A Summary Of Congenital Lactase Deficiency: Its Symptoms And Its Genetic Cause

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What Is Congenital Lactase Deficiency?

Congenital lactase deficiency (CLD), or what is otherwise known as congenital alactasia, is an autosomal recessive genetic disorder seen in infants that severely affects the gastrointestinal system. Infants who have CLD are prone to experiencing watery diarrhea after they ingest breast milk or other foods that are rich in lactose, a complex sugar that is formed from the simple sugars glucose and galactose. Later-arising symptoms that are also commonly seen include dehydration, weight loss and increased acidity of the blood. One symptom that typically is not seen, however, is loss of appetite. In fact, most infants who have CLD have an exceptionally good appetite and even appear hungry and eager to eat much of the time.

CLD is best treated by putting affected children on a lactose-free diet. The removal of lactose from their diet is often met with immediate success, as all symptoms tend to subside right away. Further, children who are treated in this manner typically go on to lead normal lives in all other respects, so there seems to be no drawback to choosing this particular treatment course.

Fortunately, CLD is a very rare disorder. It is estimated that about 1 in 60,000 infants suffer from it, although the incidence of CLD is somewhat greater in the Finnish population.

What Is Known About The Genetic Cause Of Congenital Lactase Deficiency?

In 2006, a team of mostly Finnish molecular geneticists reported the discovery of five distinct mutations in a gene that is designated LCT in the genomes of several infants who were diagnosed as having CLD. Specifically, the normal, non-mutated version of LCT gene encodes the protein lactase. Lactase, which is synthesized in cells that line the small intestine, catalyzes the break down of lactose into the simpler sugars glucose and galactose, which are capable of being absorbed into the bloodstream (whereas, lactose, which is a much larger molecule, is not).

Infants who have mutations in each one of their two copies of the LCT gene are unable to make lactase, or make a highly defective version of the lactase protein, and therefore are unable to break down lactose in their small intestine. The resulting build up of lactose is problematic for the small intestine, which is why the gastrointestinal problems described above are seen.

If your baby is experiencing the problems described above and you suspect that she may be suffering from CLD (again, CLD is a very rare condition, so it is unlikely that your child has CLD), it is recommended that you consult your doctor, who can positively diagnose the problem that your child is suffering from. This article is meant only to provide some background information regarding congenital lactose deficiency, it is not meant to replace the sound advice of your doctor.


E. Savilahti et al., Congenital lactase deficiency: A clinical study on 16 patients, Archives of Disease in Childhood 58:246-252 (1983). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1627962/pdf/archdisch00747-0010.pdf

Genetics Home Reference, National Institutes of Health, LCT: https://ghr.nlm.nih.gov/gene/LCT

M. Kuokkanen et al., Mutations in the Translated Region of the Lactase Gene (LCT) Underlie Congenital Lactase Deficiency, American Journal of Human Genetics 78:339-344 (2005). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1380240/

S. Torniainen et al., Four novel mutations in the lactase gene (LCT) underlying congenital lactase deficiency, BMC Gasteroenterology (2009). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2635369/?tool=pubmed