Myelodysplastic Syndromes is an umbrella term to describe a broad array of blood disorders, more commonly called MDS or pre-leukemia. As it was explained to me, as the stem cells divide and reproduce in my bone marrow, a mutation (or transfer error) occurs.
Most of the time, the mutated cell dies and is replaced with healthy cells. But sometimes, the mutation continues to reproduce leading to a large number of stem cells who are not functioning properly. Over time, this leads to decreased production of blood cells. In my case, it is only the red blood cells (which carry oxygen), leading to anemia. It can also affect white blood cells (which fight infection) and platelets (causes blood to clot), but it hasn’t with me.
The mutation is most commonly caused by one of two factors. The first is advanced age – the older an individual is the more likely they are to have the cells divide incorrectly, just from an increased number of divisions. Second, is exposure to radiation, such as from treatments from other forms of cancer. A non-radiation case with someone my age is not unheard of, but it is extremely rare.
That is my explanation of it. But, there are a lot better, and more detailed, descriptions out there. Here are a few other resources: