Biology Reference
In-Depth Information
the patient is packaged into a vector and introduced to the cells. The gene
is not incorporated into the germline cells. The purpose of gene therapy is
to treat the patient, not to change the genetic material that is passed to the
next generation. Many research studies are in progress to determine effec-
tive vectors and suitable approaches for delivering genetic material to spe-
cific tissues. Certain classes of viruses may be used as vectors, and ongoing
investigations are exploring their potential in gene therapy. Nonviral strate-
gies such as coating the gene in a lipid layer are also being developed.
Although still in its infancy, gene therapy holds great promise for future
treatment of genetic disorders, including hearing impairment. Cook et al.
(2000) provide a summary of ongoing gene therapy research that targets
the inner ear.
7. Summary
Genetic studies are resulting in the identification of genes for many disor-
ders. In theory, once a disease gene is identified, diagnostic tests can be
developed to detect mutations in individuals who may have the disease.
Offering such diagnostic tests can be beneficial if one or two mutations are
responsible for most cases. For many genes, however, unrelated affected
individuals are likely to have different mutations, making detection a time-
consuming and expensive task, especially if the gene is large. Moreover,
finding a sequence difference does not necessarily mean that the responsi-
ble mutation has been found; sequence variation among individuals is
common and very few of the variants are associated with a disorder. Thus,
setting up diagnostic tests that are commercially available may not be eco-
nomically feasible. On the other hand, once a mutation is identified in one
family member, related individuals can be tested for this mutation. This can
be beneficial for: (1) presymptomatic diagnosis in later age at onset disor-
ders; (2) detecting the presence of the deleterious gene when penetrance is
not complete, meaning that unaffected individuals may have the gene;
and (3) identifying carriers of the gene when the inheritance pattern is
recessive.
Many ethical issues must also be considered. Should molecular diagnos-
tic testing be offered routinely if the result will not provide an alternative
approach to treatment and management of the disorder? What are the psy-
chological effects of presymptomatic genetic testing? Should parents be
able to have their children tested for the presence of a mutation for which
the age at onset of symptoms is after they reach adulthood? What is the
obligation to other family members if a deleterious gene is detected?
Remember, genes are transmitted from one generation to the next, and the
results for one individual are pertinent to many relatives.
