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Letters |
Blackburn Cardiovascular, Genetics Laboratory, Robarts Research Institute, 406-100 Perth Dr., London, Ontario, Canada N6A 5K8, Fax 519-663-3789, E-mail robert.hegele{at}rri.on.ca
To the Editor:
APOE genotyping to identify subjects with the E4 allele is helpful in the diagnosis of Alzheimer disease when used together with clinical criteria (1). The most common APOE genotyping method involves digestion of a 244-bp PCR-amplified fragment of APOE exon 4 followed by digestion with endonuclease HhaI (2). The digestion creates a characteristic pattern of DNA bands in electrophoresis gels for each of the three common APOE alleles (E4, E3, and E2) and thus for the six common APOE genotypes (E4/4, E3/3, E2/2, E4/3, E3/2, and E4/2) (2). However, there are four additional HhaI recognition sites within the 244-bp fragment that is amplified by this method, and the fragment also harbors several sites that differ from the HhaI recognition sequence (GCG/C) by a single nucleotide (2).
In the course of >2000 APOE genotyping reactions, we have
observed two individuals who had patterns of HhaI
restriction fragments that were distinct from any that could have
resulted from the common APOE genotypes (Fig. 1
). DNA sequencing of these two individuals revealed that each
was heterozygous for a different rare APOE mutation, namely
R136C and R136S. Both of these mutations have been reported previously
in probands with hyperlipidemia and premature atherosclerosis
(3), as was the case for both subjects in the present
report.
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The frequency of rare mutations in APOE has been estimated
to be as high as 1% (3). The DNA sequence change produced
by some of these mutations will create an unusual pattern of
HhaI fragments. Thus, the increased use of APOE
genotyping for Alzheimer disease will likely identify numerous
individuals with rare mutations in APOE. This means that the
laboratories that perform APOE genotyping with
HhaI will need to be aware of the possibility of uncovering
rare APOE mutations and will need to recognize when this
occurs. Furthermore, the APOE genotype would be of
questionable benefit for the diagnosis of Alzheimer disease in a
patient with a rare mutation of APOE. In addition, before
ordering the test, the attending physician would need to be aware of,
and perhaps make the patient and family aware of, the possibility that
the routine genotyping test might uncover a new APOE
mutation. Finally, the physician who orders the test would have to be
able to interpret the possible pathophysiological and genetic
implications of a rare APOE mutation when it is found. These
potential problems could be circumvented by the use of an
APOE genotyping method that is limited only to the detection
of the C
G change underlying the R/C112 amino acid polymorphism
underlying the E4 allele (4), thus eliminating
the possibility of detecting any other APOE sequence
changes.
Acknowledgments
This work was supported by the Medical Research Council of Canada (Grant MA13430), the Heart and Stroke Foundation of Ontario (Grant 3628), and general support from the Blackburn Group. Dr. Hegele is a Career Investigator of the Heart and Stroke Foundation of Ontario (CI-2979).
References
a Author for correspondence.
1
Department of Molecular, and Cellular Engineering, and Center for Bioethics, University of Pennsylvania, 3401 Market St., Suite 320, Philadephia, PA 19104-3308
2
Department of Pathology, and Laboratory Medicine, University of North Carolina, School of Medicine, Chapel Hill, NC 27599
To the Editor:
Dr. Hegele's finding of unique disease-causing mutations in the APOE gene during routine genotyping for Alzheimer disease highlights the continuing need for broad patient-oriented clinical observation and intervention as genetic discoveries and tests move from the research laboratory into clinical use. This type of discovery, made in the course of clinical testing, can be stifled by the monopolization of testing services enabled by the exclusive licensing of genetic testing patents (1). Indeed, Dr. Hegele admits in his letter to performing more than 2000 tests, and his performance of these tests may well infringe a Canadian patent sought by Duke University on APOE4 testing. Laboratorians in the US are prevented from making similar discoveries because of the exclusive license on the test granted by Duke to Athena Diagnostics. The fear of being sued might also lead clinical laboratorians not to publish such findings, which is a foreseeable and unfortunate result of patents on medical processes such as tests, and which would be antithetical to medical and scientific norms.
Perhaps more importantly, Dr. Hegele notes the importance of working with informed patients (and perhaps involved family members) to determine the proper scope of testing to be performed. This example of the uncertainty and continuing research nature of clinical discovery about the role of genetic mutations in Alzheimer disease also supports the assertion that a patent-based monopoly on clinical testing services unreasonably interferes with both patient care and science. This will likely become more of a problem as tests move into clinical use for the rapidly growing list of known disease genes.
References
The following articles in journals at HighWire Press have cited this article:
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  A Varghese, R Deepa, M Rema, and V Mohan Prevalence of microalbuminuria in type 2 diabetes mellitus at a diabetes centre in southern India Postgrad. Med. J., June 1, 2001; 77(908): 399 - 402. [Abstract] [Full Text]
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