More than 12,000 people joined the donation registry Be The Match in the two weeks after the ABC morning show co-host announced she has MDS, a disease requiring a bone marrow transplant, on June 11, registry officials said on Tuesday. Previously, the monthly average was 9,000, they said.

"A significant number of those requests referenced Robin Roberts," said Kirsten Lesak-Greenberg, a Be The Match spokeswoman.

Jeffrey Chell, chief executive of Be The Match, said between 400,000 and 500,000 new donors are added to the registry each year.

Some 6,000 transplants are performed yearly, while more than 12,000 people need them each year, he said.

Chell praised the disclosure by Roberts, a popular television personality, saying: "It's remarkable that she would take her personal crisis and turn it into a signal of hope."

ABC has been organizing company registry drives, Be The Match said, and a drive this week resulted in signing up 230 potential donors, more than four times the typical 50.

Matches are difficult to find because tissue types, including a key marker in the immune system that recognizes which cells belong in the body, vary from person to person.

Some are common, and others extremely rare, and many patients may never find a match. Only about one in every 540 donors will actually donate bone marrow due to the difficulty of finding of matches, according to Be The Match.

Chell said thanks to the added number of donors, 50 to 70 lives may be saved in the next five years.

Some 70 diseases, many of them life-threatening, require transplanting bone marrow, Chell said. They include leukemia, which is cancer of the blood or bone marrow, lymphoma, which is cancer of part of the immune system, and sickle-cell anemia.

Roberts' disease involves damaged bone marrow, which carries a high risk of developing into leukemia.

Interested donors can sign up on www.marrow.org. A cotton swab test is sent to the address of a potential donor, who swabs the inside of his or her mouth and sends the test back to the registry.

(Editing by Ellen Wulfhorst and Gunna Dickson)

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