Users' Guides to the Medical Literature
Guyatt G, Rennie D, Meade MO, Cook DJ
Part E Prognosis
Chapter e18.1. How to Use an Article About Genetic Association
John Attia, John P. A. Ioannidis, Ammarin Thakkinstian, Mark McEvoy, Rodney J. Scott, Cosetta Minelli, John Thompson, Claire Infante-Rivard, Gordon Guyatt
Using the Guide—Part 1
Topics Discussed:
alzheimer's disease, apolipoprotein e, apolipoprotein e-4, chromosomes, human, dementia, genetic predisposition to disease, genetic research, genetic variation, genome, human, hardy-weinberg distribution, linkage disequilibrium, mutation, phenotype, polymorphism, reproducibility of results, risk assessment, rna, messenger, single nucleotide polymorphism
Excerpt:
"In 1953, James Watson and Francis Crick proposed a winding staircase
(double helix) structure of DNA (Figure e18.1-1). The sides
of the staircase or ladder, called strands,
are formed by alternating sugar (deoxyribose) and phosphate molecules;
the rungs of the ladder are formed by 4 nitrogen-containing ring
compounds called bases: adenine (A),
thymine (T), guanine (G), and cytosine (C). A pair of these bases
forms each rung of the ladder; adenine always binds to thymine and
cytosine always binds to guanine to form the full rung. Thus, each
rung of the helix ladder is called a base
pair. A single base plus its associated sugar and phosphate
groups is called a nucleotide.A 55-year-old man with a family history of dementia is inquiring
about genetic testing for Alzheimer disease, in particular testing
for APOE. Armed with knowledge of the basic genetic concepts outlined
in the introductory section of this chapter,20 you
return to your electronic medical reference discussion. Of the studies
they cite, you focus on the largest study (n=6852), with
longest follow-up (up to 9 years), representing a general, community-based
population aged 55 years and older,21 and using
the stronger of the candidate gene study designs (cohort rather
than case-control). The authors report a relative risk of 2.1 (95% confidence
interval, 1.72.7) for dementia in APOE e4 (e for epsilon) heterozygotes
and 7.8 (95% confidence interval, 5.1-11.9) for APOE e4
homozygotes compared with e3/e3 individuals. ..."
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