Center for Human Genetics and Laboratory Diagnostics, Dr. Klein, Dr. Rost and Colleagues

Congenital Lactase Deficiency (CLD, Neonatal Lactose Intolerance) [E73.0]

OMIM numbers: 223000, 603202 (LCT)

Dipl.-Biol. Birgit Busse

Scientific Background

In extremely rare cases, intolerance of lactose during infancy may be caused by congenital lactase deficiency (CLD) with severe, neonatal lactose intolerance. With an incidence of 1 in 60,000, CLD is found slighty more frequently among the Finnish population, yet still very rare. Otherwise, there is no reliable data regarding the frequency of CLD. CLD leads to very severe signs and symptoms which occur immediately after birth with the first intake of lactose. The infants show uncontrollable, watery diarrhea and vomiting, which causes danger of dehydration. If CLD is neither diagnosed at an early stage nor immediately followed by a lactose free feeding, failure to thrive and life-threatening situations may occur.

CLD is caused by loss-of-function mutations in the LCT gene that lead to a lactase deficiency. Inheritance is autosomal recessive, i.e. for the disease to cause any phenotypical signs or symptoms, both alleles of the gene have to carry a mutation.

Regarding differential diagnosis, the fact that disorders such as celiac disease and Crohn’s disease may cause secondary lactose intolerance that occurs independantly from the lactase genotype should be considered, as well as a glucose galactose malabsorption or a milk protein allergy. Testing for hereditary lactose intolerance (adult-onset), predominantly manifests in signs and symptoms during adulthood, is usually not indicated in infants or toddlers.