Anandhi,
Dacogen (decitabine) is not a cure for MDS but it can extend the lives of patients. The only cure for MDS is hematopoietic cell transplantation, i.e., a stem cell transplant or bone marrow transplant.
This article, which can be downloaded in full as a PDF file, summarizes current information about Dacogen. Although the article is written in medical language, you should be able to learn more about the effectiveness (efficacy) of Dacogen.
Studies have found that Dacogen can be more effective than supportive care alone (transfusions, growth factors like Neupogen, antibiotics, etc.) but like other drug treatments it has its own risks. The doctors have to weigh the tradeoffs for each patient.
The median age of diagnosis of MDS in the United States is 71, which limits treatment choices. At age 53 your uncle is young enough for a transplant, if he's otherwise fairly healthy and a matched donor is available. That's a potential cure but again with risks.
There are other drugs for MDS, particularly Vidaza (azacitidine) and Revlimid (lenalidomide). Revlimid is especially effective for patients who have the "5q deletion" (also called "5q minus") abnormality in their chromosomes.