The genetic basis for lactose intolerance is a change in the nucleotide sequence outside of the lactase gene.
Lactose is normally hydrolyzed and broken down in the small intestine.
Lactose intolerance is due to mutations in the MCM6 gene, which regulates the expression of the lactase gene associated with the persistence of enzyme activity in adults.
The lactase enzyme is synthesized from the expression of the LCT gene.
The expression of the LCT gene is regulated by a protein complex (MCM), which is partly encoded by a specific sequence of the MCM6 gene located on chromosome 2q21.
A genetic alteration of this gene, specifically in position 13910, is responsible for the persistence or non-persistence of lactase in the adult.
The nucleotide sequence C / C (Cytosine / Cytosine) would be the one present in the non-persistence of lactase.
Therefore, we can conclude that lactose intolerance is due to a decrease or absence of the activity of the lactase enzyme and that it is due to a change in the nucleotide sequence that helps to control the expression of the LCT gene.
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