What Causes Hereditary Diseases?

Hereditary disease is a disorder that is passed from parents to a child. It hides inside the genetic code and accompanies the person throughout his life. However, the causes of genetic abnormalities are not always clear.

Types of Hereditary Diseases 

Multifactorial And Polygenic (Complex) Genetic Disorder

A mutation is a change in the human gene when some nucleotides in the DNA structure are replaced by others. This process carries changes in the amino acid sequence of a protein - the most important nutrient in our body.

The Main Functions of Protein
  • The building material of cells, which is continuously renewed and made up of proteins. 
  • Maintaining proper functioning of the hormonal system. 
  • Transportation of hemoglobin to tissue cells. 
  • Ensuring the functioning of the immune system. 
  • Supporting the functioning of the musculoskeletal system. Muscle fibers, ligaments, joints, and bones are made up of a framework of a protein, which helps muscles contract. 
  • Ensuring the normal functioning of the sense organs, which enable a person to perceive the world (memory, sense of smell, mental process, perception of light, and color). 
  • Contributing to wound healing. Protein molecules clog up areas of tissue damage and promote skin regeneration. 
  • Maintaining the necessary fluid balance in the body. 

It should be noted that not all DNA mutations are harmful. For example, color blindness doesn't cause serious problems. However, the incorrect amino acid sequence in a protein may lead to fatal consequences in many cases. It may result in Angelman syndrome, Tourette syndrome, spinal muscular atrophy, Duchenne muscular dystrophy, and many others.

Chromosomal Disorder

Chromosomal abnormalities refer to changes in the number and structure of chromosomes passed down from parents to children. These changes include an increase in the number of chromosomes (trisomy, polysomy), the loss of a single chromosome (monosomy), the loss of parts of chromosomes (deletions), translocation (transfer of a part of a chromosome to another chromosome), and inversions, which involve the rotation of a chromosome section.

Transfer of Hereditary Information

All the genetic material of humans and animals is located in special structures - chromosomes. They have a complex structure, which stores information and transmits it to generations during the fusion of a male sex cell with a female sex cell (sperm and egg). Research shows that if we measure the DNA (genes) stored in the chromosomes in one human cell, we get a two-meter long thread of DNA. This is how the genetic material is tightly packed up to fit in the nucleus of every cell.

Under normal conditions, hereditary information, in the form of a set of chromosomes, is passed from both parents to offspring. Accordingly, the child receives the genes of the same protein from the mother and the father. If the transfer process occurs unchanged, the child receives a complete set of 46 chromosomes containing healthy genes. In this case, you can expect the birth of a healthy child with a set of genes transmitted to future generations.

Unfortunately, the human genome is prone to several effects that lead to disorders in the genetic code and the synthesis of abnormal proteins.

The main Factors Leading to a Change in Genetic Material

  • Physical factors include ionizing radiation. 
  • Common chemical mutagens include pesticides and long-term exposure to drugs.
  • Biological mutagens refer to various groups of viruses. 

Currently, there are about three thousand hereditary diseases that have been already discovered. Many of them are serious pathologies that lead to loss of socialization and disability. 

How do Genetic Diseases Develop?

A change in the genetic code can lead to significant modifications in any biochemical reactions in a human cell. They result in severe pathologies that often affect the quality of life. One such example is lactose intolerance.

Dairy intolerance is associated with the sugar in milk - lactose. An enzyme in the human intestine called lactase quickly breaks down this sugar. Lactase is found in the intestinal cells - enterocytes. Its amino acid sequence is encoded in the LCT gene, located on the second chromosome (2q21.3). In turn, the LCT gene is regulated by the MCM6 gene introns. Changes in the MCM6 gene (the replacement of cytosine (C) with thymine (T)) lead to a change in the work of the LCT gene. Accordingly, it results in a decrease in the synthesis of mRNA and a decline in lactase activity.

An excess sugar intake can lead to unpleasant symptoms like diarrhea, bloating, gas, abdominal pain. People with this condition cut out dairy products, reducing calcium intake. In the future, this affects the general growth of a child. At the same time, adults have a higher risk of osteoporosis due to calcium deficiency.

Depending on the genes received from parents (alleles), the severity of clinical manifestations may vary. It can manifest in good absorption of lactose (T/T genotype) or the development of serious clinical manifestations (C/C genotype). The C/T genotype is related to the risk of osteoporosis in adults.

Hereditary diseases can be determined by one gene, as illustrated by the example of lactase deficiency. Besides, they may arise from disorders caused by multiple genes (polygenic defects). Such polygenic diseases include diabetes mellitus, Melas syndrome, bronchial asthma, coronary heart disease, schizophrenia, and many other pathologies.

The estimation of the risks of various genetically determined diseases in a child can be identified by studying the genetic status of the parents.

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