MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY AND PATHOLOGY - Ya.I.Fedoniuk 2010

BIOLOGY

CHAPTER 1. BIOLOGICAL FOUNDATIONS OF HUMAN VITAL ACTIVITY

1.4. ONTOGENETIC LEVEL OF LIFE ORGANIZATION

1.4.2. Basics of human genetics

Hereditary diseases and their Classification

Depending on The Role of heredity and the environment, all diseases can be divided into three groups: 1) hereditary diseases; 2) Diseases with Hereditary predisposition (multifactorial); and 3) non-hereditary diseases. Hereditary diseases are disorders caused by Gene, chromosomal, or genomic Mutations. The manifestation of the pathological effect of a mutation is practically independent of the environment, which can only alter symptom expression and disease severity. Diseases with a hereditary predisposition develop in individuals with a specific genotype under the Influence of Environmental factors. Non-hereditary diseases are caused by environmental factors (trauma, Burns, infectious diseases). However, even in these conditions, heredity influences the course of the pathological process.

The term "hereditary diseases" should be distinguished from the terms "congenital diseases" and "familial diseases." They are not synonyms. Congenital diseases include all conditions present at birth, which may be caused by either hereditary or non-hereditary factors. Hereditary diseases such as hemophilia or Achondroplasia (shortening of long tubular bones), which manifest at birth, are also congenital diseases. Hereditary diseases such as myopathies or progeria (premature Aging), which appear in adolescence, and Huntington's disease (with an average onset age of 38-40 years), are not congenital in the full sense of the word. Familial diseases encompass all conditions (hereditary and non-hereditary) that occur in members of the same family. Non-hereditary familial diseases arise from exposure to a shared harmful factor within that family (for example, occupational hazards).

A distinction is made between genetic and clinical classifications of hereditary diseases. The genetic classification is based on the etiological principle, namely the type of mutation and The Nature of interaction with the environment. All hereditary pathologies can be divided into 5 groups: 1) gene disorders; 2) Chromosomal Disorders; 3) diseases with a hereditary predisposition (multifactorial); 4) somatic Cell Genetic Disorders; and 5) diseases of maternal-fetal genetic incompatibility. Strictly hereditary diseases are subdivided into two major groups: gene and chromosomal disorders.

Gene diseases are disorders caused by Gene Mutations. They are transmitted across generations according to Mendel's Laws. Chromosomal diseases are caused by chromosomal and genomic mutations. Most chromosomal disorders caused by aneuploidy are not inherited at all (due to a lethal effect), whereas structural chromosomal rearrangements are transmitted with additional recombinations occurring during the Meiosis of the aberration carrier. Diseases with a hereditary predisposition can be monogenic or polygenic. Their manifestation requires not only a specific genetic constitution of the individual, but also a factor or complex of environmental factors that act as triggers in The Development of the pathology. Somatic cell genetic disorders are associated with The Emergence of specific Chromosomal aberrations in somatic Cells during oncological neoplasms, which activate oncogenes. These include retinoblastoma and Wilms' Tumor (Kidney Cancer). Diseases of maternal-fetal genetic incompatibility develop As a result of the mother's immune reaction to fetal Antigens (hemolytic disease of the newborn).

Hereditary pathology is so diverse that it is encountered in the practice of physicians across any specialty. Corresponding to medical specialties, There is a clinical classification of hereditary diseases based on a systemic and organ-based principle. It includes: Hereditary diseases of The Nervous system; hereditary diseases of Internal Organs; hereditary Skin diseases; hereditary Diseases of the eyes and other organs. There are very few hereditary diseases that selectively affect only a single system. Most hereditary conditions manifest as a complex of pathological features—syndromes (e.g., Down syndrome, Klinefelter syndrome). The principles of diagnosing hereditary diseases are based on clinical Diagnosis data, which are refined using Genetic Methods during Genetic Counseling.