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MOCS1
molybdenum cofactor synthesis 1
The MOCS1 gene provides instructions for producing proteins crucial for the initial steps in the synthesis of molybdenum cofactor, a vital molecule for several enzyme functions in the body. MOCS1 is a gene central to the biosynthesis of molybdenum cofactor (MoCo), which is essential for the activity of key metabolic enzymes.
MOCS1 is located on the short (p) arm of chromosome 6, at band 6p21.2. Arm ratio per GRCh38 - banding schematic.
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Overview
The MOCS1 gene, also known as molybdenum cofactor synthesis 1, is critical for the production of molybdenum cofactor (MoCo). MoCo is a small molecule that acts as a prosthetic group for several important enzymes in human metabolism, enabling them to catalyse essential biochemical reactions. Dysfunction in MOCS1 can therefore have significant systemic consequences due to the broad impact of these enzymes.
Inherited in an autosomal recessive pattern, variants in the MOCS1 gene are associated with conditions like molybdenum cofactor deficiency, which often presents with severe neurological symptoms early in life.
What the gene does
MOCS1 encodes two proteins, MOCS1A and MOCS1B, both of which are involved in the biosynthesis of molybdenum cofactor (MoCo). Specifically, MOCS1A and MOCS1B facilitate the very first steps in the complex pathway that leads to MoCo formation, though the precise role of MOCS1B in this initial stage is not fully understood. MOCS1A is known to perform a critical step in converting a precursor molecule into cyclic pyranopterin monophosphate, an intermediate required for MoCo synthesis.
Molybdenum cofactor is subsequently incorporated into several enzymes, including sulfite oxidase, aldehyde oxidase, xanthine dehydrogenase, and mitochondrial amidoxime reducing component (mARC). These enzymes are vital for breaking down various substances in the body, some of which are toxic if not properly metabolised. Therefore, proper MOCS1 function is indispensable for detoxification and metabolic health.
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Chromosome location
The MOCS1 gene is located on chromosome 6, specifically at position 6p21.2. This genomic location describes the gene's physical address on the short (p) arm of chromosome 6, within band 21.2.
Protein structure
The MOCS1 protein is 636 amino acids long and contains several distinct regions and domains. It features a Molybdenum cofactor biosynthesis protein A region spanning amino acids 1-383, which includes a Radical SAM core domain from amino acids 64-277. A mitochondrial translocation signal is found within amino acids 368-463. Amino acids 384-385 are particularly important for catalytic activity. The protein also contains a Molybdenum cofactor biosynthesis protein C region from amino acids 414-636. Additionally, a disordered region is present between amino acids 456-480.
Key variants
Variants in the MOCS1 gene can affect its ability to produce functional proteins necessary for molybdenum cofactor synthesis. These genetic changes can range from single nucleotide substitutions to larger deletions or insertions, potentially altering the protein's structure or expression. Pathogenic variants in MOCS1 are typically classified as such when they are linked to the development 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.1102+2T>C | - | Pathogenic/Likely pathogenic | ★★☆☆ | Sulfite oxidase deficiency due to molybdenum cofactor deficiency type A |
c.1150+1G>T | G297V, G384V | Pathogenic/Likely pathogenic | ★★☆☆ | Sulfite oxidase deficiency due to molybdenum cofactor deficiency type A |
c.1275del | p.Gly426fs | Pathogenic/Likely pathogenic | ★★☆☆ | Sulfite oxidase deficiency due to molybdenum cofactor deficiency type A |
c.142C>T | p.Gln48Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Sulfite oxidase deficiency due to molybdenum cofactor deficiency type A |
c.271del | p.Glu91fs | Pathogenic | ★★☆☆ | Sulfite oxidase deficiency due to molybdenum cofactor deficiency type A |
c.291del | p.Ala99fs | Pathogenic/Likely pathogenic | ★★☆☆ | Sulfite oxidase deficiency due to molybdenum cofactor deficiency type A |
c.306_309dup | p.Thr104fs | Pathogenic/Likely pathogenic | ★★☆☆ | Sulfite oxidase deficiency due to molybdenum cofactor deficiency type A |
c.519del | p.Ser173fs | Pathogenic/Likely pathogenic | ★★☆☆ | Sulfite oxidase deficiency due to molybdenum cofactor deficiency type A |
c.664C>T | p.Arg222Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Sulfite oxidase deficiency due to molybdenum cofactor deficiency type A |
c.721del | p.Leu241fs | Pathogenic/Likely pathogenic | ★★☆☆ | Sulfite oxidase deficiency due to molybdenum cofactor deficiency type A |
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 MOCS1 gene are primarily associated with Molybdenum cofactor deficiency. This inherited metabolic disorder is characterised by severe neurological symptoms that often manifest shortly after birth, including intractable seizures and progressive encephalopathy (brain dysfunction). Without timely intervention, the condition is usually fatal in early childhood.
Inheritance pattern
Conditions caused by pathogenic MOCS1 variants typically follow autosomal recessive inheritance.
When both parents are carriers, each child has a 25% chance of being affected, 50% of being a carrier, and 25% of being unaffected.
UK clinical status
The MOCS1 gene is recognised in the UK's National Health Service (NHS) Genomic Medicine Service. It is listed with a 'green' status on the DDG2P panel and is included in clinical panels for Early onset or syndromic epilepsy, Foetal anomalies (R21), Intellectual disability, Likely inborn error of metabolism (R98), and Undiagnosed metabolic disorders. This indicates that variants in MOCS1 are considered to have a strong association with 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 main function of the MOCS1 gene?
The MOCS1 gene provides instructions for creating proteins involved in the initial steps of synthesising molybdenum cofactor (MoCo). MoCo is essential for several enzymes that break down various substances in the body.
What health condition is associated with MOCS1 gene variants?
Variants in the MOCS1 gene are associated with molybdenum cofactor deficiency. This severe inherited metabolic disorder typically causes neurological problems like seizures and progressive brain dysfunction from early infancy.
How is molybdenum cofactor deficiency inherited?
Molybdenum cofactor deficiency is inherited in an autosomal recessive pattern. This means an individual must inherit two copies of the altered MOCS1 gene (one from each parent) to develop the condition.
References
- Mendel RR. The molybdenum cofactor. The Journal of biological chemistry. 2013. PMID: 23539623
- Leimkühler S, Charcosset M, Latour P. Ten novel mutations in the molybdenum cofactor genes MOCS1 and MOCS2 and in vitro characterization of a MOCS2 mutation that abolishes the binding ability of molybdopterin synthase. Human genetics. 2005. PMID: 16021469
- Reiss J, Johnson JL. Mutations in the molybdenum cofactor biosynthetic genes MOCS1, MOCS2, and GEPH. Human mutation. 2003. PMID: 12754701