| Myelodysplastic Syndrome is the name given to a cluster of closely-related bone marrow diseases. Bone marrow is responsible for manufacturing the body's blood cells; in all of the diseases that comprise Myelodysplastic Syndrome, or MDS, the bone marrow fails to produce blood cells in sufficient quantity. Additionally, the blood cells which are produced do not develop properly. While the marrow is responsible for producing more than one type of blood cell, red blood cells, or erythrocytes, are particularly affected.
Processes
In MDS-affected patients, the bone marrow stem cells develop a defect, and subsequently cease to produce other stem cells, or to produce the cells which eventually mature into the three types of blood cell -- erythrocytes, leukocytes, or white blood cells, and platelets, which are crucial to the clotting process. As a result, the bone marrow, which would normally replenish the supply of blood cells, instead becomes clogged with immature cells which do not reach maturity. Because the problem is not an overproduction of blood cells, MDS is not formally classified as a cancer, although cancer may occur in some patients, and some doctors believe that it should be so classified.
Who Has MDS?
While no-one can say with any certainty that any one group is exempt from the risk of developing MDS, the most susceptible appear to be the elderly, with most cases occurring in patients over the age of 60. However, the young may also develop MDS. More males than females develop MDS. It may occur for no reason we are able to isolate, but it also appears in patients who have at some time been exposed to carcinogenic (cancer-causing) agents, which may include ionizing radiation and certain chemotherapy treatments. When it occurs without such exposure, it is classified as primary MDS. Conversely, when documented exposure precedes the syndrome's development, it is classified as secondary MDS.
Symptoms
MDS, unfortunately, may occur asymptomatically -- that is, without any symptoms at all. In such cases, only a blood test will detect its presence. In fact, diagnosis always requires a blood count. When symptoms occur, they are most often the classic pallor and chronic fatigue most often associated with anemia. In addition, but less commonly, since the leukocytes are so vital a part of the immune system, patients may find themselves susceptible to a host of opportunistic infections, in much the same way that an AIDS sufferer often develops many other illnesses. These secondary infections are unrelated except for the fact that they signal a weakened immune system. The patient may also experience excessive bruising and bleeding, due to the lack of platelets in the bloodstream. Some other symptoms may be an enlarged spleen, which may manifest as a feeling of abdominal fullness, and vaguer symptoms of poor appetite and weight loss.
Treatment and Prognosis
MDS, in and of itself, may not require treatment. Indeed, no specific treatment has been found to be truly effective. However, since something under a third of MDS patients go on to develop a cancerous condition, such as leukemia, careful monitoring should be performed. The only known cure for MDS is a bone marrow transplant. More than half the people who receive such a transplant survive, disease-free, 3 years later, with some successes as far out as 15 years post-procedure.
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Sources:
BMT Newsletter : BMTs for Myelodysplastic Syndrome
Blood and Marrow Transplant Newsletter
http://www.bmtnews.org/newsletters/sept1995/myelodysplastic.html
Dr Denis de Castro : MYELODYSPLASTIC SYNDROME - a patient's guide
The Medic8® Family Health Guide
http://www.medic8.com/healthguide/articles/myelodysplasticsyn.html | 
