September 27, 2010

Telomere Length Linked to Outcomes in Aplastic Anemia

Microscopic image of blood cells in bone marrow Microscopic image of bone marrow shows newly produced red blood cells. Ivor Mason, King's College London. All rights reserved by Wellcome Images.

Aplastic anemia patients with shorter chromosome tips, or telomeres, have a lower survival rate and are much more likely to relapse after treatment than those with longer telomeres, a new study reports. The results add to a growing body of evidence linking telomere length to disease risk and clinical outcomes.

Aplastic anemia arises when the body's bone marrow doesn't make enough new blood cells. A number of diseases, conditions and factors can damage the blood-making stem cells in bone marrow and bring about aplastic anemia. However, the cause of the disorder is unknown in more than half of the people who have it. Mild or moderate cases may not need treatment, but people who have severe aplastic anemia need medical treatment right away. Treatments include blood transfusions, blood and marrow stem cell transplants, and medicines such as immunosuppressive therapy, which can relieve symptoms and reduce complications.

In recent years, scientists have found that the blood cells of some patients with severe aplastic anemia disease have extremely short telomeres. Telomeres are molecular caps at the ends of chromosomes that protect them from erosion. They naturally become shorter with each cell division, although they can be rebuilt by enzymes. Genetic factors and environmental stressors can affect telomere length. Over the past decade, telomere length has been linked to the aging process and to several types of cancer.

To learn more about the role of telomeres in severe aplastic anemia, a team of NIH scientists led by Dr. Phillip Scheinberg of NIH’s National Heart, Lung and Blood Institute (NHLBI) measured telomere length in the white blood cells of 183 patients with severe disease before they began immunosuppressive therapy. The patients were equally divided into 4 groups based on the lengths of their telomeres. Follow-up clinical assessments continued for an average of 5 years.

As reported in the September 22, 2010, issue of the Journal of the American Medical Association, the scientists found that nearly 60% of the patients responded to immunosuppressive therapy. Of those who responded, the patients with the shortest telomeres were most likely to have a later relapse. The scientists found that the rate of relapse dropped as telomere lengths increased.

The group of patients with the shortest telomeres was also at greater risk for a conversion to bone marrow cancer (24%) than the other 3 groups (3% to 13%). Survival rates differed as well. Only 66% of patients with the shortest telomeres survived at least 6 years, compared to an 84% survival rate for the other 3 groups combined.

"We were somewhat surprised to find that these later events were so clearly associated with telomere measurements that were taken years before," says Scheinberg. "Knowing that a person's at high risk for developing major complications several years down the road can have a major impact on the clinical management of that individual."

These findings may have implications for treating this rare and sometimes deadly disorder. Further study is needed, though, before they can be applied to medical practice.

—by Vicki Contie

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