Lactose intolerance (Lactose intolerance) - LCT and MCM6 genes.

Lactose intolerance is an impaired ability to digest lactose, a carbohydrate found in milk and other dairy products. Lactose typically decomposes by the lactase enzyme, which is encoded by the cells of the small intestine mucosa. Congenital lactase deficiency, also called congenital lactase deficiency is a disorder in which children are unable to break down lactose, resulting in severe diarrhea. If they are not provided to children affected infant formula lactose, they can have severe dehydration and weight loss. For its part, the lactose intolerance in adulthood is due to reduced encoding lactase after infancy (lack of lactase persistence). If people with lactose intolerance consume lactose - containing dairy products, may have abdominal pain, bloating, flatulence, nausea and diarrhea.

Most people with lack of lactase persistence retain some lactase activity and may include varying amounts of lactose in their diet without symptoms. Often, affected individuals have difficulty digesting fresh milk, but they can eat certain dairy products such as cheese or yogurt without discomfort. These foods are made by fermentation processes that break down much of the lactose in milk.

The lactose intolerance in infants (congenital lactase deficiency) is caused by mutations in the gene LCT. The lactose intolerance in adults is caused by the gradual decrease in expression of the gene LCT after infancy. LCT gene expression is controlled by a DNA sequence called regulatory element, which is in the MCM6 gene.

The LCT gene, located on the long arm of chromosome 2 (2q21), encoding an enzyme called lactase. This enzyme helps digest lactose. Lactase is produced by intestinal epithelial cells. These cells have microvilli that absorb nutrients from food as it passes through the intestine to be absorbed in to the blood stream. They have been identified at least 9 LCT gene mutations in people with lactose intolerance. LCT gene mutations change the amino acid or lactase result an enzyme that is abnormally short enzyme. It is considered that these changes interfere with the function of the enzyme lactase, causing lactose to be undigested the small intestine and cause severe diarrhea.

The MCM6 gene, located on the long arm of chromosome 2 (2q21), encoding part of the MCM complex, a group of proteins that functions as a helicase. Helicases bind to particular DNA regions. When a cell prepares to divide, helicases unwind the DNA so that it can be copied. DNA doubles up chromosomes for each new cell for a complete set of chromosomes. Helicases are also involved in coding RNA. A specific DNA sequence in the MCM6 gene, called regulatory element, helps to control the expression of the gene LCT. At least four variations have been identified in the regulatory element modulates the expression of the gene LCT. These nucleotide variations change in the regulatory element. Each of the variations results in sustained encoding lactase in the small intestine and the ability to digest lactose throughout life. People without these changes have reduced to digest lactose as they age capacity, which leads to the signs and symptoms of lactose intolerance.

The type of lactose intolerance which occurs in infants (congenital lactase deficiency) is inherited as an autosomal recessive pattern, which means that both copies of the gene in every cell must have mutations for alteration is expressed. The parents of an individual with an autosomal recessive disease have a copy of the mutated gene, but usually show no signs and symptoms of the disease. The ability to digest lactose in adulthood depends on variations in inherited from his parents regulatory element. Variations promoting continuous lactase coding considered autosomal dominant, which means that a copy of the altered regulatory element in each cell is sufficient to support the encoding lactase. People who have inherited these variations of either parent will have some degree of lactose intolerance.

Tests in IVAMI: in IVAMI perform detection of mutations associated with lactose intolerance, by complete PCR amplification of the exons of LCT and MCM6 gene, respectively, and subsequent sequencing.

Samples recommended: EDTA blood collected for separation of blood leukocytes, or impregnated sample card with dried blood (IVAMI may mail the card to deposit the blood sample).