Causes
In a healthy person, bone marrow makes new, immature blood cells that mature over time. Myelodysplastic syndromes occur when something disrupts this process so that the blood cells don't mature.
Instead of developing normally, the blood cells die in the bone marrow or just after entering the bloodstream. Over time, there are more immature, defective cells than healthy ones, leading to problems such as fatigue caused by anemia, infections caused by leukopenia, and bleeding caused by thrombocytopenia.
Some myelodysplastic syndromes have no known cause. Others are caused by exposure to cancer treatments, such as chemotherapy and radiation, or to toxic chemicals, such as tobacco, benzene and pesticides, or to heavy metals, such as lead.
Types of myelodysplastic syndromes
The World Health Organization divides myelodysplastic syndromes into subtypes based on the type of blood cells â red cells, white cells and platelets â involved.
Myelodysplastic syndrome subtypes include:
- Myelodysplastic syndrome with unilineage dysplasia. One blood cell type âwhite blood cells, red blood cells or platelets â is low in number and appears abnormal under the microscope.
- Myelodysplastic syndrome with multilineage dysplasia. In this syndrome, two or three blood cell types are abnormal.
- Myelodysplastic syndrome with ring sideroblasts. This type, which has two subtypes, involves a low number of one or more blood cell types. A characteristic feature is that existing red blood cells in the bone marrow contain a ring of excess iron called ring sideroblasts.
- Myelodysplastic syndrome associated with isolated del chromosome abnormality. People with this syndrome have low numbers of red blood cells, and the cells have a specific mutation in their DNA.
- Myelodysplastic syndrome with excess blasts â types 1 and 2. In both these syndromes, any of the three types of blood cells â red blood cells, white blood cells or platelets â might be low and appear abnormal under a microscope. Very immature blood cells (blasts) are found in the blood and bone marrow.
- Myelodysplastic syndrome, unclassifiable. In this uncommon syndrome, there are reduced numbers of one of the three types of mature blood cells, and either the white blood cells or platelets look abnormal under a microscope.
Source: http://www.mayoclinic.com