Heide et al. 2023

Quick Summary

For several years, the *IRF2BPL* gene has been linked to a severe condition called NEDAMSS, where children often lose skills like walking and talking early in life. This paper, published by Dr. Solveig Heide and her team in 2023, changes that perspective by showing that *IRF2BPL* can also cause a much milder, slower-progressing condition. The researchers followed 18 people who carry changes in this gene, most of whom belong to one very large family.

In these cases, the "story" of the condition looks different. Instead of a sudden loss of skills in early childhood, these individuals usually had mild learning or developmental delays throughout school. Many attended school and some reached adulthood with milder difficulties than those described in earlier severe childhood reports. However, as they got older—typically between their 20s and 50s—they began to develop "ataxia," which is a medical term for shakiness, poor balance, and difficulty coordinating movements.

The study also reveals that some people can carry a "pathogenic" (disease-causing) variant of the *IRF2BPL* gene but never actually develop symptoms, or develop them so mildly they go unnoticed. This is known as "incomplete penetrance." This discovery is a major step forward because it helps families and doctors understand that the same genetic change can affect two people—even a parent and child—in very different ways.

Finally, the researchers emphasize that *IRF2BPL* acts as a bridge between "neurodevelopmental" (how the brain grows) and "neurodegenerative" (how the brain ages) processes. By studying these adult patients, the team provides a roadmap for what families might look for as children with milder forms of the condition grow into adulthood.

Why This Paper Matters

This article is a landmark in the *IRF2BPL*/NEDAMSS story because it significantly expands the "spectrum" of the disorder. Before this, most scientific papers focused on the most severe cases involving rapid regression in toddlers. This paper shows that *IRF2BPL*-related disorders are not always a "one-way street" to severe disability in childhood.

Specifically, it introduces three new concepts to the community:

1. Late-Onset Symptoms: It shows that movement disorders like ataxia can wait until adulthood to appear, even if the genetic change has been there since birth. 1. Inheritance Patterns: While most NEDAMSS cases are "de novo" (meaning they happen by chance and aren't inherited), this study shows the gene change being passed down through generations in a large family. 1. Variable Severity: It shows that within a single family, one person might have severe movement issues while another (like a mother in the study) might have no symptoms at all during her lifetime.

This matters for families because it suggests that a diagnosis of an *IRF2BPL* variant doesn't always mean the most severe outcome. It also provides a reason for adults with unexplained "familial ataxia" to be tested for this specific gene.

What The Researchers Studied

The researchers looked at a total of 18 individuals. The bulk of the data came from one large French family (referred to as Family SAL-394) which included 16 affected members across multiple generations. They also studied a second, smaller family with a mother and daughter.

This was a "primary cohort study," meaning the researchers gathered new clinical data directly from patients or their medical records rather than just reviewing old papers. They used advanced genetic tools called "Exome Sequencing" and "Genome Sequencing" to find the specific mistakes in the DNA code of the *IRF2BPL* gene.

The team combined this genetic information with detailed clinical exams. They looked at:

* Developmental History: How the patients did in school and when they reached milestones like walking. * Neurological Exams: Testing balance, reflexes, and muscle control. * Brain Imaging: Using MRIs to see if specific parts of the brain, like the cerebellum, had changed over time. * Nerve Tests: Specialized tests (like "Evoked Potentials") to see how fast signals travel from the eyes, ears, and limbs to the brain.

What Was Learned About Symptoms

The symptoms described in this paper are notably different from the "classic" NEDAMSS descriptions. The researchers found a two-stage pattern in most of the patients.

Early Childhood and School Age

Most patients started with mild "neurodevelopmental" symptoms. This usually meant mild intellectual disability or learning delays. Unlike the severe forms of NEDAMSS, these children did not typically lose their ability to speak or walk during their early years. Many attended school and some reached adulthood with milder difficulties than those described in earlier severe childhood reports.

Adulthood and Regression

The "regression" or decline happened much later than expected. In the large family studied, 8 out of 16 people developed cerebellar ataxia.

* Onset Age: This started anywhere from age 21 to age 53. * The First Signs: Usually, it began with an "unsteady gait" (feeling wobbly while walking). * Progression: For some, the balance issues became severe enough that they needed a wheelchair by their 40s or 50s. * Other Movement Signs: Many had "pyramidal signs," which means their reflexes were very jumpy or "brisk." Some also had dystonia (unusual posturing of the arms) or a "loss of facial mimicry" (the face appearing less expressive).

Speech, Swallowing, and Senses

As the ataxia progressed, some patients developed dysarthria (slurred or difficult-to-understand speech). A few experienced difficulty swallowing. Interestingly, tests showed that some patients had trouble sensing vibrations at their ankles, suggesting the condition affects the sensory nerves or the pathways leading to the brain, not just the motor (movement) areas.

MRI and Brain Findings

When the researchers looked at brain scans (MRIs), they saw a specific pattern: cerebellar atrophy. This means the cerebellum—the part of the brain that controls balance—was smaller than it should be. They also saw "global cortical atrophy," which is a slight thinning of the brain’s outer layer.

What Was Learned About Genetics

The researchers found two specific "nonsense variants" in these families. A nonsense variant is a type of genetic "typo" that tells the cell to stop building the protein before it is finished. This usually results in a shortened, non-functional protein.

1. The p.Gln117Ter variant: This was found in the large family of 16. Because it appeared in so many people across generations, it confirms that this gene can be inherited in an "autosomal dominant" way—meaning a parent has a 50% chance of passing it to their child. 1. The p.Ser313Ter variant: This was found in the second family. The most surprising finding here was that the daughter had mild intellectual disability, but her mother, who carried the exact same variant, had no symptoms at all until her death at age 45.

The paper explains that these variants are "truncating," meaning they cut the IRF2BPL protein short. The researchers believe that the *location* of the variant on the gene might influence how severe the symptoms are, but they also note that "modifier genes" (other genes that act like a volume knob) or environmental factors probably play a role in why one person gets sick and another doesn't.

Patient And Cohort Details

The cohort of 18 people provides a clear look at how the disease changes over a lifetime:

* Family SAL-394 (16 people): This family showed a very consistent pattern of mild learning issues in childhood. However, the age when the movement issues (ataxia) started was very unpredictable. Some felt it in their early 20s, while others didn't notice it until their 50s. Those who lived the longest (into their 70s) tended to have the most significant physical challenges. * Family II (2 people): This case was unique because it showed the variant could be completely "silent" in one generation (the mother) before appearing as a learning delay in the next (the daughter). * Common Threads: Across both families, the most common symptom was a "brisk reflex" (hyperreflexia), which was found in 11 out of the 16 family members who were physically examined. This suggests that even if someone doesn't have balance issues yet, a doctor might see these "jumpy" reflexes as an early clue.

What Families Can Take Away

* A Broader Outlook: If your child has an *IRF2BPL* variant, this paper shows that a severe, early loss of skills is not the only possible outcome. There are "milder" versions of the condition that progress much more slowly. * Adult Monitoring: For individuals with *IRF2BPL* who are doing well in their teens and 20s, it is still important to stay connected with a neurologist. This study suggests that balance and movement should be monitored as they enter adulthood. * Genetic Counseling: Because this study shows the condition can be inherited (dominant) and can be "hidden" in some parents, families may want to consider testing for other family members, especially if there is a history of balance issues or learning delays. * Hope for Understanding: This paper helps scientists understand *why* the brain might struggle. It shows that *IRF2BPL* is important for both the "construction" of the brain during childhood and the "maintenance" of the brain as we age.

*Note: Every person with an IRF2BPL variant is different. Clinical decisions and the interpretation of genetic results should always be made in consultation with your medical team and a genetic counselor.*

Limits Of The Paper

While this study is very detailed, it has some limitations:

* Retrospective Information: Much of the childhood data for the older family members was gathered by asking them to remember their school years ("retrospective"), rather than using official school records or IQ tests from that time. This makes the childhood data less precise. * Small Number of Variants: The study only looks at two specific genetic "typos." We don't yet know if every "nonsense" variant in *IRF2BPL* behaves this same way. * Unpredictable Progression: The study shows *that* the disease progresses, but it cannot yet explain *why* it starts at age 20 for one person and age 50 for another. * Missing Data on Youngest Generation: Some of the younger members of the family carry the gene but are currently healthy. The researchers cannot say for certain if or when those younger members will develop symptoms.

Source Notes

The information in this summary was drawn from the following sections of the Heide et al. 2023 article:

* Main text: Results section detailing "Family SAL-394" and "Family II." * Table 1: Clinical characteristics for all 18 individuals. * Figure 1: The family pedigree chart showing inheritance. * Figure 2: MRI images showing cerebellar and cortical atrophy. * Discussion: The analysis of "Neurodevelopmental and Neurodegenerative" connections.