Worldwide, there may be more than 7,000 different genetic diseases, ranging from mild to truly serious conditions. Most of these diseases are very little known and rare and are extremely difficult to diagnose.
BETTER UNDERSTANDING GENETIC DISEASE
The human body is made up of billions of cells, each with a nucleus in which all our genetic information is contained. This information is then spread over 23 pairs of chromosomes. These, of course, are made up of DNA and carry our genes. It is possible that this plan does not work properly, hence the appearance of genetic abnormalities, particularly at the level of the chromosomes (chromosomal abnormality) or DNA (mutations). It is therefore these anomalies that are responsible for genetic diseases such as trisomy (an extra chromosome is added to one of the pairs of chromosomes), monosomy (the absence of a chromosome on one of the pairs), monogenic diseases (mutation of a single gene), multifactorial hereditary diseases (dysfunction of several genes).
MODES OF TRANSMISSION OF GENETIC DISEASES
As mentioned above, the genetic information is spread over 23 pairs of chromosomes. Therefore, for each pair, there is one chromosome from the mother and one from the father, for a total of 46 chromosomes. It is the 23rd pair that will determine the sex of the person and the 22 others are called “autosomes”. There are currently two forms of transmission, dominant and recessive. If only one of the two copies of the gene is altered or mutated, it can transmit dominant genetic diseases even if the second copy of the gene is healthy. On the other hand, if the person inherits two mutated copies of the same gene, we are talking about recessive genetic diseases. On the other hand, there is also what is called a healthy carrier, a person who is not sick, but who can pass on the disease to their children. This person has inherited a mutated copy of the gene from his or her parents and a normal copy that will compensate for the defect of the abnormal copy.
X-LINKED TRANSMISSION: WHAT IS TO BE UNDERSTOOD?
X-linked transmission occurs when a normal gene that induces the disease is found on the sex chromosome X. In fact, there are several genes on the sex chromosome that promote growth and development in an individual. First, in women, two X chromosomes can be found. If one of these X chromosomes is mutated, the gene on the other can effectively compensate for its defect, making a woman a healthy carrier of X-linked disease. On the other hand, in men who have both an X and a Y chromosome, if one of the genes on the X is mutated, the Y will not be able to compensate for the defect, since the X chromosome is much smaller and contains very few genes.