Pediatric Medical Genetics - S.I. Smiian 2003

General Principles of Medical Genetics
Blood Group Genetics

In 1900, Landsteiner discovered the A, B, and O Blood Groups, and 7 years later, Jansky identified the fourth group, AB. Depending on the presence of Antigens A and B on red Blood Cells, all people are divided into 4 blood groups. Blood groups are genetically determined and remain unchanged throughout a person's life. Genes A and B are dominant over Gene O. As a result, AA homozygotes and AO heterozygotes are phenotypically identical. The inheritance of blood groups follows Mendel's Laws. For example, children of a woman with blood group AB receive either A or B. Therefore, they cannot have blood group O, regardless of which gene they inherit from their father. Conversely, a mother with blood group O cannot have children with blood group AB, since they will receive either A or B from their father.

In 1940, Landsteiner and Wiener discovered the Rhesus (Rh) antigen system. It has been established that 85% of Europeans are Rh-positive, while 15% are Rh-negative. Rh-positive individuals can have two genotypes: Rhrh and RhRh (heterozygotes and homozygotes). The Rh-negative trait is inherited recessively, and these individuals are always homozygous (rh, rh).

Antibodies specific to the Rh antigen are not inherited and are absent from normal human blood. They are produced in Rh-negative mothers pregnant with an Rh-positive fetus, or as a result of transfusing Rh-positive blood to such women. If the father is heterozygous, the probability of an Rh conflict is 1/2 (50% of children); if he is homozygous, all children will have an Rh incompatibility with the mother. In addition to Rh incompatibility, ABO blood group incompatibility is sometimes observed. In some cases, children with blood group A or B born to mothers with blood group O may develop hemolytic disease of the newborn, when the mother's body produces antibodies against these antigens.

Regarding The Development of blood incompatibility between mother and fetus, it should be noted that if the mother has blood group II (A) or IV (AB), all marriages are compatible. If the mother has blood group O (I) and the father has A (II), B (III), or AB (IV); or if the mother is A (II) and the father is B (III), or the mother is B (III) and the father is AB (IV) — these marriages are incompatible.

Observations show that spontaneous miscarriages occur significantly more often in incompatible marriages than in compatible ones. Apparently, in such cases, zygote mortality due to ABO incompatibility occurs at such Cytology/cytology/16.html">Early stages of embryonic development that it can only be detected statistically by comparing the frequency of miscarriages in compatible and incompatible marriages.

Approximately 10% of all pregnancies are potentially at risk for hemolytic disease of the newborn. In reality, this figure is much lower, accounting for 0.4% of all newborns, and among potential cases of Rh incompatibility, 2–5%. This is explained by the fact that concurrent maternal-fetal blood incompatibility for both the ABO and Rh systems significantly reduces the likelihood of developing hemolytic disease of the newborn.

Secondly, for a woman to have a high concentration of antibodies against fetal blood, prior sensitization is required (either from a previous Pregnancy or a blood transfusion). The individual Properties of the placental barrier, which influence the passage of antigens from the child to the mother and antibodies from the mother to the child, must also be taken into account.

Accumulated statistical data show that certain diseases are more common in people with specific blood groups. For instance, duodenal ulcers are observed more frequently in individuals with blood group O (I), while patients with Cancer and pernicious anemia are 20% more prevalent among people with blood group A (II). Bronchopneumonia occurs more often in children with blood group A (II) than in others.

Generalized data from England, the USA, Italy, France, and Germany show that children with blood group B (III) are less likely to contract poliomyelitis.

The application of ABO and Rh genotypes helps resolve paternity or maternity issues in forensic medical examinations. The core criterion is the fact that a child inherits genes from its parents. ABO genotypes are used more frequently. Paternity is excluded if the suspected father or mother lacks a gene that is present in the child. When comparing two men regarding paternity, a necessary condition is a difference in their genotypes. For example, if the mother and the first man have the OO genotype, while the second man has AB, and the child is A (II), then only the man with AB can be the father, since he passed his A gene to the child. However, if the mother has the AO (AA) genotype, paternity cannot be definitively established in this case, as either man could potentially be the father. Forensic medical examination provides a definitive answer only regarding the exclusion of paternity or the possibility that given individuals could be the parents of the child.

Control Questions

1. State the main principles that determine The Significance of medical genetics.

2. Define the Subject and Tasks of medical genetics.

3. List the MAIN TYPES OF inheritance and illustrate them graphically.

4. Provide a Classification of Hereditary diseases from the perspective of medical genetics.

5. What is the general semiotics of hereditary pathology?

6. Indicate the indications for MEDICAL Genetic Counseling.

7. Name the MAIN OBJECTIVES OF medical genetic counseling.

8. List the primary Methods used in medical genetic counseling.

9. Outline the stages and their objectives in the medical genetic counseling process.

10. Indicate possible recommendations resulting from medical genetic counseling.

11. List Ways to improve human heredity.

12. How is the degree of risk for hereditary pathology determined, and what recommendations can be given to the family?