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FEATURES OF CLINICAL MANIFESTATIONS OF HEREDITARY DISEASES
Despite the diversity of the clinical picture of hereditary diseases, their common features can be distinguished, which allows to identify or exclude the presence of pathology in the subject. The basis for the formation of a community of clinical characteristics of various forms of hereditary diseases is the genetic control of key links in metabolism and morphogenetic processes.
Although hereditary diseases, like any other diseases, have their own characteristic features, none of the following features can be considered as something absolute: only the presence of characteristic features as a whole allows one to suspect a hereditary pathology in a patient.
TIME FOR MANIFESTATION OF HEREDITARY DISEASES
Most inherited diseases are recognized in perinatal and early childhood. As a rule, the first symptoms of the disease are diagnosed from birth or shortly after. For example, some hereditary syndromes accompanied by malformations (cleft lip or palate, extra fingers on the hand and foot, lack of limbs, defects of the anterior abdominal wall, umbilical hernia, non-perforated anus, etc.) may be suspected from the moment of birth. An example of an early manifestation (or congenital character) of hereditary diseases is- By about 3 years another 50% of gene diseases appear. However, hereditary diseases with late manifestations are known (Alzheimer's disease, Huntington's chorea).
It must also be emphasized that there are a number of differences in diseases that manifest themselves at different age periods of postnatal ontogenesis (Table VIII.2)
The table shows that with age, the incidence of monogenic diseases decreases and the proportion of diseases increases, the manifestation of which requires the participation of environmental factors.
In general, the presented differences in the characteristics of diseases can be explained by a decrease in the lifetime contribution of hereditary factors to their etiological structure.
> PROGRESSION AND CHRONIC CHARACTER OF HEREDITARY DISEASES
Progression is called the course of the disease with a constant deterioration in the general condition and with an increase in negative symptoms in the patient. Many hereditary diseases are characterized by a gradual increase in their severity as the pathological process develops. For example, with phenylketonuria, as a child grows up, symptoms of psychomotor retardation arise and increase, mental retardation and secondary microcephaly form; with Tay-Sachs disease, starting from 6 months of age, demyelination of nerve fibers develops, which gradually leads to death. For hereditary diseases starting at any age, a chronic course is characteristic. For example, children with Verdnig-Hoffmann spinal amyotrophy gradually lose their motor activity as a result of the death of motor neurons of the anterior horns of the spinal cord; in patients with a pulmonary form of cystic fibrosis, chronic pneumonia is formed due to the increased viscosity of the secrets of the apocrine glands; with homozygous (? -thalassemia against the background of increasing anemia, hepatosplenomegaly, abnormalities of the bone and immune system as a result of ineffective erythropoiesis are gradually formed. Many forms of hereditary diseases were revealed during examination of patients with a chronic course of the disease.
The genetic basis of progreduation and the chronic course of hereditary diseases are, as a rule, two phenomena:
1) the continuity of the functioning of the pathological gene, leading to disruption of the normal functioning of cells, tissues and organs;
2) the absence of a mutant gene product, causing the development of decompensated states.
The degree of chronicity and progression for the same disease may vary.
INVOLVEMENT OF MANY BODIES AND SYSTEMS
IN THE PATHOLOGICAL PROCESS IN HEREDITARY DISEASES
Almost all forms of hereditary pathology are characterized by a multiplicity of lesions.
This is primarily due to the pleiotropic effect of the gene, i.e. his ability to control the development of various signs of the body. For example, with Marfan syndrome, the bone, cardiovascular systems and organs of vision are affected; with Lawrence-Moon syndrome, the bone, urogenital, endocrine systems and organs of vision are affected; with galactosemia, the liver, central nervous system, and vision are involved. In some hereditary diseases, the mechanisms of the primary pleiogropic action of genes are known. These are, as a rule, metabolic diseases, including diseases of accumulation. So, with an autosomal recessive Wilson-Konovalov disease, an abnormality in the serum protein of cerullostazmin does not provide efficient copper transport. This leads to the deposition of excess in various organs and tissues, which causes multiple lesions.
FAMILY CHARACTER OF HEREDITARY DISEASES
For a large number of hereditary diseases, repeated cases of a similar pathology in members of the same family are characteristic. In contrast to infectious diseases, the distribution of patients by sex and in generations with hereditary diseases is carried out according to Mendelian laws.
However, the presence of a disease in only one of the members of the pedigree (sporadic case) does not exclude the hereditary nature of this disease. A similar situation may be due to:
1) the presence of a new dominant mutation (occurred both in the autosomal and X-chromosome of one of the parents);
2) the phenomenon of incomplete penetrance of the dominant gene;
3) heterozygous carriage of both parents;
4) the presence of recessive X-abated pathology.
SPECIFIC SYMPTOMS OF HEREDITARY DISEASES
The presence of rare specific symptoms or their combinations in a role-playing patient gives reason to think about the hereditary or congenital nature of his disease. For example, in a child with a cleft palate, the presence of symmetrical "fossae" or fistulas on the mucosa of the lower lip allows thinking about the autosomal dominant Van der Wood syndrome; the presence of a wide 1st finger on the hands and feet of a child with progressive mental retardation suggests an autosomal dominant Rubinstein-Theyry syndrome, etc. In some cases, symptoms of the manifestation of genes that do not have any clinical significance are supportive diagnosis. For example, the detection of incisions in the earlobe (ear in a child with macroglossia and discrepancy between the rectus muscles of the rickett is crucial for the diagnosis of Beckwith-Wiedemann syndrome and, therefore, justified choice of adequate therapy.
“RESISTANCE” OF HEREDITARY DISEASES
TO THE MOST COMMON METHODS OF THERAPY
Speaking about the resistance (from lat. Resistentia - counteraction, resistance) of hereditary diseases to treatment, first of all, it is necessary to keep in mind the relativity of this clinical characteristic.
On the one hand, this clinical feature is explained by the fact. that in many cases it will not always be possible to correct the primary links of the pathogenesis of diseases, even if the primary product of the mugant gene is known. (However, this stability is not absolute). On the other hand, the phenomenon of “resistance” is due to the fact that the symptoms of hereditary diseases are often mistaken for the disease itself. This explains the failure of using standard regimens, approaches and methods of therapy. For example, the treatment of eczema, which is a skin manifestation of protocoproporphyria, is a treatment for the symptom, while reliable methods of prevention and therapy based on the laws of its pathogenesis have been developed for this disease. With unrecognized Costman's syndrome, intensive antibiotic therapy of pustular lesions of the mucous membranes and skin does not save the child from the progressive course of the disease, manifested in the form of boils, abscesses of the subcutaneous tissue, severe stomatitis, blepharitis, etc.
It is important to emphasize that any separately taken from the above clinical features is not an absolute criterion for a hereditary disease. However, if several features characteristic for this hereditary pathology are identified, the conclusion about the disease can be more definite.
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