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Lactase enzyme, found in the cells lining the small intestine of mammals, cleaves lactose, a disaccharide, into the constituent monosaccharides, galactose and glucose, which are readily absorbed by the intestine. The amount of lactase activity decreases substantially after weaning in mammals, as lactose is no more a major part of their diet. This condition in humans is referred to as lactase non-persistence (LNP) or adult-type hypolactasia or primary lactose mal-digestion (LM). In several human societies all over the world, lactose is a part of the diet of adults due to the prevalence of dairy products and fresh milk in diet; this has been the case ever since human societies had domesticated cattle. A genetic mutation seems to have occurred in one (or more) such society (ies) resulting in lactase activity persisting in the cells lining the intestine even in adult stage. This condition is referred to as lactase persistence (LP). This mutation, due to its selective advantage, had spread extensively in such cattle rearing societies; this is the generally accepted explanation for Northern European societies having a large proportion (up to 90%) of the population being LP. Human genome sequencing studies done since 2001 have led to uncovering the molecular basis of this mutation. A single nucleotide polymorphism (SNP) at the position 13910 nucleotide upstream to the gene coding for lactase (LCT; located on chromosome 2) appears to determine the LP/LNP status of most populations studied. The nucleotide C at this position (which is the ancestral condition as determined by comparison with primate genome sequence data) corresponds to the LNP status whereas the nucleotide T at this position (which is a mutation) corresponds to the LP status. LP allele is dominant over LNP. This relationship between the SNP at -13910 upstream of LCT and LP/LNP has been verified for several populations including East Asia, East Europe etc and holds good nearly universally with the exception of some small pockets of indigenous populations in African Continent and Arabian peninsula. Studies carried out (to be published) in the Indian population by scientists at Biotools Technologies Pvt Ltd., and a Govt. Medical Research Laboratory show that the SNP at -13910 upstream of LCT does determine LP/LNP status in Indian population as well.

When Lactose Mal-digestion (LM) is associated with symptoms such as bloating, flatulence, abdominal pain or diarrhea, lactose intolerance (LI) is said to occur. In clinical practice the diagnosis of LI involves diagnosis of LM. Lactose Hydrogen Breath Test (LHBT) and Lactose Tolerance Test (LTT) and Stool Acidity Test are commonly used to diagnose LM.

LHBT is a clinical test used to diagnose lactose mal-absorption. The person after an overnight fast, takes the basal reading of hydrogen level in breath (usually below 20 parts per million (ppm). He/ She is then administered 25-50grams of liquid lactose and breath readings taken every 15 or 30 minutes for about 2-3 hours. Based on the readings, the person is diagnosed as lactose mal-absorber/absorber. In some cases the person may produce methane instead/in addition to hydrogen, then methane levels in the breath is read.

LTT is a clinical test that monitors the rise in blood glucose level. Lactose in small intestine is broken down to glucose and galactose by lactase enzyme. The person after an overnight fast is administered 25 - 50grams of liquid lactose. The blood sample taken after ½ and 1 hour is tested for rise in the blood glucose level above the basal level (initial test before giving lactose). Person is considered lactose mal-digester if the glucose level does not rise, indicating inability/ failure to digest lactose by intestinal lactase.

Stool Acidity Test is a method of detecting lactose intolerance in children. The large lactose doses are not given to infants and children to determine lactose mal-digestion. Bacteria in colon produce lactic acid that can be detected in stool. This test measures acidity of a stool sample after ingestion of small amount of lactose.

The availability of the genetic test to determine the LP/LNP status provides a reference standard. The genetic analysis is done in our lab either by Restriction fragment length polymorphism (RFLP) or by DNA Sequencing.

RFLP: Variation in the DNA sequence of a genome can be detected by breaking the DNA into fragments with restriction enzymes. The resulting size variations in DNA fragments are analysed by gel electrophoresis. The sequence variation is determined by this technique when the variation occurs in a restriction site.

DNA Sequencing is a biochemical method used to determine the exact order of the nucleotide bases, A,T,G,C in a piece of DNA molecule. The genomic DNA is used as a template to generate a set of fragments that carry the inherited differences found among individuals. The DNA fragment is read base by base by an automated DNA sequencer and the normal/ variant (LNP/LP) condition is determined.

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