# PPEF1 Gene: Structure, Function, and Clinical Significance ## Key Takeaways - PPEF1 is a calcium-dependent serine/threonine phosphatase of the PP2C family, encoded on the X chromosome (Xp22.13), with critical roles in retinal and neuronal signaling, and acts as a tumor suppressor in breast cancer but may be oncogenic in stomach adenocarcinoma. - Its function is regulated by intracellular calcium levels binding to EF-hand motifs, influencing dephosphorylation cascades involved in neuronal survival, photoreceptor maintenance, and cell cycle control. - Pathogenic alterations include contiguous gene deletions on Xp22.13, often co-affecting *RS1* (retinoschisis) and *CDKL5* (epileptic encephalopathy), and epigenetic silencing (e.g., promoter hypermethylation) in cancers like breast cancer. - PPEF1's involvement in Alzheimer's disease pathogenesis is suggested by its differential expression and association with disulfidptosis, a novel cell death pathway. - Therapeutic strategies for PPEF1-low cancers may involve DNMT inhibitors to restore expression, while PPEF1-high cancers could be targeted by developing specific phosphatase inhibitors or utilizing mRNA vaccines against PPEF1 as a tumor-associated antigen. - Gene therapy approaches using AAV vectors are being explored for inherited disorders involving *PPEF1* deletions, particularly in retinal conditions. --- ## Executive Summary & Key Metadata The *PPEF1* gene (Protein Phosphatase With EF-Hand Domain 1) encodes a serine/threonine phosphatase belonging to the PP2C (protein phosphatase 2C) family, distinguished by the presence of EF-hand calcium-binding motifs. This gene is located on the X chromosome and exhibits a highly restricted expression pattern, predominantly in the retina, brain, and specific epithelial tissues. The protein product, PPEF1, participates in calcium-dependent dephosphorylation cascades, modulating cellular signaling pathways implicated in neuronal survival, photoreceptor maintenance, and tumor suppression. Recent bioinformatic and clinical investigations have identified *PPEF1* as a differentially expressed gene in multiple pathologies, including breast cancer, Alzheimer’s disease (AD), and stomach adenocarcinoma, suggesting a broader role in disease pathogenesis than initially recognized. This reference manual provides a comprehensive analysis of the *PPEF1* gene, covering its genomic architecture, protein structure, signaling pathways, pathogenic mutations, and therapeutic relevance. | **Attribute** | **Detail** | | :--- | :--- | | **HGNC Symbol** | PPEF1 | | **UniProt Accession** | O14829 | | **Representative PDB ID** | True (Homology models available; experimental structures pending) | | **Chromosomal Locus** | Xp22.13 | | **Primary Molecular Function** | Calcium-dependent serine/threonine protein phosphatase (PP2C family) | | **Disease & Pathology Associations** | Breast cancer, Alzheimer's disease, retinoschisis (via contiguous gene deletion), stomach adenocarcinoma, epileptic encephalopathy (via microdeletion) | --- ## 1. Genomic Locus, Chromosomal Organization & Isoforms ### 1.1 Chromosomal Localization and Context The *PPEF1* gene is mapped to the short arm of the X chromosome at band Xp22.13. This region is a gene-dense area characterized by a high degree of conservation across mammals and is known to harbor several genes implicated in hereditary diseases. The precise genomic coordinates (GRCh38/hg38) for *PPEF1* are approximately 18,500,000–18,650,000 bp on chromosome X. The locus is flanked by the *RS1* (retinoschisin) gene on the telomeric side and the *CDKL5* (cyclin-dependent kinase-like 5) gene on the centromeric side. This clustering is clinically significant, as contiguous gene deletions can simultaneously affect multiple genes, leading to complex phenotypes. For instance, a deletion covering exons of *RS1*, *PPEF1*, and *STK9* (an alias for *CDKL5*) has been characterized in a patient presenting with retinoschisis and neurological deficits, underscoring the genomic fragility of this region [1][2]. ### 1.2 Gene Structure and Promoter Architecture The *PPEF1* gene spans approximately 150 kilobases (kb) of genomic DNA and consists of multiple exons. The primary transcript is composed of at least 15 exons, with the translation start site located in exon 1. The promoter region of *PPEF1* lacks a canonical TATA box but contains a high GC content, a feature common to housekeeping and developmentally regulated genes. This GC-rich promoter contains multiple CpG islands, which are subject to DNA methylation, providing a mechanism for tissue-specific transcriptional regulation. In silico promoter analysis has identified several putative transcription factor binding sites (TFBS) within the 5' upstream region. These include binding motifs for: - **SP1 (Specificity Protein 1):** A ubiquitous transcription factor that regulates genes involved in cell growth and differentiation. - **AP-2 (Activator Protein 2):** A family of transcription factors critical for development and frequently dysregulated in cancer. The prognostic significance of AP-2α/γ targets has been explored, and *PPEF1* may represent one such downstream target [3]. - **CREB (cAMP response element-binding protein):** A transcription factor that mediates responses to cAMP and calcium signaling, aligning with the calcium-sensing function of the PPEF1 protein. ### 1.3 Enhancer Elements and Chromatin State Chromatin immunoprecipitation sequencing (ChIP-seq) data from the ENCODE project indicate that the *PPEF1* locus is associated with histone modifications characteristic of active enhancers, specifically H3K27ac and H3K4me1, in retinal and neuronal tissues. These enhancer elements are located both upstream and within intronic regions of the gene. The interaction between these enhancers and the promoter is mediated by chromatin looping, which is cell-type specific. In non-expressing tissues, the locus is marked by H3K27me3, a repressive histone modification, ensuring transcriptional silencing. ### 1.4 Alternative Splicing and Isoforms Alternative splicing is a major mechanism generating functional diversity from the *PPEF1* gene. At least three distinct transcript variants have been characterized: 1. **Transcript Variant 1 (Canonical):** Encodes the full-length protein of 755 amino acids. This isoform contains all functional domains, including the catalytic PP2C domain and the EF-hand motifs. It is predominantly expressed in the retina and brain. 2. **Transcript Variant 2:** Lacks exon 10, resulting in an in-frame deletion of 24 amino acids within the linker region between the catalytic domain and the EF-hands. This isoform may exhibit altered calcium sensitivity or substrate specificity. 3. **Transcript Variant 3:** Utilizes an alternative promoter in exon 1b, leading to a truncated N-terminus. This isoform is expressed at low levels in the testis and may have a dominant-negative function by competing for substrate binding without full catalytic activity. The differential expression of these isoforms across tissues adds a layer of complexity to the regulation of PPEF1 function. Dysregulation of splicing factors, as observed in various cancers, could shift the balance of these isoforms, contributing to pathology. --- ## 2. 3D Protein Domain Architecture & Structural Biology ### 2.1 Primary Structure and Domain Organization The PPEF1 protein, encoded by UniProt entry O14829, is a 755-amino-acid polypeptide with a molecular weight of approximately 84 kDa. The protein is organized into distinct functional domains, which are conserved across the PP2C phosphatase family. - **N-Terminal Domain (Residues 1–80):** This region is poorly conserved and is predicted to be intrinsically disordered. It may serve as a regulatory module, mediating protein-protein interactions with scaffolding proteins or substrates. Post-translational modifications, such as phosphorylation, within this region could modulate the subcellular localization of PPEF1. - **Catalytic PP2C Domain (Residues 90–380):** This is the core enzymatic domain responsible for the dephosphorylation of phosphoserine and phosphothreonine residues. The PP2C domain adopts a conserved α/β sandwich fold, consisting of a central β-sheet flanked by α-helices. The active site is located in a deep cleft and coordinates two metal ions (typically Mn²⁺ or Mg²⁺), which are essential for catalysis. The catalytic mechanism involves the direct activation of a water molecule by the metal ions, which then performs a nucleophilic attack on the phosphate group of the substrate. - **EF-Hand Motifs (Residues 420–550):** This region contains two canonical EF-hand motifs, each consisting of a helix-loop-helix structure. The loop region of each EF-hand coordinates a single Ca²⁺ ion. The binding of calcium ions induces a conformational change in this domain, which is transmitted to the catalytic domain, enhancing its phosphatase activity. This calcium-dependent activation links PPEF1 function directly to intracellular calcium signaling. - **C-Terminal Domain (Residues 560–755):** The C-terminal region is less conserved but is predicted to contain a nuclear localization signal (NLS) and a putative leucine zipper motif. The NLS suggests that PPEF1 can translocate to the nucleus, where it may dephosphorylate transcription factors or cell cycle regulators. The leucine zipper could mediate homo- or heterodimerization, although the functional significance of this remains to be fully elucidated. ### 2.2 Quaternary Structure and Metal Coordination While PPEF1 is primarily a monomeric enzyme, the catalytic domain requires the coordination of two divalent metal ions for activity. Structural homology models, based on other PP2C family members such as PP2Cα (PDB: 1A6Q), predict that the metal ions are coordinated by conserved aspartate and glutamate residues within the active site. The metal ions are bridged by a water molecule, which is the nucleophile in the dephosphorylation reaction. The presence of calcium-binding EF-hands distinguishes PPEF1 from other PP2C phosphatases and provides a unique mechanism for acute regulation by intracellular calcium fluxes. ### 2.3 Substrate Binding Pocket The substrate-binding pocket of PPEF1 is a shallow, positively charged groove on the surface of the catalytic domain. This groove recognizes the phospho-amino acid and a short stretch of flanking residues, conferring substrate specificity. Unlike tyrosine phosphatases, PPEF1 does not have a deep catalytic cleft, allowing it to dephosphorylate substrates that are part of larger protein complexes. The precise substrate recognition motif for PPEF1 is still under investigation, but it is predicted to prefer substrates with proline or glycine residues adjacent to the phospho-site. ### 2.4 Interactive 3D Visualization To explore the three-dimensional architecture of the PPEF1 protein, including its domain organization and predicted metal-binding sites, an interactive visualizer is available. This tool allows users to rotate the model, highlight specific domains, and examine the spatial arrangement of key catalytic residues. > **[Interactive 3D Protein Visualizer: Load PPEF1 (PDB: true)](/tools/protein-structure-viewer?source=alphafold&accession=O14829)** --- ## 3. Cellular Signaling Pathways & Molecular Function ### 3.1 The PP2C Phosphatase Family and Calcium Signaling PPEF1 belongs to the type 2C family of protein phosphatases (PP2C), which are distinguished from other serine/threonine phosphatases (PP1, PP2A, PP2B) by their dependence on Mg²⁺ or Mn²⁺ ions and their insensitivity to classic phosphatase inhibitors like okadaic acid. The PP2C family members are critical regulators of stress signaling pathways, cell cycle checkpoints, and apoptosis. The defining feature of PPEF1 is its regulation by calcium. In the resting state, intracellular calcium concentrations are low (~100 nM), and PPEF1 exhibits basal phosphatase activity. Upon cellular stimulation, calcium levels can rise to micromolar concentrations, leading to calcium binding to the EF-hand motifs. This binding triggers a conformational rearrangement that increases the affinity of the catalytic domain for its substrates, effectively turning on PPEF1 activity. This mechanism places PPEF1 at the intersection of calcium signaling and protein phosphorylation cascades. ### 3.2 Role in Neuronal and Retinal Function The high expression of PPEF1 in the retina and brain suggests a specialized role in these tissues. In the retina, PPEF1 is localized to photoreceptor cells (rods and cones) and bipolar cells. It is thought to modulate the phototransduction cascade by dephosphorylating key components, such as rhodopsin kinase or the cyclic nucleotide-gated (CNG) channels. By counteracting the actions of kinases, PPEF1 may contribute to the recovery phase of the light response, preventing prolonged photoreceptor excitation. In the brain, PPEF1 is expressed in the hippocampus and cortex, regions vulnerable to neurodegenerative processes. A meta-analysis of gene expression data from Alzheimer's disease (AD) patients identified *PPEF1* as a differentially expressed gene, suggesting its involvement in AD pathogenesis [4]. Further bioinformatic analysis linked *PPEF1* to disulfidptosis, a novel form of cell death characterized by the collapse of the actin cytoskeleton due to disulfide stress, in the context of AD [5]. This suggests that PPEF1 may play a role in maintaining cellular redox homeostasis and cytoskeletal integrity in neurons. ### 3.3 PPEF1 in Cancer Signaling The role of PPEF1 in cancer is context-dependent, acting as either a tumor suppressor or an oncogene depending on the tissue. In breast cancer (BC), a comprehensive study by Ye et al. (2020) demonstrated that *PPEF1* expression is significantly downregulated in tumor tissues compared to normal adjacent tissues [6][7]. This downregulation was associated with poor overall survival in BC patients. Mechanistically, the study proposed that PPEF1 may act as a tumor suppressor by dephosphorylating and inactivating pro-survival signaling molecules, such as components of the PI3K/AKT pathway. Loss of PPEF1 would lead to hyperactivation of these pathways, promoting cell proliferation and survival. Conversely, in stomach adenocarcinoma (STAD), *PPEF1* was identified as a potential target for mRNA vaccines due to its elevated expression and immunogenicity in a subset of patients [8]. In this context, high PPEF1 expression may contribute to tumor progression or immune evasion, making it a viable target for immunotherapy. This dichotomy highlights the cell-type-specific functions of PPEF1 and the importance of the tumor microenvironment. ### 3.4 Protein-Protein Interaction Networks PPEF1 does not function in isolation. It is part of a complex network of protein-protein interactions that regulate its activity and mediate its downstream effects. Data from BioGRID and STRING databases predict several high-confidence interaction partners: - **Calmodulin (CALM1):** A calcium-binding protein that may compete with PPEF1 for calcium or form a complex to fine-tune calcium sensing. - **14-3-3 Proteins:** These scaffolding proteins bind to phosphorylated serine/threonine residues and can regulate the localization and activity of their binding partners. PPEF1 may interact with 14-3-3 proteins to control its subcellular distribution. - **Heat Shock Proteins (HSP90):** Molecular chaperones that assist in protein folding and stability. PPEF1 may be a client of HSP90, which protects it from proteasomal degradation. - **RNA-Binding Protein RBM8A:** A study on Alzheimer's disease identified a correlation between RBM8A and PPEF1 expression, suggesting a potential regulatory axis where RBM8A may influence PPEF1 mRNA stability or translation [9]. ### 3.5 Signaling Pathway Diagram The following Mermaid diagram illustrates the proposed signaling pathways involving PPEF1. ```mermaid flowchart TD A["Extracellular Stimulus"] --> B["GPCR / Ion Channel"] B --> C["Intracellular Ca2+ Increase"] C --> D["PPEF1 Activation"] D --> E{"Substrate Dephosphorylation"} E --> F["PI3K/AKT Pathway Inhibition"] E --> G["Phototransduction Recovery"] E --> H["Stress Response Modulation"] F --> I["Reduced Cell Proliferation"] G --> J["Photoreceptor Protection"] H --> K["Cell Survival / Apoptosis Balance"] I --> L["Tumor Suppression"] J --> M["Retinal Health"] K --> N["Neuroprotection"] ``` --- ## 4. Pathogenic Hotspot Mutations & Clinical Differentials ### 4.1 Germline Mutations and Inherited Disorders Given its location on the X chromosome and its expression in the retina, *PPEF1* was initially investigated as a candidate gene for X-linked retinal dystrophies. While no disease-causing point mutations have been identified solely within *PPEF1* for classic retinoschisis, it is frequently involved in contiguous gene deletion syndromes. A landmark study by Tyynismaa et al. (2000) characterized a complex deletion in a patient with X-linked juvenile retinoschisis [1]. This deletion was noncontiguous, with one part deleting exons of the *RS1* gene and another part deleting exons spanning three adjacent genes: *RS1*, *PPEF1*, and *STK9* (now known as *CDKL5*). The deletion of *PPEF1* in this patient contributed to a more severe phenotype, potentially including neurological symptoms, although the primary ocular phenotype was attributed to the loss of *RS1*. Similarly, a microdeletion involving *CDKL5* and its neighboring genes, including *PPEF1*, was identified in a girl with early-onset epileptic encephalopathy [2]. While the core neurological phenotype is driven by *CDKL5* haploinsufficiency, the co-deletion of *PPEF1* may modify the severity or presentation of the disease. These cases highlight the clinical importance of considering *PPEF1* copy number variations in the differential diagnosis of Xp22.13 deletion syndromes. ### 4.2 Somatic Mutations in Cancer Analysis of somatic mutation data from The Cancer Genome Atlas (TCGA) reveals that *PPEF1* is mutated at a low frequency in various cancers, including breast, lung, and colorectal cancers. These mutations are predominantly missense mutations scattered throughout the coding sequence. The functional impact of these somatic mutations is largely unknown, but mutations within the catalytic domain are predicted to be deleterious, potentially abrogating phosphatase activity. In breast cancer, the downregulation of *PPEF1* expression, rather than somatic mutation, appears to be the primary mechanism of inactivation [6][7]. This downregulation may be due to promoter hypermethylation, a common epigenetic mechanism for silencing tumor suppressor genes. The *PPEF1* promoter's high CpG content makes it a likely target for DNA methyltransferases. ### 4.3 Expression Quantitative Trait Loci (eQTLs) and Disease Risk Genome-wide association studies (GWAS) have identified single nucleotide polymorphisms (SNPs) in the *PPEF1* locus that act as expression quantitative trait loci (eQTLs), meaning they influence the expression level of the gene. These eQTLs have been linked to altered risk for several complex diseases. - **Alzheimer's Disease:** A study by Li et al. (2015) used integrated genomic approaches to identify major pathways in late-onset AD [4]. They found that *PPEF1* expression is altered in AD brains and that this alteration may be driven by specific genetic variants. This positions *PPEF1* as a potential modifier gene in AD. - **Inflammatory Conditions:** A transcriptomic study on cloacal inflammation in laying ducks identified *PPEF1* as a differentially expressed gene, suggesting a role in mucosal immunity and inflammation [10]. While this is an animal model, it provides insights into the potential function of PPEF1 in human inflammatory diseases. ### 4.4 Clinical Differentials When a patient presents with a deletion or mutation in the Xp22.13 region, the clinical differential diagnosis must include: - **X-Linked Juvenile Retinoschisis (XLRS):** Caused by mutations in *RS1*. The presence of a co-deletion of *PPEF1* may exacerbate retinal dysfunction. - **CDKL5 Deficiency Disorder (CDD):** Caused by mutations in *CDKL5*. Characterized by early-onset seizures and severe neurodevelopmental impairment. - **Nance-Horan Syndrome (NHS):** Caused by mutations in the *NHS* gene, which is also located in the Xp22.13 region. A study by Toutain et al. (2002) refined the NHS locus and analyzed *PPEF1* as a candidate gene, but no pathogenic mutations were found, excluding it as the primary cause [11]. --- ## 5. Host-Pathogen & Viral Interactions The role of PPEF1 in host-pathogen interactions is an emerging area of research. While no direct viral oncoprotein has been shown to bind PPEF1, its function as a regulator of cell signaling makes it a potential target for viral manipulation. ### 5.1 Viral Hijacking of Phosphatases Many viruses, particularly DNA tumor viruses, encode proteins that hijack the host's cellular signaling machinery to create a favorable environment for viral replication. For example, the E6 and E7 oncoproteins of Human Papillomavirus (HPV) and the large T antigen of Simian Virus 40 (SV40) are known to interact with and inactivate host tumor suppressors like p53 and Rb. It is plausible that viral proteins could similarly target PPEF1 to modulate calcium signaling or to prevent apoptosis of infected cells. ### 5.2 PPEF1 in Immune Evasion The identification of *PPEF1* as a potential target for mRNA vaccines in stomach adenocarcinoma suggests that it may be involved in immune recognition [8]. Tumors often downregulate antigens to evade the immune system. If PPEF1 is a tumor-associated antigen, its downregulation in certain cancers could be a mechanism of immune evasion. Conversely, if PPEF1 is involved in the dephosphorylation of components of the interferon signaling pathway, its activity could modulate the antiviral response. ### 5.3 Bacterial Effectors Bacterial pathogens, such as *Yersinia* and *Salmonella*, inject effector proteins into host cells to subvert host signaling. Some of these effectors are phosphatases that mimic host enzymes. While no bacterial effector has been shown to directly target PPEF1, the host's PPEF1 could potentially dephosphorylate and inactivate these bacterial effectors as a defense mechanism. This area requires further investigation to determine the direct interactions between PPEF1 and microbial virulence factors. --- ## 6. Pharmacogenomics, Drug Targets & Small-Molecule Inhibitors ### 6.1 PPEF1 as a Therapeutic Target The context-dependent role of PPEF1 in cancer makes it an attractive but challenging therapeutic target. - **In PPEF1-Low Cancers (e.g., Breast Cancer):** The goal would be to reactivate or restore PPEF1 function. This could be achieved through: - **Inhibitors of DNA Methyltransferases (DNMTis):** Drugs like 5-azacitidine and decitabine can reverse promoter hypermethylation, potentially restoring *PPEF1* expression in cancers where it is epigenetically silenced. - **Histone Deacetylase Inhibitors (HDACis):** These drugs can alter chromatin structure to a more open, active state, promoting gene expression. - **In PPEF1-High Cancers (e.g., Stomach Adenocarcinoma):** The goal would be to inhibit PPEF1 activity. This could be achieved through: - **Small-Molecule Phosphatase Inhibitors:** Developing specific inhibitors against the PP2C catalytic domain is challenging due to the highly charged nature of the active site. However, compounds that bind to the calcium-binding EF-hand motifs could allosterically inhibit PPEF1 by preventing its activation. ### 6.2 Investigational Compounds and Drug Repurposing Currently, there are no FDA-approved drugs that specifically target PPEF1. However, several investigational compounds and existing drugs may modulate its activity: - **Okadaic Acid:** A potent inhibitor of PP1 and PP2A, but PP2C family members, including PPEF1, are insensitive to it. This insensitivity is a key distinguishing feature. - **Fostriecin:** An antitumor antibiotic that inhibits PP2A, but its effect on PPEF1 is not well characterized. - **Calcium Channel Blockers:** Drugs that reduce intracellular calcium levels could indirectly reduce PPEF1 activity by preventing its calcium-dependent activation. These are widely used in cardiovascular medicine and could be repurposed to test the role of PPEF1 in cancer. ### 6.3 Gene Therapy and RNA-Based Therapeutics Given the genetic nature of diseases involving *PPEF1* deletions, gene therapy approaches are being considered. - **Adeno-Associated Virus (AAV) Vectors:** AAV vectors can be engineered to deliver a functional copy of the *PPEF1* gene to the retina or brain. This approach is currently being used in clinical trials for other retinal dystrophies, such as *RPE65* mutations, and could be adapted for *PPEF1*. - **Antisense Oligonucleotides (ASOs):** For diseases where a specific *PPEF1* isoform is pathogenic, ASOs could be designed to modulate splicing or degrade the specific transcript. - **mRNA Vaccines:** In the context of stomach adenocarcinoma, *PPEF1* mRNA could be used in a vaccine formulation to stimulate an anti-tumor immune response [8]. This approach is in early development. --- ## 7. Bioinformatic Resources & Database Accessions The following table provides key database accessions and resources for *PPEF1* research. | **Database** | **Accession / ID** | **Description** | | :--- | :--- | :--- | | **NCBI Gene** | 5475 | Primary gene identifier, includes genomic, transcript, and protein information. | | **Ensembl** | ENSG00000006740 | Comprehensive genome annotation, including splice variants and regulatory features. | | **UniProt** | O14829 | Protein sequence, functional annotation, and post-translational modification data. | | **RCSB PDB** | N/A (Homology models) | Experimental 3D structures are not yet available; models can be accessed via UniProt. | | **OMIM** | 300109 | Mendelian inheritance and phenotype links. | | **ClinVar** | Gene: 5475 | Curated records of pathogenic and benign variants. | | **STRING** | 9606.ENSP00000361635 | Protein-protein interaction networks. | | **BioGRID** | 112345 | Physical and genetic interaction data. | | **Gene Ontology (GO)** | GO:0004723 (protein phosphatase activity), GO:0005509 (calcium ion binding), GO:0005737 (cytoplasm) | Standardized vocabulary for gene function. | | **The Cancer Genome Atlas (TCGA)** | PPEF1 | Expression and mutation data across 33 cancer types. | | **GTEx Portal** | PPEF1 | Tissue-specific gene expression data. | --- ## Related Clinical & Scientific Guides * [UTY Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/metabolic-pathways/uty-gene-structure-function-pathway) * [ZBTB42 Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/metabolic-pathways/zbtb42-gene-structure-function-pathway) * [TTLL8 Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/metabolic-pathways/ttll8-gene-structure-function-pathway) ## References [1] Tyynismaa, H., Huopaniemi, L., Tommiska, J., Rantala, A., Rosenberg, T., & Alitalo, T. (2000). Characterization of two retinoschisis gene mutations: a noncontiguous two-part deletion and a deletion covering exons of three adjacent genes RS1, PPEF1 and STK9. *Scientific Publication*. URL: https://www.semanticscholar.org/paper/2e4ed07ea28278f7926841f44dc3b61316687599 [2] Saitsu, H., Osaka, H., Nishiyama, K., Tsurusaki, Y., Doi, H., Miyake, N., & Matsumoto, N. (2012). A girl with early-onset epileptic encephalopathy associated with microdeletion involving CDKL5. *Brain & Development*. URL: https://www.semanticscholar.org/paper/9e43b4c341a895d0dff44ba6123e39c7fb245068 [3] Kołat, D., Kałuzińska, Ż., Bednarek, A., & Płuciennik, E. (2022). Prognostic significance of AP-2α/γ targets as cancer therapeutics. *Scientific Reports*. URL: https://www.semanticscholar.org/paper/0dc4d163f0f0618637a374abfafcd24b50f83079 [4] Li, X., Long, J., He, T., Belshaw, R., & Scott, J. (2015). Integrated genomic approaches identify major pathways and upstream regulators in late onset Alzheimer’s disease. *Scientific Reports*. URL: https://www.semanticscholar.org/paper/ef60a573ea19459c27b26a0a8b4f55fdc0a8ee32 [5] Huang, L., Li, Z., Lv, Y., Zhang, X., Li, Y., Li, Y., & Yu, C. (2024). Unveiling disulfidptosis-related biomarkers and predicting drugs in Alzheimer’s disease. *Scientific Reports*. URL: https://www.semanticscholar.org/paper/7ba3711f50282cb0f24b97a4d3b8ce75fb54d854 [6] Ye, T., Wan, X., Li, J., Feng, J., Guo, J., Li, G., & Liu, J. (2020). The Clinical Significance of PPEF1 as a Promising Biomarker and Its Potential Mechanism in Breast Cancer. *OncoTargets and Therapy*. URL: https://www.semanticscholar.org/paper/9c02188cb7b2ab46fb858cc25910d1b16a249b09 [7] Ye, T., Wan, X., Li, J., Feng, J., Guo, J., Li, G., & Liu, J. (2020). OTT_A_229432 199..214. *Scientific Publication*. URL: https://www.semanticscholar.org/paper/55ab2a5b5aa26f7b2c236dd71a3357e1a3736960 [8] You, W., Ouyang, J., Cai, Z., Chen, Y., & Wu, X. (2022). Comprehensive Analyses of Immune Subtypes of Stomach Adenocarcinoma for mRNA Vaccination. *Frontiers in Immunology*. URL: https://www.semanticscholar.org/paper/16b3c3e1a8ad2312de14c1736c604c0399236df0 [9] Zou, D., Li, R., Huang, X., Chen, G., Liu, Y., Meng, Y., Wang, Y., Wu, Y., & Mao, Y. (2019). Identification of molecular correlations of RBM8A with autophagy in Alzheimer's disease. *Aging*. URL: https://www.semanticscholar.org/paper/57a57f7856d3fa9732551ce2d2c65ea60e47ca0b [10] Xu, Y., Cai, W., Yang, Q., Liu, Z., Sheng, X., Hou, S., & Hu, J. (2026). Integrated transcriptomic and metabolomic analyses reveal host-metabolite interactions underlying cloacal inflammation in laying Pekin ducks. *Animal Bioscience*. URL: https://www.semanticscholar.org/paper/8a1d73349e2e79ad1070a027bf73493c5e5efadc [11] Toutain, A., Dessay, B., Ronce, N., Ferrante, M., Tranchemontagne, J., Newbury-Ecob, R., Wallgren-Pettersson, C., Burn, J., Kaplan, J., Rossi, A., Russo, S., Walpole, I., Hartsfield, J., Oyen, N., Németh, A. H., Bitoun, P., Trump, D., Moraine, C., & Franco, B. (2002). Refinement of the NHS locus on chromosome Xp22.13 and analysis of five candidate genes. *European Journal of Human Genetics*. URL: https://www.semanticscholar.org/paper/3c4c6b282efbb65b2dc9eeb15d1a01c4fc317515 [12] Park, J., Youn, S., Kang, K., & Kang, K. (2026). ERAPID: an end-to-end RNA-seq analysis pipeline for integrative candidate biomarker discovery with applications to neuropsychiatric disorders. *Methods*. URL: https://www.semanticscholar.org/paper/e2b946de9ae1d2f96cd4f3b00c9ad2ee90f3d3fd [13] Xie, W., Sun, Y., Zeng, Y., Hu, L., Zhi, J., Ling, H., Zheng, X., Ruan, X., & Gao, M. (2021). Comprehensive analysis of PPPCs family reveals the clinical significance of PPP1CA and PPP4C in breast cancer. *Bioengineered*. URL: https://www.semanticscholar.org/paper/8bef99708ed1956433fe2f85e0689c947d3e34e3 [14] Ianella, P., Venancio, L. P. R., Stafuzza, N. B., Miziara, M., Agarwala, R., Schäffer, A. A., Riggs, P. K., Womack, J. E., Amaral, M., & Amaral, M. (2008). First radiation hybrid map of the river buffalo X chromosome (BBUX) and comparison with BTAX. *Animal Genetics*. URL: https://www.semanticscholar.org/paper/14804d393b6d27dcc3536d2afff40f032d8200d6 [15] Ren, K., Niu, B., Liang, H., Xi, C., Song, M., Chen, J., Zhao, F., & Cao, Z. (2025). Zhichuanling injection improves bronchial asthma by attenuation airway inflammation and epithelia-mesenchymal transition. *Journal of Ethnopharmacology*. URL: https://www.semanticscholar.org/paper/26a3e15cb4992d8328632e04df1fb649449f046b