Wang et al. 2024

Quick Summary

This paper described three young boys with developmental delay, early seizures, and developmental regression who were found to have disease-causing or likely disease-causing variants in IRF2BPL. All three children had infantile epileptic spasms, a seizure type that can be difficult to treat and can strongly affect early development.

The researchers also studied IRF2BPL in zebrafish. They disrupted the zebrafish version of the gene, called irf2bpl, and found that the young fish had shorter body length and seizure-like electrical activity in brain recordings. This provided functional evidence that loss of IRF2BPL can affect nervous system development and seizure tendency.

A major practical point from the paper is that the children showed some developmental improvement after their spasms were better controlled, although they continued to have developmental delays. The paper does not prove a specific treatment plan, but it supports the importance of recognizing epileptic spasms and understanding the genetic cause when possible.

Why This Paper Matters

Earlier IRF2BPL papers had already linked this gene to neurodevelopmental disorders with regression, seizures, abnormal movements, speech loss, dystonia, ataxia, and other neurological features. This paper added three more affected children, including two variants the authors described as newly reported for IRF2BPL-related developmental epileptic disorder.

The paper also added an animal-model piece. Previous work had used fruit fly and zebrafish models to support a role for IRF2BPL in neuronal development and maintenance. In this study, the authors used CRISPR-Cas9 to disrupt irf2bpl in zebrafish larvae and then recorded brain electrical activity. They reported spontaneous seizure-like discharges, which is important because epilepsy was a key feature in the children.

This matters for families because it connects three levels of evidence: the children's symptoms, their de novo IRF2BPL variants, and a laboratory model showing that disruption of the gene can produce seizure-like brain activity. Together, these findings support IRF2BPL as a gene that can contribute to developmental epileptic encephalopathy, especially when infantile spasms and regression are present.

What The Researchers Studied

This was a combined clinical case series and laboratory study. The clinical part included three male probands with developmental delay and epilepsy. The researchers collected clinical histories, neurological findings, EEG results, brain MRI findings, developmental assessments, routine hospital examinations, and genetic testing results.

All three children had whole-exome sequencing, a genetic test that looks across the protein-coding parts of the genome. The researchers used trio testing, meaning they compared the child's DNA with the parents' DNA. This allowed them to show that the IRF2BPL variants were de novo, meaning they were present in the child but not detected in either parent. The variants were then confirmed with Sanger sequencing.

The laboratory part used zebrafish because zebrafish have a version of the IRF2BPL gene. The authors identified the zebrafish ortholog as irf2bpl and reported that the zebrafish and human proteins share 66% identity. They used CRISPR-Cas9 to disrupt irf2bpl in early zebrafish embryos, creating what are often called F0 CRISPR "crispants." At 5 to 6 days after fertilization, they measured body and brain-related features and recorded electrical activity from the optic tectum, a brain region in the larvae.

The study did not test a treatment in zebrafish. It used the zebrafish model mainly to ask whether disrupting irf2bpl could affect development and produce seizure-like electrical activity.

What Was Learned About Symptoms

All three children had developmental delay before regression, epilepsy, language disability, and developmental regression. The paper states that seizure onset ranged from 5 to 19 months, and two children had seizure onset before 8 months, fitting early-onset epilepsy. The seizure pattern in all three children included infantile epileptic spasms.

EEG was a major part of the clinical picture. All three children had hypsarrhythmia, a very disorganized EEG pattern often associated with infantile spasms. The figure on page 3 shows a typical hypsarrhythmia EEG tracing. Patients 1 and 3 also had focal-onset seizures reported in addition to spasms.

Patient 1 was a boy whose early development included the ability to raise his head steadily and follow lights and sounds at 3 months. At 5 months, he developed clustered epileptic spasms, often around sleep or waking. After the spasms began, he lost ground developmentally: head control became less steady, reactions to faces slowed, and he could no longer find the source of sounds. His developmental testing showed delays across several areas. His seizures did not respond fully to initial treatments, but after additional treatment including vigabatrin, the spasms stopped. Later follow-up described gradual developmental progress, including crawling, standing, and saying "baba" and "mama," although he remained delayed compared with other children his age.

Patient 2 was a boy with low muscle tone in the neonatal period and delayed motor development. He had slow progress despite rehabilitation. Around 1 year and 5 months, he developed epileptic spasms and motor regression, including loss of abilities such as holding up his head, sitting, and rolling over. He was treated with several approaches, including a ketogenic diet, ACTH, and multiple anti-seizure medicines. At 2 years and 6 months, he had corpus callosotomy, a type of epilepsy surgery used in selected cases. The paper reports that the spasms were effectively controlled afterward, and he gradually gained some motor and communication skills, although intellectual development remained delayed.

Patient 3 was a boy referred at 10 months because of recurrent convulsions for 2 months. He had several findings noted in the newborn period, including congenital bilateral hip dislocation, newborn jaundice, patent ductus arteriosus, patent foramen ovale, and micrognathia. Before seizure onset, he could listen, look, eat, laugh, hold his head up, and roll over. After the spasms began, he gradually lost the ability to follow sound or light and to laugh. He was diagnosed with developmental epileptic encephalopathy and infantile spasm. ACTH reduced but did not stop the spasms, and topiramate was added. At 13 months, he still had about one spasm attack per day, but his mental state and development had improved somewhat.

Movement findings were present in some but not all children. The results section states that two patients had movement abnormalities. The table lists dyskinesia for Patient 2 and hypertonia for Patient 3, while Patients 1 and 3 were listed as having no dyskinesia. The paper did not describe dystonia as a main feature in these three children.

Speech and language were affected in all three children. Patient 1 could say "baba" and "mama" after improvement. Patient 2 could say "Papa" and "Mama" and later gained the ability to repeat some words and understand a small amount of daily language. Patient 3 had no language at the time described in the table. The paper did not report swallowing problems.

Brain MRI findings varied. Patient 1's MRI at 8 months showed widened subdural spaces over the bilateral frontal and temporal regions and a slightly expanded ventricular system. Patient 2's MRI was described as normal in the case text and table. Patient 3's MRI showed a slightly wider subarachnoid space of the frontal and temporal poles. Figure 1 on page 3 shows the MRI panels for the three children.

What Was Learned About Genetics

The researchers found three de novo IRF2BPL variants. "De novo" means the change was new in the child and was not detected in either parent. This is an important point for families because an IRF2BPL-related condition can happen even when there is no known family history.

The variants were:

* NM\_024496.4: c.1171 C>T, p.Arg391Cys in Patient 1 * NM\_024496.4: c.273\_307del, p.Ala92Thrfs\*29 in Patient 2 * NM\_024496.4: c.1157 C>T, p.Thr386Met in Patient 3

Two of these were missense variants: p.Arg391Cys and p.Thr386Met. A missense variant changes one amino acid in the protein to a different amino acid. The authors classified both missense variants as likely pathogenic because they were de novo, very rare in population databases, and predicted to be damaging by computational tools.

The third variant, p.Ala92Thrfs\*29, was a frameshift variant. A frameshift changes how the genetic code is read, usually disrupting the protein more severely. The authors classified this variant as pathogenic because it was de novo, was expected to cause early termination of the protein, and was very rare in population databases.

The authors stated that two of the variants were newly reported and one had been reported previously. They did not present these variants as mild or predictable based on the variant name alone. Instead, they used the children's shared clinical pattern, the de novo inheritance, population database information, prediction tools, and zebrafish experiments to support the role of IRF2BPL.

The zebrafish work did not recreate each exact human variant. Instead, it disrupted the zebrafish irf2bpl gene more broadly. The disrupted fish showed spontaneous ictal-like and interictal-like electrical discharges. In plain language, these are seizure-like and between-seizure-like brain activity patterns. This supports the idea that loss of normal IRF2BPL function can contribute to seizures.

Patient And Cohort Details

This article did not describe a large patient cohort. It described three affected boys and then added functional testing in zebrafish. All three children had developmental delay before regression, all had infantile epileptic spasms, all had hypsarrhythmia on EEG, all had language disability, and all had developmental regression.

The three children were not identical. Patient 1 had spasms beginning at 5 months and later became seizure-free on maintenance vigabatrin after several treatment steps. He made developmental progress but remained delayed. Patient 2 had neonatal hypotonia and significant motor delay before spasms began. His epilepsy was difficult to control and eventually involved corpus callosotomy. After spasms were controlled, he gained some motor and communication skills. Patient 3 had congenital findings noted at birth, developed spasms in infancy, and continued to have about one spasm per day at 13 months, though his development and mental state improved somewhat after treatment.

MRI findings also differed. Two children had mild structural or space-related MRI findings, while Patient 2's MRI was reported as normal. EEG findings were more consistent, with hypsarrhythmia reported in all three.

The zebrafish part included comparisons between Cas9-injected control larvae and irf2bpl crispants. The disrupted fish did not show a significant difference in eye distance or measured central nervous system area, but they did show shorter body length. Most importantly for this paper, electrophysiology showed spontaneous epileptiform events in the irf2bpl crispants, while controls showed baseline activity.

What Families Can Take Away

This paper supports IRF2BPL as a possible genetic cause when a child has early developmental delay, infantile spasms, abnormal EEG, and developmental regression. The pattern in these three children was especially centered on epileptic spasms and loss of developmental skills after seizure onset.

The paper also shows why a genetic diagnosis can matter. A child with IRF2BPL-related disease may not have a family history, and routine exams may not clearly explain the symptoms. Trio exome sequencing helped identify the cause in all three children described here.

Another takeaway is that seizure control and development were closely connected in the authors' descriptions. The children remained developmentally delayed, but the paper reported some developmental improvement after spasms were better controlled. This should not be read as a guarantee, and it does not mean the same treatment will work for every child. It does support careful seizure evaluation and close follow-up with the child's neurology team.

Families should also know that IRF2BPL-related disorders can vary widely. Some reported people have prominent movement disorders, ataxia, dystonia, or later-onset symptoms. In this paper, the three children mainly had early epileptic spasms, developmental delay, language impairment, and regression. Each child's care plan needs to be individualized with their clinicians.

Limits Of The Paper

The clinical part of the paper included only three children. That is helpful for a rare disease, but it is still too small to define the full range of IRF2BPL-related developmental epileptic disorder or to estimate how common each symptom is.

The treatment observations are important but limited. The paper reported that developmental progress improved after spasms were controlled, but this was not a clinical trial. The children received different treatments, and one child had epilepsy surgery. The paper cannot prove which treatment was responsible for improvement or predict what will work for another child.

The zebrafish model supports a role for irf2bpl in development and seizure-like brain activity, but it has limits. The researchers disrupted the zebrafish gene rather than recreating each child's exact variant. The fish were studied very early in development, at 5 to 6 days after fertilization, so the model cannot show the full long-term course of the human condition.

Some clinical details were not reported in depth. For example, the paper did not provide detailed swallowing information, did not fully describe long-term developmental outcomes for every child, and did not deeply explore why the three children had somewhat different severity.

The paper also cannot prove a simple genotype-phenotype rule. The authors added two new variants and one previously reported variant, but many more patients and functional studies will be needed to understand how different IRF2BPL variants relate to epilepsy severity, movement symptoms, MRI findings, and long-term development.

Source Notes

* Uploaded PDF: full article text, figures, and Table 1. * Main text: Abstract, Introduction, Materials and methods, Results, Discussion, Conclusion. * Results: Clinical features; Identification of IRF2BPL variants; Zebrafish validation; Phenotype correlation. * Table 1: Clinical features of patients with IRF2BPL variants. * Figure 1: MRI images for the three probands and typical hypsarrhythmia EEG. * Figure 2: Zebrafish irf2bpl disruption, body length measurements, CNS imaging, CRISPR efficacy, and electrophysiology recordings.