Problems in the Blood
Since so many components of the blood are essential for so many biological activities, it is not surprising that diseases and disorders affect this system and the blood itself. Here are some common ones.
Sickle Cell Anemia
Common in populations of sub-Saharan African descent, sickle cell anemia (SCA) is a condition in which a mutation in the hemoglobin gene causes the molecule to become rigid and form crystalline structures within the RBC. These abnormal molecules give the RBCs a sickle shape and cause them to flow less efficiently through the tight passages of the capillaries.
Hemoglobin is formed from 4 protein chains; a person with SCA has a mutation in the beta chains. Only a single nucleotide in the beta chain gene is altered, but this is enough to change a glutamic acid into a valine at amino acid 6 and create the disease.
The inheritance of this gene stems from its survival in regions of malaria infection. The parasite of malaria reproduces itself within the RBC of a human host. However, a carrier of this mutation (someone with only one mutant gene who does not have the disease) will have RBCs that, when infected by the parasite, rupture prematurely, making it impossible for the parasite to reproduce. But as this gene has been passed down through generations that have not been impacted by malaria, the incidence of the condition has increased.
Anemia
This condition is most commonly associated with someone having too few RBCs (less than 40 percent hematocrit, or percentage of blood cells, in most individuals). However, a person may also be anemic if their RBCs do not contain enough hemoglobin. There are a number of causes for anemia that include insufficient iron in the diet, kidney disorders that result in lowered erythropoietin production, and abnormalities of the stem cells in the bone marrow.
Another cause of anemia, termed pernicious anemia, stems from a vitamin B12 deficiency. While this may be due to a diet insufficiency, pernicious anemia is an absence of a cofactor that is essential for B12 to be absorbed by the intestinal epithelium intrinsic factor, which is normally produced by the cells in the stomach. This cofactor usually enables the cells of the small intestine to effectively absorb dietary B12. Without it, B12 cannot be used and RBC formation declines.
What is the difference between sickle cell anemia and thalassemia?
While sickle cell anemia is a qualitative defect in hemoglobin, thalassemia results when one or more chains of hemoglobin are not produced in sufficient amounts. Thalassemia is a type of anemia. If the problem is with the beta chain, the classification is beta-thalassemia; if there is a deficiency in the production of the alpha chain, it is alpha-thalassemia.
Hemolytic Disease of the Newborn
This condition only occurs when an Rh-negative female becomes pregnant with an Rh-positive baby. If the father is Rh negative, there is no possibility of this occurring. However, if the father is Rh positive, there is a 50 to 100 percent chance of the baby being Rh positive (depending on whether the father has 1 or 2 Rh alleles).
For a first pregnancy, there is no danger to an Rh-positive baby, since the mother does not have pre-existing anti-Rh-factor antibodies circulating in her plasma. However, during the birth process, fetal and maternal blood combine as the fetal portion of the placenta detaches from the uterus, stimulating an immune response in the mother. Antibodies produced against the Rh factor now circulate in the plasma, presenting a significant risk to the baby in any subsequent pregnancy (if that baby is also Rh positive). These antibodies cross the placenta and destroy Rh-positive RBCs in the baby, causing this disorder.
Preventing the mother from mounting an immune response against her baby’s blood is an easy task. Prior to delivery, the mother is given an injection of anti-Rh-factor antibodies. These antibodies bind to any Rh factor that makes its way into the maternal blood stream. This effectively eliminates the rogue Rh factor from the blood, renders it unable to stimulate an immune response, and protects any future babies. This procedure needs to be done with each potential Rh-positive pregnancy.