Understanding ReNU2
A research summary for families who want more detail
ReNU2 is the name used for neurodevelopmental conditions caused by variants (changes) in a gene called RNU2-2. For many years, RNU2-2 was labelled a pseudogene, meaning scientists thought it was an inactive copy of another gene. Research published in 2025 and 2026 showed that it is an active gene and that variants in it can cause developmental delay, intellectual disability, and epilepsy.
Two forms have been described. The dominant form, reported in 2025, involves a change in one copy of the gene. The recessive form was described in three studies published online in Nature Genetics on March 30, 2026, and involves changes in both copies. This research is new, and understanding of ReNU2 is still developing.
This page summarizes what those studies found, including study sizes and figures. If you are looking for a plain-language introduction, start with our family guide. Clinicians and researchers can find more technical information in our guide for clinicians and researchers.
This page is for information only and is not medical advice. Please talk with your child's clinician or a genetic counselor about your family's situation.
The gene behind ReNU2: RNU2-2
Many genes carry instructions for making proteins. RNU2-2 does not. Instead, it makes a small RNA molecule called U2-2 small nuclear RNA (snRNA).
U2-2 is one part of the spliceosome. The spliceosome edits RNA messages copied from DNA. It removes sections called introns and joins the remaining sections so the message can be used to make a protein.
RNU2-2 is very short: only 191 building blocks (nucleotides) long. Although databases had labelled it a pseudogene, studies showed that cells actively make U2-2. In blood, it is found at levels comparable to U2-1, a nearly identical molecule made by a closely related gene, RNU2-1. Unlike RNU2-2, which is a single gene, RNU2-1 exists in many repeated copies.
Where variants have been found along the 191 nucleotides of RNU2-2
Swipe sideways to see the whole gene.
What RNA studies have found so far
- Lower U2-2 in the recessive form. Greene et al. (2026) and Jackson et al. (2026) both found much lower levels of U2-2 in blood from people with the recessive form.
- U2-1 may compensate. In the five people analyzed by Greene et al. (2026), U2-1 levels rose, so total U2 was normal. The authors interpreted this as possible compensation. The study was small, and this should not be treated as a proven response in every person.
- A proposed ratio marker. Jackson et al. (2026) found a lower ratio of U2-2 to U2-1 in people with the recessive form, and proposed the ratio as a possible marker for diagnosis.
- A limit on the ratio. Leitão et al. (2026) suggested the ratio may only be useful for some types of recessive variants.
- The dominant form. U2-2 levels in blood were similar to those of people without the condition.
The RNA ratio is a research finding, not an established clinical test. How RNU2-2 variants affect brain development is still being studied.
The two inheritance patterns
Dominant form
Most reported dominant cases involve one of two recurring variants, n.4G>A or n.35A>G. The number refers to the position in the gene where the change occurs.
In most reported cases, these variants were de novo. That means they arose new in the child and were not inherited from either parent. Leitão et al. (2026) also described a person who had the n.35A>G variant in only some of their cells (mosaicism).
Other single-copy variants in RNU2-2 have been reported, but they are harder to interpret. In Leitão et al. (2026), several children who first appeared to have a single new variant were found to have a second variant on the other copy of the gene. That pointed to the recessive form instead. The researchers recommend checking for a second variant whenever a new RNU2-2 variant is found.
A genetic counselor can explain what a specific result means for a family, including the chance of it happening again in a future pregnancy.
Recessive form
The recessive form occurs when both copies of RNU2-2 carry a disease-causing variant. The two variants can be the same or different. In Leitão et al. (2026), most people with the recessive form had two different variants.
In many families, each parent carries one variant. In others, one variant is inherited from a parent and the other arises new in the child.
In reported recessive families, relatives who carry only one variant have generally been described as unaffected. Leitão et al. (2026) noted a few exceptions: five carrier parents who had epilepsy or intellectual disability. The studies are still too small to say whether carrying a single variant has any effect.
More than one affected child in the same family has been reported. Leitão et al. (2026) described 16 families with more than one affected sibling.
When each parent carries one variant, each pregnancy has these chances
How the disorder was identified
- Before 2025RNU2-2 was listed in gene databases as a pseudogene, under the name RNU2-2P.
- 2025Two research groups published studies in Nature Genetics describing the dominant form (Greene et al. 2025 and Jackson et al. 2025). Greene et al. (2025) first identified recurring new variants at positions 4 and 35 of RNU2-2 in 9 people, then confirmed the finding in 16 more, for a total of 25.
- March 30, 2026Three studies describing the recessive form were published online in Nature Genetics. Leitão et al. (2026) also included people with the dominant form and compared the two.
Greene et al.
Led from the Icahn School of Medicine at Mount Sinai in New York, with collaborators in the UK and elsewhere. Analyzed rare disease cohorts from the UK, the USA, Italy, and the Netherlands.
Jackson et al.
Led from the Manchester Centre for Genomic Medicine in the UK. Drew mainly on the UK 100,000 Genomes Project, with additional cases from other countries.
Leitão et al.
Led by researchers in France, including at the Paris Brain Institute. Analyzed genomes from 34,329 people with rare disorders in France, and added cases through international collaboration.
Greene et al. (2026) and Jackson et al. (2026) both drew largely on the same UK genome data, from Genomics England. Leitão et al. (2026) used separate cohorts. Their findings were broadly consistent, though the researchers interpreted some results differently.
Why RNU2-2 was overlooked for so long
- It was labelled a pseudogene.
- Standard exome sequencing, which focuses on protein-coding genes, generally does not assess it.
- An older version of the reference genome that labs use to read DNA data was missing the related RNU2-1 genes. That could cause real RNU2-2 variants to be missed.
What researchers are still learning
Because the spliceosome edits RNA messages, researchers expected to find clear editing (splicing) errors in people with ReNU2. So far the findings are limited and not fully consistent:
- Greene et al. (2025) found no evidence of splicing errors in blood from people with the dominant form.
- Greene et al. (2026) found no clear pattern of abnormal splicing in blood from five people with the recessive form. The authors note that the group may have been too small to detect one.
- Jackson et al. (2026) found some signs of splicing errors in blood from people with the dominant form, but not the recessive form.
- Leitão et al. (2026) found subtle effects that differed by variant, rather than one shared pattern.
Blood may not show the full picture. Jackson et al. (2026) and Leitão et al. (2026) both note that, compared with RNU2-1, RNU2-2 makes up a smaller share of U2 in blood than in the brain. Findings in blood do not necessarily reflect what happens in the brain.
Researchers also differ on how separate the two forms are. Jackson et al. (2026) describe the dominant and recessive forms as genetically, molecularly, and clinically distinct. Leitão et al. (2026) see them as points on a continuum: some variants can cause disease on their own, while others cause disease only when paired with a second variant.
What research says about frequency
These figures come from specific research cohorts. They do not tell us how common ReNU2 is in every country or population.
Leitão et al. (2026): 141 people from 122 unrelated families with RNU2-2 variants
- 91people from 73 families had the recessive form
- 35had one of the two recurring dominant variants
- 15had other single new variants
UK 100,000 Genomes Project: the most frequent recessive diagnoses among people with neurodevelopmental disorders
Greene et al. (2026)
The recessive form accounted for about 10% of families with a recessive neurodevelopmental disorder that can currently be diagnosed by sequencing. It affected about 60% as many families as ReNU syndrome. The authors note that how common it is in other countries is unknown.
About the 1.5% figure
You may see a figure of about 1.5%. It counts a group of related conditions involving RNU4-2, RNU2-2, and RNU5B-1: 118 of 7,968 people with previously undiagnosed neurodevelopmental disorders in the UK 100,000 Genomes Project. RNU2-2 on its own accounted for 49 of those 7,968 people (0.61%).
These findings show why RNU2-2 deserves attention in genetic testing. They do not mean every child with unexplained developmental differences or epilepsy has an RNU2-2 variant.
Symptoms and clinical features
Features vary from person to person, even among people with the same variant. Studies describe patterns across groups. They cannot predict any one person's abilities, medical needs, or future development.
In the figures below, each percentage is based on the people in that study who had information available for that feature.
Features reported across both forms
In Leitão et al. (2026), all participants with available information had developmental delay. Seizures usually began before age 3, though onset ranged from 8 weeks to 16 years. Seizure types varied.
Epilepsy was reported at similar rates in both forms
The range within the recessive form
Greene et al. (2026) described a wide range in the recessive form. Overall severity ranged from mild learning disability with autism to severe epilepsy with developmental impact, and walking ranged from normal to not walking at all.
One detailed group: 34 people with the recessive form, aged 5 to 34
Features that differed between the two forms
Seizure types and movement disorders in Leitão et al. (2026)
This difference was not statistically significant.
Within the dominant form, febrile seizures occurred in 11 of 16 people with n.4G>A (69%) and none of 10 people with n.35A>G.
Also reported more often in the recessive form
Spasticity (muscle stiffness) and seizures beginning in the first year of life (Jackson et al. 2026).
Also reported more often in the dominant form
Stereotyped (repetitive) hand movements and differences in facial features (Jackson et al. 2026). Leitão et al. (2026), however, found minor differences in facial features to be common in both forms.
These are group-level findings. They do not apply to everyone in either group.
ReNU2 and ReNU Syndrome (RNU4-2)
ReNU2 is caused by variants in RNU2-2. ReNU Syndrome is caused by variants in a related gene, RNU4-2. Both genes make small RNAs that are part of the spliceosome. The two conditions share some features, including developmental delay, intellectual disability, and epilepsy.
They are different genetic conditions. Findings and care recommendations for one do not automatically apply to the other.
Diagnosis and genetic testing
Because RNU2-2 does not carry instructions for a protein, it may not be included or reliably analyzed in every genetic test. Families can ask the ordering clinician or laboratory whether RNU2-2 is covered and whether results in this region are clinically validated.
| Test type | What to ask |
|---|---|
| Whole-genome sequencing (WGS) | Does the analysis include RNU2-2, and can the laboratory interpret variants in this region? The 2026 studies relied mainly on genome sequencing. You can also ask which version of the reference genome was used, since Jackson et al. (2026) found that an older version (GRCh37) can cause RNU2-2 variants to be missed. |
| Whole-exome sequencing (WES) | Standard exome sequencing focuses on protein-coding regions and generally does not assess RNU2-2. Ask the laboratory whether this region was covered and analyzed. |
| Autism, intellectual disability, or other gene panels | Is RNU2-2 included, and has the laboratory validated testing for it? |
| Targeted testing for a known family variant | Can a clinical laboratory validate testing for the specific variant and test relatives or carrier status? |
| RNA testing | Is any RNA test, such as the U2-2 to U2-1 ratio, available clinically? Researchers have described the ratio as a potential marker for the recessive form, but it is not an established routine test. |
Understanding a result
Even when a variant is found, interpreting it can be difficult. In the recessive form, variants are spread across the whole gene, and some variants that cause disease are found at similar frequencies to harmless ones in the general population. Jackson et al. (2026) noted that many of the recessive variants they identified would currently be classified as variants of uncertain significance under standard clinical guidelines.
A genetic counselor or clinical genetics team can help review a result, family testing, and possible next steps.
If a child has unexplained neurodevelopmental challenges or epilepsy and has not had testing that looks at non-coding regions, families may wish to ask their clinician or genetic counselor whether further testing is appropriate.
Key studies
All five studies are open access and free to read.
- Greene D, De Wispelaere K, Lees J, et al. Mutations in the small nuclear RNA gene RNU2-2 cause a severe neurodevelopmental disorder with prominent epilepsy. Nature Genetics 57:1367–1373 (2025). Read the study
- Jackson A, et al. Analysis of R-loop forming regions identifies RNU2-2 and RNU5B-1 as neurodevelopmental disorder genes. Nature Genetics 57:1362–1366 (2025). Read the study
- Greene D, Mendez R, Lees J, et al. Biallelic variants in RNU2-2 cause the most prevalent known recessive neurodevelopmental disorder. Nature Genetics 58:774–781 (2026). Read the study. A publisher correction was published on April 23, 2026: read the correction.
- Leitão E, Santini A, Cogne B, et al. Systematic analysis of snRNA genes reveals frequent RNU2-2 variants in dominant and recessive developmental and epileptic encephalopathies. Nature Genetics 58:782–797 (2026). Read the study
- Jackson A, Blakes AJM, et al. Biallelic variants in RNU2-2 cause a remarkably frequent developmental and epileptic encephalopathy. Nature Genetics 58:798–809 (2026). Read the study
Connect with ReNU2 Foundation
Whether you are navigating a new diagnosis or seeking information as a clinician, ReNU2 Foundation can help connect families with support and resources.
info@renu2.org