Dopamine receptor inhibition underlies both the therapeutic and adverse effects of antipsychotics, but the mechanisms modulating these effects in patients with schizophrenia remain incompletely understood. Hyperprolactinemia (HPRL), a direct consequence of D2 dopamine receptor blockade, provides a unique clinical model to investigate how genetic variation in glutamatergic signaling influences the downstream effects of dopaminergic disruption. We hypothesized that polymorphisms in GRIN2A and GRIN2B, encoding NMDA glutamate receptor subunits, modify the neuroendocrine consequences of dopamine receptor inhibition. By studying antipsychotic-induced HPRL, we aimed to demonstrate that NMDA receptor genetic variants shape the functional outcomes of dopaminergic perturbation.
In a cross-sectional analysis of 536 schizophrenia patients, we measured prolactin levels—a sensitive biomarker of D2 receptor inhibition—and genotyped 23 GRIN2A/GRIN2B variants. Logistic regression assessed gene-drug relationships while controlling for clinical covariates.
NMDA receptor genetic variation significantly influenced susceptibility to HPRL, with distinct effects observed between antipsychotic classes with the highest effect for the typical antipsychotics, which are D2 dopamine receptor antagonists. This demonstrates that glutamatergic genotypes predict interindividual variability in the neuroendocrine response to dopamine receptor blockade.
These results provide the first clinical evidence in support of the hypothesis that NMDA receptor polymorphisms modulate the effects of dopaminergic inhibition in schizophrenia. Beyond HPRL, this dopamine-glutamate relationships paradigm may extend to other clinical outcomes of antipsychotic treatment, including therapeutic response and neurological side effects. Our findings underscore the importance of glutamatergic pathways in determining the functional consequences of dopamine receptor targeting.