Disaccharidase deficiency is a condition characterized by the insufficient or inactive production of specific enzymes within the small intestine. These enzymes, known as disaccharidases, break down complex sugars (disaccharides) into simpler, absorbable sugars (monosaccharides). This final stage of carbohydrate digestion occurs at the small intestine’s brush border. When the enzyme is lacking or impaired, the sugar cannot be properly processed and absorbed, leading to malabsorption and subsequent digestive distress.
Understanding Disaccharidase Function and Malabsorption
Disaccharidases act directly on specific sugar molecules in the gut lumen. For example, lactase breaks down lactose into glucose and galactose, while the sucrase-isomaltase complex breaks down sucrose and starch products into glucose and fructose. These simpler sugars are hydrophilic and are quickly transported into the bloodstream for use as energy.
When a disaccharidase is deficient, the intact sugar passes undigested into the large intestine, creating an osmotic load that draws water into the bowel. Commensal bacteria then ferment these unabsorbed sugars, producing gases such as hydrogen, methane, and carbon dioxide. The resulting combination of excess water and gas production causes the majority of physical symptoms.
Categorizing the Forms of Deficiency
Disaccharidase deficiencies are classified based on their underlying cause, which is important for determining the course of treatment.
Primary Deficiencies
Primary deficiencies are typically genetic, resulting from inherited conditions that affect enzyme production or function. Congenital Sucrase-Isomaltase Deficiency (CSID) is a rare autosomal recessive disorder where the body either produces a non-functional enzyme or none at all. Primary Adult-Type Hypolactasia, commonly known as lactose intolerance, is the most common form globally. It involves a genetically programmed decline in lactase production after infancy, representing a normal genetic variation. Primary deficiencies usually result in permanent disaccharide intolerance.
Secondary Deficiencies
Secondary deficiencies are acquired and arise from damage to the small intestinal lining. Conditions causing inflammation or atrophy of the intestinal villi impair the brush border where the enzymes reside. Examples include Celiac disease, Crohn’s disease, acute gastroenteritis, and small intestinal bacterial overgrowth (SIBO). Treating the underlying intestinal disorder is key to resolution, as healing the intestinal mucosa often restores normal disaccharidase activity. A deficiency in all four disaccharidases is known as pan-disaccharidase deficiency, which can present with more pronounced weight loss.
Recognizing Symptoms and Diagnostic Procedures
The clinical presentation is directly linked to carbohydrate malabsorption and fermentation in the large bowel. Undigested sugars draw water into the colon, manifesting as watery diarrhea or loose stools shortly after consuming the offending sugar. Bacterial fermentation generates significant quantities of gas, leading to uncomfortable abdominal bloating, fullness, and distension. This gas accumulation also results in excessive flatulence and cramping abdominal pain. Since symptoms overlap with other gastrointestinal disorders, accurate diagnosis is necessary.
Diagnosis typically begins with a detailed dietary history and symptom assessment. The most common confirmatory test is the Hydrogen Breath Test, which leverages the metabolic activity of colonic bacteria. The patient consumes a measured dose of the suspect sugar (e.g., lactose or sucrose). If the sugar is unabsorbed, bacteria ferment it in the colon, producing hydrogen and methane gas. Elevated levels of these gases in the patient’s exhaled breath confirm malabsorption.
For definitive identification, a small intestinal biopsy may be performed during an endoscopy. This procedure allows for a direct measurement of enzyme activity in the brush border tissue sample, which is the gold standard for diagnosis. Genetic testing is also used to confirm inherited conditions, such as mutations associated with congenital sucrase-isomaltase deficiency.
Treatment and Dietary Management
Management focuses primarily on reducing the intake of the offending sugar to alleviate symptoms and ensure nutrient absorption. For lactase deficiency, this involves limiting dairy products containing lactose based on the individual’s tolerance threshold. For sucrase-isomaltase deficiency, dietary modification requires limiting sucrose and specific starches. Working with a registered dietitian is beneficial to ensure nutritional needs are met while specific sugars are eliminated.
Enzyme replacement therapy offers an alternative to strict dietary avoidance. Supplemental lactase enzyme, available over-the-counter, can be taken before consuming dairy products to help break down lactose. For sucrase-isomaltase deficiency, a prescription enzyme replacement containing sacrosidase is available as an oral solution. This therapy manages symptoms but does not cure the underlying condition.
In cases of secondary deficiency, treating the underlying condition, such as managing Celiac disease or resolving acute gastroenteritis, is the therapeutic goal. When the intestinal lining heals, enzyme function often returns naturally, and the deficiency resolves.