Scientists Rewrite Textbooks: First Single Gene Confirmed to Independently Cause Mental Illness

According to statistics from the World Health Organization (WHO), approximately one in eight people worldwide suffered from mental and psychological disorders in 2019, with anxiety disorders and depression being the most prevalent. For a long time, the scientific community has generally held that mental illnesses result from the combined effects of tiny variations in thousands of genes (polygenic inheritance) and environmental factors, lacking a single, clear “culprit.” This complexity has made precision treatment extremely challenging.

However,RecentA landmark study published in the top-tier journal Molecular Psychiatry has overturned this perception.

(Source: Molecular Psychiatry)

A team led by Professor Johannes R. Lemke from the University of Leipzig Medical Center, together with international collaborators, has discovered that specific variants in the GRIN2A gene can directly cause psychiatric disorders, marking the first time the scientific community has confirmed that a single gene can independently trigger such conditions. More encouragingly, through clinical observations, the research team found that supplementation with the amino acid L-serine may significantly improve symptoms in these patients, shedding new light on precision treatment for psychiatric disorders.

The etiology of mental disorders has long remained one of the greatest enigmas in the medical community. Traditional theories posit that common psychiatric disorders, such as schizophrenia and depression, are typical “complex diseases,” whose genetic architecture is built upon the cumulative effects of thousands of common variants across the entire genome, with each variant contributing only a minuscule increase in risk.

Although scientists have previously identified certain rare genetic variants (such as copy number variations, CNVs) that significantly increase disease risk, these variants typically lead to comprehensive developmental disorders. Patients often present with severe intellectual disability, epilepsy, or physical malformations, with psychiatric symptoms being only part of their systemic manifestations.

Although the theory of “polygenic pathogenesis” explains most cases, it also poses significant challenges to clinical diagnosis and treatment. Due to the lack of clear molecular targets, existing psychiatric medications are largely administered empirically; they often only alleviate symptoms rather than provide a cure, and are associated with pronounced side effects.

For a long time, the search for a single gene capable of independently causing “pure” mental illness has been considered an almost impossible task.

The GRIN2A gene encodes the GluN2A subunit of the N-methyl-D-aspartate receptor (NMDA receptor), a key channel in the brain responsible for neurotransmission. Previously, variants in this gene were primarily associated with childhood epilepsy and language disorders. However, scientists have keenly observed that behind the vast genomic landscape, there appears to be a deeper link between this gene and psychiatric symptoms. Confirming that a single-gene variant is sufficient to cause mental illness would not only rewrite textbooks but also open a breakthrough for developing precision medicines targeting molecular mechanisms.

To validate the direct association between the GRIN2A gene and psychiatric disorders, the research team conducted a large-scale, international, multicenter retrospective study leveraging the world’s largest GRIN disorder registry. They systematically investigated 235 patients carrying pathogenic GRIN2A variants, representing the largest cohort study in this field globally to date.

The research team divided patients into two groups: one group carried “null variants” (GRIN2A null variants) that resulted in a complete loss of protein function, while the other group carried “missense variants” (GRIN2A missense variants) that only altered protein structure. Through rigorous statistical analysis and comparison with big data from over 5 million individuals in the Finnish National Health Registry (FinRegistry), the study revealed a striking pattern:

Data show that individuals carrying GRIN2A loss-of-function variants have a 6.5-fold higher risk of developing psychiatric disorders compared with carriers of missense variants. More importantly, after excluding the confounding effects of epilepsy, intellectual disability, and other factors,GRIN2A Loss-of-Function Variants Show a Strong Association with Early-Onset Schizophrenia, Mood Disorders, and Anxiety DisordersCompared with the general population, these patients develop psychiatric symptoms at a much earlier age, predominantly during childhood or adolescence rather than in adulthood.

The most disruptive finding among these is that researchers identified in the cohortSix patients without intellectual disability, among whom two individuals did not even have a history of epilepsy and presented solely with psychiatric symptoms (such as schizophrenia or mood disorders). This indicates that GRIN2A gene defects are fully capable of “independently” inducing psychiatric disorders.

Furthermore, data analysis of patients with comorbid epilepsy and psychiatric disorders revealed that in nearly 60% of cases, psychiatric symptoms emerged only after the cessation of epileptic seizures, with a strong temporal correlation between the two. This finding robustly refutes the traditional view that “psychiatric symptoms are merely sequelae of epileptic seizures,” confirming that GRIN2A deficiency itself is the root cause of abnormalities in the brain’s psychiatric networks.

The significance of this study extends far beyond the identification of a disease-causing gene; it also directly points to potential therapeutic strategies. Since GRIN2A loss-of-function variants lead to reduced numbers and impaired function of NMDA receptors in the brain (resulting in glutamate signaling deficits), researchers hypothesize that supplementing with agents capable of activating NMDA receptors may compensate for this deficiency.

Based on this mechanism, the research team attempted to administer oral treatment to four patients with GRIN2A-related neuropsychiatric disorders.L-SerineTreatment. L-serine can be converted into D-serine in the body, and the latter is a potent co-agonist of NMDA receptors. Encouragingly, all treated patients exhibited significant clinical improvement.

In one patient, the hallucinations that had long plagued him completely disappeared after treatment; in another, paranoid symptoms were alleviated; and in others, behavioral disturbances showed significant improvement. These real-world clinical cases strongly suggest that “precision therapy” targeting specific genetic defects is no longer an empty promise in psychiatry. Unlike traditional antipsychotic drugs that block dopamine receptors, L-serine directly addresses the pathological mechanism of NMDA receptor hypofunction, representing a novel “etiology-targeted” therapeutic approach.

Although current treatment data are still based on small-sample observational studies, they lay a solid theoretical foundation for future clinical trials. This finding also suggests that genetic testing may have significant diagnostic and therapeutic value for patients with mental disorders onset in childhood or adolescence, particularly those with a family history or mild neurodevelopmental abnormalities.

As the first single gene confirmed to directly cause mental illness, the discovery of GRIN2A marks psychiatry’s entry into a new era of “genomic medicine.” This breakthrough not only challenges traditional perceptions of the complex etiology of mental disorders but also demonstrates a closed-loop precision medicine pathway—from genetic diagnosis to mechanism-based therapy—through the successful trial of L-serine.