Genetics: Rare Genetic Variants

Rare genetic variants are uncommon changes in DNA that can sometimes have larger effects than individual common variants. These include certain copy-number changes, where a section of genetic material is deleted or duplicated. Some are associated with increased risk of schizophrenia and other developmental or health conditions.

Genetics influences susceptibility to schizophrenia, but inheritance is complex. Many genetic differences can contribute, and their effects interact with development and environment. A genetic association describes probability across populations, not an inevitable outcome for one person. Most findings do not provide a simple explanation for an individual diagnosis.

An association does not mean that everyone carrying the variant will develop psychosis. Effects can vary substantially, and many people with schizophrenia do not have an identifiable rare variant explaining their condition. Testing may be considered in selected clinical circumstances, particularly when other developmental or medical features suggest a broader syndrome. The purpose and possible outcomes should be explained before testing. Findings may have implications beyond mental health, including for relatives. Specialist interpretation is important because a genetic result can be uncertain and should not be treated as a complete explanation of personality, abilities or future functioning.

Penetrance describes how often a genetic variant is associated with a particular outcome among people who carry it. Expressivity concerns variation in the features that occur. Both can vary, helping explain why the same variant need not produce the same presentation in relatives. These concepts are important when discussing a result without treating it as a fixed personal forecast.

Further reading: National Institute of Mental Health; Nature: schizophrenia genetics study.