Silencing Mutant GRIA1 Protects Mouse Brains From Damage

A single letter's worth of genetic error can flood a developing brain with calcium, and a Johns Hopkins team has shown in mice that silencing just the faulty copy can stop it. The study, from Johns Hopkins University School of Medicine and Academia Sinica in Taiwan and published in Neuron, targets GRIA1, the gene for the GluA1 subunit of AMPA receptors, the receptors neurons use to talk to each other during learning and memory. The work is in mice, not patients, and the authors frame it as proof of principle.

The mutation is called A636T, and it has been identified in people with autism spectrum disorder and intellectual disability. As the brain develops, AMPA receptors normally change in a way that limits how much calcium enters neurons. A636T interferes with that protective change, so too much calcium gets in. In mice carrying the mutation, the result was progressive damage to the hippocampus, neuronal degeneration and inflammation, and significant impairments in learning, memory and social behavior, along with anxiety-like and repetitive behaviors.

The treatment is selective in a way older approaches aren't. An antisense oligonucleotide, a short synthetic molecule built to recognize one specific RNA message, was designed to silence the RNA from the mutant GRIA1 copy only. The normal copy keeps working. That's the contrast the paper draws with conventional treatments that broadly suppress AMPA receptor activity, healthy receptors included.

The result, from one dose, is the finding. A single administration of the optimized molecule shortly after birth prevented the hippocampal neuronal damage, restored more normal synaptic function, reduced neuroinflammation and significantly improved learning, memory and social behavior in the mutant mice. “Our findings show how a single genetic mutation can disrupt brain development and lead to significant neurological impairments,” said Richard L. Huganir, professor of neuroscience at Johns Hopkins and a co-corresponding author. “Importantly, we demonstrate that selectively targeting the mutant gene can prevent neuronal damage and improve behavioral function.”

The approach has a track record to borrow. Antisense drugs are already developed therapies for spinal muscular atrophy and certain forms of Batten disease, and similar strategies are under investigation for ALS, Huntington's disease and rare genetic epilepsies. What this study adds is a case where the target is one copy of a receptor gene and the defect is too much activity, a gain of function, rather than a missing protein.

The distance to a clinic is the honest part of the story. The team plans to keep working in mice and in human stem cell models, and to keep optimizing the molecule, before any clinical application is on the table. Delivery to a human brain, dosing after birth rather than before symptoms, and the rarity of the specific mutation all stand between this result and a treatment. What the paper establishes is that the strategy can work in a living brain, which is the fact every later step depends on.