Imagine waking up one day and realizing that the world around you no longer looks the same. Faces are harder to recognize, navigating familiar streets feels confusing, and reading a book becomes a frustrating puzzle. This unsettling scenario is a reality for many people affected by Huntington’s disease (HD). Dr Juan Carlos Gómez-Esteban and his team of researchers from Spain, investigated if HD affects the brain’s ability to process and understand what people can see. They also researched when these changes in processing and understanding occur in people with HD. 

Bringing HD Into Focus

You might be wondering why is it important to focus on how people with HD see and understand things? This is because the part of the brain that is most affected by HD, called the striatum, is not just responsible for controlling movement – it also helps the brain process and understand what we see. As HD progresses, it becomes more and more difficult for the brain to handle visual information, making everyday tasks that used to be second nature, more and more challenging.

Picture trying to cross a busy street but struggling to judge how fast cars are moving. Or meeting an old friend but not recognizing their face right away. These are the kinds of frustrating, everyday obstacles that can come with visual thinking problems in HD. Understanding these challenges is crucial, not just for diagnosing HD earlier, but for developing therapies and treatments that help people with HD, navigate the world more confidently and independently.

Seeing the Early Signs

This study involved 181 participants, including people spanning different stages of HD. Beside each stage, we included the Huntington’s disease Integrated Staging System (HD-ISS) that best describes these categories. For more information on HD-ISS categories, please see our article about this system. A control group of individuals who do not have HD were also recruited to the study. This is because the researchers wanted to find out whether HD affects visual thinking skills, and if so, when these changes begin. People with HD were grouped into one of four categories for the purpose of this research:

Category 1 – People who have had the genetic test for HD and have a reduced penetrance allele (slightly lower number of CAG repeats, spanning 36-39 CAGs). This means that it is uncertain if these individuals will or will not go on to develop the symptoms of HD in their lifetime.

Category 2 (similar to Stage 0 of the HD-ISS) – The person has tested positive for HD (CAG number is 40 or more) but does not yet display any recognisable symptoms.

Category 3 (similar to Stage 2 of the HD-ISS) – The person with HD begins to experience symptoms. There may be noticeable changes in their motor abilities, mind, and mood symptoms. The individuals affected may still be fairly independent at this stage.

Category 4 (similar to Stage 3 of the HD-ISS) – The person with HD experiences fully developed HD symptoms, which significantly impacts their daily life. Individuals at this stage require significant support with their activities of daily living.

As HD progresses, it becomes more and more difficult for the brain to handle visual information, making everyday tasks that used to be second nature, more and more challenging.

Measuring What the Eyes Cannot See

To investigate if HD affects visual thinking skills (the brain’s ability to process and understand what people with HD can see), participants completed a variety of tasks that could measure these skills. These tasks assessed different ways people see and understand things. For example: remembering what we see; understanding where things are and how they move; focussing on what we see; how quickly we make sense of what we see.

But what tasks were used to measure these abilities? How well participants could remember what they see, was assessed by asking participants to copy a shape presented to them by drawing it. After a small amount time delay, the participants had to draw this shape again, from memory. Another example of a task that measured how well participants could remember what they see, involved showing participants a set of different shapes. After, the participants had to remember what shapes they were shown, and in what order they were displayed.

The team of researchers also investigated how well the brain was functioning, more generally. Brain functioning was assessed in each participant by performing tasks that measured vocabulary skills, attention levels, and problem-solving abilities. It was important to include these more general measures to understand how the brain’s ability to understand what people can see may ‘fit’ into wider brain functioning.

Together, the variety of tasks performed helped Dr. Gómez-Esteban and his team to build a better picture of how visual thinking abilities change in people with HD who are at different stages of the condition, as well as compared to individuals who do not have HD.

Through the Lens

Here’s the twist: Dr. Juan Carlos Gómez-Esteban and his team did not find any major differences in general thinking skills between people who did not have HD, people with the reduced penetrance allele (Category 1), and people who have tested positive for HD, but do not yet display any symptoms (Category 2).

But here’s where it gets interesting: visual memory abilities (think back to the task involving drawing shapes from memory) differed between the groups in this study. People with reduced penetrance (Category 1) had greater visual memory abilities compared to people with HD, who do not yet display recognisable HD symptoms (Category 2).

What’s even more intriguing is that when looking at people with HD experiencing early symptoms (Category 3) and people experiencing fully developed HD symptoms (Category 4), visual memory abilities remained relatively unchanged. This could suggest that a change in visual memory abilities could be one of the first signs of changes in thinking in people with HD. This could make visual memory skills a valuable clue in spotting HD early on.

It’s not just about what the eyes see – it’s about how the brain makes sense of it. Understanding this connection could make all the difference.

Seeing the Bigger Picture

Understanding how HD affects the brain’s ability to make sense of what we see could lead to an earlier diagnosis of HD and better treatment options. If having reduced visual memory abilities tends to appear before motor symptoms, testing for this could help to identify signs of HD sooner in individuals giving them more time to plan and seek support.

Visual memory changes could be an early warning sign of HD, offering a chance for earlier diagnosis and treatment. It’s not just about what the eyes see – it’s about how the brain makes sense of it. Understanding this connection could make all the difference.

Spotting visual memory changes in people with HD is not just about early diagnosis, it’s about making life better. So, if you or your loved one with HD can be forgetful when trying to remember a familiar face, keeps losing their phone or glasses, or keeps getting lost in the grocery store, you could consider using some helpful visual reminders.

Learn More

Original research article, “Characterization of visual cognition in pre-manifest, manifest and reduced penetrance Huntington’s disease” (open access.