Is Schizophrenia Genetic? Family Risk in Numbers

Schizophrenia is highly heritable, and most children of an affected parent don't develop it. In Danish national registers, 7.0% of people with one parent admitted for schizophrenia had developed schizophrenia by age 52, compared with 0.86% of those with neither parent ever admitted.¹

In the Danish Twin Register, heritability was estimated at 79%, and when one identical twin had schizophrenia the concordance rate was 33%.² The US National Library of Medicine states that "most people with an affected relative will not develop the disorder."³

Risk by number of affected parents

The Danish study followed a population-based cohort of 2.7 million people and calculated the cumulative incidence of schizophrenia by age 52.¹

Source: Gottesman et al., 2010.¹ Parents were classified by admission to a psychiatric facility with the diagnosis.

When both parents had schizophrenia, the figure was 39.2% once schizophrenia-related disorders were included.¹

A meta-analysis of 33 studies found that children of parents with schizophrenia, bipolar disorder, or major depressive disorder had a 32% probability of developing any severe mental illness by adulthood (age over 20).⁴ That number covers any severe mental illness across all three parental diagnoses.

Siblings and other relatives

For siblings, the available figures are relative risks. In Swedish registers covering more than 2 million families, the relative risk of schizophrenia was 9.9 (95% CI, 8.5 to 11.6) for a child of an affected parent and 9.0 (8.1 to 9.9) for a full sibling. It was 3.6 for maternal half-siblings and 2.7 for paternal half-siblings.⁵ Adopted children whose biological parents had schizophrenia also had an increased risk.⁵

In a Taiwanese national study, having an affected second-degree relative was associated with an adjusted relative risk of 2.44, and an affected first-degree relative with 6.30.⁶ A relative risk describes how many times higher the risk is than in the comparison group. None of the studies reviewed here gives a sibling's lifetime risk as a percentage.

Twin concordance and heritability

The Danish twin study covered 31,524 twin pairs born between 1951 and 2000. The concordance rate was 33% in identical twins and 7% in fraternal twins.² The authors wrote that the low concordance of 33% in identical twins shows that vulnerability to the illness is not solely genetic.²

Twin studies give 79% in Denmark and 81% in a meta-analysis of twin studies.^{2, 7} Family studies give lower figures: 64% in Sweden and 47.3% in Taiwan.^{5, 6} Heritability describes variation across a population, and the parental and twin figures above describe risk among relatives.

What genome-wide studies found

A 2022 genome-wide association study of up to 76,755 people with schizophrenia and 243,649 controls reported common variant associations at 287 distinct genomic loci. Loci are regions of the genome, and the authors identified 120 genes likely to underpin associations at some of them.⁸

A polygenic risk score built from those results explained a median of 0.073 of the variance in liability, about 7%. That 7% is a share of the variation in liability between people, a different quantity from the 7.0% risk with one parent admitted. The score explained most variance in cohorts of European ancestry, and even there the median area under the curve was 0.72, meaning, the authors wrote, that the liability explained is "insufficient for predicting diagnosis in the general population."⁸

Genetic testing for schizophrenia

The International Society of Psychiatric Genetics states, on a web page accessed November 12, 2026, that polygenic risk scores "are currently considered research analyses and are not recommended for clinical use."⁹

In a consortium study of 1,402 people with 22q11.2 deletion syndrome, psychotic disorders were present in 41% of adults over age 25.¹⁰ That figure is for psychotic disorders as a group, in participants referred from both medical and nonmedical sources.

The society's committee did not reach consensus on widespread copy number variant testing in adult-onset disorders. Most members agreed that such tests may have value when the presentation is atypical or occurs with intellectual disability, autism spectrum disorder, learning disorders, or certain medical syndromes, and the society recommends counseling by a professional with expertise in both mental health and genetic test interpretation.⁹

Paternal age and environmental exposures

Several exposures are associated with schizophrenia in observational studies:

• Paternal age. The relative risk was 1.66 for children of fathers aged 50 or older, compared with fathers aged 25 to 29.¹¹
• Cannabis. The heaviest users had an odds ratio of 3.90 for schizophrenia and other psychosis-related outcomes compared with nonusers. The authors noted that a causal link cannot be unequivocally established.¹²
• Urban environment. The risk in the most urban environment was estimated at 2.37 times that in the most rural.¹³
• Pregnancy and birth complications. Complications of pregnancy, abnormal fetal growth, and complications of delivery were significantly associated with schizophrenia, with pooled effect sizes generally less than 2.¹⁴

These are relative figures, and the abstracts don't give the absolute risk for an exposed person. The authors of the cannabis meta-analysis judged the evidence sufficient to justify harm reduction prevention programs. I've written separately about drug-induced psychosis and schizophrenia.

Limitations of the evidence

This evidence has limitations. First, the Danish study classified parents by psychiatric admission and stopped at age 52, so it can miss parents who were never admitted. Second, the relative risks and the environmental findings come from observational data and can't establish cause in any one person. Nevertheless, the family figures are consistent across national registers: risk rises with each affected close relative, and with one parent admitted for schizophrenia it was 7.0% by age 52.

A family history is a reason to take early symptoms seriously and to have them evaluated by a psychiatrist.

In a crisis: call or text 988, or go to the nearest emergency department. A first episode of psychosis belongs in a hospital-based or coordinated specialty care program.

I start and manage clozapine in an outpatient practice in Chelsea, Manhattan. Details are on the schizophrenia care in NYC page. Clozapine should not be stopped, skipped, or restarted without the prescriber. This page is general information and does not replace an evaluation.

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