Insufficiency of intestinal disaccharidases
Mar 16, 2018
Hereditary defects in the intestinal disaccharidase system are manifested by persistent gastrointestinal disorders and dystrophy, which is caused by a disruption in the cleavage and absorption of disaccharides in the intestinal mucosa. In 1958, P. Durand discovered in a child with hypotrophy a low activity of the enzyme that breaks down the milk sugar, while a significant amount of lactose was detected in the patient's urine. It should be said about the autosomal dominant type of inheritance.
Lactase deficiency occurs more often than other forms of disaccharidic insufficiency, therefore it attracts the most attention, since milk and dairy products are the main food of many peoples, especially in childhood. If in Europe the deficiency of lactase is relatively rare( 2-30%), in some parts of Africa and Asia - more than 90% of the total population. In our country, only a single population study of the spread of the disease.
Already in the first reports on ethnic differences in the incidence of lactase deficiency, there are suggestions about the genetic nature of this kind of pathology, according to which the ability of lactose cleavage in adults is considered an inherent property inherited. The ability to break down lactose( milk sugar) is transmitted by an autosomal dominant type with a high incidence of the mutant gene, and the primary lactase deficiency is autosomal recessive. There is a so-called geographical variant of the genetic hypothesis, the essence of which is as follows. It is assumed that in the Paleolithic epoch, in humans, as in other mammals, after the end of the feeding period, the activity of lactase in the intestine decreased significantly or disappeared altogether, but in some individuals lactase activity persisted for life. When dairy farming arose and dairy products appeared, lactose absorbers began to predominate in certain geographical areas where the population was fed milk and its products. Special calculations show that, since the beginning of the use of milk, enough time has passed for appropriate selection to take place. So, in Finland, where milk is consumed for about 3000 years, lactase deficiency occurs in 17% of the population. Inhabitants of the northern regions of Finland, the Laplandians consume milk only 150-300 years old, and their detection rate is 34%.Of course, one can hardly agree with the fact that only the activity of lactase in the intestine can become a leading factor in selection. Presumably, resistance to infection and other genetic features contributed to survival. The ability of splitting lactase, obviously, must be considered as one of the components of a multifactorial selection process.
There are hypotheses about the existence of other genetic mechanisms of lactase deficiency. The congenital deficiency of the enzyme that breaks down the milk sugar is explained by the mutation of the gene responsible for the synthesis of lactase, as a result of which this enzyme is either not synthesized at all or its inactive form is formed. If adult lactase is deficient, a mutation of the genes is assumed, resulting in a normal enzyme structure, but this process is very slow, possibly due to hormonal disorders. This viewpoint considers lactase deficiency as a mutation, as a defect of certain genes, and the ability to split lactase - as a human species ability. In addition to the genetic theory of lactase deficiency, which, despite certain shortcomings, has been universally recognized, hypotheses are considered that are considered as a consequence of intestinal diseases, as well as the assumption that the enzyme deficiency arises from the inhibitory effect of certain foods on the activity of lactase in the intestinal mucosa. In people who eat milk, the level of the enzyme in the intestinal mucosa is high, and among people who use it in small quantities or do not at all eat milk products, there is often a deficit. However, all attempts by the researchers to cause an increase in the amount of lactase( enzyme) with the help of lactose or milk nutrition were unsuccessful.
Sahaznom-isomaltaznaya failure - a variant of hereditary intolerance of disaccharides, caused by a decrease in the activity of enzymes such as isomaltase and maltase, as well as the absence of an enzyme invertase in the intestinal mucosa. The genetic nature of this pathology has been revealed. Some authors talk about autosomal dominant inheritance, others argue that the inheritance of a sugar deficiency is autosomal recessive, especially in cases of blood marriages. Homozygous individuals remain intolerant to sucrose for life, while in heterozygous the enzyme deficiency can be asymptomatic, or the sugar deficiency is noted only in childhood. Boys and girls suffer equally.
The incidence of such enzymes as sucrose, isomaltase and maltase is quite rare. There is a congenital defect of the enzyme sucrose, as a result of which sucrose is not broken down into glucose and fructose. Insufficiency of maltase and isomaltase is usually combined with deficiency of other disaccharidases. With severe starch intolerance, in addition to the deficiency of maltase and isomaltase, chronic pancreatic insufficiency should be kept in mind, as well as the extremely rare condition of congenital absence of pancreatic amylase. With maltose and isomaltaznym deficiency can be combined lactase deficiency, especially acquired. Combined sucrose, isomaltase and maltase deficiency occurs much more often. The loss of function of several enzymes is a consequence of one mutation or polyfunctionality of the missing enzyme, which explains the combination of exchange defects and the cleavage of several disaccharides. It is believed that the structural gene controlling the synthesis of several enzymes is damaged by toxic or infectious effects, or the same factor, toxic or infectious, damages several enzymes simultaneously.