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The Group Specific Component globulin (GC) gene is associated with the synthesis of Group Specific Component globulin (GC), also called the Vitamin D Binding Protein (VDBP), which binds to vitamin D and its plasma metabolites, transporting them to the target tissue. This protein is synthesized by the hepatic parenchymal cells and then secreted into the blood stream. People with the C variant of the gene are shown to be associated with lower vitamin D levels.
Vitamin D is necessary for strong bones and for the absorption of calcium, low level of vitamin D is associated with brittle bones and poor muscle function. Vitamin D deficiency is identified by measuring the level of 25, hydroxy vitamin D in the blood. Increased plasma concentration of plasma 25, hydroxy vitamin D is associated with reduced risk of hypertension.
| CHIP Version | GC SNPs |
| 23andMe (Use your 23andme raw data to know your GC Variant) | |
| v1 23andme | Present |
| v2 23andme | Present |
| v3 23andme | Present |
| v4 23andme | Present |
| V5 23andme (current chip) | Present |
| AncestryDNA (Use your ancestry DNA raw data to know your GC Variant) | |
| v1 ancestry DNA | Present |
| V2 ancestry DNA (current chip) | Present |
| Family Tree DNA (Use your FTDNA raw data to know your GC Variant) | |
| OmniExpress microarray chip | Present |
The GC gene is found to be the strongest genetic determinant of the bioavailability of 25, hydroxy vitamin D. There are three isoforms of GC- GC1F, GC2 and GC1S, they are based on a combination of alleles of the SNPs rs7041 and rs 4588 (rs 2282679 is a close proxy). The isoform GC1F is more common among people with dark skin when compared with people with pale skin. GC2 and GC1S are more common among people with pale skin than among people with dark skin.
The vitamin D binding protein (VDBP) in people with the GC1 isoform has a higher affinity for vitamin D metabolites. This is shown to be associated with variations in the bioavailability of circulating 25, hydroxy vitamin D levels among ethnicities.
| Genotype | Phenotype |
|---|---|
| CC | [Limitation] More likely to have lower plasma 25, hydroxy vitamin D |
| CA | Moderate plasma 25, hydroxy vitamin D |
| AA | [Advantage] More likely to have higher plasma 25, hydroxy vitamin D |
How can this information be used?
It is important to choose an appropriate diet based on the genetic profile
| For people with C variant (Decrease in plasma 25, hydroxy vitamin D) Likely decrease in plasma 25, hydroxy vitamin D Include 1000 I.U of vitamin D per day Ensure sufficient exposure to sunlight; include enjoyable activities like taking the dog for a walk or a day at the beach with family. |
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| For people with A variant (Normal plasma 25, hydroxy vitamin D) Increased likelihood for normal level of plasma 25, hydroxy vitamin D if the dietary intake is sufficient Spend time outdoors for adequate exposure to sunlight |
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“Nutrigenetics, fitness genetics, health genetics are all nascent but rapidly growing areas within human genetics. The information provided herein is based on preliminary scientific studies and it is to be read and understood in that context.”
