Disaccharidase deficiency

　　The causes and pathogenesis of disaccharidase deficiency:

　　Etiology
　　Normal small intestinal mucosa contains various disaccharidases, such as lactase, which can break down lactose into galactose and glucose; maltase, which can break down maltose into glucose and isomaltose; isomaltase, which can break down isomaltose into two molecules of glucose; sucrase, which can break down sucrose into glucose and fructose; and trehalase, which can break down trehalose into two molecules of glucose. Due to some reasons, the deficiency of disaccharidases can cause obstacles in the digestion and absorption of disaccharides, leading to diarrhea. This disease is not uncommon in clinical practice, but it is often not paid much attention to.

　　Pathogenesis
　　Infants may have deficiencies in sucrase and isomaltase due to genetic factors. The defect in the absorption of sucrose and isomaltose is mainly in sucrose, while the defect in isomaltose is secondary. Studies have shown that the enzyme has a defect in processing within the cell, accumulates in the endoplasmic reticulum, and the enzyme complex is blocked in the Golgi apparatus, while the altered enzyme is transported to the cell surface. Due to these various factors, this monogenic disease can present with heterogeneity. The gene for human lactose permease hydrolase is located on chromosome 2. When the villi of the small intestine of infants lack lactase, water泻 appears after the first breastfeeding.
　　The most common form of disaccharidase deficiency in adults is lactase deficiency. The activity of lactase is highest at birth and can decrease to 10% of its maximum level later on. Individuals with lactase deficiency are at this level. After weaning, lactase gradually decreases, and consuming milk can easily cause diarrhea. This enzyme deficiency is related to heredity, accounting for 5% to 30% in whites, while 75% of cases are in people of color, including Asians and Africans.

　　Deficiency of disaccharidase has a significant impact on infants and young children, with common complications including diaper rash, delayed growth and development, and chronic diarrhea can cause infants to lack calcium, zinc, iron, and anemia. In severe cases, complications can threaten the life of the child. The main symptoms of adult disaccharidase deficiency are diarrhea, and it usually does not lead to severe complications.

　　When lactase is deficient, consuming milk or lactose can cause borborygmi, abdominal pain, or even colic, and severe diarrhea can cause watery stool with an acid smell and foam. Symptoms disappear after stopping the consumption of foods containing lactose. The patient's general condition is usually good. When sucrose and isomaltose are deficient, diarrhea occurs after consuming sucrose and starch, and the symptoms are similar to those of lactase deficiency.
　　1. Congenital lactase deficiency:Infants may experience vomiting soon after eating breast milk or cow's milk, accompanied by dehydration, acidosis, galactosemia, and aminoaciduria. The condition is severe, and the prognosis is poor.
　　2. Congenital lactose intolerance:This is a disease different from congenital lactase deficiency, belonging to autosomal dominant inheritance. Infants may experience explosive diarrhea, watery and foamy acidic stools, accompanied by diarrhea, which can lead to vomiting, dehydration, tubular acidosis, and liver and brain damage. If diagnosed too late, it can cause death. The diarrhea disappears after stopping breastfeeding, and there is no galactosemia and aminoaciduria.
　　3. Adult acquired lactose intolerance:Drinking cow's milk can cause watery acidic stools accompanied by abdominal discomfort such as bloating.
　　4. Malabsorption of sucrose and isomaltose:It is caused by a deficiency of sucrose α-amylase, which leads to high osmotic pressure and fermentative diarrhea in the intestinal lumen due to excessive unabsorbed sucrose, resulting in acidic stool, with a pH of 4.0 to 5.0, a sour taste, and a large amount. Generally, infants have severe diarrhea, while adults may only experience discomfort in the stomach, and symptoms may appear after consuming sweet foods and fruits.
　　5. Trehalase deficiency:Trehalase deficiency is less common. Patients may experience abdominal pain, diarrhea, bloating, and vomiting after eating mushrooms, and the stool is often watery. Mushrooms contain trehalose, which is a 1,α-glucose-1-α-glucoside.

　　Preventive measures for disaccharidase deficiency mainly include:
　　1. Consume milk products in small amounts multiple times.Even for individuals with lactase deficiency, consuming small amounts of milk products multiple times can reduce lactose intolerance reactions, and it is recommended not to exceed 250ml per time. As long as the reasonable interval time between each milk consumption and the total daily milk intake are controlled, lactose intolerance symptoms can be avoided.
　　2. It is not advisable to drink milk on an empty stomach.People with lactose intolerance should not drink milk on an empty stomach in the morning. Drinking milk while eating other foods, such as dairy products, meat, and fatty foods at the same time, can alleviate or prevent lactose intolerance symptoms.
　　3. First, use fermented milk instead of fresh milk.Lactose in fermented milk has already been degraded by 20% to 30%, making it easy to digest and absorb. Eating yogurt can also improve lactose malabsorption and lactose intolerance, and it is very convenient to eat.
　　4. Drink goat milk.Goat milk has a lower lactose content than cow's milk and is rich in ATP (adenosine triphosphate) components, which can promote the decomposition and utilization of lactose, making it less likely to cause lactose intolerance after consumption. It is recommended to drink goat milk for infants, as it is more nourishing to the stomach than cow's milk and contains more nutrients on average.

　　The main methods of examination for lactase deficiency are:
　　1. Stool examination Acidic stool, pH 5.0-6.0.
　　2. Lactose tolerance test 50g of lactose mixed with 400ml of warm water is taken on an empty stomach. Blood is drawn to measure blood sugar before and 15, 30, 60, 90, and 120 minutes after taking the test. During the test and for several hours after the test, observe the patient's symptoms and check the nature of the stool. Blood sugar levels above 1.4mmol/L are normal, below 1.1mmol/L are abnormal, and between 1.1 and 1.4mmol are uncertain. Lactose test patients often have colic and diarrhea during the test or after the test.
　　3. Lactose hydrogen breath test Oral lactose 1g/kg, if the hydrogen in the exhaled air exceeds the baseline by 20×10-6, it indicates poor lactose absorption. Lactose ferments in the intestinal lumen to produce too much water. Lactase is genetically regulated at the gene level; type I is the reduction of lactase rhamnosidase activity; type II is abnormal post-translational processing and retention in the endoplasmic reticulum. This low lactase is an autosomal recessive inheritance.
　　4. Small intestinal mucosal biopsy Intestinal mucosal active test determination of lactase, showing low activity.

　　Consume dairy products in small amounts multiple times. Even individuals with lactose intolerance can tolerate small amounts of milk (120ml to 240ml) without intolerance symptoms. Limit the total intake of lactose in a day, with a general lactose limit of 12 grams. Eating in small amounts multiple times can also reduce lactose intolerance reactions, and it is advisable to not exceed 250ml in one sitting. As long as a reasonable interval and daily total milk intake are maintained each time milk is consumed, lactose intolerance symptoms can be avoided.

　　Lactase deficiency mainly involves restricting diet, avoiding milk and lactose-containing foods. For mild cases, milk intake is limited, and for severe cases, complete fasting is required. Infants can be given sugar-free milk or added lactase. Those with sucrose-isomaltase deficiency should limit the intake of sucrose and, if necessary, limit starch intake. In addition, it is necessary to actively treat the primary disease, such as adult celiac disease, lymphoma, and excessive bacterial overgrowth in the small intestine.