A genetic test for lactose intolerance has been devised by researchers at the Canterbury Health Laboratories in Christchurch.

Lactose intolerance is common

Most of the world’s population (about 75%) are lactose intolerant and can’t consume milk or milk products without feeling ill. This is because they lack the enzyme lactase, which digests the milk sugar lactose.

Lactose tolerance arises from a genetic mutation

In New Zealand, most of the population are lactose tolerant and can consume milk and milk products. A single point mutation in the DNA ensures that the lactase enzyme is produced in adults. At a specific site in the DNA, a cytosine (C) nucleotide is replaced with a thymine (T). This type of mutation is called a single nucleotide polymorphism.

If the thymine (T) nucleotide is present, the lactase enzyme continues to be made after weaning, and adults can consume milk without any ill effects. This mutation is thought to have emerged relatively recently (less than 10,000 years ago) as farming and dairying practices became commonplace.

A genetic test for lactose intolerance

Previous tests for lactose intolerance were time-consuming and invasive. Recently, researchers at the Canterbury Health Laboratories in Christchurch have devised a simple genetic test for lactose intolerance. This test determines whether a subject has the cytosine (C) or thymine (T) nucleotide in their DNA close to the lactase gene.

This test uses a number of common molecular biology techniques including polymerase chain reaction, restriction enzyme digests and gel electrophoresis – see the steps below:

Obtain a DNA sample: A small amount of blood (about 5ml) is taken from a test subject.

Polymerase chain reaction (PCR) amplifies the DNA: The subject’s DNA is amplified using polymerase chain reaction (PCR). PCR uses primers to amplify the specific region of DNA that contains the single nucleotide polymorphism.

Find out more about polymerase chain reaction (PCR).

Restriction enzymes cut the DNA into fragments: The amplified DNA is cut into fragments with restriction enzymes.

Find out more about restriction enzymes.

Gel electrophoresis separates DNA fragments: The DNA fragments are separated by size using gel electrophoresis.

Find out more about gel electrophoresis.

Analyse results: The pattern of DNA fragments indicates whether a person is lactose intolerant (C/C) or lactose tolerant (C/T) or (T/T).

Testing for lactose intolerance

A test for lactose intolerance is needed to help doctors diagnose and treat people. If a person has lactose intolerance, they could avoid milk and milk products, to see if this helps symptoms, or explore some biotechnological solutions.

Find out more about Treating lactose intolerance.

Useful links

This article, looking at the prevalence of lactose intolerance in a randomly selected New Zealand population, in the New Zealand Medical Journal notes that a random sample of the Christchurch population found more than 8% are genetically lactose intolerant. Use of a simple and rapid genetic test should make diagnosis of lactose intolerance considerably easier.

A summary of data from foodreactions.org showing the percentage of people with lactose intolerance in different world regions.

 

    Published 3 September 2009