This is an abstract of a study published in The Lancet Psychiatry titled “Absolute and relative risks of mental disorders in families: a Danish register-based study” by Carsten Bøcker Pedersen et al.
Here’s a breakdown of the key facts:
Background:
While relative risks of mental disorders in families are known,absolute risk estimates are scarce.
The study aims to quantify the proportion of mental disorders that occur in individuals without affected relatives (non-familial cases).
Methods:
A prospective cohort study using Danish population-based registers (Civil Registration System,Multi Generation Register,psychiatric Central research Register,National Patient Register).
Followed Danish individuals from January 1, 1970, to December 31, 2021.
Investigated a range of mental disorders including substance use disorders,schizophrenia and related disorders,mood disorders (including depression and bipolar disorder),and personality disorders (including borderline and antisocial).
Estimated lifetime risk (up to age 60), age-specific absolute risk, and relative risk for each disorder based on the degree of affected relatives (first, second, third-degree).
Calculated heritability estimates and the proportion of non-familial cases.
involved individuals with lived experience in the study design.
Findings:
The study included over 3 million individuals, followed for over 80 million person-years.
Individuals with an affected family member had higher lifetime and relative risks of developing the same mental disorder. The risk increased with closer kinship. Example for Depression:
Lifetime risk was 15.48% for those with affected first-degree relatives.
It was 13.50% for those with affected second-degree relatives. It was 7.80% in the general population.
It was 4.68% for those without affected first or second-degree relatives.
Heritability and non-Familial Cases for Depression:
Heritability was estimated at 45.4%.
60.0% of depression cases were non-familial.
Interpretation:
Having a family member with a mental disorder increases an individual’s risk of the same disorder.
However, from a population perspective, the majority of mental disorders occur in individuals without affected close relatives.
This highlights the importance of prevention strategies that target the entire population, not just those with a family history.
Funding:
* Novo Nordisk Foundation.
