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ORC4
origin recognition complex subunit 4
The ORC4 gene provides instructions for a protein that is a key component of the origin recognition complex (ORC), essential for initiating DNA replication and maintaining genomic stability. The ORC4 gene encodes a protein integral to the origin recognition complex, which plays a crucial role in DNA replication.
ORC4 is located on the long (q) arm of chromosome 2, at band 2q23.1. Arm ratio per GRCh38 - banding schematic.
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Overview
The ORC4 gene is responsible for producing a protein known as origin recognition complex subunit 4. This protein is part of a larger multi-protein complex, the origin recognition complex (ORC), which is fundamental to the process of DNA replication in human cells. The ORC complex initiates the copying of a cell's DNA, a tightly regulated process that ensures genetic information is accurately passed to new cells during cell division.
Disruptions in the ORC4 gene or its protein product can affect this critical cellular machinery. Such disruptions are associated with certain health conditions, highlighting the gene's importance in normal growth and development.
What the gene does
The ORC4 gene directs the synthesis of one of the six core subunits (ORC1-ORC6) that form the origin recognition complex (ORC). This complex serves as the primary initiator of DNA replication within a cell. The ORC specifically binds to designated sites on the DNA, known as origins of replication, marking where DNA copying should begin.
Upon binding to these origins, the ORC complex recruits other proteins to form a larger assembly called the pre-replication complex. This expanded complex enables the initiation of DNA synthesis. This tightly controlled mechanism, termed replication licensing, prevents DNA from being copied more than once per cell division, which is critical for maintaining genomic integrity and successful cell proliferation.
The ORC also interacts with heterochromatin, a densely packed form of DNA important for chromosome structure and gene regulation, though the precise implications of this interaction are still being investigated.
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Chromosome location
The ORC4 gene is located on the long arm of chromosome 2, specifically at position 2q23.1. This precise genomic address helps in identifying and studying the gene within the human genome.
Protein structure
Domain architecture has not been experimentally characterised in detail for this protein.
Key variants
Genetic variations within the ORC4 gene can arise from several types of changes, including alterations in single protein building blocks (amino acids) or modifications that lead to the production of an abnormally short protein. These variants can affect the ORC4 protein's function, potentially disrupting its role in DNA replication and other cellular processes.
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.521A>G | p.Tyr174Cys | Pathogenic/Likely pathogenic | ★★☆☆ | ORC4-related disorders |
c.623C>G | p.Ser208Ter | Pathogenic/Likely pathogenic | ★★☆☆ | ORC4-related disorders |
c.914dup | p.Ser306fs | Pathogenic/Likely pathogenic | ★★☆☆ | ORC4-related disorders |
GRCh37/hg19 2q22.3-23.1(chr2:148698835-148778440)x1 | - | Pathogenic | ★☆☆☆ | not specified |
g.(?_148709922)_(148710113_?)del | - | Pathogenic | ★☆☆☆ | not provided |
c.36del | p.His13fs | Pathogenic | ★☆☆☆ | not provided |
c.41_42del | p.Thr14fs | Pathogenic | ★☆☆☆ | not provided |
c.767_770del | p.Leu256fs | Pathogenic | ★☆☆☆ | not provided |
c.919C>T | p.Gln307Ter | Pathogenic | ★☆☆☆ | not provided |
c.927dup | p.Ser310Ter | Pathogenic | ★☆☆☆ | not provided |
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
Variations in the ORC4 gene have been linked to specific inherited conditions. One such condition is Meier-Gorlin syndrome, which is characterised by features such as short stature, underdeveloped kneecaps, and small ears. These clinical manifestations arise from the compromised function of the ORC4 protein, affecting critical developmental processes.
No disease links recorded for this gene in our reference set.
UK clinical status
The ORC4 gene is included on several NHS Genomic Medicine Service clinical panels, indicating its recognised role in various inherited conditions. It holds a 'green' status for conditions such as DDG2P, Deafness and congenital structural abnormalities, Foetal anomalies, IUGR and IGF abnormalities, Severe microcephaly (R88), and Skeletal dysplasia (R104). This signifies that variants in ORC4 are considered causative for these conditions within a clinical diagnostic context.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What is the primary role of the ORC4 gene?
The ORC4 gene provides instructions for a protein that is a vital component of the origin recognition complex (ORC). This complex is essential for initiating DNA replication, ensuring that the cell's genetic material is accurately copied before cell division.
What happens if the ORC4 gene has a pathogenic variant?
Pathogenic variants in the ORC4 gene can impair the function of the ORC4 protein, disrupting DNA replication. This can lead to developmental conditions such as Meier-Gorlin syndrome, characterised by features like short stature and specific physical abnormalities.
Is ORC4 included in genetic testing panels in the UK?
Yes, the ORC4 gene is part of several NHS Genomic Medicine Service clinical panels, including those for Foetal anomalies, Severe microcephaly, and Skeletal dysplasia. Its inclusion indicates its clinical relevance for diagnosing these conditions.
References
- Niida H, Kitagawa M. Regulation of DNA replication licensing. Current drug targets. 2012. PMID: 22998185
- Guernsey DL, Matsuoka M, Jiang H. Mutations in origin recognition complex gene ORC4 cause Meier-Gorlin syndrome. Nature genetics. 2011. PMID: 21358631
- Bicknell LS, Bongers EM, Leitch A. Mutations in the pre-replication complex cause Meier-Gorlin syndrome. Nature genetics. 2011. PMID: 21358632
- Prasanth SG, Shen Z, Prasanth KV. Human origin recognition complex is essential for HP1 binding to chromatin and heterochromatin organization. Proceedings of the National Academy of Sciences of the United States of America. 2010. PMID: 20689044