BASICS OF MEDICAL BIOLOGY - 2012

Molecular Diseases. Biochemical Method and DNA Diagnostics. Gene (Molecular) Diseases

Gene diseases are hereditary disorders caused by Gene Mutations. The underlying cause is an alteration in the Chemical Structure of a gene (DNA molecule). Therefore, gene diseases are also referred to as molecular diseases. Classical gene mutations are inherited as Mendelian traits. They result from a mutation in a single gene (Monogenic Disorders). Generative mutations are considered full forms. Mosaic forms are also known to occur, arising when mutations take place during early zygote Cleavage in a single Cell. Such an Organism will be mosaic for the given gene: some Cells will contain the normal allele, while others will carry the mutant one. Mosaic forms of gene disorders can be diagnosed using modern molecular Genetic Methods.

Monogenic and polygenic diseases are distinguished. Monogenic disorders are caused by the action of a single mutant gene. Polygenic disorders are determined by multiple genes, the expression of which depends on environmental factors. Monogenic Diseases are inherited according to G. Mendel's Laws. Depending on the inheritance pattern, monogenic disorders are classified into autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, and Y-linked.

Autosomal dominant diseases are caused by a mutation of a dominant gene in an autosome. The pathological trait appears in every generation. The gene is phenotypically expressed in both homozygous AA and heterozygous Aa states, assuming complete penetrance and expressivity. In homozygotes, the clinical course is more severe than in heterozygotes. Recessive homozygotes aa are healthy. Examples of autosomal dominant diseases include Marfan Syndrome, Achondroplasia, Huntington's disease, Polycystic Kidney Disease, aniridia (absence of the iris), hypercholesterolemia, Steinert's disease, polydactyly (6 or more fingers), and brachydactyly (short fingers).

Autosomal recessive diseases are caused by a mutation of a recessive gene in an autosome. The inheritance pattern is autosomal recessive. Only recessive homozygotes (aa) are affected; heterozygotes (Aa) do not manifest the disease, but are carriers of the pathological gene. This group of hereditary disorders includes phenylketonuria, galactosemia, cystic fibrosis, spinal muscular atrophy, primary hemochromatosis, amaurotic idiocy, and others.

X-linked dominant diseases are caused by a mutation of a dominant gene on the X chromosome. A key feature is that an affected father (X^AY) will have all daughters affected and all sons healthy. This group of disorders includes hypophosphatemia (vitamin D-resistant Rickets), Goltz syndrome (focal dermal hypoplasia), and Coffin-Lowry syndrome (intellectual disability and osteocartilaginous anomalies).

Vitamin D-resistant rickets (hypophosphatemia) is a form of rickets that does not respond to vitamin D Treatment. Hypophosphatemia can be detected immediately after birth, while the signs of rickets appear at the end of the first or beginning of the second year of life, when children begin to walk. The most pronounced changes affect the lower limbs, specifically the bowing of long tubular bones. Characteristic features include short stature, restricted mobility in large joints, dolichocephaly, and nail Dysplasia (improper formation). The condition is caused by impaired renal tubular reabsorption of phosphates.

X-linked recessive diseases are caused by a mutation of a recessive gene on the X chromosome. The inheritance pattern is X-linked recessive. This group includes hemophilia, color blindness (daltonism), Duchenne muscular dystrophy, Lesch-Nyhan syndrome, and others.

Hemophilia is a classic example of an X-linked recessive abnormal gene that is phenotypically expressed in males. In heterozygous females, its effect is suppressed by the dominant allele for normal Blood clotting. Fathers with hemophilia never transmit the hemophilia gene to their sons. Therefore, their sons are healthy, but all their daughters are born as disease carriers. Various clinical manifestations of hemophilia are observed—ranging from mild bleeding to massive hemorrhages. This likely depends on different mutations of the same gene. The two most common forms of hemophilia are A and B. They are characterized by the absence of specific antihemophilic globulins in Blood Plasma. The frequency ratio of hemophilia A to B is 5:1. Both forms of hemophilia occur with a frequency of 1:5000 newborn boys.

Color blindness (Daltonism) is one of the most common hereditary disorders linked to the X chromosome. It is characterized by impaired color perception (primarily red and green). Its inheritance principles are identical to those of hemophilia.

Y-linked diseases. The mutant gene is localized in the non-homologous region of the Y chromosome. Inheritance is exclusively patrilineal (through the male line). Examples include hypertrichosis and ichthyosis.

Monogenic diseases are also divided into groups based on The Nature of the metabolic or structural disruption:

- enzymopathies (metabolic enzyme defects);

- defects in structural and transport Proteins;

- disorders of circulating blood proteins;

- gene diseases with an unknown primary biochemical defect.

According to the WHO Classification, monogenic or molecular diseases are divided into the following groups defined by metabolic or structural impairments:

1) Amino acid METABOLISM disorders: phenylketonuria, tyrosinemia, alkaptonuria, homocystinuria, cystinuria, Hartnup disease, tryptophanemia, maple syrup urine disease, histidinuria, histidinemia, and others;

2) Carbohydrate Metabolism disorders: galactosemia, fructosemia, Glycogen Storage Diseases, carbohydrate malabsorption syndrome, Mucopolysaccharidoses;

3) Lipid Metabolism disorders: hyperlipoproteinemias, sphingolipidoses (Niemann-Pick disease), gangliosidoses (Tay-Sachs disease);

4) steroid metabolism disorders: adrenogenital syndrome;

5) purine and pyrimidine metabolism disorders: Lesch-Nyhan syndrome;

6) Connective Tissue, bone, and Muscle metabolism disorders: Marfan syndrome;

7) heme and porphyrin structure disorders: hemoglobinopathies, Sickle cell anemia, thalassemia;

8) metabolism in erythrocytes and structural abnormalities thereof: hereditary microspherocytosis;

9) metal metabolism disorders;

10) disorders characterized by defective transport of various substances;

11) disorders characterized by structural anomalies: Functions of Enzymes and Plasma Proteins.

The basis of genetic diseases is mutations in the respective genes, which lead to the synthesis of enzymes with altered activity. In homozygotes, enzyme activity is low, leading to specific Metabolic Disorders, whereas in heterozygotes, activity is often around ≈ 50%, which is why most of these disorders are inherited in an AR or XR manner.

Metabolic changes follow this pathway:

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Therefore, enzyme mutation results in an excess of certain substances (B, D) and a deficiency of other products (C, G). Enzymopathies constitute the largest group of genetic diseases. The enzyme either alters its Structure and Functional properties or is not formed at all. In such cases, the biochemical reaction involving this enzyme is blocked. This may result in: 1) insufficient Formation of the products of this reaction or more distant conversion products; 2) accumulation in the organism of the substrate of the blocked reaction or its precursors; 3) a shift in the main reaction pathway and increased production of substances that are normally present in negligible amounts.

Diagnostics of enzymopathies is carried out using Biochemical Methods. Early Diagnosis and pharmacological or dietary correction make it possible to treat and prevent The Development of these inherited disorders.

Phenylketonuria is an inherited disease—an enzymopathy caused by a genetic deficiency of the enzyme phenylalanine hydroxylase, which is necessary for converting The amino acid phenylalanine into Tyrosine. This leads to the accumulation of phenylalanine, phenylpyruvate, and phenylacetate in the blood, CEREBROSPINAL FLUID, and Tissues, exerting a toxic effect on the Central Nervous system. Children are born healthy, but as phenylalanine enters the body through mother's milk, mental retardation gradually develops. Since impaired phenylalanine metabolism leads to decreased tyrosine levels, patients exhibit reduced pigmentation of the Skin, Hair, and irises. The frequency of phenylketonuria in European populations averages 1:10,000 newborns. The inheritance pattern is autosomal recessive. The phenylalanine hydroxylase gene is located on chromosome 12.

Clinical diagnostic features include fair hair, blue eyes, unpigmented skin, a "mousy" odor (due to urinary excretion of phenylalanine); after 6 months—drowsiness, lethargy, loss of all acquired psychomotor functions, seizures, and progressive mental retardation up to idiocy.

The diagnosis is established based on clinical examination and biochemical detection of phenylpyruvate in urine and phenylalanine in blood. Treatment involves diet therapy: the exclusion of phenylalanine-containing foods (eggs, meat, milk) from the diet. Early diagnosis and diet therapy prevent the Development of the clinical picture of the disease.

Albinism is an inherited disease—an enzymopathy caused by a deficiency of the enzyme tyrosinase, which catalyzes reactions necessary for The production of dark pigments—Melanins. The absence of melanins in skin melanocytes manifests as insufficient (or absent) pigmentation of the skin and hair, increased skin sensitivity to sunlight, and visual impairment. The inheritance pattern is autosomal recessive.

Alkaptonuria is an inherited disease with an Autosomal Recessive Inheritance pattern, caused by a genetically determined deficiency of homogentisic acid oxidase. A characteristic manifestation of the disease is the excessive excretion of homogentisic acid in the urine, which turns dark upon The addition of alkalis. Homogentisic acid accumulates in connective tissue. Articular Cartilage turns yellow-orange (ochronosis), the cartilage of the auricles and Nose darkens, and Arthritis develops.

Tyrosinosis (tyrosinemia) is a defect in tyrosine aminotransferase or p-hydroxyphenylpyruvate oxidase. It is accompanied by the accumulation of tyrosine in the Blood and Its excretion in the urine, leading to Homeostasis disruption. In its acute form, the disease is characterized by delayed infant development, hepatosplenomegaly, hemorrhages, and renal changes. Without treatment, infants die in infancy from Liver or respiratory failure. The chronic course of the disease is characterized by liver cirrhosis, rachitic bone changes, and renal tubular lesions. The inheritance pattern is autosomal recessive.

Leucinosis (maple syrup urine disease) involves mutations in three different enzymes (decarboxylase, transacylase, a flavin enzyme), disrupting The oxidative decarboxylation of the 3 keto acids derived from leucine, isoleucine, and valine. Clinically, several forms of this disease are distinguished—classic, intermediate, mild, and thiamine-responsive. The main symptoms are associated with nervous system damage: seizures, respiratory disorders, and an excess of keto acids in the urine giving it a maple syrup odor.

Inherited Disorders of Carbohydrate Metabolism include galactosemia and mucopolysaccharidosis.

Galactosemia is a disorder of Galactose Metabolism, which comes from diet and is produced during lactose Hydrolysis. The inheritance pattern is AR, with homozygote enzyme activity at 3–12% of normal, and heterozygote activity at 50%. The frequency is 1:35,000–150,000 births. Galactosemia is characterized by heterogeneity (various gene mutation variants). For example, galactosemia with a mild clinical picture occurs with a frequency of 1:100,000–200,000. Phenotypically (clinically), it manifests as neonatal jaundice, vomiting, diarrhea, mental retardation, liver damage, and dystrophy. With early diagnosis, the child is prescribed a special diet (similar to phenylketonuria)—excluding mother's milk and other products containing lactose or galactose. Development normalizes.

Mucopolysaccharidoses are inherited diseases involving impaired glycosaminoglycan (GAG) metabolism and GAG accumulation due to mutations in lysosomal enzymes (Hydrolases). Genetic heterogeneity is determined by mutations in different genes encoding various enzymes. The inheritance pattern is AR, XR. Phenotypically (clinically), they manifest as developmental disorders (dwarfism, facial dysmorphism, joint stiffness, microcephaly, early mortality at 12–20 years). Large amounts of mucopolysaccharides are excreted in the urine. The most common are Hurler syndrome (gargoylism) and Hunter syndrome (mucopolysaccharidosis type II).

Inherited defects of lipid metabolism—sphingolipidoses—involve impaired lipid breakdown and plasma lipid metabolism disorders. Inheritance pattern: AR, XR. The frequency of various forms ranges from ≈ 1:4,000 to 1:300,000 newborns, and frequencies can vary significantly across populations. Inherited purine and pyrimidine disorders. Example: Lesch-Nyhan syndrome. Frequency: 1:300,000. The inheritance pattern can be XR or AR. Metabolic defect: deficiency of an enzyme required for DNA Synthesis. Uric acid accumulates in the urine of patients. Phenotypic abnormalities: mental retardation, sympathetic paralysis, purine metabolism disorders, aggressive behavior, urolithiasis.

Inherited defects of vitamin metabolism—homocystinuria—genetic defect of Vitamin B6 and B12 Coenzymes (pyridoxine-dependent enzymopathies). AR inheritance pattern. Population frequency: 1:50,000. Characteristic phenotypic diversity is determined by heterogeneity. Ocular lesions (ectopia lentis), skeletal changes, mental retardation, blood vessel dilation, thrombosis, central nervous system dysfunction, and dementia are observed.

Inherited diseases—disorders of steroid hormone Biosynthesis occur with a frequency of 1:5,000–10,000; AR inheritance pattern. This group includes:

adrenogenital syndrome (mutations in genes controlling the synthesis of androgens—male Hormones; testicular feminization, in which androgen receptors are not formed). In these diseases, sex differentiation is disrupted (pseudohermaphroditism), along with anomalies and Malformations of the genital Organs (hypospadias, hypoplasia).

Hemoglobinopathies are a group of inherited diseases in which Hemoglobin (Hb) protein chains are impaired, leading to changes in their functions and properties. Such diseases include methemoglobinemia, erythrocytosis, sickle cell anemia, and thalassemia.

The best-known disease is sickle cell anemia, which occurs with high frequency in malaria-endemic regions. The inheritance pattern is autosomal incompletely dominant. The mutant gene (S) causes the synthesis of hemoglobin S, which alters the shape of erythrocytes (see figure) and binds oxygen poorly, resulting in anemia and Hypoxia. Heterozygotes have both normal HbA and mutant HbS, but they are resistant to malaria.

Thalassemias are disorders characterized by a reduced content of the globin protein in the hemoglobin (Hb) molecule. Their inheritance pattern is AR, or they arise As a result of deletions. Molecular genetic methods and Electrophoresis are used to diagnose specific types of thalassemias.

Collagen diseases are fundamentally rooted in genetic defects of collagen BIOSYNTHESIS AND DEGRADATION (a structural component of connective tissue). This group includes Ehlers-Danlos syndrome, which is characterized by genetic polymorphism and AD or AR inheritance patterns, as well as Marfan syndrome (AD inheritance). Phenotypically, the pleiotropic effect of mutant genes manifests as joint hypermobility, increased skin elasticity, internal hemorrhages, joint abnormalities, and blue sclerae. Primary defects involve impaired collagen biosynthesis or the Processing of fibrils and collagen.

Hereditary single-gene disorders with an unknown primary biochemical defect include:

1) Achondroplasia (AD inheritance, frequency 1:100,000; arises from a de novo mutation). Phenotypically, it manifests as skeletal abnormalities (impaired cartilage formation in the epiphyses of tubular bones and Skull bones).

2) Cystic fibrosis (AD or AR inheritance, frequency 1:2,500 newborns). The Pathogenesis of all forms is fundamentally based on the involvement of exocrine glands (secreting Cells of the Bronchi, Pancreas, intestines, Sweat Glands, and liver), accompanied by the secretion of thick mucus, along with inflammatory and sclerotic Changes in the organs. The main forms are pulmonary and intestinal. Diagnosis relies on specialized comprehensive tests (determining Na content in secretions, assessing digestive enzyme activity...). It is believed that a significant number of cases in children go undiagnosed.

3) Myopathies (muscular dystrophies), a group of Hereditary diseases affecting striated and smooth Muscles. The inheritance pattern may be XR, AD, or AR. Myopathies are characterized by progressive muscle degeneration with age and pronounced clinical polymorphism.

Human Erythrocyte Shapes

Fig. 35. Changes in erythrocyte shape in Sickle-Cell Anemia.

Diseases with Hereditary predisposition. Diseases with a hereditary predisposition (Multifactorial Diseases) are caused by a combination of genetic and non-genetic factors. The latter are related to the environment. For these diseases to manifest, not only a susceptible genetic constitution of the individual is required, but also an environmental factor or a complex of factors that serve as triggers in the development of the pathology. Such conditions include atherosclerosis, Gout, rheumatism, ischemic Heart disease, Hypertension, Epilepsy, PEPTIC ULCER DISEASE of The Stomach and duodenum, liver cirrhosis, Diabetes Mellitus, Bronchial Asthma, tuberculosis, psoriasis, Schizophrenia, and others.

Characteristic Features of multifactorial diseases: 1) extensive polymorphism of clinical forms and individual manifestations, with transitional forms ranging from healthy individuals to patients, and from subclinical presentations to severe courses; 2) high population frequency (diabetes mellitus affects 5% of the global population, allergic diseases over 10%, schizophrenia 1%, and hypertension about 30%); 3) non-compliance with Mendel's laws of inheritance; 4) variable age of onset.

What is transmitted hereditarily is a predisposition to a specific disease. For certain clinical forms, The Role of the familial (genetic) factor is decisive. The degree of risk for a patient's relatives depends on the disease frequency in the population and increases with the severity of the patient's condition. The closer the degree of biological kinship to the affected individual, the higher the probability of having an affected child. In some cases, the frequency of pathology varies depending on sex; for instance, congenital hip dysplasia is more common in girls, whereas pyloric stenosis is more frequent in boys.

Diseases with a hereditary predisposition can be monogenic or polygenic. They are fundamentally based on polygenic inheritance and frequently heterozygosity. In polygenic inheritance, a trait is determined by several non-allelic genes, but its expression depends on environmental conditions. In heterozygous carrier states, the pathological recessive gene is not manifested in the heterozygous condition, but it may manifest under unfavorable living conditions. Because diseases with a hereditary predisposition are determined by a combination of hereditary and environmental factors, they are classified as disorders with penetrance that is largely dependent on environmental conditions. By modifying environmental factors, the expression of such diseases can be significantly altered or even prevented. Monogenic disorders are numerous (>3,000 different diseases) and are characterized by heterogeneity (different mutations in any region of the gene for the respective enzyme, or in various non-allelic genes) and phenotypic (clinical) polymorphism. Heterogeneity has been established for the majority of monogenic diseases, such as phenylketonuria (>15 forms), galactosemia (>12 forms), albinism (>6 forms), and others (at the phenotypic level, heterogeneity manifests as various variants of clinical presentations of hereditary pathology). For certain diseases, heterogeneity is determined by the presence of genocopies (mutations of different non-allelic genes that cause identical metabolic disorders), which also dictates the genetic diversity and clinical polymorphism of hereditary diseases. Examples of human genocopies include classical and diet-resistant forms of phenylketonuria, as well as Various Forms of hemophilia and collagenoses.

Biochemical Methods

Biochemical methods make it possible to diagnose hereditary diseases caused by gene mutations that result in metabolic disturbances or structural alterations, as well as molecular polymorphism in molecular disorders.

There are two main approaches:

1) studying the metabolic products of genetically determined processes (an increase or decrease in the concentration of specific metabolites indicates A change in enzyme activity or its mutation);

2) identifying structural abnormalities in transport Proteins and Enzymes.

Biochemical diagnosis of hereditary disorders is carried out in 2 stages. At the first (screening) stage, rapid methods are used to select the most probable cases of the disease, while at the Second Stage, the diagnosis is refined using more complex methods. Microbiological testing is commonly employed for rapid diagnostics.

Biochemical methods are also used in prenatal or postnatal Diagnosis of Monogenic Disorders, enabling timely detection of pathology and the Implementation of specific medical interventions (preventive or therapeutic).

Introduction/32.html">Genetic Engineering

Genetic engineering is a set of experimental techniques used to transfer genes from one organism to another with the aim of purposefully conferring new hereditary traits upon the recipient. Taxonomic barriers do not exist for genetic engineering. It allows for the manipulation of genetic material from diverse sources and enables the programmable construction in vitro of functionally active recombinant (hybrid, chimeric) DNA molecules that do not occur in nature. The prefix "re-" implies that the DNA is not created de novo (anew), but is instead formed by joining fragments of pre-existing molecules. Recombinant DNA molecules are termed chimeric because they can combine seemingly incompatible Genes from different organisms. The theoretical foundation of genetic engineering is the universality of The Genetic Code.

Genetic engineering encompasses the following stages: 1) obtaining genes via artificial (chemical or template-mediated) synthesis or by isolating them from natural sources; 2) inserting the gene into a vector DNA molecule, thereby creating recombinant DNA molecules; 3) introducing the vector DNA molecule carrying the inserted gene into a recipient cell; 4) establishing conditions for the expression of the transferred gene and its stable inheritance; 5) selecting cells containing the active transferred gene, known as molecular cloning.

The artificial Chemical synthesis of a gene was first accomplished in 1969 by the Indian scientist H. Khorana and his coworkers. This was the Yeast Alanine tRNA gene, consisting of 77 nucleotide pairs. However, the synthesized gene lacked a regulatory region and was therefore functionally inactive. Later, these authors synthesized a functionally active gene—the suppressor tyrosine tRNA gene of E. coli, approximately 200 nucleotide pairs in length. Chemical gene synthesis was facilitated by the development of Methods for determining the Primary Structure of DNA, namely The nucleotide sequence within its molecule (sequencing). The chemical gene synthesis method opened up broad possibilities for the artificial synthesis of human genes. The human Growth Hormone (somatotropin) gene and the human Insulin gene have both been obtained via chemical synthesis.

Artificial template-mediated gene synthesis is carried out using the enzyme Reverse Transcriptase (revertase). This enzyme is capable of synthesizing DNA copies on various RNA templates, including synthetic ones. Using the template method, virtually any gene can be synthesized on an mRNA template. In this manner, the gene for human interferon—a valuable pharmaceutical agent used to combat viral infections—was synthesized.

The method of isolating a gene from natural DNA is based on incubating total DNA with various Restriction Endonucleases (restriction enzymes). Restriction enzymes are enzymes ("molecular scissors") that cleave DNA molecules at specific sites into fragments (restriction). These fragments are then separated by electrophoresis, isolated in pure form, and their nucleotide sequence is determined.

After obtaining genes through synthesis or isolation from natural sources, the next step in genetic engineering is inserting the target gene into a vector DNA molecule. Plasmids, Bacteriophages, certain Viruses, and Mitochondrial DNA serve as vectors. Plasmids are most commonly used as vectors. Plasmids are small, extrachromosomal circular DNA molecules capable of autonomous Replication; they reside in the Cytoplasm of a bacterial cell or are integrated into its chromosome, in which case they are called episomes. Episomes replicate as part of the chromosome. The circular vector DNA molecule is cleaved by restriction enzymes into linear fragments. Vector DNA fragments and foreign DNA fragments can join together via complementary ("sticky") ends to form a single recombinant (hybrid) DNA molecule. Phosphodiester bonds between NUCLEOTIDES are formed using ligase enzymes. The transfer of target genes (transgenesis) is achieved through various methods: transformation (if the vector is a plasmid) or Transduction (if the vector is a bacteriophage).

Genetic engineering METHODS have enabled the creation of Transgenic Plants and animals (organisms carrying foreign genes). Transgenic Animals are used in biomedicine as models for human diseases (mice carrying Cancer genes, pigs with human heart pathologies, cows producing human IMMUNOGLOBULINS in their blood). Progress is also being made toward producing human blood proteins in the milk of transgenic animals.

To a large extent, the success of genetic engineering is owed to the creation of gene banks (libraries). A gene bank is a collection of genes derived from recombinant molecules. A geneticist can screen a gene library to isolate genes of interest for research using specially developed genetic, biochemical, radioisotope, or immunological methods. Gene banks have been established for Drosophila, Escherichia coli, and many other organisms, including humans.

Genetic engineering was born in 1972 when American geneticists P. Berg, H. Boyer, and S. Cohen created the first in vitro recombinant DNA molecule, combining genetic material from three distinct sources: the complete genome of the oncogenic simian virus SV40, a segment of the temperate bacteriophage λ (lambda) genome, and the GENES OF THE galactose Operon of Escherichia coli (E. coli). However, the functional activity of this constructed recombinant molecule was not tested out of concern that genetic engineering techniques might produce organisms hazardous to human health. Interfering with an organism's genotype can lead to unforeseen consequences for humans, plants, animals, and the environment as a whole. For instance, Escherichia coli, normally harmless under standard conditions, could potentially transfer oncogenic animal viruses into the human gut. Specially engineered biological agents designed to harm Living organisms are classified as biological weapons. The International Conference on Recombinant DNA Molecules held in Asilomar, USA, in 1975 established safety guidelines to eliminate potential hazards associated with genetic engineering. In 1985, the Biosafety Information Working Group was formed.

Biotechnology

Biotechnology (from Greek bios - life, techne - craft/art, logos - science) is the discipline that studies the application of living organisms or biological processes in industry. Biotechnological methods have been known to humanity for ages. Microorganisms are widely used in industries such as winemaking, baking, brewing, and cheesemaking. To produce BIOLOGICALLY ACTIVE SUBSTANCES (Antibiotics, hormones, enzymes, Vaccines), modern biotechnology relies on the latest Achievements of Genetic engineering in constructing recombinant DNA molecules. A new branch known as the DNA industry has emerged within the pharmaceutical sector. The microbiological industry utilizes transgenic strains of the bacterium Escherichia coli (E. coli), into which human genes encoding the synthesis of human insulin, interferon, and somatotropin have been introduced via genetic engineering techniques. Consequently, Bacteria synthesize these therapeutic substances under industrial conditions. Microbiological synthesis is an exceptionally efficient process. For instance, obtaining 5 mg of somatotropin (growth hormone) traditionally required processing the brains of 500,000 sheep over 5 years, whereas an equivalent amount of the hormone can be yielded from just 9 liters of an Escherichia coli broth culture.

Prospects of Gene Therapy

Gene Therapy is a method of introducing a DNA fragment into the cells of a patient to compensate for a mutated gene's function and treat hereditary disorders. As early as the late 1960s, it was discovered that animal and human cells are capable of taking up exogenous DNA and integrating it into their genome, which subsequently leads to the expression of the introduced genes—specifically resulting in the synthesis of previously absent proteins and enzymes. Methods for delivering DNA into cells using viruses and other vectors were subsequently developed.

The first clinical attempt at gene therapy was performed by M. Cline in 1983, when he introduced a normal β-globin gene into patients with β-thalassemia. Later, a gene therapy protocol was developed for hereditary adenosine deaminase deficiency (severe combined immunodeficiency): a normal gene was introduced into the patient's Bone Marrow cells, and following their retransplantation, enzyme activity was restored, leading to an improvement in the patient's condition. Clinical experiments in cancer gene therapy have also been conducted. Marker genes were introduced into the leukocytes of patients with malignant melanoma and advanced-stage cancer to tag malignant cells so they could be recognized by The Immune System. In half of the patients, tumor sizes decreased by half or more. Gene therapy methods have been developed for approximately 40 diseases. This approach is set to expand rapidly in the near future, largely owing to the decoding of The Human Genome.