2. Toxic Chemicals
Benzene was the first chemical linked to aplastic anemia, based on studies of factory workers before 20th century. Benzene is used as a solvent t in manufacturing of chemicals, drugs, dyes and explosives. It is used as a vital chemical in the rubber and shoe industry. Benzene can be metabolized in the liver to a series of phenolic and open ring structures, including hydroquinones, which can inhibit the maturation and amplification of bone marrow stem and blast cells. In addition, the metabolites of benzene alter the function of stromal cells in the bone marrow so that they cannot adequately support the growth and differentiation of hematopoietic cells. Other chemicals are Chlorinated hydrocarbons and organophosphate compounds. Chlorophenothane (DDT), lindane and chlordane are the most common insecticides involved. Other chemical include Pentachlorophenol (PCP) and Trinitrotoluene (TNT – an explosive used during World War I and II) .
3. Viruses
Viral infections particularly hepatitis B, Hepatitis Measles, Epstein- Barr virus and cytomegalovirus are also responsible for acquired cases of aplastic anemia.
4. Autoimmune Tissue Diseases
Autoimmune diseases like lupus, rheumatoid arthritis, Eosinophilic fasciitis, immune thyroid diseases and thymoma are associated with aplastic anemia.
5. Pregnancy
In some cases, pregnancy can make a preexisting aplastic anemia worse, which improves after the pregnancy is terminated. In some cases aplasia develops during pregnancy, with reoccurrences during subsequent pregnancies. Termination of pregnancy or delivery may improve bone marrow function but the disease may progress even after delivery. In such cases the therapy may include termination of early pregnancy, supportive care, immunosuppressive therapy or marrow transplantation after delivery.
6. Iatrogenic causes
Chronic exposure to low doses of radiation or use of spinal radiation for ankylosing spondylitis is associated with an increased but delayed , risk of developing aplastic anemia. Chemotherapy and radiation therapy for cancer treatment may also result in aplastic anemia.
II. Hereditary Aplastic Anemia
Hereditary aplastic anemia is passed down through the genes from parent to child. It is usually diagnosed in childhood and is much less common than acquired aplastic anemia. People who develop hereditary aplastic anemia usually have other genetic or developmental abnormalities that cause the aplastic anemia.
Some inherited conditions can damage stem cells and lead to aplastic anemia, including:
1. Fanconi anemia
Fanconi anemia (FA) is a rare genetic disease. Among those affected, the majority develops cancer, most often acute myelogenous leukemia, and 90% develop bone marrow failure (the inability to produce blood cells) by age 40.FA is the result of a genetic defect in a cluster of proteins responsible for DNA repair.
2. Dyskeratosis Congenita
People with dyskeratosis congenita have an increased risk of developing several life-threatening conditions. They are especially vulnerable to disorders that impair bone marrow function. These disorders disrupt the ability of the bone marrow to produce new blood cells. Affected individuals may develop aplastic anemia. They are also at higher than average risk for myelodysplastic syndrome, a condition in which immature blood cells fail to develop normally; this condition may progress to a form of blood cancer called leukemia.
3. Shwachman Diamond Syndrome
It is a rare congenital disorder characterized by exocrine pancreatic insufficiency, bone marrow dysfunction, skeletal abnormalities, and short stature. It is caused due to mutation in SBDS gene.