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Gene diseases

The most typical gene diseases are hereditary metabolic diseases or molecular diseases. Their development is due to a change in the genes that regulate protein production. As a result of the changes, the formation of a specific protein is disrupted or completely stopped. Currently, more than 500 forms of such diseases are known. Gene diseases are conventionally divided into three groups:

1) developing in connection with the production of protein molecules with an irregular structure (hemoglobinoses S, C, D and others, common among the peoples of Asia and Africa);

2) due to a violation of the formation of a protein molecule (hemophilia, afibrinogenemia, agama globulinemia, etc.);

3) associated with impaired function of protein molecules (enzymeopathy).

The basis for the development of enzyme pathologies is the main violation of the conversion of one substance to another due to the lack of production or weak activity of the enzyme. As a result, a disturbance in the exchange chain occurs in the body - a deficiency of a number of subsequent metabolic products and the accumulation in significant quantities of the starting substance, which causes a toxic effect. One enzyme stimulates only one reaction of transformation of a substance and is controlled by one gene. The chain of exchange transformations is often long and complex, and the processes of change of substances in it are controlled by many genes. In this regard, various variations of hereditary diseases are observed due to possible changes in various genes that control individual parts of the metabolic process. For example, in the metabolism of the phenylalanine amino acid, there are three genetically determined blocks that result in phenylketonuria, alkaptonuria and albinism.

Phenylketonuria (phenylpyruvic oligophrenia)

The disease occurs in newborns with a frequency of 1: 10,000, is inherited in an autosomal recessive manner (manifested only in some cases). Due to the absence or insufficient activity of the enzyme that promotes the conversion of the amino acid phenylalanine to tyrosine, which serves as the starting material for the synthesis of thyroid hormones, adrenaline. As a result, due to insufficient protein production, phenylalanine and certain acids accumulate in the blood as intermediate products of its metabolism. Excess of these acids and phenylalanine is partially removed with urine. However, in large numbers, they linger in the body and disrupt the normal development of the child, and the nervous system and brain suffer, which is accompanied by mental retardation - oligophrenia. In addition, a violation of the normal formation of tyrosine, which is the main material for the production of hormones: adrenaline and norepinephrine, also plays a role in the formation of the disease. The development of the disease begins in the first weeks of a child’s life, but the lag in neuropsychic development becomes noticeable by 6 months. Already in early infancy, the leading sign of the disease is oligophrenia, which is rapidly progressing. There is an increase in general arousal, an increase in reflexes and muscle tone, in some cases convulsions are observed. Among other changes associated with a metabolic defect, insufficient staining of tissues and organs in patients is noted. Many of them are blue-eyed, have fair skin and blond hair. Physical functions are late - the child later begins to sit, stand, walk. Does not show interest in the environment, in parents and other children. He doesn’t say, but with a mild illness, speech begins to develop after 3 years. Often there is a mild decrease in the size of the skull and brain, congenital malformations of the heart, bone system and other organs. Growth and weight are usually kept within the age limits. Blood pressure is usually low. Sweat of patients has an unpleasant "mouse" smell.

It is important to make a diagnosis during the neonatal period or in the first months of life, because only in this case, using special diet therapy, it is possible to prevent the development of the disease at its initial stage.

Phenylalanine and its metabolic products can be found in blood and urine. The content of phenylalanine in the blood is many times higher than the upper limit of the norm (1.5 mg%). In the neonatal period, Nutria test gives more accurate results: a microbiological method based on the effect that phenylalanine has on the growth of hay bacillus (increases the number of bacteria). At a later time, at the 2-3rd month of life and later, they put the Felling test. At the same time, a 10% solution of iron trichloride is added to the patient’s urine or the test paper “Biofan II” is moistened. Dark green staining of a piece of paper or urine indicates an excess of phenylalanine and intermediate metabolic products of this amino acid (phenylpyruvic acid, phenyl lactic acid, felylacetic acid and other acids) in it.

The diagnosis is confirmed by detection in the blood using chromatography, in which the analyzed solution is passed through a column where a substance is absorbed that absorbs various molecules at different speeds. Thanks to this method, a high concentration of phenylalanine was determined (the norm for the blood serum of children is 1-2 mg%).

Treatment methods. It is necessary to reduce the number of breast-feeding and the appointment of a diet, which includes products containing a minimum amount of phenylalanine. Currently, special drugs have been proposed for the treatment of phenylketonuria - berlofen, lofenaloac, minafen, hypophenate, which are satisfactorily tolerated by patients. Give vitamins. With treatment started in late infancy, only the cessation of further disease progression can be achieved.


A disease resulting from impaired metabolism of phenylalanine and tyrosine. Due to the lack of the necessary enzyme, the process of acid formation is disrupted, as a result of which joints can be affected. At the same time, they are deformed, and their motor activity is disturbed, due to the destruction of cartilage tissue. It is also noted that acids accumulate in the body and are excreted in urine in large quantities. The disease is rare. The main manifestation of the disease in children is the darkening of urine when standing in the air due to the oxidation of homogenizinic acid. Dark brown spots remain on the diapers after such urine. In adults, the skin turns yellow. Treatment in childhood is not carried out. Adults are advised to take vitamin C in large doses.


It is also a hereditary anomaly in the exchange of aromatic amino acids (phenylalanine and tyrosine). The absence of the tyrosinase enzyme disrupts the conversion of tyrosine to dioxiphenylalanine, which is necessary for the formation of melanin, a skin pigment. The skin of such children is milky white with whitish-yellow hair. In the complete absence of melanin, translucence of the iris, photophobia, cramps of the eye muscles, in the form of spontaneous movements of the eyeballs, are noted. Intelligence usually remains normal, although cases of deafness in combination with dumbness, epilepsy, and mental retardation are described. Direct sunlight in these children causes severe inflammation of the skin. There is no cure. It is necessary to protect the child from burns in direct sunlight.

Maple Syrup Disease

Maple syrup disease develops as a result of the absence of decarboxylase, which ensures the normal exchange of amino acids: valine, leucine and isoleucine. Violation of the production of the enzyme leads to the accumulation in the body of amino acids and their decay products, which poison the central nervous system. They are excreted in the urine and give it the specific smell of maple syrup. Already in the first weeks of life, such children develop cramps, vomiting, stiff neck muscles, in which case the child cannot tilt his head forward. In this case, the disease ends with the death of the child. In children with brain disorders, the diagnosis is made on the basis of a specific smell of urine and a chromatographic study of the amino acid composition of blood serum.


Enzymopathy occurs due to a lack of the histidinase enzyme that breaks down the histidine amino acid.
In this case, children have fair hair, blue eyes, slow development of speech, incorrect pronunciation of words, some lag in physical and neuropsychic development. The level of histidine in the blood and urine is increased. When iron trichloride is added to the urine, a green color slowly appears, which holds steady. The diagnosis is confirmed by a study of the amino acid composition of blood serum using chromatography. For treatment, a diet with a minimum histidine content is recommended, vitamin therapy is performed.

Hartnup Disease

The disease is associated with impaired tryptophan metabolism, an amino acid forming nicotinic acid. Patients develop changes resembling pellagra: redness on the skin of open parts of the body, but it happens on the surface of the whole body. On the part of the nervous system, cerebellar disorders are noted in the form of a lack of coordination, impaired movement, sometimes the psyche is disturbed, depression, fear, hallucinations occur. In most patients, the intellect is preserved, but there may be a progressive delay in mental development. The diagnosis is made on the basis of the listed symptoms, elevated levels of tryptophan in the blood serum. Nicotinamide in combination with B vitamins is recommended for treatment.

Liver enzyme deficiency

Glycogenoses are diseases in which glycogen accumulates in the liver. Deficiency of glucose-6-phosphatase (type 1a) or glucose-6-phosphate translopase (type 1c) leads to a significant decrease in fasting blood glucose and 4-6 hours after eating. In the liver, this is the most important enzyme complex involved in the release of glucose during glycogenolysis (glycogen breakdown). Its deficiency leads to the accumulation of glycogen and fat in the liver, which is accompanied by an increase in the liver. Even after short starvation, before enough glucose is released, glycogen is converted into pyruvic and lactic acids. As a result, a decrease in blood sugar is combined with the accumulation of acids in the body, resulting in metabolic disturbances. In patients, the glucose level may be less than 5 mmol / l, and lactic acid is significantly higher than normal. As a rule, sick children do not experience mental retardation or a tendency to convulsions even at low glucose levels. With enzyme deficiency, glycogen breaks down only into large blocks or links. A decrease in the release of glucose from the liver leads to a decrease in blood sugar, which in most cases is offset by increased glycogen formation. This condition is characterized by an increase in the liver and stunted growth. In children with a deficiency of the phosphorylase system, which stimulate the breakdown of liver glycogen, the liver increases, muscle weakness, growth retardation, and a decrease in blood sugar are noted; the amount of glycogen in the liver is slightly increased (10% with a norm of less than 5%) and muscles (1.4% with a norm of less than 1%). Its decrease is possible after the introduction of the drug - glucogon, which may be accompanied by an increase in blood glucose. These and other defects of the liver enzyme systems are associated with the X chromosome and can be transmitted to offspring, both from the mother and from the father. With glycogenosis due to congenital deficiency of enzymes, glycogen accumulates in the tissues (skeletal muscle, heart muscle) and liver. There are several types of glycogenoses.

The first type of glycogenosis is Girke's disease. This is the most common type of glycogenosis. Already in the neonatal period, the most noticeable sign is an enlargement of the liver, which grows, and the liver reaches unusual sizes. The kidneys are also enlarged, the spleen is normal. The growth and development of the child is noticeably impaired. Even with short-term fasting, a decrease in blood sugar and the accumulation of acids appear. The deposition of glycogen in the kidneys is not accompanied by special disorders. Children lag behind in physical development. Frequent meals with a higher protein content are recommended. With a decrease in sugar and an increase in acidity, intravenous administration of glucose or sodium bicarbonate is necessary. In most cases, the disease ends in death, but some patients survive to adulthood.

The second type of hypoglycemia is Pompe disease. Among the diseases of glycogen accumulation, this form is the most malignant, patients die in infancy. This form makes up almost 10% of all glycogenoses.

The leading sign of the disease is an increase in heart beginning in infancy, followed by rapidly developing heart failure (shortness of breath, palpitations, increased blood pressure). In addition, muscle weakness and a large tongue are characteristic.

The third type of glycogenosis is Forbes disease. Due to the lack of the enzyme, abnormal glycogen is formed. The characteristic signs resulting from an enzyme defect are similar to Girke's disease, but are usually more moderate. And in this case, the liver is large and when fasting, the blood sugar level decreases. The diagnosis of glycogenosis is based on the detection of a large amount of glycogen in the blood and muscle fibers. With glycogenosis of the second type, the amount of sugar in the blood on an empty stomach does not develop, samples with a load of glucose and galactose (the patient takes sweet food before testing), as well as normal reactions to the administration of adrenaline and glucagon. The treatment is aimed at eliminating heart and respiratory failure.

Galactosemia. A disease associated with impaired conversion of galactose to glucose. Violations arise due to the lack of the necessary enzyme, and leads to the accumulation of glucose phosphate in the blood, which is toxic to the child's body. The disease is characterized by a triad of signs: an increase in the liver, cataracts and a delay in psychophysical development. The disease begins to develop shortly after birth, because a baby with breast milk begins to receive lactose, which in the intestine breaks down into glucose and galactose. The first signs are vomiting, diarrhea, increased dehydration and exhaustion. The liver grows, bile pigment bilirubin accumulates in the blood, due to which the skin and membranes of the eyes become icteric. Urine and feces retain their normal color. The level of galactose in the blood rises to 200 mg%, and it is excreted in large quantities in the urine, which is taken into account in the diagnosis. The disease usually ends with the death of the child in the first year of life. With timely treatment, especially with mild to moderate forms of the disease, the child can develop almost normally. For the purpose of treatment, from the first days of life until the age of three, a child should receive food that does not contain galactose. Female and cow's milk are excluded from food. Almond milk, synthetic milk, puddings are prescribed together, vegetable dishes and meat broth are introduced early. For infants, a domestic therapeutic dairy product is used - lactose-free enpit, in which all the useful components of milk are stored. A liquid mixture is prepared from the dry powder, sterilized by boiling and given to children from the first days of life.

Lipidosis. Hereditary diseases caused by the deposition of fats in the cells of various organs and tissues. These include: Tay-Sachs disease, Gaucher disease, Nyman-Peak disease, and some others. All these diseases are characterized by the accumulation of fats inside the cells of the body. Diseases appear already in the first months of life and often lead to the death of the child during the first year.
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Gene diseases

  1. Gene diseases
    Gene diseases are a large group of diseases resulting from DNA damage at the gene level. The term is used in relation to monogenic diseases, in contrast to a wider group - hereditary
    Gene diseases are a group of diseases that are numerous and diverse in the clinical picture, based on a mutation of one gene. Currently, about 4000 monogenic hereditary diseases are known. The nature of inheritance of gene diseases is determined by the laws of G. Mendel (see chap. V). In this chapter, we provide a brief description of some diseases with different types.
  3. Gene diseases
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  6. Hereditary Gene Diseases
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