Thyroid Hormone, ASXL3, and Brain Circuits: What a New Mouse Study Suggests

In one sentence

A new mouse study suggests that losing one copy of the autism risk gene ASXL3 disrupts thyroid hormone signaling in the brain, changes a specific type of brain cell, and produces autism-like behaviors — and that giving thyroid hormone right after birth can reverse these effects.

What the researchers did

The team used mice that were missing one copy of the Asxl3 gene (called Asxl3+/− mice), a setup that mimics the gene loss seen in some children with autism. They measured brain structure, counted different types of brain cells, and tested social and memory behaviors. They also tested whether giving thyroid hormone (T3) at different ages, or restoring the ASXL3 gene itself using a gene-therapy tool, could fix the problems. This was a controlled laboratory study in mice, not a human trial.

What they found

• Asxl3+/− mice had thinner cortex (the brain's outer layer) and fewer upper-layer and layer 5 projection neurons.
• They had more parvalbumin (PV) interneurons — a type of inhibitory brain cell — in the retrosplenial cortex and hippocampus. Other interneuron types and glial cells were unchanged.
• The mice showed a specific social memory deficit: they did not prefer a new mouse over a familiar one, though basic sociability was intact.
• Asxl3 loss raised levels of DIO3, an enzyme that breaks down thyroid hormone, leading to lower thyroid hormone in blood and brain.
• Giving T3 right after birth (neonatal period) restored PV interneuron numbers and rescued behavior. Giving it during adolescence did not work.
• Restoring full-length ASXL3 with a gene-therapy tool also normalized brain structure and behavior in mice, and the tool worked in non-human primate brains.

What this means for families and therapists

• This study points to a possible early window — right after birth — when thyroid hormone might help in ASXL3-related autism. It does not mean thyroid supplements help all autistic children.
• If your child has an ASXL3 variant, ask your clinician whether thyroid hormone levels have been checked and whether any hormonal concerns need monitoring.
• For therapists: the findings highlight that early developmental periods may matter more for some genetic subtypes. Tracking social memory and attention in early sessions could be useful, but this is not yet a treatment protocol.

Limitations and what we don't know yet

• This is a mouse study. Mouse brains and behaviors are not the same as human ones, so results may not translate.
• The number of mice per group was small (often 3–5), which limits how confident we can be in the findings.
• The study did not include a long-term follow-up, so we don't know if benefits last.
• The gene-therapy approach is experimental and has not been tested in children.
• We don't know whether these findings apply to autistic people without ASXL3 variants.

This is a plain-language summary of Thyroid Hormone, ASXL3, and Brain Circuits: What a New Mouse Study Suggests by Ding C., Yuan Y., Hu Y., Zhang Y. et al., Science Advances (2026). Source license: CC-BY-NC-4.0. It is not medical advice — talk to a qualified clinician before changing therapy.