Can we test lactose intolerance at home? Or do we need “genome testing”?

Last update and review: October 20, 2020.

Milk and fermented milk can be used as effective tools for optimizing metabolism and hormonal profile. However, lactose intolerance can be an obstacle. Keller, 2017, believes that, clinically, lactose intolerance is one of the most frequent cases of carbohydrate malabsorption:

“Clinically by far the most important carbohydrate malabsorption syndromes are caused by lactase deficiency leading to lactose intolerance as well as relative deficiency of GLUT-5
leading to intestinal fructose malabsorption.
…lactase deficiency has been shown to be normal in non-Caucasian adults. In these and in Caucasians who are homozygous for the autosomal recessive wild-type gene, a progressive decline of lactase activity is observed, frequently starting in older children or youths.”

Terminology:

Homozygous
adjective
GENETICS
having two identical alleles of a particular gene or genes.
“homozygous embryos”

From the National Human Genome Research Institute’s Glossary:

“Autosomal” means that the gene in question is located on one of the numbered, or non-sex, chromosomes. “Dominant” means that a single copy of the disease-associated mutation is enough to cause the disease. This is in contrast to a recessive disorder, where two copies of the mutation are needed to cause the disease.”

Below, there is some useful figures and explanations on autosomal inheritance from Tafakhori, 2015 (1).

Mendelian modes of Inheritance (a) autosomal recessive inheritance and (b) autosomal dominant inheritance. — Mendelian modes of Inheritance (a) autosomal recessive inheritance. In this case “a” is the mutated allele of the gene and “A” is non-mutated. Individual who receives mutated allele from both parents (aa) would be affected with disease. Another persons “AA” and “Aa” do not show phenotypes of disease. (b) Autosomal dominant inheritance. In this model “A” (the dominant allele) is mutated allele and can cause disease, so any individual who receives just one mutated allele (AA, Aa) would be affected. (c) X-linked recessive inheritance. This mode has sex-based transmission because the gene is located on X chromosome, therefore females have two alleles of the gene and males have just one allele. If the mother is carrier, 50% of her boys will be affected and none of the girls in such pedigrees would show the phenotype of disease. (d) X-linked Dominant inheritance. In this example, the disease is caused by dominant mutated allele located in chromosome X. So if the father is affected, all the girls would be affected and no boys would show the disease phenotype. If the mother was affected too (Aa or AA) so the boys would have shown the phenotype of disease with different percentage. From Tafakhori, 2015.

Returning to lactose intolerance, here is a description of symptoms and of the underlying mechanisms from Keller, 2017:

“Since intact lactose cannot be absorbed from the small bowel, lactose may bind water osmotically and will be metabolized by
colonic bacteria, leading to production of gas in the large
bowel if ingested by a lactase-deficient subject. Typical symptoms such as diarrhea, bloating, and abdominal pain may arise
from increased water load and gas content as well as from
motor responses to increased distension.”

So, it appears that a medical practitioner should ask his or her patients or consulting clients if they did a genome test. On a genome test, we can see if the patient or consulting client is homozygous for the autosomal recessive wild-type gene causing lactose intolerance.

The messy world of direct to consumer genome testing.

There is, however, another way to check if a person is lactose intolerant. Lactose intolerance can, in fact, be easily checked in the office of a medical practitioner or even at home, by the patients themselves.

We, traditionally, do not give answers to all the questions. The goal of our articles is not only to provide an explanation and analysis, but also to stimulate thinking, to stimulate curiosity. Therefore, we end this article with a “Test of Physiological Literacy”.

A Test of Physiological Literacy:

1. Propose a way to test lactose intolerance at home, by the patients themselves.

2. Can a daughter be affected by a disease caused by an autosomal recessive mutation?

3. Can a son be affected by a disease caused by an autosomal recessive mutation?

4. What is the difference between a mutation and a polymorphism?

5. If only the mother is a carier of a mutated allele, can her daughters or her sons be affected by a disease caused by this autosomal recessive mutation?

6. If only the father is a carier of a mutated allele, can his daughters or sons be affected by a disease caused by this autosomal dominant mutation?

Selected References:

1. Tafakhori et al., Iran J Neurol 2015; 14(1): 1-7 .

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