DGAT1 is an enzyme that creates a fat called triglyceride. Every person has two copies of the DGAT1 gene and when a child gets an altered gene from each parent the ability to make triglycerides is affected. For reasons that are not well understood, children with two altered genes develop diarrhea shortly after birth. Children who are Ashkenazi Jewish who have a defect in both DGAT1 genes usually have a complete loss of DGAT1 activity and develop diarrhea with protein loss in the stool in the first week of life. Children of other ethnic groups may an alteration in a different part of the gene and only have a partial loss of DGAT1 activity. These children may not have such severe diarrhea and/or may develop symptoms later in life. There may be other alterations in the gene that have yet to be described with other clinical symptoms.
Patients who have DGAT1 deficiency respond to treatment with a low-fat diet. This results in improvement in diarrhea and growth. Children with complete loss of function tolerate between 4-7% of calories from fat; whereas, children with some DGAT1 function might tolerate up to 10% of calories from fat. Some patients tolerate fat best when given in small amounts at multiple feedings, but this varies from individual to individual. To prevent deficiencies, infants who are treated with a fat-free formula should be supplemented with appropriate amounts of canola oil or a mixture of sunflower and flaxseed oils. Monitoring of essential fatty acids is an important aspect of care. Most children who are monitored carefully grow normally and may even catch up when on a fat restricted diet.