Blood Disorders Defined
Blood disorders are diseases and abnormalities of the fluid and cellular components of blood. More specifically, they involve the plasma, red blood cells, white blood cells and platelets. Although some are acquired disorders they comprise a broad group of inherited diseases. Below are some of the more common disorders along with terms for understanding them.
Disseminated intravascular coagulation (DIC) – Is uncontrolled coagulation resulting in the depletion of clotting proteins. The shortage of those proteins in turn tends to cause excessive bleeding. Clot formation in blood vessels can cause destruction of RBCs and ischemia. Damage to the walls of blood vessels resulting from insufficient blood flow causes them to leak. Leakage of blood from vessels into surrounding tissues causes the blood pressure to drop. The resulting deficient blood flow often causes damage to various other tissues and organs. There are various causes. Common ones are:
- severe infection, particularly caused by bacteria or fungi
- blood transfusion reaction
- certain forms of cancer, particularly leukemia
- severe tissue injury, especially of the brain and burns
- advanced liver disease
- complications of pregnancy
Erythrocytosis – Is a higher than normal number of red cells in blood. It is the opposite of anemia. Secondary polycythemia is an alternate term for it when it is a response to a known stimulus. Low oxygen in tissues is a common cause.
Hemochromatosis – Is an inherited disorder which affects the body’s handling of iron. It results in excessive buildup of iron in the body tissues. Bronze diabetes due to the buildup in the pancreas and skin is a common characteristic of it. Liver dysfunction is also a common feature.
Hemoglobin S – Is the most common abnormal hemoglobin. It is the result of a substitution of an amino acid at position 6 on the beta chain of the hemoglobin molecule. That substitution is valine for glutamic acid. The cause of the substitution is a mutation in the gene that contains the code for it. When both beta chains are defective because of abnormal genes from both parents sickle cell disease is the result.
Hemoglobinopathy – Is any of a group of disorders in which the structure of hemoglobin in red blood cells is abnormal. The structural abnormality is of the globin protein portion of the molecule and is due to a genetic mutation from one or both parents. Since this type of disorder is purely a qualitative one, thalassemia which is a quantitative one is not a form of it. Sickle cell disease is one of the more common forms of it.
Hemophilia – Is a genetic disease which predisposes to hemorrhage due to its adverse effect on normal blood clotting. The underlying problem is a deficiency of one of two particular clotting proteins known as coagulation factors. The deficiency can be of factor VIII or factor IX. Classic hemophilia – hemophilia A – is a deficiency of factor VIII. Christmas disease – hemophilia B – is a deficiency of factor IX. The cause of the deficiency is a mutation of the gene responsible for the factor’s production. Either parent can transmit the mutant gene to an offspring. But the disease occurs almost exclusively in males because the genetic defect is on the X chromosome of which males only have one. Since females have two X chromosomes it is unlikely that both would have the mutation.
Leukemia – In simple terms, is cancer of the white blood cell producing portion of the bone marrow. It results in proliferation of any of the various different types of white blood cells or their precursors. The names for the various types are in accordance with the type of white blood cell that is overproduced. Anemia, abnormal blood clotting, and enlargement of the lymph nodes, liver and spleen are often associated with it.
Lymphadenopathy (Adenopathy) – Is enlargement of one or more lymph nodes. In addition to blood disorders there are several other causes. Various types of cancer, acute and chronic infections and autoimmune disease are some of the more common ones.
Lymphoproliferative disorder (LPD)–Is a group of diseases characterized by the production of excessive quantities of lymphocytes. They usually occur in persons with weakened immune systems. The disturbance is at one or more of the control points of the differentiation and development pathway of a lymphoid stem cell within the bone marrow. In addition to producing lymphocytes, the lymphoid stem cell also produces plasma cells which form from lymphocytes. Thus, a given disorder can be one of B cell, T cell, natural killer cell, or plasma cell proliferation. Some are inherited disorders with known gene mutations. Others are acquired conditions, some of which are iatrogenic.
The following are some examples of LPDs:
- acute lymphoblastic leukemia
- chronic lymphocytic leukemia
- multiple myeloma
- autoimmune lymphoproliferative syndrome
- hairy cell leukemia
- post transplant lymphoproliferative disorder
- autoimmune lymphoproliferative syndrome
- Wiskott-Aldrich syndrome
Multiple myeloma –Is a malignant neoplasm of plasma cells. It begins with the overproduction of a single clone of cells in the bone marrow. The crowding out effect of it causes bone pain, which is one of the main symptoms among many it can cause. As a form of bone marrow cancer, it is incurable and shortens life.
Myelofibrosis – Is the formation of scar tissue in the bone marrow, leading to decreased blood cell production. It can be the result of a myeloproliferative disorder or can be due to other diseases or factors.
Myeloid metaplasia – Is the occurrence or presence of blood cell producing tissue in sites outside of the bone marrow. It is the result of a malignant change in the tissue where it develops. The tissues in which it usually develops are those of the spleen and liver. It is often the result of myelofibrosis; it is the substrate of extramedullary hematopoiesis.
Myeloproliferative disorder – Is a group of neoplasms of the bone marrow which leads to the production of too many of one or more types of cells it is capable of producing. The primary defect appears to be of the common myeloid progenitor (myeloid stem cell). It is the offspring stem cell that forms from the hematopoietic stem cell that is capable of differentiating into red blood cells, granulocytes, monocytes or platelets. The most common of these disorders are:
- chronic myelogenous leukemia – overproduction of granulocytes
- primary myelofibrosis – the buildup of fibrous or scar tissue in the bone marrow as a result of uncontrolled blood cell production
- essential thrombocytosis (essential thrombocythemia) – excessive production of platelets
- polycythemia vera
Pancytopenia – Is a deficiency of all of the cellular elements of blood. More specifically, it is a state in which the number of white cells, red cells and platelets in blood is lower than normal.
Polycythemia – Is an increase in the total mass of red cells in the blood. It is usually a synonym for erythrocytosis except when it is a primary disease.
Polycythemia Vera – Is a primary blood disorder characterized by proliferation of red blood cells, white bloods and platelets, but particularly red blood cells. The net result is an increase in the red cell mass and total blood volume. Splenomegaly and extra-medullary hematopoiesis are common features of it.
Sickle cell disease – Is any of the group of inherited diseases in which hemoglobin S is present in red blood cells. If a person is homozygous – has a gene from both parents – for hemoglobin S sickle cell anemia is the result. The predominant presence of hemoglobin S causes red blood cells to become crescent-shaped and stiff. The resulting loss of elasticity leads to their destruction by the spleen, the basis of hemolysis and anemia. The decreased flexibility of the red cells and reduced binding of hemoglobin S to oxygen are responsible for the other signs and symptoms of the disease.
Sickle cell trait on the other hand is a state in which the person is heterozygous – has a gene from only one parent – for hemoglobin S. This state consists of sufficient amounts of normal hemoglobin A and only limited amounts of hemoglobin S. Thus, individuals with it don’t experience sickling of their red blood cells and are usually asymptomatic.
There are other forms of sickle cell disease in which hemoglobin S coexists with other abnormal hemoglobin in red blood cells. The name reflects the abnormalities. Sickle cell-hemoglobin C disease and sickle cell hemoglobin D disease are some cases in point. The condensed terms for them are SC disease and SD disease respectively. By the same token, the shortened name for sickle cell anemia is SS disease.
Thalassemia – Is any of the group of inherited disorders in which there is a decreased rate of production or no production at all of one or more of the four globin chains of hemoglobin. A missing or mutated gene that encodes a given chain is the cause of the disorder. The globin chain allele which is involved, the structure of the mutant gene and whether the mutation is from one or both parents determine the expression of the disease. Depending on these factors a disorder might be asymptomatic or symptomatic. Signs and symptoms when present might range from mild to severe depending on the given disease. They might include the following:
- Dark urine
- Spleen enlargement
- Liver enlargement
- General weakness
- Shortness of breath
- Skull and facial bone deformities
- Slow growth or short stature
Thrombocytopenia – Is a decrease in the number of platelets in blood.
– Thrombocytopenic – adj.
Von Willebrand Disease – Is the most common inherited bleeding disorder. It is due to a deficiency or defect in von Willebrand factor. The pattern of inheritance is autosomal dominant – is caused by the passing on of a mutant gene not present on an X or Y (sex determining) chromosome from one parent. There are different types and subtypes. Type 1 is the most common and is due to a deficient quantity of the protein. Type 3 is also a quantitative defect but is a result of both parents passing on the mutant gene to the affected offspring. Consequently, the degree of von Willebrand factor deficiency is much greater in type 3 disease than type 1 disease. Thus, the bleeding tendency is mild in type 1 disease and severe in type 3 disease. With type 2 disease the amount of the protein is normal, but its structure and function are defective. The bleeding tendency in this form of the disease is moderate. There is also a rare acquired form of the disease that infrequently occurs with some other diseases and with the use of certain medications.
Von Willebrand Factor – Is a protein in plasma which helps platelets clump together to prevent bleeding from broken blood vessels. It also has a secondary role as a carrier for clotting factor VII, serving to prevent its degradation. If it is deficient in quantity or defective in its function excessive bleeding can result.