Good Morning America host Robin Roberts told viewers in an emotional announcement this morning that she has the rare disorder myelodysplastic syndromes.

She will soon get a bone marrow transplant from her older sister.

It's probably fair to say that many people probably haven't heard of the disease that also goes by MDS.

MDS is actually a group of disorders that cause the bone marrow to produce an inadequate number of healthy red blood cells, white blood cells and platelets, according to the Mayo Clinic. Cells in the bone marrow that make blood cells don't mature, don't make enough blood cells or make defective cells, according to the Mayo Clinic.

About 10,000 to 15,000 people in the United States are diagnosed with the disease each year and 80 percent of cases are in people over age 60, says marrow.org.

In some cases, MDS can lead to cancer, the Mayo Clinic says.

Treatments include blood cell and platelet transfusions, chemotherapy and bone marrow transplants, according to The Myelodysplastic Syndromes Foundation. Roberts told viewers she was extremely lucky that her sister was a match for a transplant, 

The Foundation says the disease can develop after exposure to certain chemicals or radiation. Roberts was treated for breast cancer five years ago and told her colleagues in a letter that the treatment likely caused the disease.

Roberts will begin treatment Monday when she receives a drug to prepare her for the transplant. She will continue her morning hosting duties for now, but will not be on air during recovery from the transplant.