Biology Reference
In-Depth Information
7.1 A Look to the Future
Routine molecular diagnostic testing for many of the genes causing hearing
impairment is likely to be available within the next few years, and genetic
testing may become the method of choice for newborn hearing screening.
Although the development of effective therapies based on gene identifica-
tion is still in its infancy, promising new advances made possible by research
are arising at a rapid rate, and the potential for developing molecular inter-
vention strategies as a treatment, and perhaps cure, is encouraging. A pre-
requisite, though, is determining the normal function of proteins encoded
by hearing impairment genes.
Knowing the gene mutation that is responsible for hearing impairment
in an individual provides information that is relevant to all family members.
Based on this information, they may choose to be tested in order to help
in making reproductive decisions. In addition to genetic tests, a desirable
goal is to be able to predict the phenotype based on the genotype, and vice
versa. However, defining the precise phenotype and providing an accurate
prognosis based on the mutation is not yet straightforward. Physiologic
indices that correlate with the presence of a mutation are valuable pheno-
typic measures that will enhance our understanding of the function of the
normal gene product
(
Hood 1998; Huang et al. 1996, 1998; Liu and Newton
1997; Morell et al. 1998). The development of such measures that accurately
define the phenotype, together with the application of microarray technol-
ogy to diagnostic testing and functional studies of hearing impairment genes
and the proteins they encode, will lead to improved classification and pre-
diction of outcomes, as well as to rational and effective therapies for all
forms of hearing impairment.
Glossary
ABR/EcochG:
Auditory brainstem response and electrocochleography are com-
panion evoked-potential studies that reveal the cochlear microphonic, summat-
ing potential, action potential and synchronous discharge of neural elements in
the auditory pathway from cochlea to lateral lemniscus. The tests are used as
tools to evaluate both auditory and neural integrity of the auditory system. While
neither is a direct test of hearing, the results are powerful predictors of hearing
status, when they are normal. In contrast, the absence of a synchronous ABR or
EcochG does not always mean deafness is present.
Allele:
One of several alternative forms of a gene or DNA sequence at a specific
chromosomal location.
ATP (adenosine triphosphate):
The principal immediate-energy source in all
eukaryotic cells.
Autozygosity:
Homozygosity for an allele that is identical by descent.
BAC (bacterial artificial chromosome):
A vector designed for cloning relatively
large DNA fragments between 50 and 200 kb. BACs are propagated in a host
bacterial cell.
