Indirect genetic effects of siblings

Area of Science:

• Behavioral Genetics
• Quantitative Genetics
• Human Genetics

Background:

• Within-family designs are crucial for dissecting genotype-trait associations into direct and indirect genetic effects.
• Many existing designs, such as trio or within-sibship models, often assume no sibling indirect genetic effects.

Purpose of the Study:

• To extend established molecular genetic within-family designs to estimate sibling indirect genetic effects.
• To investigate direct and indirect genetic effects on educational performance and attention-deficit hyperactivity disorder (ADHD) symptoms in siblings.

Main Methods:

• Utilized variance component (genome-based restricted maximum likelihood) and trait-based (structural equation modeling with polygenic indices) approaches.
• Linked the Norwegian Mother, Father, and Child Cohort Study (MoBa) with national education data.
• Analyzed data from up to 15,971 genotyped siblings for educational testing results and parent-rated ADHD symptoms.

Main Results:

• Estimates from both methods converged, with variance component estimates generally larger than trait-based estimates.
• No significant sibling indirect genetic effects were found for educational performance across all ages.
• Slightly negative sibling indirect genetic effects were observed for ADHD symptoms at age 3, potentially due to parental rating biases.

Conclusions:

• Within-family models for educational performance are likely not significantly biased by the assumption of absent sibling indirect genetic effects.
• Integrating trait-based and variance component analyses improves the understanding of indirect genetic effects, particularly when mechanisms are not narrowly defined.