us understand the relative contributions of genes and environment to phenotypic trait variation, including attentional and brain activation measures. In terms of applying methodologies such as electroencephalography (EEG) and eye tracking, which are key methods in developmental neuroscience, infant twin studies are almost nonexistent. Here, we describe the Babytwins Study Sweden (BATSS), a multi-method longitudinal twin study of 177 MZ and 134 DZ twin pairs (i.e., 622 individual infants) covering the 5−36 month time period. The study includes EEG, eye tracking and genetics, together with more traditional measures based on in-person testing, direct observation and questionnaires. The results show that interest in participation in research among twin parents is high, despite the comprehensive protocol. DNA analysis from saliva samples was possible in virtually all participants, allowing for both zygosity confirmation and polygenic score analyses. Combining a longitudinal twin design with advanced technologies in developmental cognitive neuroscience and genomics, BATSS represents a new approach in infancy research, which we hope to have impact across multiple disciplines in the coming years.

Infants’ sense of approximate numerosity: Heritability and link to other concurrent traits

“…For the main eye-tracking analysis, each infant viewed eight stimulus videos (each lasted for 16 s) in a unique pseudo-random order, interspersed with other videos (consisting of social stimuli, such as F U R E 1 Experimental stimuli from the 1:4 ratio condition. Each image consisted of two sets of dots that was presented for 500 ms, followed by a blank screen for 300 ms. Every other image showed identical sets of dots on the right and left side the screen while remaining images differed in numerosity on the two sides static and dynamic faces) not related to the current research question (Falck-Ytter et al, 2021). Incorporating unrelated social videos in non-social stimuli is a typical strategy to increase infants' attention to the screen in eye tracking experiments.…”

Global motion processing in infants’ visual cortex and the emergence of autism

“…Similarly, to the EASE LL group, twin families were recruited from the Swedish Population Registry. Complete demographics and procedures of BATSS study are provided elsewhere 14 .…”

“…Both the BATSS sample and the LL group from the EASE sample consisted of infants without increased likelihood of autism, and together these groups comprised 473 individuals. This combined group is not representative of the entire population in all respects 14 , but given its size and the basic nature of the phenotype in question (basic visual processing in infancy), we termed it Normative Sample. In addition to contributing to such normative reference data, the BATSS sample, consisting of monozygotic (MZ) and same sex dizygotic (DZ) infant twins, was used to study the contribution of genetic and environmental influences to the variation in the included EEG phenotypes.…”

Pupil size and pupillary light reflex in early infancy: heritability and link to genetic liability to schizophrenia

“…Participants were part of the BabyTwins Study Sweden (BATSS), a longitudinal infant twin study (Falck‐Ytter et al., 2021). BATSS has a classic twin design, in which similarity is compared between monozygotic twin pairs (MZ; who share 100% of their segregating alleles) and dizygotic same‐sex pairs (DZ; who on average share 50% of their segregating alleles).…”