International Left-Handers Day 2025: Higher Risk of Brain Disorders, Including Schizophrenia Is Associated With Left-Handers; Study
For decades, researchers have observed that left-handers often show different patters of brain for organisation, which is known as atypical brain lateralisation.
Published : August 13, 2025 at 11:59 AM IST
Each year August 13 marks International Left-Handers Day. It is also a celebration of the 10% of the world's population who hold their pens, stir their tea, and throw their cricket balls with their left hand. Although there's the quirky charm and creative reputation about left-handers, scientists have been investigating a more complex story: a possible link between left-handedness and an elevated risk of certain brain disorders, including schizophrenia.
The Science Behind the Connection
For decades, researchers have observed that left-handers often show different patters of brain for organisation, which is known as atypical brain lateralisation. It means how the brain functions for language processing and spatial awareness, which are distributed between its two hemispheres. While most people are right-handed, a minority are left-handed or mixed-handed. According to a research published in National Library of Medicine, it has been suggested that mental and developmental disorders are associated with increased prevalence of left-handedness and mixed-handedness. However, substantial heterogeneity exists across disorders, indicating that not all disorders are associated with a considerable shift away from right-handedness.
Additionally, Increased frequencies in left- and mixed-handedness have also been associated with more severe clinical symptoms, indicating that symptom severity rather than diagnosis explains the high prevalence of non-right-handedness in mental disorders.
A Yale University study found that nearly 40% of people diagnosed with schizophrenia or schizoaffective disorders were left-handed, which is higher than the 10% prevalence in the general population.
Other Mental Health Risks
Researchers have extended their conversation beyond schizophrenia. A 2025 meta-analysis published in Psychological Bulletin found a stronger link between left-handedness (or mixed-handedness) and disorders that develop early in life, such as autism, dyslexia, and schizophrenia—particularly those involving language impairments.
Several meta-analyses on hand preference in mental and neurodevelopmental disorders have been published in the last decade. Analyses indicated that case–control differences varied with diagnosis. Some diagnoses, like schizophrenia, are associated with a high frequency of atypical hand preference. Moderator analyses showed that neurodevelopmental conditions, non-neuro developmental conditions with an early age of onset, and conditions that include symptoms related to language were all associated with higher rates of atypical hand preference.
Autism associated with Left-handedness
Several large-scale association studies based on rare, coding variants identified 24 genes associated with autism 10 genes associated with schizophrenia, 4 genes associated with Parkinson’s disease and 5 genes associated with Alzheimer’s disease, at exome-wide significance levels.
"We queried each of these 43 genes in the rare-variant association results of the present study of left-handedness. The autism-associated gene DSCAM (Down syndrome cell adhesion molecule) showed significant association with left-handedness after Bonferroni correction for 43 tests DSCAM is involved in central and peripheral nervous system development, including through affecting the interaction of other autism-linked synaptic adhesion molecules," the study mentions.
In addition, the autism-associated gene FOXP1 showed significant association with left-handedness after Bonferroni correction for 43 tests for the broad set only . FOXP1 encodes a transcription factor in which disruptive coding variants are known to cause a developmental disorder that includes intellectual disability, autistic features, speech/language deficits, hypotonia and mild dysmorphic features.
Possible Explanations
Researchers propose several overlapping explanations. For instance, brain structure differences propose that left-handers often process language and spatial tasks differently, which may overlap with the neurological patterns seen in certain psychiatric disorders. Another one is genetic overlap, where studies have identified shared genes such as YWHAH and MAPT that appear in both left-handed individuals and those with schizophrenia. Additionally, factors during fetal brain development may influence both handedness and vulnerability to mental health disorders.
Though, there are several studies suggesting mental health disorders associated with left-handedness, not all studies agree on this link. Moreover, left-handedness is also associated with positive traits. Studies suggest left-handers may have advantages in creativity, sports, and spatial reasoning (the ability to analyse and manipulate objects). History has record of leaders and innovators like Leonardo da Vinci and Barack Obama.
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