Dear Doctor: I was a huge Luke Perry fan in high school, and like so many others, I was shocked that he had a stroke at just 52 years old. Isn’t that awfully young? How do you know if you’re having a stroke?

Dear Reader: While it’s true that the majority of strokes occur in people 65 and older, they can happen in people of any age. This includes not only young and middle-aged adults, but also children and even infants in utero.

Stroke is the fifth-leading cause of death in the United States. Risk factors include high blood pressure, high cholesterol, smoking, obesity and diabetes. Of the 795,000 people each year who have a stroke, 140,000 do not survive. A significant percentage of those who do survive are left with a range of disabilities that affect speech, movement and cognition. One of the challenges for younger stroke victims is misdiagnosis. Symptoms can be mistaken for conditions like migraine, seizure and inner ear disorders.

A stroke occurs when the blood supply to the brain is interrupted, which happens in two ways. The most common type of stroke, known as an ischemic stroke, occurs when blood is unable to travel through a blood vessel and reach the brain. This can be due to a clot that arises in or travels to the brain and blocks the vessel, or to narrowing of the blood vessel itself. In a hemorrhagic stroke, the second major type of stroke, the blood vessel tears or ruptures. In both types of stroke, the result is the same -- the oxygen and nutrients carried by the blood can’t reach the brain cells. In a very short period of time, the brain cells begin to die.

A third type of stroke is known as a transient ischemic attack, or TIA. This is when stroke symptoms appear for a brief period of time but then go away. These so-called "mini strokes" can sometimes be precursors to a major stroke, so it’s important to take TIAs seriously and seek medical treatment immediately.

Signs of stroke include sudden weakness or numbness in a limb or in the face, often on just one side of the body. Sudden dizziness, confusion, garbled speech, loss of balance or coordination, or problems with eyesight in one or both eyes can also signal a stroke. So can the advent of a sudden headache, often quite severe, sometimes accompanied by tingling sensations in the face or body.

A useful memory prompt for stroke symptoms is the word FAST. The letters represent three major indicators of stroke. F is for face drooping, A is for arm weakness and S is for speech. The final letter, T, stands for “time to call 911.” That’s particularly important because swift treatment can be the difference between life and death. It can also affect the level of disability that the stroke causes in a survivor. Studies show that receiving emergency medical care within three hours of the first symptoms of stroke results in less disability three months later as compared to those for whom medical care was delayed. So no matter someone’s age, when symptoms suggest a stroke, seek immediate medical help.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: Stem cell therapies are being heavily marketed here in Florida as promising treatments for a variety of illnesses, but I have my doubts. As a retired doctor, I hate to see people go into debt to pay for something fraudulent or unsafe. Am I being too critical?

Dear Reader: Stem cell therapies are making headlines right now in two very different ways. One is the news that a patient infected with HIV has been in remission for 18 months following a stem cell transplant. The other stem cell news arises from the subject of your letter. That is, unproven and unapproved stem cell treatments. These are being widely marketed as miracle cures for everything from Parkinson’s disease, autism, arthritis and dementia to depression, multiple sclerosis, macular degeneration and traumatic brain injury.

Although the use of embryonic stem cells is federally monitored, adult stem cells can be extracted from a patient’s own body. That makes regulation and oversight challenging.

Despite extravagant claims of success by stem cell clinics, outcomes are largely unproven. However, the potential dangers are clear. In the past year, at least 17 people in five states have become gravely ill following stem cell treatments that used injections of umbilical cord blood and required hospitalization. In one such case, a man who received an injection of umbilical cord blood to address joint pain developed sepsis, a life-threatening infection. He spent 58 days in the hospital.

Last December, the Centers for Disease Control and Prevention published a report warning about unapproved stem cell treatments. The Food and Drug Administration has issued numerous warnings on the issue as well.

The allure of stem cells is that they are a kind of blank canvas. These "unprogrammed" cells divide rapidly and have the ability to change into other types of cells, such as bone, brain or muscle cells. As a result, stem cells are the centerpiece of regenerative medicine, in which disease and injury are treated by growing new cells, or by replacing or repairing those that are dead and damaged.

Thanks to their unique properties, stem cells are seen as important tools in potential new therapies for diabetes, Parkinson’s and heart disease, among others. But because stem cells are undifferentiated, they must first go through a special process, somewhat like programming, in which they are prepared to become specific types of cells. It is during this process, as well as during the act of transplantation, that potential risks to patients can arise.

According to the CDC, a number of vials of stem cell products made from umbilical cord blood were found to be contaminated with E. coli. Even before this latest spate of bad news, various unapproved stem cell treatments were found to cause harm to patients that included severe respiratory illness, blindness and even death.

With few consumer protections in place at this time, the FDA recommends that patients avoid stem cell therapies that are not part of an approved clinical trial. To find ongoing and upcoming clinical trials that use stem cells, visit clinicaltrials.gov. The home page contains a form that you can use to focus your search.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I read with interest your column about how sugar likely affects the gut, and I now have questions concerning antibiotic treatment. Are all gut bacteria eliminated? Can they be restored? Do probiotic supplements help the gut return to normal? I thought the body produces its own.

Dear Reader: In the same way that the discovery of penicillin launched a medical revolution in the late 1920s, the near-daily discoveries about the power and potential of the gut microbiome are now transforming our understanding of both health and disease.

The 10 trillion to 100 trillion microorganisms that each of us harbors in our digestive tract consist of more than a thousand species with more than 3 million genes. Not only do they play significant roles in digestion, synthesize vitamins and other nutrients, and coordinate with the immune system, research shows that our gut flora has a hand in regulating mood, weight, inflammation and certain disease processes.

So what happens to the gut microbiome after antibiotic treatment? Two well-regarded studies into the question, one performed in mice and one in healthy men, had similar answers. An outcome common to both studies was that, following antibiotic therapy, the numbers and diversity of the microbial communities were vastly reduced. The other was that once antibiotic therapy concluded, the gut microbiome began to quickly repopulate. However, in both the mouse and human studies, a comparison of pre- and post-therapy fecal samples revealed that the landscape of the new gut microbiomes had changed significantly.

The mouse study found that in addition to nearly eradicating the native microbes, antibiotic therapy reduced the metabolic rate of those that managed to survive. The antibiotics also caused certain changes to the environment of the gut itself. These two factors opened the door to repopulation of the mouse guts by new species, some of them potentially harmful.

The human study found that although the gut had repopulated the majority of its original species six months after antibiotic therapy, nine common beneficial bacteria failed to return. At the same time, several potentially harmful bacteria made an appearance. The takeaway is that while the gut microbiome in most healthy adults is resilient in the face of antibiotics, the breadth and diversity of our microscopic partners do take a hit.

One new area of research is the use of fecal transplants to both restore the original ecosystem of the gut and protect against colonization by undesirable species. This was done in a recent study in patients undergoing intense cancer treatment. Using fecal samples that were frozen and stored prior to their procedures, patients recovered a significant portion of their pre-treatment gut flora.

When it comes to countering the effects of antibiotics with probiotic supplements, though, the jury is still out. One study found that while probiotic supplements successfully colonized the gut, they also delayed the return of native flora. Until we have definitive answers, time and diet look like best approach for gut recovery. That means eating from a wide range of fermented, cultured and fiber-rich foods, and limiting sugar and red meat, all of which have been shown to contribute to gut health.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)