DEAR DR. DONOHUE: My dad died last August of confirmed sporadic CJD, Creutzfeldt-Jakob disease. He had a very short and terrible illness. Although this is a very rare disease, will you explain it to your readers to make more doctors and families aware of it? – D.G.

ANSWER: Only about 300 cases of Creutzfeldt-Jakob are diagnosed yearly in the United States. It is an awful illness, caused by a most unusual infectious agent, a prion. Prions are remarkable life forms. They are proteins, and they lack nucleic acid, something all other living things have. Most Creutzfeldt-Jakob disease is sporadic – happening in a random fashion to people without a known source of transmission.

It’s a dementia, an illness where there is a deterioration of mental function. With CJD, the dementia is rapid, occurring in a matter of months. The infected person loses memory, reasoning, judgment and even the basics of a thinking life. Myoclonus is another hallmark of the illness. It’s sudden, profound jerks of the arms or legs or other muscles. A loud noise, a bright light or any stimulus can cause this exaggerated startle reaction.

There are forms of Creutzfeldt-Jakob disease in which the mode of transmission is on more certain grounds. The outbreak of mad cow disease (another prion disease) in England gave a small number of people a variant form of CJD.

I am sorry for your father’s death and for the illness that led to it.

DEAR DR. DONOHUE: I am an 86-year-old woman in good general health. My blood pressure is normally 118/73. I read recently that low blood pressure can be a risk factor for heart problems. Is this true? If so, how can it safely be raised? – M.S.

ANSWER: Your blood pressure is excellent. It’s not a problem.

Normal blood pressure is any reading less than 120 over 80. You’re there. Be glad.

Symptoms from low blood pressure don’t usually develop until the systolic pressure (the first number) is lower than 90 and the diastolic pressure (the second number) is less than 60. Symptoms are things like dizziness, feeling about to faint and profound weakness.

You don’t need any medicine. Medicines do exist for those who have both low blood pressure and symptoms. Low blood pressure can mean that a person has a fluid deficit, a hormone deficit or a heart that can’t pump with vigor.

DEAR DR. DONOHUE: I lost my husband, daughter, mother-in-law and her mother to ALS, amyotrophic lateral sclerosis. My grandson has some symptoms, and so do a daughter and son. – E.P.

ANSWER: ALS, amyotrophic lateral sclerosis, is better known as Lou Gehrig’s disease. That famous baseball player died of it. It’s a destruction of nerve cells in the brain and spinal cord that eventually make a person unable to move, swallow or talk.

Only about 5 percent to 10 percent of ALS patients have the hereditary form, the kind that appears to be at work in your family.

You and your family can get all the information you need from two groups that actively support ALS patients and their families. The Amyotrophic Lateral Sclerosis Association can be contacted at 818-880-9007 and on the Internet at www.alsa.org. The Muscular Dystrophy Association has an ALS division that can be reached at 800-344-4863 and on the Internet at www.als.mdausa.org.

DEAR DR. DONOHUE: I am a 41-year-old woman, very petite, 5 feet 1 inch tall, and weigh 95 to 105 pounds. I am being bullied about this by my doctors. Have they supersized the height-weight tables to accommodate our increasingly obese population? I am lightweight but have no health problems. Your thoughts are welcome. – L.N.

ANSWER: Your body mass index is 18.9, which puts you in the normal weight category but at its lower end. If you feel healthy and eat a balanced diet, bully those doctors back.

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.