Everywhere we turn
lately, articles appear lauding the astounding developments in molecular
genomics. These developments stand to have greater impact than the Internet.
Although we are bombarded with the changes molecular biology will bring
about in our lives, in our practices, and in the lives of our patients,
I, for one, daily feel overwhelmed. Unlike other changes in our professional
careers, genomics offers promises that are limited only by our imaginations.
In an era when 40-50% of physicians consider leaving the practice of
medicine and many would not advise their offspring to pursue a medical
career, it is no exaggeration to envision molecular biology as scientific
medicine's salvation. Genomics carries the potential to allow physicians
to shake off the current doldrums of medicine by providing us with a
means of restoring our loss of autonomy and personal relationships with
patients. Imagine how individualized our care will become when we can
examine a patient's basic genetic constitution. This will only occur
if we become sophisticated in genomic applications and advocate its
appropriate application.
Despite the pending publication of the "first draft" of the humane genome,
there remains a huge amount of work to be done to establish causality
between genotype (genetic makeup) and phenotype (genetic expression).
To properly apply this information to risk stratification and disease
management requires that practicing physicians assume center stage.
Some feel we should be budding geneticists and that this is a role we
should embrace and not shirk. The basic scientists are providing us
with a wealth of tools, but it requires the real world clinician (and
not businessmen or bureaucrats) to properly use the information. Genomics
will not instantly cure cancer or eliminate disease as some project,
but it will have a huge impact.
What is genomics? I'll define it simply as the study of the total DNA
sequence and its variations within a species, be it human, dog, mouse,
Drosophila; you name it. This is in contradistinction to genetics, the
study of how the genome is expressed and functions. Strides made in
mapping and characterizing genes have accelerated with the recent completion
of the entire human genome, 2 years ahead of schedule. The entire human
genome is composed of roughly 3 x 109 base pairs found on a complement
of 22 homologous pairs of autosomal chromosomes (numbered on the basis
of size, 1 - the largest, 22 the smallest) and a pair of sex chromosomes
(#23). The 46 chromosomes carry 60 - 140,000 genes, although less than
3% of these genes actually encode peptide sequences. As an aside, the
June 12, 2000, issue of The New Yorker has an insightful commentary
by Richard Preston profiling the players in the ongoing human genome
project. It is a tale of ego, power and, naturally, gobs of money, but
it is also a description of breathtaking speed and scope. Sequencing
steps that were once onerous and costly in time and resources are now
automated and performed in subfractions of the time.
As an overview
and introduction to the concepts and technology, Dr. Kirk Hogan from
the University of Wisconsin-Madison has written a compelling chapter
on Principles and Techniques of Molecular Biology in Hemmings
and Hopkins' new book, Foundations of Anesthesia: Basic and Clinical
Sciences [1]. This text is impressive; it is a reasonable size,
at 748 pages, and price, at $129.00, and has a distinguished international
group of authors, excellent color figures and tables, and brief but
focused bibliography. The text covers the four major areas of basic
science that impact our clinical practice: molecular and cell biology,
physiology, pharmacology, and physics and measurement [1]. I encourage
you to take a look at it.
Hogan succinctly
puts matters in perspective by framing the crucial role of nucleic acids
[deoxyribonucleic acid (DNA), ribonucleic acid (RNA)] as the sole signaling
system able to leap the biological imperative of cell death by coordinating
mechanisms fundamental to growth, reproduction, development, and response
to disease. By preserving the biochemical morphology of an organism,
successful genetic adaptations can be passed on to profit future generations.
Covalently linking pentose sugars (deoxyribose) to a purine base [adenine
(A), guanine (G)] or pyrimidine base [cytosine (C), thymine (T)] linked
in parallel comprise the DNA portions of the code. RNA differs in being
single stranded and having ribose as the pentose sugar and a substitution
of uracil for thymidine. There are three types of RNA; messenger (mRNA),
ribosomal (rRNA), and transcriptional (tRNA). Hogan outlines how genetic
information encoded by DNA is converted into protein assembly. The first
step is transcription, wherein mRNA is assembled to be complementary
to the DNA sequence. In the next step, translation, mRNA acts as the
template for synthesis of amino acid into protein with the aid of rRNA
as a docking station, and twenty distinct tRNAs function as shuttles
for specific amino acids. Hogan explains the coding process in some
detail and informs us of its redundancy and sequencing. He reviews how
nucleic acids repair, adapt, and develop mutations, and how we measure
their activity and detect their sequence. This includes commentary on
the use of complementary DNA (cDNA) and in situ hybridization techniques
to create libraries of nucleotides (DNA fragments) that can be used
to form specific proteins. He reviews blot technology; Southern blots,
which quantify DNA, Northern blots, which measure RNA, and Western blotting
to quantify protein. He discusses the polymerase chain reaction (PCR),
a process that is used to amplify incredibly small amounts of DNA as
a means to directly identify viruses such as HIV, hepatitis A, B, C,
other microorganisms, and human phylogeny.
In a personal conversation I had with Professor Hogan, he emphasizes
that the concepts are not complex, but beautiful in their simplicity.
The basic principles of genomics are the same for corn, whales, and
humans. He feels the applications for anesthesiologists are not arcane,
but highly relevant to preoperative diagnosis of pharmacogenomics and
genomic toxicology and co-existing disease (MH, pseudocholinesterase,
others) and to elucidation of the mechanism(s) of general anesthesia.
Furthermore, genomics will provide increased safety in the workplace
(rapid detection of pathogens, genetic variability in the metabolism
of nitric oxide) and innovative therapies (use of recombinant proteins,
drugs, receptor specific products, and pain management modalities).
The foundation of
knowledge that Hogan elucidates can be rapidly applied and expanded
through a review of an ongoing series presented in the New England
Journal of Medicine (NEJM) on Advances in Immunology [2,3]. This
series started in the July 6, 2000, issue of NEJM and will continue
into 2001 with monthly reviews. The inaugural presentation is a two-part
overview of the immune system by Drs. Peter Delves and Ivan Roitt of
the Windeye Institute of Medical Sciences at the University College
London [2]. The review focuses on "the cellular and humoral constituents
of the immune system, the function and organization of these components,
and how they interact in protecting the body against the microbial world
[3]." In his accompanying editorial, Schwartz comments on the number
of fields that will be impacted by the new developments, and includes
Anesthesiology on this list [3].
The immune system
commentary includes an excellent glossary that defines terms in common
use in molecular biology and genomics. It then discusses basic defenses
and immune recognition. Soluble mediator function (the complement cascades,
cytokine and chemokine action) and cellular responses [WBCs; particularly
macrophages (derived from monocytes) and lymphocytes; and interdigitating
dendritic cells, a key component of innate immunity] are presented concisely.
The remainder of part I discusses B and T cell lymphocytes. It focuses
on the development, differentiation, activation, function, signaling,
tolerance, and memory of this cell line. The review establishes the
bases of normal host defense, excessive host response, autoimmune injury,
and immunopathology.
Part II extends
commentary on lymphocyte and lymphoid tissue action. It discusses the
role of the spleen as the center of immune response to blood-borne infection
vs. local mucosa-associated lymphoid tissue response to inhalation or
ingestion of pathogens. Antigen processing and activation and regulation
of lymphocytes are also described. Activation occurs via interaction
with cluster of differentiation (CD) cells [an example of the role of
CD cells is the CD-4 subtype, a cytokine-secreting helper cell, which
is monitored for progression of the human immunodeficiency virus (HIV)].
The authors comment
on the continual mutation of microorganisms, a phenomenon that causes
"antigenic drift". These mutants pose significant problems for the immune
memory system. Furthermore, organisms can cause "antigenic shift" by
exchanging genetic material. This limits or eliminates effective immune
response to organisms that were previously recognized by the immune
system.
The final section
of Part II touches on immunologic technology where selected genes are
expressed (transgenic application) or eliminated (knockout technique).
These approaches have been used to overexpress or eliminate a host of
specific enzymes and proteins as well as develop models of autoimmune
and immunodeficiency states. Recombinant-DNA technology is discussed--for
example, rodent genetic expression can be humanized to form a large
library of specific monoclonal antibodies or proteins.
The remainder of
this series promises a broad coverage of additional immune, molecular,
and genomic studies and applications. I look forward to being educated.
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