Pharmacology & Genetics
It has been known
for centuries that certain diseases are inherited, and we now understand that
individuals with such diseases have a heritable abnormality in their DNA.
During the last 10 years, the genomes of humans, mice, and many other organisms
have been decoded in considerable detail. This has opened the door to a
remarkable range of new approaches to research and treatment. It is now
possible in the case of some inherited diseases to define exactly which DNA
base pairs are anomalous and in which chro-mosome they appear. In a small
number of animal models of such diseases, it has been possible to correct the
abnormality by gene therapy, ie, insertion of an appropriate “healthy” gene
into somatic cells. Human somatic cell gene
therapy has been attempted, but the technical difficulties are great.
Studies of a newly
discovered receptor or endogenous ligand are often confounded by incomplete
knowledge of the exact role of that receptor or ligand. One of the most
powerful of the new genetic techniques is the ability to breed animals (usually
mice) in which the gene for the receptor or its endogenous ligand has been “knocked
out,” ie, mutated so that the gene product is absent or nonfunctional.
Homozygous knockout mice usually
have complete suppression of that function, whereas heterozy-gous animals
usually have partial suppression. Observation of the behavior, biochemistry,
and physiology of the knockout mice often defines the role of the missing gene
product very clearly. When the products of a particular gene are so essential
that even heterozygotes do not survive to birth, it is sometimes possible to
breed “knockdown” versions with only limited suppression of function.
Conversely, “knockin” mice, which overexpress certain proteins of interest,
have been bred.
Some patients
respond to certain drugs with greater than usual sensitivity to standard doses.
It is now clear that such increased sensitivity is often due to a very small
genetic modification that results in decreased activity of a particular enzyme
responsible for eliminating that drug.) Pharmacogenomics
(or pharmacogenetics) is the study of thegenetic variations that cause
differences in drug response among individuals or populations. Future
clinicians may screen every patient for a variety of such differences before
prescribing a drug.
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