Twin-singleton differences in brain structure using structural equation modelling

Area of Science:

• Neuroscience
• Human Genetics
• Developmental Biology

Background:

• Twin studies are crucial for understanding genetic influences on brain morphology.
• Concerns exist regarding the generalizability of twin study findings due to environmental differences between twins and singletons.

Purpose of the Study:

• To investigate whether twin-singleton differences impact the interpretation of genetic contributions to brain volume variation.
• To assess the influence of birth order, zygosity, and twin-sibling status on brain morphology.

Main Methods:

• Magnetic Resonance Imaging (MRI) scans of 112 twin pairs and 34 siblings (mean age 30.7 years).
• Maximum-likelihood model fitting to analyze variances related to birth order, zygosity, and twin-singleton status.
• Comparison of intracranial volume, grey matter, white matter, and ventricle volumes.

Main Results:

• Homogeneous variances observed across birth order, zygosity, and twin-singleton status.
• Second-born twins had smaller intracranial volume than first-born twins and siblings.
• Differences in grey and white matter volumes between groups were not significant after correcting for intracranial volume.

Conclusions:

• Second-born twins exhibit reduced intracranial volume, potentially due to suboptimal perinatal environments.
• Despite birth order effects, twin studies provide reliable and generalizable estimates of brain volume heritability for the singleton population.