Genetic Influences on Eight Psychiatric Disorders Based on Family Data of 4 408 646 Full and Half-siblings, and Genetic Data of 333 748 Cases and Controls

Background. Most studies underline the contribution of heritable factors for psychiatric disorders.
However, heritability estimates depend on the population under study, diagnostic
instruments, and study designs that each has its inherent assumptions, strengths, and biases.
We aim to test the homogeneity in heritability estimates between two powerful, and state of
the art study designs for eight psychiatric disorders.
Methods. We assessed heritability based on data of Swedish siblings (N = 4 408 646 full and
maternal half-siblings), and based on summary data of eight samples with measured genotypes
(N = 125 533 cases and 208 215 controls). All data were based on standard diagnostic
criteria. Eight psychiatric disorders were studied: (1) alcohol dependence (AD), (2) anorexia
nervosa, (3) attention deficit/hyperactivity disorder (ADHD), (4) autism spectrum disorder,
(5) bipolar disorder, (6) major depressive disorder, (7) obsessive-compulsive disorder
(OCD), and (8) schizophrenia.
Results. Heritability estimates from sibling data varied from 0.30 for Major Depression to
0.80 for ADHD. The estimates based on the measured genotypes were lower, ranging from
0.10 for AD to 0.28 for OCD, but were significant, and correlated positively (0.19) with
national sibling-based estimates. When removing OCD from the data the correlation
increased to 0.50.
Conclusions. Given the unique character of each study design, the convergent findings for
these eight psychiatric conditions suggest that heritability estimates are robust across different
methods. The findings also highlight large differences in genetic and environmental influences
between psychiatric disorders, providing future directions for etiological psychiatric research.