Auditory Evoked Potentials Differ from Controls and Correlate with Aspects of Cognition in Kabuki Syndrome and Rubinstein-Taybi Syndrome

The human brain is a vast network of electrical signals, constantly firing to interpret the world. When we hear a sound, a specific chain reaction begins: the ear captures the noise, and the brain's auditory cortex lights up to process it. Scientists can measure this lightning-fast activity using electrodes placed on the scalp, capturing the brain's immediate, involuntary reaction to a tone. These reactions, known as auditory evoked potentials, act like a snapshot of the brain's internal machinery. In typical development, these electrical waves follow a predictable pattern, rising and falling at precise moments after a sound occurs. However, in conditions where the brain's genetic instructions for building and maintaining these circuits are altered, this electrical signature can look different. Understanding these differences is crucial for rare genetic disorders that affect learning and behavior, as finding a reliable way to measure brain function could help doctors test whether new treatments actually work.

Two such disorders, Kabuki syndrome and Rubinstein-Taybi syndrome, stem from errors in the body's epigenetic machinery—the system that controls how genes are turned on or off without changing the DNA code itself. Both conditions lead to intellectual disability and distinct physical features, but they also share a history of promising results in mouse models, where cognitive problems were reversed using epigenetic therapies. Yet, moving these treatments to human trials has been stalled by a lack of clear biomarkers, or measurable signs, to track progress. Without a way to objectively see if the brain is responding to a drug, clinical trials become difficult to design and interpret. To address this gap, researchers set out to see if the brain's electrical response to sound could serve as that missing link, measuring how the brains of people with these syndromes react to simple tones compared to those without the conditions.

The study recruited thirty-five individuals with Kabuki syndrome, twenty-three with Rubinstein-Taybi syndrome, and forty typically developing participants to sit in a soundproof room. While listening to a series of identical, quiet tones played through speakers, the participants wore a cap fitted with sensors to record their brain activity. The goal was to keep the experience passive; the participants did not need to press buttons or solve puzzles. They could watch a silent movie or look at pictures, allowing the researchers to capture the brain's natural, unforced reaction to the sounds. Alongside this recording, every participant underwent a comprehensive assessment of their cognitive abilities, including tests for language, memory, attention, and problem-solving skills. This dual approach allowed the team to connect the dots between the electrical waves in the brain and the actual thinking skills of the individuals.

When the researchers analyzed the recordings, they found that the brains of individuals with both syndromes reacted differently than those of the control group. Specifically, the electrical waves that occur slightly later in the processing chain—those associated with making sense of the sound rather than just detecting it—were significantly larger in magnitude for the syndrome groups. The difference was most pronounced in the Rubinstein-Taybi group, whose brain waves showed the greatest deviation from the typical pattern. Interestingly, the researchers observed that the size of these electrical waves was not random; it was linked to how well the individuals performed on their cognitive tests. For instance, in the Kabuki syndrome group, larger waves in certain timeframes were associated with stronger language skills and better visual-motor coordination. When the two syndrome groups were looked at together, these same brain waves also showed a connection to executive functions, such as the ability to focus and inhibit distractions.

The findings suggest that these larger electrical responses might indicate that the brain is working harder to process information. In a typical brain, the neural circuits for hearing and understanding are highly efficient, requiring fewer resources to achieve the same result. In contrast, the brains of individuals with these syndromes may need to recruit additional neural resources to complete the same task, resulting in a stronger electrical signal. This extra effort correlates with better cognitive performance, implying that the more successfully the brain can mobilize these extra resources, the better the individual functions. While the study noted that some participants with Rubinstein-Taybi syndrome had brain wave patterns that appeared in different locations on the scalp than expected, the overall trend held true: the brain's electrical signature is distinct in these conditions and reflects the severity of cognitive challenges.

This research marks the first time such electrical measurements have been taken in people with Kabuki or Rubinstein-Taybi syndrome, offering a new window into how these brains function. The results provide a foundation for future studies to determine if these brain waves can serve as a reliable tool for tracking the effectiveness of new therapies. If a treatment successfully improves the underlying epigenetic function, it might be possible to see a corresponding change in these electrical signals, providing a concrete measure of progress that goes beyond behavioral observations. While the sample sizes were small and further research is needed to confirm these patterns across different ages and genetic variations, the study establishes a clear path forward. It demonstrates that the brain's response to a simple sound can reveal complex truths about how genetic differences shape the mind, offering hope for more precise and effective medical interventions in the future.