Summary: Researchers have identified a precise molecular approach to restore NMDA receptor (NMDAR) function, a central deficit in autism spectrum disorder (ASD). Instead of targeting broadly expressed glycine transporters that cause dangerous systemic side effects, the team focused on Slc6a20a/SLC6A20 — a glycine transporter concentrated in cognition-related regions such as the cortex and hippocampus — and used antisense oligonucleotides (ASOs) to safely normalize NMDAR activity.
In adult mouse models carrying mutations in SHANK2 and SHANK3 and in CRISPR-edited human cortical organoids, Slc6a20a/SLC6A20-directed ASOs restored NMDAR signaling, corrected abnormal synaptic phosphorylation patterns, and reversed persistent behavioral deficits without producing the respiratory or motor toxicities associated with earlier GlyT1-targeting approaches.
Key Facts
- NMDAR co-agonist requirement: NMDA receptors require both glutamate and glycine for full activation. NMDAR hypofunction is implicated in ASD, schizophrenia and intellectual disability.
- Why prior trials failed: Earlier attempts focused on GlyT1 inhibition to raise glycine levels. Because GlyT1 is abundant in brainstem centers that control breathing and basic motor functions, these approaches caused dangerous side effects.
- Targeting SLC6A20 for anatomical precision: Slc6a20a/SLC6A20 is enriched in higher-order cognitive areas (cortex, hippocampus) and is sparse in brainstem regions, offering a safer, localized strategy to enhance NMDAR activation.
- Behavioral rescue in adults: A single administration of Slc6a20a-ASO in adult Shank2- and Shank3-mutant mice increased NMDAR function and reversed long-standing social interaction deficits, impaired communication, and repetitive behaviors.
- Phospho-proteomic mechanism: Large-scale phospho-proteomics showed the ASO did not broadly alter protein abundance but instead restored abnormal phosphorylation states across synaptic signaling networks and NMDAR regulators.
- Human cortical organoid validation: CRISPR-engineered human cortical organoids with SHANK2 or SHANK3 mutations showed reduced NMDAR activity that was restored by a human-targeted SLC6A20-ASO, supporting translational potential.
- Durable single-dose effect: One ASO dose maintained beneficial effects for at least eight weeks in vivo with no detectable adverse effects or toxicity trends.
- Broader neuropsychiatric implications: Because this method modulates endogenous signaling rather than reintroducing missing genes, it may be adaptable to treat diverse disorders linked to NMDAR hypofunction, including schizophrenia.
Source: Institute of Basic Science
A team led by Director Eunjoon Kim at the IBS Center for Synaptic Brain Dysfunctions reports a targeted, anatomically informed therapeutic strategy to restore NMDA receptor function by inhibiting the glycine transporter Slc6a20a (mouse) / SLC6A20 (human) with antisense oligonucleotides. The work addresses long-standing challenges in restoring NMDAR function safely in neurodevelopmental and neuropsychiatric disorders.
Background: NMDARs are central to synaptic plasticity and cognition. Their activation requires both glutamate and glycine; inadequate co-agonist availability leads to NMDAR hypofunction, a feature shared across several brain disorders. Past strategies that inhibited GlyT1 to elevate glycine failed to deliver consistent clinical benefits because GlyT1 inhibition affected critical brainstem circuits, producing respiratory and motor toxicities.
Approach and models: The researchers identified Slc6a20a as a glycine transporter preferentially expressed in cortex and hippocampus and used ASOs to selectively reduce its expression. They tested the intervention in adult mouse models carrying SHANK2 or SHANK3 mutations—established genetic models for autism-related phenotypes—and in human cortical organoids engineered with the same mutations using CRISPR.
Results: Slc6a20a-ASO normalized NMDAR-mediated synaptic responses in multiple mouse models and restored behavioral measures of social interaction, communication, and repetitive behaviors in adult animals. Phospho-proteomic profiling revealed that therapeutic benefit is linked to the normalization of abnormal phosphorylation signatures across synaptic proteins and NMDAR regulatory pathways, rather than wholesale changes in protein expression. In human cortical organoids, a human-specific SLC6A20-ASO restored reduced NMDAR function to near-normal levels, supporting relevance to human biology.
Safety and durability: A single ASO dose produced sustained benefit for at least eight weeks without observable adverse effects in treated mice. Because Slc6a20a is largely absent from brainstem centers, the approach avoided the respiratory and motor risks that plagued GlyT1 inhibitors.
Implications: By modulating a regionally restricted glycine transporter, this approach provides an anatomically precise method to boost NMDAR function. The strategy’s success in adult animals emphasizes a therapeutic window that extends beyond early development, and the phospho-proteomic findings point to functional restoration of synaptic signaling as the core mechanism. The work suggests a translational pathway for treating ASD and other conditions associated with NMDAR hypofunction, with potential applicability to schizophrenia and certain intellectual disabilities.
Key Questions Answered:
A: Earlier therapies targeted GlyT1, a glycine transporter abundant in brainstem areas that control breathing and motor function. Those treatments inadvertently disrupted vital brainstem circuits, causing severe respiratory and motor side effects that undermined clinical trials.
A: SLC6A20 is predominantly expressed in higher-order cognitive regions such as the cortex and hippocampus and is largely absent from the brainstem. Using ASOs to silence SLC6A20 raises local glycine availability where it supports cognition without interfering with brainstem circuits that control breathing.
A: No. The study demonstrated robust restoration of receptor function and behavioral recovery in fully mature adult mice, indicating that correcting NMDAR dysfunction can be effective long after early developmental windows.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The referenced journal paper was reviewed in full.
- Additional context was added by staff to clarify translational and mechanistic points.
About this genetics and autism research news
Author: William Suh
Source: Institute for Basic Science
Contact: William Suh – Institute for Basic Science
Image: The image is credited to Neuroscience News
Original Research: Open access. “Glycine-modulating Slc6a20a-ASO restores NMDA receptor function in SHANK2 and SHANK3-mutant mice and cortical organoids” by Junyeop Daniel Roh et al., published in Nature Communications. DOI: 10.1038/s41467-026-73881-9
Abstract
Glycine-modulating Slc6a20a-ASO restores NMDA receptor function in SHANK2 and SHANK3-mutant mice and cortical organoids
Suppressed NMDA receptor (NMDAR) function contributes to multiple brain disorders, including schizophrenia, autism spectrum disorder (ASD), and NMDAR encephalitis. Previous attempts to restore NMDAR activity by increasing ambient glycine via GlyT1 inhibition produced mixed outcomes, in part because GlyT1 is extensively expressed in essential brainstem regions. Slc6a20a, a glycine transporter enriched in cognition-relevant regions such as the cortex and hippocampus, offers a focused alternative.
This study shows that ASO-mediated Slc6a20a inhibition normalizes ASD-related phenotypes in Shank2- and Shank3-mutant mice, rescues NMDAR hypofunction and synaptic phospho-proteomic profiles in the prefrontal cortex, and that ASO targeting human SLC6A20 restores suppressed NMDAR function in cortical organoids carrying SHANK2 or SHANK3 mutations. These findings highlight both the potential and the limits of Slc6a20a/SLC6A20-ASO as a treatment strategy for disorders characterized by NMDAR hypofunction.