Interpretation
Disaccharidases in the small intestine are responsible for the breakdown of disaccharides (double sugars) into monosaccharides (simple sugars). Patients with a disaccharidase deficiency fail to absorb that specific disaccharide. The osmotic effect of the unabsorbed disaccharide increases fluid transfer into the gut lumen, causing abdominal discomfort and diarrhoea.
Patients with a deficiency of one or more disaccharidase enzymes may experience intolerance to foods containing complex sugars resulting in a range of gastrointestinal symptoms including diarrhoea or constipation, abdominal pain and cramping, bloating and nausea. In addition, patients may experience malnutrition, weight loss, or failure to thrive. Given the non-specificity and frequency of abdominal symptoms, misdiagnosis or delayed diagnosis of disaccharidase deficiencies may occur.
Primary and secondary causes of disaccharidase deficiencies exist, and age of onset may vary from birth through adulthood. Primary causes are rare and result from genetic alterations in a variety of genes. Secondary deficiencies typically result from small intestinal mucosal damage.
Adult type hypolactasia post weaning is the most common type of lactase deficiency. Secondary lactase deficiency from intestinal disorders like Crohn’s disease, coeliac disease and gut infection is also commonly seen. Lactase deficiency associated with prematurity may resemble the congenital form, but usually disappears within a few days of birth. Congenital lactase deficiency is rare, but will produce severe symptoms when the infant is fed milk.
Genetic testing for lactase deficiency is also available.
Sucrase and maltase deficiency usually coexist. The test result is only useful if specific disaccharidase deficiencies are demonstrated; with at least one other disaccharidase showing normal activity. If the activity of all three are reduced proportionately, then either the specimen was unsuitable, or there is some other disorder (mainly coeliac disease) affecting the mucosa in the region where the biopsy was taken from.
The reliability of analysis is entirely dependent on a suitable biopsy specimen, which must include a reasonable sized sample of the mucosa. Specimen handling is also critical.
Treatment of both primary and secondary disaccharidase deficiencies involves dietary management. While primary deficiencies require lifelong treatment, secondary disaccharidase deficiencies may require treatment only until the intestinal lining recovers.
Reference Intervals
Maltase = 1000 – 2000 U/g wet tissue
Lactase = 50 – 300 U/g wet tissue
Sucrase = 200 – 600 U/g wet tissue
Test Method
Enzyme end point, colourimetric
