Genetics and neuroimaging of mental disorders

Concept

Most mental disorders run in families through many small-effect genes plus environment; brain scans are used to look for other, medical causes.

Updated Nov 13, 2026

Key points

Heritability is the share of variation in risk in a population explained by genetic differences; it does not say how much of one person's illness is genetic.
Bipolar disorder is one of the most heritable medical disorders (genetic influences explain about 60–85% of risk); identical twins are concordant far more often than fraternal twins, but not 100%.
Schizophrenia shares the high end of the heritability range with bipolar disorder; other disorders lie lower in that range.
22q11.2 deletion syndrome, the most common recurrent pathogenic deletion, raises the risk of a schizophrenia spectrum disorder to about 20–25%.
Polygenic risk scores explain only a small part of risk and are not yet clinically useful; genetic testing is used mainly for neurodevelopmental disorders and syndromes.
Brain imaging (CT or MRI) is used to look for medical causes such as a brain tumour, stroke or multiple sclerosis.

What it is

Twin, family and adoption studies show that genes contribute strongly to many mental disorders: across psychiatric conditions heritability estimates range from about 40% to over 80%, with schizophrenia and bipolar disorder at the high end. Much of the risk is polygenic, spread across many common variants of small effect, plus rare variants of large effect such as copy number variants (CNVs). Genes confer vulnerability to environmental stressors such as childhood trauma, infection in pregnancy and substance use. In the clinic, brain imaging is used mainly to look for medical causes of psychiatric symptoms.

Key facts

Identical twins share nearly all their genes, so concordance below 100% shows that environment and chance also matter.
Many genetic risk factors are shared across diagnoses, which fits overlapping symptoms and family patterns.
Other rare CNVs (16p11.2, 3q29 and 1q21.1 deletions) also raise rates of autism, schizophrenia spectrum disorders or both.
22q11.2 deletion also causes heart and palate malformations, immune deficiencies and endocrine problems, so a medical history may reveal it.
Gene–environment interaction: genetic risk acts as vulnerability to stressors such as childhood trauma, maternal infection in pregnancy and substance use.

Genetic contribution to selected disorders

Disorder	Genetic contribution	Note
Schizophrenia	High end of the heritability range; polygenic plus rare CNVs	CNVs such as 22q11.2 deletion confer significant risk
Bipolar disorder	Very high (about 60–85% of risk)	Shares genetic risk with schizophrenia
Autism spectrum disorder	Rare variants raise risk (22q11.2, 16p11.2, 1q21.1 deletions)	Genetic testing is most useful in neurodevelopmental disorders
Major depression	Lower than bipolar disorder and schizophrenia	Childhood trauma and other stressors also matter
22q11.2 deletion syndrome	A single large CNV, about 1 in 2,000–6,000 births	About 20–25% schizophrenia spectrum; intellectual disability (~45%), ADHD and anxiety (~35%), autism (10–40%)

Clinical notes

Family history is still the most practical genetic tool: ask about mental illness, suicide and substance use in first-degree relatives.
Recurrence risk is given as empirical risk from family studies; genetic counselling helps families understand that risk is raised, not certain.
Order brain imaging in new psychiatric presentations with red flags: an unusual age of onset, neurological signs or symptoms unlike the person's usual pattern.
Genetic testing is offered mainly in neurodevelopmental disorders such as autism and intellectual disability, and when a syndrome such as 22q11.2 deletion is suspected (heart or palate defects).

Test yourself

Think of the answer, then tap the question to see it.

What does a heritability of 80% mean?

That about 80% of the variation in risk across a population is explained by genetic differences; it does not mean an individual's illness is 80% genetic.

Which copy number variant gives about a 20–25% risk of a schizophrenia spectrum disorder?

The 22q11.2 deletion, the most common recurrent pathogenic deletion.

Why does twin concordance below 100% matter?

Identical twins share nearly all genes, so discordance shows that environment and chance also shape who becomes ill.

What is the role of brain imaging in a first episode of psychosis?

To look for medical causes such as a tumour, stroke or multiple sclerosis before a primary psychotic disorder is diagnosed.

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Educational content on behavior and the clinical relationship; not a diagnostic or treatment guide and no substitute for assessment by a health professional. If you or someone near you is at risk, seek help now from an emergency service or a mental-health helpline.

Sources: Genetic Risk Assessment in Psychiatry (Cold Spring Harbor Perspectives in Medicine (PubMed Central), 2020); The Genetics of Bipolar Disorder (Neuroscience (PubMed Central), 2009); A genetics-first approach to understanding autism and schizophrenia spectrum disorders: the 22q11.2 deletion syndrome (Molecular Psychiatry (PubMed Central), 2023); Medical Assessment of the Patient With Psychiatric Symptoms (MSD Manual Professional Edition, 2026).

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