Can you hear me now?

About one out of every 10 Americans suffers from hearing impairment, according to a survey conducted by the Better Hearing Institute, a nonprofit advocacy group.  By far, the most common cause of hearing loss is damage to the so-called hair cells in the inner ear as a result of excessive noise, certain illnesses and drugs, and simple aging.  The problem is that once hair cells die, humans (like other mammals) aren't able to grow new ones.

Hair cells, which took their name because under the microscope they look like cells with little hairs growing out of them, are an essential link in hearing.  The filament hairs, or cilia, bend with vibrations caused by sound waves entering the ear.  That induces the hair cell to create an electrical signal that is passed on to the auditory nerve and sent to the brain.  Devices such as hearing aids, which amplify sounds, and cochlear implants, which stimulate the auditory nerve directly, help people hear, but neither restores hearing to normal.

There are two main approaches to efforts aimed at inducing hair cells to regenerate:

1.  Get stem cells to turn into hair cells, either by transplanting them from other parts of the body or by stimulating stem cells naturally occurring in the inner ear to transform themselves.

2.  Mimic the process of hair cell regeneration in animals that don't spontaneously regenerate hair cells. 

Scientists say aspects of such research, likely will be first to have application in humans.  There could be therapeutic trails to prevent hearing loss using drugs within a decade.  However, finding a cure for hearing loss using hair cell regeneration is likely to be at least 20 years away.

Source: The Wall Street Journal, August 4, 2009