Spinal-bulbar muscular atrophy (SBMA) mostly affects men and usually begins between the ages of 30 and 50, although symptoms have begun in boys as young as 15 or men as old as 60. In those few women who have the disease, the symptoms are usually mild.
The bulbar muscle involvement in SBMA can be significant, affecting speech, chewing and swallowing. The swallowing muscle weakness can lead to choking on food or liquids or inhaling them into the lungs. This kind of inhalation can lead to obstruction of airways or infection. Weakness in the throat muscles also can make breathing during sleep difficult.
Facial muscle weakness can occur, making it hard to smile or convey emotion through facial expressions.
SBMA also involves weakness and atrophy of the arm and leg muscles, particularly those nearest the center of the body. Twitching or cramping of muscles can occur.
Weakness of the limb muscles is often first noticed as trouble with stairs or difficulty walking long distances, such as through malls or parking lots.
In addition, men with SBMA can develop enlarged breasts (gynecomastia), and may have reduced fertility and atrophy (shrinkage) of the testicles. These symptoms, which are important clues to the cause of the disease, are related to abnormal processing of male hormones, known as androgens.
Female carriers of the flawed gene that causes SBMA can develop muscle cramps and twitches, particularly as they get into their 60s or 70s.
Although women also produce and use androgens, they do so at lower levels than men and hormonal differences between the sexes are thought to contribute to SBMA's milder course in women.