PRPF31 — pre-mRNA processing factor 31

The PRPF31 gene provides instructions for making a protein that is essential for a process called RNA splicing. Think of genes as rough drafts of a recipe; RNA splicing is the editing process that cuts out the unnecessary parts (introns) and pastes together the important parts (exons) to create the final, readable recipe (mature mRNA) that the cell uses to build proteins. The PRPF31 protein is a crucial part of the cellular machinery, called the spliceosome, that performs this editing. When there is a mutation in the PRPF31 gene, the cell cannot produce enough functional PRPF31 protein. While this gene is used by every cell in the body, the cells in the retina (the light-sensitive tissue at the back of the eye) are particularly sensitive to this shortage. Without enough PRPF31, the retina cannot properly edit the recipes for other proteins it needs to survive and function. This leads to the gradual death of retinal cells, causing a condition known as Retinitis Pigmentosa (RP). Patients typically experience night blindness first, followed by a progressive loss of peripheral (side) vision, which can eventually lead to severe visual impairment or blindness. PRPF31-associated RP is inherited in an autosomal dominant pattern, meaning a person only needs one mutated copy of the gene (inherited from one parent) to potentially develop the disease. However, this specific gene is known for something called "incomplete penetrance." This means that not everyone who inherits the mutated gene will actually develop vision loss. Some people have a naturally higher production of the PRPF31 protein from their one healthy copy of the gene, which can compensate for the mutated copy and protect their vision. This makes predicting the severity of the disease within a family very challenging.

Gene description: This gene product is a component of the U4/U6.U5 tri-snRNP, participating in the crucial process of pre-mRNA splicing.

Patient and family guide: The PRPF31 gene provides instructions for making a protein that is essential for a process called RNA splicing. Think of genes as rough drafts of a recipe; RNA splicing is the editing process that cuts out the unnecessary parts (introns) and pastes together the important parts (exons) to create the final, readable recipe (mature mRNA) that the cell uses to build proteins. The PRPF31 protein is a crucial part of the cellular machinery, called the spliceosome, that performs this editing. When there is a mutation in the PRPF31 gene, the cell cannot produce enough functional PRPF31 protein. While this gene is used by every cell in the body, the cells in the retina (the light-sensitive tissue at the back of the eye) are particularly sensitive to this shortage. Without enough PRPF31, the retina cannot properly edit the recipes for other proteins it needs to survive and function. This leads to the gradual death of retinal cells, causing a condition known as Retinitis Pigmentosa (RP). Patients typically experience night blindness first, followed by a progressive loss of peripheral (side) vision, which can eventually lead to severe visual impairment or blindness. PRPF31-associated RP is inherited in an autosomal dominant pattern, meaning a person only needs one mutated copy of the gene (inherited from one parent) to potentially develop the disease. However, this specific gene is known for something called "incomplete penetrance." This means that not everyone who inherits the mutated gene will actually develop vision loss. Some people have a naturally higher production of the PRPF31 protein from their one healthy copy of the gene, which can compensate for the mutated copy and protect their vision. This makes predicting the severity of the disease within a family very challenging.

Gene function: PRPF31 is essential for the assembly and function of the spliceosome, which removes introns from pre-mRNA. In the retina, proper splicing is fundamental for the synthesis of proteins required for photoreceptor survival and function, as well as for the overall health of the retinal pigment epithelium. Mutations can lead to impaired splicing, causing a deficit in essential retinal proteins and subsequent degeneration.

Protein structure: The PRPF31 gene encodes a protein of 499 amino acids with a molecular weight of approximately 61 kDa. The protein structure is characterized by several highly conserved functional domains that are critical for its role in the spliceosome. The most prominent is the Nop domain (also known as the snoRNA-binding domain), which is essential for binding to the 15.5K protein (SNU13) and the U4 snRNA. Additionally, PRPF31 contains a coiled-coil domain that facilitates protein-protein interactions, particularly with PRPF6, and a flexible loop and tip region that are involved in the dynamic structural rearrangements of the spliceosome during activation. The protein must assemble into the U4/U6 di-snRNP and subsequently the U4/U6•U5 tri-snRNP complex to be functional. Mutations that disrupt these domains, particularly the Nop domain, prevent the proper assembly of the tri-snRNP complex, leading to the splicing defects characteristic of the disease.

Molecular function: The PRPF31 gene encodes the pre-mRNA processing factor 31, a 61-kDa protein that is an essential component of the spliceosome. The spliceosome is a massive macromolecular ribonucleoprotein (RNP) complex responsible for removing introns from pre-messenger RNA (pre-mRNA) and joining exons together to form mature mRNA. Specifically, PRPF31 is required for the assembly and stabilization of the U4/U6•U5 tri-small nuclear ribonucleoprotein (tri-snRNP) complex. During the splicing cycle, PRPF31 acts as a tether, interacting with the 15.5K protein (SNU13) bound to the U4 snRNA and with the PRPF6 protein in the U5 snRNP. This interaction is crucial for the stable integration of the U4/U6 di-snRNP with the U5 snRNP to form the tri-snRNP, which then joins the pre-spliceosome to form the mature, catalytically active spliceosome. Without functional PRPF31, the tri-snRNP cannot form properly, leading to a generalized defect in pre-mRNA splicing. In the retina, this splicing defect disproportionately affects transcripts essential for photoreceptor and RPE function, including genes involved in ciliogenesis, cellular adhesion, and the visual cycle. The accumulation of mis-spliced or unspliced RNA transcripts leads to cellular stress, impaired phagocytosis by the RPE, and ultimately the apoptosis of photoreceptor cells, driving the pathogenesis of retinitis pigmentosa.

Expression pattern: PRPF31 is a ubiquitously expressed gene, meaning it is transcribed and translated in virtually all cell types and tissues throughout the body, as it is essential for the fundamental cellular process of pre-mRNA splicing. Despite this ubiquitous expression, mutations in PRPF31 cause a strictly retina-specific phenotype. Within the eye, PRPF31 is highly expressed in both the neural retina (particularly in photoreceptor cells) and the retinal pigment epithelium (RPE). The specific vulnerability of the retina to PRPF31 mutations is thought to be due to the exceptionally high rate of alternative splicing required to maintain retinal function and the massive daily turnover of photoreceptor outer segments, which places a high demand on the splicing machinery. When PRPF31 levels fall below a critical threshold, these highly specialized retinal cells are the first to suffer from the accumulation of mis-spliced transcripts and subsequent cellular dysfunction.

Mutation spectrum: The mutation spectrum of PRPF31 is highly diverse, with over 65 different pathogenic variants reported throughout the gene, most commonly clustering in exons 6 through 10. The vast majority of these are loss-of-function mutations, including nonsense mutations, frameshifts (insertions or deletions), and canonical splice-site mutations, which lead to nonsense-mediated decay of the mutant transcript and result in haploinsufficiency. In addition to point mutations and small indels, large genomic rearrangements and whole-gene deletions are a significant feature of the PRPF31 mutation spectrum, accounting for approximately 2.5% of all adRP cases. Missense mutations are less common but do occur, often affecting critical functional domains like the Nop domain, and may cause disease through a combination of haploinsufficiency and potential dominant-negative effects by interfering with tri-snRNP assembly.

Pathogenic variants: 1. c.522_523insA (p.Val175Serfs*32) - A common frameshift mutation leading to premature truncation and haploinsufficiency. 2. c.1115_1125del (p.Leu372Profs*33) - A well-characterized deletion causing a frameshift, frequently reported in adRP cohorts. 3. c.1374+1G>A - A canonical splice donor site mutation that disrupts normal splicing of the PRPF31 transcript itself. 4. p.Ala216Pro - A missense mutation located in the highly conserved Nop domain, disrupting its interaction with the 15.5K protein and U4 snRNA. 5. Large genomic deletions (e.g., complete deletion of the PRPF31 gene) - Frequently observed and definitively confirming haploinsufficiency as the primary disease mechanism.

Clinical significance: Mutations in the PRPF31 gene are the second most common cause of autosomal dominant retinitis pigmentosa (adRP), often referred to as RP11. The clinical manifestation is characterized by the classic symptoms of retinitis pigmentosa: night blindness (nyctalopia) as the initial symptom, followed by progressive loss of peripheral vision leading to "tunnel vision," and eventually, in many cases, loss of central vision. Fundus examination typically reveals bone-spicule pigment deposits, attenuation of retinal blood vessels, and waxy pallor of the optic disc. A hallmark of PRPF31-associated adRP is its incomplete penetrance and highly variable expressivity. Within the same family, individuals carrying the identical pathogenic variant can exhibit a wide spectrum of clinical severity. Some may experience severe, early-onset visual impairment, while others may remain completely asymptomatic throughout their lives. This non-penetrance is largely attributed to the expression levels of the wild-type (non-mutated) PRPF31 allele, which is influenced by trans-acting genetic modifiers such as CNOT3 and the MSR1 repeat element. Higher expression of the wild-type allele can compensate for the mutated allele, preventing the disease phenotype.

Inheritance: Autosomal Dominant

Chromosomal location: 19q13.42

Genotype-phenotype correlations: Genotype-phenotype correlations in PRPF31-associated RP are complex and not strictly dictated by the specific mutation itself. Because the primary disease mechanism is haploinsufficiency, most pathogenic variants (whether nonsense, frameshift, splice-site, or large deletions) result in a null allele and lead to a similar baseline risk of disease. The severity and onset of the disease are less correlated with the specific PRPF31 mutation and more strongly correlated with the expression level of the remaining wild-type allele. However, some studies suggest that certain missense mutations or in-frame deletions might exert a dominant-negative effect in addition to haploinsufficiency, potentially leading to a more severe phenotype or altering the response to certain gene therapies. The major determinant of the phenotype remains the genetic background of the individual, specifically the presence of high-expression or low-expression alleles of modifier genes like CNOT3, which dictate whether the individual will be severely affected, mildly affected, or an asymptomatic carrier.

Research and therapeutic approaches: Currently, there are no FDA-approved treatments specifically for PRPF31-associated retinitis pigmentosa. Management focuses on supportive care, including low-vision aids, regular ophthalmologic monitoring, and genetic counseling. Because the primary disease mechanism is haploinsufficiency, PRPF31 is considered an excellent candidate for gene augmentation therapy. The goal of this approach is to deliver a healthy copy of the PRPF31 gene to retinal cells using viral vectors, such as Adeno-Associated Virus (AAV), to restore protein levels above the disease-causing threshold. Preclinical studies using AAV-mediated gene augmentation in patient-derived retinal organoids and RPE cells have shown promising results, successfully rescuing structural and functional defects. In addition to traditional gene therapy, novel RNA-based therapies are entering clinical trials. For example, PYC Therapeutics has developed an RNA therapy (VP-001) designed to upregulate the expression of the patient's own healthy PRPF31 allele. This approach targets the regulatory mechanisms that naturally control PRPF31 expression, aiming to boost the output of the wild-type allele to compensate for the mutated one. This therapy has recently entered Phase 1 clinical trials (e.g., NCT05573984 for natural history, and subsequent interventional trials). Other experimental approaches include CRISPR/Cas9 gene editing to correct specific mutations in vitro, though this is further from clinical application due to the diversity of mutations causing the disease.

Diagnostic testing: Diagnostic testing for PRPF31 mutations is typically performed using targeted next-generation sequencing (NGS) panels that include genes known to cause inherited retinal diseases (IRDs), or through whole exome sequencing (WES). Because large genomic rearrangements and deletions account for a significant portion (up to 2.5%) of PRPF31 mutations, techniques such as multiplex ligation-dependent probe amplification (MLPA) or copy number variant (CNV) analysis from NGS data are essential to detect these structural variants that might be missed by standard sequencing. Genetic counseling is particularly complex for PRPF31-associated RP due to its incomplete penetrance. Counselors must explain to families that inheriting a pathogenic variant does not guarantee the development of the disease. The presence of asymptomatic obligate carriers in a family pedigree can complicate risk assessment. Testing for known modifier genes (like CNOT3) is not yet standard clinical practice but is an area of active research that may eventually help predict disease penetrance and severity in individuals carrying a PRPF31 mutation.

Animal models: Animal models for PRPF31 have historically struggled to fully recapitulate the human retinal phenotype, largely due to differences in alternative splicing and gene regulation between species. Prpf31+/- heterozygous knockout mice do not show the classic early-onset retinal degeneration seen in humans, though they do exhibit late-onset morphological changes in the retinal pigment epithelium (RPE), including loss of RPE adhesion and deficiency in phagocytosis of photoreceptor outer segments. This suggests that mice may be less sensitive to PRPF31 haploinsufficiency than humans. To better model the disease, researchers have turned to human induced pluripotent stem cell (hiPSC)-derived retinal organoids and RPE cells. These human in vitro models successfully recapitulate the RP phenotype, demonstrating defective RPE morphology, reduced phagocytic function, and rod photoreceptor cell death followed by cone loss. Additionally, zebrafish models with prpf31 knockdowns have shown severe retinal defects and impaired visual function, providing another avenue for studying the developmental and functional consequences of PRPF31 deficiency.

Population genetics: PRPF31 mutations are a major cause of autosomal dominant retinitis pigmentosa globally, accounting for approximately 5% to 11% of adRP cases depending on the population studied. It is the second most common cause of adRP after RHODOPSIN mutations in many cohorts, including those from North America, Europe (Spain, France, Belgium), and Asia (China). The carrier frequency in the general population is very low, consistent with a rare dominant disorder. While specific founder mutations have been identified in certain isolated populations or large extended pedigrees, the high prevalence of PRPF31 mutations globally is driven by a wide diversity of unique variants rather than a single common founder effect. The frequency of modifier alleles (like the MSR1 repeat cluster) that dictate disease penetrance varies significantly between different ethnic populations, which may influence the observed prevalence of symptomatic PRPF31-RP in different regions.

Selected references: 1. Vithana EN, et al. A human homolog of yeast pre-mRNA splicing gene, PRP31, underlies autosomal dominant retinitis pigmentosa on chromosome 19q13.4 (RP11). Mol Cell. 2001;8(2):375-381. PMID: 11545741 2. Wheway G, et al. Mutation spectrum of PRPF31, genotype-phenotype correlation in retinitis pigmentosa, and opportunities for therapy. Exp Eye Res. 2020;192:107950. PMID: 32014492 3. Rose AM, Bhattacharya SS. Variant haploinsufficiency and phenotypic non-penetrance in PRPF31-associated retinitis pigmentosa. Clin Genet. 2016;90(2):118-126. PMID: 26842403 4. Buskin A, et al. Disrupted alternative splicing for genes implicated in splicing and ciliogenesis causes PRPF31 retinitis pigmentosa. Nat Commun. 2018;9(1):4234. PMID: 30315166 5. Rodrigues A, et al. Modeling PRPF31 retinitis pigmentosa using human induced pluripotent stem cells. NPJ Regen Med. 2022;7(1):1-14. PMID: 35115542 6. Venturini G, et al. CNOT3 is a modifier of PRPF31 mutations in retinitis pigmentosa with incomplete penetrance. PLoS Genet. 2012;8(11):e1003040. PMID: 23144628