DEAR DR. DONOHUE: I am inquiring about myasthenia gravis. Two of my sisters have been diagnosed with it. One of them was in the hospital for seven weeks with it.

Am I apt to get it too? What are the symptoms? What can be done to prevent it? – B.T.

ANSWER: Myasthenia gravis is an autoimmune disease. For unclear reasons, the immune system begins making antibodies that plug receptors on muscle cells. Receptors are the docking stations for the chemical messenger that nerves release. The messenger is acetylcholine. When it lands on a receptor, muscles contract forcefully.

When the receptor is clogged with antibodies, acetylcholine can’t reach it. The prominent myasthenia symptom, therefore, is muscle weakness, and the weakness worsens with repetitive movement. It often starts as double vision because the weakened eye muscles can’t align the eyes to produce a single image. Eyelids droop. Food might stick on its way down to the stomach. Weakness of the arms and legs can set in.

Your one sister had an extreme episode probably because her breathing muscles were involved.

The thymus gland in the upper chest is a gland of mystery. Somehow, in some people, it plays a role in myasthenia. Removal of the gland, in selected patients, can frequently make myasthenia easier to treat. If the gland has gotten very large, then it should definitely be removed.

There is no cure for myasthenia, but there are effective treatments. Mestinon is one of them.

Your family history made me sit up and take notice. No myasthenia gene has yet been found, but if a family member has it, the risk for other family members getting it increases. There are no preventive medicines.

Are your sisters members of the Myasthenia Gravis Foundation of America? They should be. It provides timely information on the disease and its treatment. They can reach the association by calling 800-541-5454.

DEAR DR. DONOHUE: Two years ago, before hernia surgery, I had an EKG. It showed a massive heart attack. I consulted a heart doctor and had tests done. Everything was OK. The EKG was misleading. Three months ago, I was scheduled for outpatient surgery. Again surgery was postponed because of my EKG. Is this going to happen every time I have an EKG? – P.D.

ANSWER: Probably, unless you get in writing from the cardiologist what tests were done for you and what their results were. No test is perfect, including the EKG. It’s a wonderful and usually reliable indication of heart health. You happen to have an EKG that looks abnormal, but your heart is normal. This happens. An explanation from the heart doctor will save you much grief in coming years.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from www.rbmamall.com.