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CUL4B
cullin 4B
The CUL4B gene provides instructions for making a protein that is a key component of an E3 ubiquitin ligase complex, essential for protein degradation and various cellular processes. CUL4B plays a crucial role in forming a protein complex responsible for tagging other proteins for destruction within the cell.
CUL4B is located on the long (q) arm of chromosome X, at band Xq24. Arm ratio per GRCh38 - banding schematic.
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Overview
The CUL4B gene, or cullin 4B, encodes a protein that belongs to the cullin family. Cullin proteins serve as scaffolds for E3 ubiquitin ligase complexes, which are critical for the ubiquitin-proteasome system (UPS). The UPS is a major pathway responsible for selectively degrading proteins within cells, thereby controlling their levels and activity.
The CUL4B protein's function in this complex regulatory system highlights its importance in cellular homeostasis and development. Abnormalities in CUL4B can disrupt these finely tuned cellular processes, leading to various developmental and neurological conditions.
What the gene does
The CUL4B protein acts as a core component of the CUL4B-RING E3 ubiquitin ligase complex. These complexes function by attaching ubiquitin molecules to specific target proteins, marking them for degradation by the proteasome. This ubiquitination process is fundamental for regulating a wide array of cellular functions.
Key functions of CUL4B-mediated ubiquitination include regulating the cell cycle, ensuring proper DNA replication and repair, and controlling gene expression. It is also involved in maintaining chromatin structure and influencing neurodevelopment. By precisely controlling the degradation of specific proteins, CUL4B helps to ensure cell integrity and proper tissue development, particularly in the brain. Dysfunction of this protein can lead to the accumulation of unwanted proteins or the premature degradation of essential ones, impacting cellular health.
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Chromosome location
The CUL4B gene is located on the long arm of the X chromosome, specifically at position Xq24. As an X-linked gene, its inheritance pattern can vary and often presents differently between males and females. The proximity to other genes on the X chromosome may influence its expression and regulatory mechanisms.
Protein structure
The CUL4B protein is composed of 913 amino acids, exhibiting a complex domain architecture essential for its function. It features a Disordered region at its N-terminus, spanning amino acids 1-100, which often plays a role in protein-protein interactions and regulatory processes. A Nuclear localisation signal, located from amino acids 55-58, directs the CUL4B protein to the cell's nucleus, where many of its regulatory activities occur. Towards the C-terminus, from amino acids 845-905, lies the Cullin neddylation domain, which is crucial for the activation of the CUL4B-containing E3 ubiquitin ligase complex through the attachment of NEDD8, a ubiquitin-like protein.
Key variants
Variants in the CUL4B gene can impact its structure and function, leading to a range of clinical presentations. These genetic changes can include single nucleotide changes, insertions, or deletions, all of which may alter the protein's ability to participate in ubiquitination. The diverse nature of these variants means their effects can vary, influencing the severity and specific characteristics of associated conditions.
Sample of pathogenic variants
10 pathogenic / likely-pathogenic variants from ClinVar, ranked by review status (expert-panel-reviewed first). This is a sample; recurrent founder variants in a specific population may not appear here - see the full ClinVar listing via the link above.
| Variant (HGVS) | Protein change | Classification | Evidence | Associated condition |
|---|---|---|---|---|
c.1108C>T | p.Arg370Ter | Pathogenic | ★★☆☆ | X-linked intellectual disability Cabezas type |
c.2139_2140del | p.Leu714fs | Pathogenic | ★★☆☆ | not provided |
c.2439G>A | p.Thr813= | Pathogenic/Likely pathogenic | ★★☆☆ | X-linked intellectual disability Cabezas type |
c.721C>T | p.Gln241Ter | Pathogenic | ★★☆☆ | X-linked intellectual disability Cabezas type |
c.953_957del | p.Ile318fs | Pathogenic | ★★☆☆ | X-linked intellectual disability Cabezas type |
c.1079T>A | p.Leu360Ter | Pathogenic | ★☆☆☆ | X-linked intellectual disability Cabezas type |
c.1201_1204del | p.Lys401fs | Pathogenic | ★☆☆☆ | X-linked intellectual disability Cabezas type |
c.1741_1741+8del | - | Pathogenic | ★☆☆☆ | X-linked intellectual disability Cabezas type |
c.1742-2A>G | - | Pathogenic | ★☆☆☆ | X-linked intellectual disability Cabezas type |
c.2069dup | p.Lys691fs | Pathogenic | ★☆☆☆ | X-linked intellectual disability Cabezas type |
Evidence stars indicate ClinVar review status. Individual variant interpretation should always be performed by a qualified clinical laboratory - many variants remain classified as Variants of Uncertain Significance (VUS) pending more research.
Associated conditions
Pathogenic variants in the CUL4B gene are primarily associated with intellectual disability, which is often syndromic, meaning it occurs alongside other developmental and physical features. Due to the X-linked nature of the gene, males are typically more severely affected than females, though female carriers may also exhibit milder symptoms or specific features. The broad role of CUL4B in cellular regulation contributes to the varied clinical manifestations observed in individuals with CUL4B-related disorders.
No disease links recorded for this gene in our reference set.
UK clinical status
In the UK, the CUL4B gene is recognised on several NHS Genomic Medicine Service (GMS) approved panels. It is listed as 'green' in the DDG2P panel, indicating strong evidence for gene-disease association. Furthermore, CUL4B is included in panels for Differences in sex development (R146), Early onset or syndromic epilepsy (R59), Foetal anomalies (R21), Hypogonadotropic hypogonadism (R148) and Intellectual disability (R29), signifying its importance in diagnosing these conditions within the UK healthcare system.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What is the main function of the CUL4B gene?
The CUL4B gene provides instructions for creating a protein that serves as a crucial component of an E3 ubiquitin ligase complex, which tags other proteins for degradation within the cell. This process is essential for regulating various cellular activities, including the cell cycle and DNA repair.
What conditions are associated with CUL4B gene variants?
Variants in the CUL4B gene are primarily associated with syndromic intellectual disability. The specific symptoms can vary, but generally involve developmental and neurological challenges, often more pronounced in males due to the gene's location on the X chromosome.
Is CUL4B included in genetic testing panels in the UK?
Yes, CUL4B is included in several NHS Genomic Medicine Service approved panels in the UK. These include panels for developmental disorders, differences in sex development, early onset epilepsy, foetal anomalies, hypogonadotropic hypogonadism, and intellectual disability.