Glycosylphosphatidylinositol Biosynthesis Defect 11 (GPIBD11) Cell Models for Research

Glycosylphosphatidylinositol Biosynthesis Defect 11 (GPIBD11) is an ultra-rare autosomal recessive disorder caused by mutations in the PIGV gene. The exact prevalence is unknown, but fewer than 50 cases have been reported worldwide (WHO, 2023). The condition is characterized by intellectual disability, seizures, and distinctive facial features. There is no cure, and management is symptomatic. The 5-year survival is high, but quality of life is significantly impacted (NCI, 2023).

GPIBD11 serves as a valuable model for studying GPI biosynthesis, a fundamental post-translational modification. The disease is monogenic, making it ideal for functional studies. Public datasets include ClinVar and OMIM, but there is a lack of comprehensive molecular data. Open questions include the precise role of PIGV in neuronal development and the potential for targeted therapies.

• • GPIBD11 is not a cancer, but the underlying pathway is GPI biosynthesis. The pathway involves:
• • Synthesis of N-acetylglucosaminyl-phosphatidylinositol (GlcNAc-PI)
• • Deacetylation and acylation
• • Mannosylation steps
• • Addition of phosphoethanolamine
• • Transfer of GPI anchor to proteins
• • Mutations in PIGV disrupt the second mannosylation step, leading to deficient GPI-anchored proteins.

| Gene | Frequency (%) | Mutation Type | Functional Effect |

|------|---------------|---------------|-------------------|

| PIGV | 100% | Missense, frameshift, splice-site | Loss of function, reduced GPI-anchor synthesis |

| PIGO | Rare | Missense | Impaired phosphoethanolamine transfer |

| PIGW | Rare | Missense | Defective inositol acylation |

Data from ClinVar and OMIM.

• • GPI-anchored proteins are involved in multiple signaling pathways:
• • Complement regulation (CD55, CD59)
• • Cell adhesion (NCAM, L1CAM)
• • Enzymatic activity (alkaline phosphatase)
• • Receptor signaling (folate receptor)
• • Deficiency leads to impaired cell-cell interactions and signaling, contributing to neurological symptoms.

| Cell Line | Origin | Key Mutations |

|-----------|--------|---------------|

| HEK293 | Human embryonic kidney | Wild-type PIGV |

| HeLa | Human cervical cancer | Wild-type PIGV |

| SH-SY5Y | Human neuroblastoma | Wild-type PIGV |

| iPSC-derived neurons | Patient-derived | PIGV mutations |

Organoids, especially cerebral organoids, can recapitulate neurodevelopmental defects and are useful for studying GPIBD11.

• • Pigv knockout mouse: Shows embryonic lethality, indicating essential role.
• • Conditional knockout mouse: Tissue-specific deletion to study developmental roles.
• • Zebrafish models: Morpholino knockdown of pigv to study neurological phenotypes.
• • Patient-derived xenografts (PDX) are not applicable as it is not a cancer.

• • CRISPR-Cas9 gene editing enables the creation of isogenic cell lines with specific PIGV mutations. For example:
• • PIGV knockout HEK293 cells: Complete loss of function, useful for studying GPI-anchor deficiency.
• • PIGV knock-in with a patient-specific mutation (e.g., c.1024C>T): Allows modeling of specific variants.
• • These sequence-verified models are commercially available and accelerate research by providing consistent, reproducible systems.

Knockout and knock-in lines are used to validate the functional impact of PIGV mutations. For example, comparing GPI-anchor protein expression between wild-type and knockout cells confirms the role of PIGV. Additionally, complementation assays with wild-type PIGV rescue the phenotype, confirming causality.

Isogenic pairs (wild-type vs. PIGV knockout) are used to screen for compounds that can restore GPI-anchor synthesis. High-throughput screens can identify small molecules that bypass the defect. Resistance studies are less relevant, but the models can be used to test drug toxicity in GPI-deficient cells.

CRISPR-based synthetic lethality screens can identify genes that are essential in PIGV-deficient cells but not in wild-type cells. These genes could serve as therapeutic targets. Additionally, cell surface markers like CD59 can be used as biomarkers for GPI-anchor deficiency.