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Northwestern University Law Review : Colloquy : 2007 : Kaye
Please, Let’s Bury the Junk: The CODIS Loci and the Revelation of Private Information
By D.H. Kaye[*]
In a recent essay, Professor Simon Cole asks “Is the ‘Junk DNA’ designation bunk?”[1] He concludes that in one sense, it is not. There is no scientific evidence that the specific DNA variations used to identify the sources of crime-scene DNA perform any biological functions. Nonetheless, he contends that this fact, in and of itself, does not obviate the concern that the specific STR profiles stored in law enforcement databases of offenders (and sometimes arrestees) might be used to extract medically or socially sensitive information. I agree and have said as much in the past.[2]
Professor Cole also writes that “[t]he
privacy threat posed by forensic STRs may not be great,”[3] but he does not explain the basis for this
view, and many of his remarks could be construed as being more consistent with
the opposite conclusion—that the privacy threat may well be great. He criticizes the assurances of forensic
scientists and human geneticists that, at present, “forensic DNA has no predictive
value or medical significance”[4]
as “misleading” and “not fully informative.”[5] He proposes that the records of the STR types of offenders contained in existing
law enforcement databases “may, in fact, be precisely the kind of ‘predictive
medical information’ that concerns privacy advocates,”[6] and he refers to STRs as potential “markers”
having “predictive utility.”[7] In
particular, he asserts that “the forensic STRs . . . correlate with . . .
disease-causing genes”[8] and “phenotypically perceived race.”[9] He
concludes that “[i]f some forensic STRs are correlated with genes that cause
physical traits, . . . the public can [and should] be informed of that fact”[10] so that it “can decide for itself whether
and to what extent the privacy risk offsets the benefits of genetic databases.”[11] The genetically influenced physical traits
that he proposes are discernible from the DNA sequences used in criminal
identification databases in the United States include diseases that would be of
interest to insurance companies or employers and physical features associated
with conventional racial categories.
These remarks require clarification. Just as the argument that nonfunctional DNA
cannot be a threat to privacy is superficial, it would be incomplete and
misleading simply to inform the public that an STR profile contains information
that is correlated to physical traits such as disease and possibly behavioral
predispositions and hence could be used to predict whether an individual will
develop a disease. By innuendo, this
formulation suggests that these nonfunctional loci, which are very weakly associated
(if at all) with disease or behavior, are comparable to the loci used in much
more powerful modern genetic testing for the DNA sequences of mutations that do
cause disease.
This Colloquy Essay therefore analyzes in
greater depth the medical and biological implications of the DNA records in the
National DNA Index System (NDIS) and its local and state components. It explains why the STR profiles are useless
as a “genetic test to screen for any particular disease.”[12] No
one can say for certain what the future of genetics holds, but based on current
knowledge and practice, the information coded in the databases is and will
remain, with the limited exceptions noted below,[13] useful only for identification.
To develop these points, Part I briefly
describes the four possible ways in which genetic loci could possess predictive
or diagnostic value with regard to diseases and explains why these mechanisms
have not led, and probably cannot lead, to useful screening tests with the
Convicted Offender DNA Index System (CODIS) profiles in national, state, and
local databases. Part II considers the
“physical traits” and familial relationships that the CODIS STRs can be used to
identify. That the profiles carry
limited information about an individual’s race and familial relationships has
long been part of the public dialogue, and Part II places the resulting privacy
issues in perspective. Part III comments
on analogies between STR types and fingerprints, social-security numbers, and
the like, employed when discussing these issues in the public forum.
I. The CODIS STR Profiles As a Source of Health Information
There are only four mechanisms through which
a genetic locus could have predictive or diagnostic value: (1) mutations at the locus itself; (2)
physical linkage of this locus to a locus at which a disease-causing mutation
is present; (3) population structure; and (4) trisomies. In the first situation, certain DNA sequences
at the locus cause a disease. In the
other three situations, no alleles at the locus cause a disease, but they could
be correlated with a disease. This Part
explains why, for the CODIS STR loci, none of these mechanisms can be exploited
to produce a valid and useful disease-screening test in the offender databases
and why this situation is unlikely to change.
A. Gene Mutations
As the first mechanism, certain DNA sequences
are transcribed into RNA that either regulates gene expression or is translated
into proteins. Some of these
DNA-sequence variations (“alleles” is the technical term) at various locations
on the chromosomes could be harmful. For
example, individuals afflicted with von Hippel-Lindau disease (VHL) develop
tumors or cysts in the eyes, brain, spinal cord, kidneys, or a few other sites.[14] The
VHL gene normally is transcribed into RNA molecules that are translated into a
tumor-suppressor protein. The protein
stops cells from forming tumors. VHL
disease occurs when a cell has two defective copies of the gene. A man born with a normal copy of the gene on
one chromosome and a defective copy on the other produces the tumor suppressor
because he has a functioning gene. No
VHL tumors occur. If this gene mutates
in just one cell out of the trillions in his body, however, the cell no long
produces the tumor-suppressing protein and can turn cancerous and
proliferate. If the DNA sequence of the
original, defective mutation is known, it may be possible to develop a genetic
test that recognizes that specific sequence. Directly testing for the mutation thus identifies asymptomatic
individuals at risk to develop VHL.[15]
As Cole recognizes, there is currently no
indication that the CODIS STRs are transcribed into RNA that would affect gene
expression.[16] Since
the CODIS STR alleles are not disease-causing mutations, they cannot be the basis
of a genetic test that directly detects such mutations. Furthermore, even if these STRs someday prove
to be functional through an as-yet-unknown mechanism, this would not
necessarily confer predictive medical value on them. For instance, hypothetically, STRs could be
essential to embryonic development: an
embryo with no STRs will not survive in the womb. In this case, the STRs would be functional,
but this functionality would have no privacy implications for the offender
databases. Variations in these
biologically significant DNA sequences would convey no information about the
health status or any other trait of any living human being.
Cole does not dispute the fact that the
mutations that have given rise to the many alleles in CODIS STR loci do not
affect phenotypes. He suggests, however,
that a nontranscribed DNA sequence might be statistically associated with a
disease-causing allele, and this correlation might be exploited to provide a
useful genetic screening test.[17] To
assess this speculation, we need to examine the remaining three ways in which
an association can arise.
B. Physical Linkage
The second possible mechanism for an
association between an STR locus and disease status or propensity is physical
linkage between a functional gene and an STR. For example, consider the same man who was born with a normal VHL allele
(which we can designate as VHL–) and a mutant allele (VHL+). If some STR locus is very near the VHL locus
then the two DNA sequences will tend to be inherited as a package.[18] In
particular, suppose that the man has an STR allele consisting of twelve repeats
on the VHL+ chromosome and a different STR allele on the VHL– chromosome. This man will transmit the 12-allele along
with VHL+ mutation to about half his children, while the other half will
inherit the other STR allele along with the VHL– allele. Assuming that the mother does not have a
12-allele, their children with the 12-allele are much more likely to have
inherited the father’s VHL+ allele than the normal VHL–. These children are at high risk for
tumors. This STR is not functional, but
in this one family it is a marker for VHL. If the physical linkage between the STR and the VHL gene occurs
throughout the population, and if the 12-allele is associated with the VHL
mutation throughout the population, then the STR could be used to predict the
occurrence of VHL tumors in the population.
Cole apparently believes that physical
linkages with disease loci are known to exist and that they could be the basis
for a useful screening test. He quotes
two sentences from an article in the Journal
of Forensic Sciences[19] that supposedly “state[] that some forensic
STRs are already predictive, though
not causal, of disease.”[20] However,
neither this article nor other scientific literature asserts that “the forensic
STRs . . . may be useful for tracking which individuals have the
disease-causing genes.”[21] The
two sentences allude only to the possibility that “many or possibly most STRs
will eventually be shown to be useful in following a genetic disease or other
genetic trait within a family” and that “a number of the core STR loci . . .
have been reported to be useful in tracking various genetic diseases through
loss of heterozygosity or allelic imbalance.”[22] These
remarks sound ominous, but this sort of “following” and “tracking” is not a
privacy problem for law enforcement databases because neither family studies
nor loss-of-heterozygosity (LOH) studies would be useful in discerning the
disease status of individuals in these databases via examination of their STR
alleles. To see why, we need to
understand how STRs are used in these two types of research studies.
1. LOH studies. An LOH study is useless for discerning
disease status from the NDIS records. This type of study tracks the progression of cancer in a patient by
gross changes in the DNA of a patient’s cells. The technique requires tissue from cancerous tumors.[23] Needless to say, the law enforcement database records do not include the
genetic profiles of an offender’s normal tissues and of his tumors.
2. Family studies. Gene hunters use STRs in studies of specific
families with rare, single-locus disease in order to zero in on the location of
the disease-causing mutation within the family. If the gene is located, then the mutation can be sequenced, and a
genetic test for the mutated sequence itself can be devised.[24] For
this purpose, STRs have played an important role in biomedical research. But the STRs are not used in the genetic
tests, and the fact that an STR locus was helpful in localizing a gene does not
make that locus predictive of a disease in the general population. In the earlier example of the hypothetical
STR marker for the VHL gene, the 12-allele is informative for the family
studied. In the general population, however,
the same correlation will not exist. This is because STRs have a high mutation rate, and each different STR
allele is fairly common.[25] The
number of people who have the 12-allele but do not have the VHL mutation will
swamp the tiny number who have 12-allele along with the mutation. Learning that an unrelated individual happens
to have the 12-allele does not appreciably increase the probability that this
person has the VHL+ allele or bring it to a level that would have any screening
utility. Some crude calculations suggest
that a positive result on the 12-allele “test” for a VHL mutation in the NDIS
database might be correct in less than one case in a thousand.[26] Parties with access to the database cannot use the recorded STR profiles
to pick out people who carry the VHL allele or have developed the heritable
disease. This exemplifies a well known
statistical phenomenon: even a fairly
accurate test for a disease with a small prevalence in the population has low
predictive value.[27]
One might think that there could be greater
predictive value if an STR locus is physically linked to a gene involved in a common
disease such as diabetes or coronary disease. But common diseases and health problems are affected
by multiple genes and strongly influenced by environmental factors. The same is true of the behavioral traits
that Cole “more speculatively” proposes some day might be the target of a
screening test in NDIS.[28] Even
if a CODIS STR turned out to be tightly linked to one gene in such a
system—something that is unlikely given that there are only thirteen such STRs
and 20–25,000 genes sprinkled across billions of base pairs—the correlation
with the disease will be highly diluted. Again, a genetic test using such an STR will have very little predictive
value.[29] As
such, the medical community cannot simply use forensic STRs or some other
genetic test to screen for a particular disease. Nature is not this generous.
C. Population Stratification
Third, a statistical association
theoretically could arise without physical linkage but through population
structure. The U.S. population is
composed of many subpopulations that have somewhat different allele frequencies
at various loci. These frequency differences
disappear over time as people mate outside their ancestral groups, but there
are some disease-related genetic differences across different
subpopulations. As a group, African-Americans,
for example, are at greater risk than Caucasians for sickle-cell disease;
conversely, cystic fibrosis occurs more often in Caucasians.[30] Inasmuch
as certain combinations of CODIS STRs occur more frequently in
African-Americans than in Caucasian-Americans and vice versa,[31] one can conceive of STRs being exploited to
produce a probability that an individual is an African-American or a Caucasian.
It is not clear whether Cole believes that
putting together these two sets of correlations will result in a valid
screening test for disease, but he expresses concern about using STRs to infer
race, and he writes that this possibility takes us “back to disease
prediction.”[32] If
the argument is that even in the absence of physical linkage, STRs will be useful
in predicting disease because of their correlation to self-reported or
socially-perceived race, there is little cause for alarm. Not only is the correlation between the CODIS
STRs and racial classifications weak, but even if it were perfect, no one can
make useful predictions about an individual’s disease prospects merely on the basis
of that person’s race. Knowing that a
person in the database is white or black warrants no prediction or diagnosis of
sickle-cell disease or cystic fibrosis. That an individual has an STR profile that is more often seen in one
census category than another is even less useful as a test for disease.
D. Abnormal Chromosome Numbers
Finally, genetic tests with three of the CODIS STRs could indicate the presence of certain chromosome-number abnormalities.[33] Cole does not note this possibility, and it is not a significant threat to the privacy of individuals with profiles in the NDIS database. Two of the conditions (trisomy 18 and 13) are irrelevant to the offender database-privacy issue because they are so debilitating.[34] The third abnormality (trisomy 21, or Down syndrome) is more common and less incapacitating, but given the health problems and physical appearance of individuals with this syndrome, in virtually all of the very rare cases among convicted offenders, the existence of the condition would already be known to the government and the public.[35]
II. The CODIS STR Profiles as a Source of Information on Other Phenotypes and Genetic Relationships
As Professor Cole remarks, at issue in the
lingering debate over the biology of STRs “is what is meant by the term
‘medical significance.’”[36] With
regard to the privacy threat of law enforcement databases, it is essential to
ask how the data—the STR profiles—sitting inside the FBI’s computers could be
misused. Can the government, employers,
or insurers employ the identification profiles to predict or infer something
useful about an individual’s health status? As we have seen, the “medical significance” of STRs (and other classes
of markers) in biomedical research does not make the STR profiles contained in
the law enforcement databases medically significant in the sense of revealing
health status or disease risks. At
present, the CODIS STR profiles cannot be used in this way.
But what about other phenotypes? Cole implies that forensic STRs are “socially
or medically significant [because] [t]hey . . . predict . . . phenotypically
perceived race.”[37] We
already have discussed the lack of medical significance of an STR profile as an
indicator of race-related diseases. As
for social significance, it would be very peculiar for the police to want to
use STRs to draw any conclusion about the race of an offender who already has
been convicted.[38] Having seen him, they already have perceived his race. They have his photograph and probably his own
statement as to race or ethnicity. As
one forensic biologist noted, a “photograph reveals a lot more about the person’s
physical, social and maybe even mental state than the anonymous patterns in
genetic fingerprints.”[39] Why use the STRs to make uncertain
inferences about race when there are simpler methods?
Professor Cole gives an answer when he
observes that the “memories of Japanese internment in the United States are not
so old. A government agency ordered to
round up individuals of a certain ethnic descent could, conceivably, perform
ancestry testing on a genetic database to automate the process.”[40] Even
if the prospect of a new internment program (of dubious constitutional
provenance) were deemed realistic, it is doubtful that the 13 CODIS STRs could
be used to pick out Japanese-Americans, Iranian-Americans, or some other
conceivable xenophobic target group. Inasmuch as the CODIS STRs were chosen in part because most population
groups contain the same alleles, it would be surprising if they were to prove
useful for distinguishing between, say, Japanese-Americans and
Chinese-Americans. A substantial
fraction of people would be misclassified, and many of them easily could prove
that they are from other groups. If so,
the automated round-up would be both costly and inaccurate compared to looking
at other records on file.
Another fact that could be exposed from STR
database profiles is kinship. Although
Professor Cole does not pursue this concern[41] and it is not part of his theory of
statistical correlations to genes that cause physical traits, STRs, like other
inherited characteristics, could be used to try to ascertain whether particular
individuals are related. For example, a
population-wide database would make it possible to determine if a given
individual is an illegitimate child. In
a small, local database of convicted offenders it might be possible to identify
some parent-child and sibling pairs. For
the five million or so individuals represented in NDIS, however, a mere 13 loci
will yield a very large list of people with an above-average chance of being
related in these ways.[42] Most
of them will not be relatives after all, and the profiles of many of these
nonrelatives will give a stronger appearance of relatedness than the profiles
of the true relatives.[43] In
assessing the privacy threat from relatedness testing, it also should be noted
that most parent-child and sibling relationships are not private facts, but
matters of public knowledge and official records. Still, in some instances unsuspected
relationships could be revealed. To this
extent, the STR profiles recorded in offender databases could be used to
uncover and expose private information.
III. Informing the Public
The preceding discussion has probed the ways
in which a law enforcement database of STR profiles might reveal private information—both
today and in the future. As Professor
Cole emphasizes, the mere fact that the CODIS STR loci are not implicated in
gene expression does not logically establish that the STR profiles are useful
only for identification. The full
argument is complex, and the genetics and statistics of the situation are subtle. In a world of sound bites and editorials,
this poses a problem for experts asked to opine on the dangers of the STR
profiles. They can repeat the full
explanation provided here—and even this exposition is oversimplified—but not
many reporters or readers will listen to or read all of it, and even fewer will
understand it.
To cut to the chase, it can be helpful to use
certain metaphors that place the true privacy risk of DNA databases in
perspective. Commentators have suggested
that the 13 STR loci used in state and federal convicted-offender DNA databases
are no more revealing of personally sensitive information than a fingerprint
and that they are much more like a passport, social-security, or license-plate
number than a medical record.[44] Professor Cole worries that these analogies can be misunderstood, and
that is certainly possible. Nevertheless,
such similes are roughly accurate in the context of disease screening. To scientists, the CODIS STRs are of
negligible value for ascertaining information about an individual’s
health. The simplest way to say this is
to refer to the loci as having “no predictive value,” for that is what it means
to the scientist seeking to exploit such data. Technically, a genetic marker may have a non-zero correlation with some
disease, in which case it is literally true that it is “predictive.” However, the same can be said of a fingerprint
and a social security number. The former
reflects both genetics and influences in utero. The latter is correlated with age, which is correlated with the
incidence of many diseases. Predictive
utility, however, depends on the magnitude of the association, and the
predictive power of any plausible associations of the CODIS STRs with disease
in the general population is trivial.
Outside the context of disease-screening, the
metaphors are less apt. As I cautioned
in an article contemplating a population-wide database, “the profile can be
used in investigations of kinship, such as parentage determinations. This biological fact makes DNA profiles
potentially more revealing than fingerprints or social security numbers . . .
.”[45] Perhaps
it would better to draw an analogy to other biological variations that have
been used in forensic science for decades. Arguably, scientists, politicians, lawyers, criminologists, and advocacy
groups could communicate more accurately by saying that the information content
in a person’s STR-identification profile is no more threatening than that of a
blood group or tissue type. Blood groups
and tissue types are correlated to the incidence of certain diseases, they vary
by ancestry, and they are useful in kinship testing. Nonetheless, like the CODIS STRs, they do not
provide useful predictive or diagnostic tests for diseases, and this situation
is not likely to change.
* * *
Toward the end of his essay, Professor Cole indicates that his fundamental concern is not so much whether the CODIS STRs really possess current or future predictive or diagnostic validity and utility, but rather whether scientists will be deluded into thinking that they have found predictive value even when it does not exist.[46] The sordid history of genetic determinism and genetic theories of racial inferiority should give us pause, as he advocates. Fortunately, genetics has progressed since the enactment of the eugenics laws of the 1920s. As I see it, the scenarios for the misuse by the government, insurers, or employers of the STR-identification profiles in NDIS and other law enforcement databases border on science fiction. And, as Cole notes, the debate about the information content in an STR profile is a distraction from the scientifically tenable claim that the DNA molecules in a sample are a threat to privacy. It is time to move on from the debate over “junk DNA” and to address realistically the true privacy problems posed by the growing repositories of DNA samples.
————
*. Freeman Foundation Visiting Professor of Law, Hopkins-Nanjing Center for Chinese-American Studies; Regents’ Professor, ASU Sandra Day O’Connor College of Law; Professor, ASU School of Life Sciences; Fellow, ASU Center for the Study of Law, Science, and Technology. I am indebted to Bruce Budowle, John Butler, James Crow, Elliot Goldstein, and the law review editors for noting errors, omissions, and ambiguities in a draft of this essay.
1. Simon A. Cole, Is the “Junk”
DNA Designation Bunk?, 102 Nw. U. L.
Rev. Colloquy 54 (2007),
http://www.law.northwestern.edu/lawreview/colloquy/2007/23/ (link).
2. See infra note 16 and text accompanying note 41.
3. Cole, supra
note 1, at 63.
4. Originally, scientists provided such assurances with respect to
the VNTRs used in forensic DNA typing from approximately 1985–1995. E.g., Randall S. Murch & Bruce
Budowle, Are Developments in Forensic Applications of DNA Technology
Consistent with Privacy Protections?, in Genetic Secrets: Protecting Privacy and Confidentiality in the
Genetic Era 212, 224–25 (Mark Rothstein ed., 1997); National Commission on the Future of DNA
Evidence, National Institute of Justice, The Future of Forensic DNA Testing:
Predictions of the Research and Development Working Group 37 (2000)
[hereinafter NCFDNA], available at
http://www.ncjrs.gov/pdffiles1/nij/183697.pdf (link).
5. Cole, supra
note 1, at 59, 61.
6. Id. The response here focuses on the STR profiles in the context of offender
databases. I discuss more fully the
privacy implications of expanding these databases to other groups in D.H. Kaye, DNA Identification and the Threat to
Civil Liberties (forthcoming 2008).
7. Id. at 59.
8. Id.
at 59, 62.
9. Id.
at 62.
10. Cole, supra note 1, at
63.
11. Id.
12. Id. at 59. But see
infra Part I.D.
13. See infra
Parts I.D, II.
14. The information on VHL presented here can be found in an educational
module on genetics for high school students prepared at the National Institutes
of Health, titled VHL: A Genetic Disease by Ruth Levy Guyer, and
disseminated at http://science-education.nih.gov/home2.nsf/Educational+ResourcesTopicsGenetics/ 4C2BAD0D0ED8F6C985256CCD00701E43 (link).
15. If other mutations in the population also inactivate the gene,
then the test will not be very specific. It will miss those individuals who are at risk due to these other
mutations.
16. See
D.H. Kaye, Science Fiction and Shed DNA, 101 Nw. U. L. Rev. Colloquy 62 (2006),
http://www.law.northwestern.edu/lawreview/colloquy/2006/7/ (link). Other STRs have been implicated in certain inheritable diseases. See generally Genetic Instabilities and Hereditary Neurological Diseases
(Robert D. Wells & Stephen T. Warren eds., 1997); Roger N. Rosenberg, DNA-Triplet
Repeats and Neurologic Disease, 335 New
Eng. J. Med. 1222 (1996). These
STRs differ from the forensic STRs in that the core sequences are triplets
(usually with both a G and a C in these repeated units), and the disease-related
alleles have more repeats than the CODIS STRs.
17. This thought is not new. Cole accuses me of blurring or eliding “the distinction between causal
and predictive significance,” but I address this distinction in David H. Kaye, Two
Fallacies About DNA Data Banks for Law Enforcement, 67 Brook. L. Rev. 179 (2001) (link). It is not repeated in Kaye, supra note 15, because that essay is
a short rebuttal of a claim regarding causation, not correlation, in Elizabeth
Joh, Reclaiming “Abandoned” DNA: The Fourth Amendment and Genetic Privacy,
100 Nw. U. L. Rev. 857 (2006) (link).
18. Elaine J. Mange & Arthur P. Mange,
Basic Human Genetics
194–98 (1st ed. 1994).
19. John M. Butler, Genetics and Genomics of Core Short Tandem
Repeat Loci Used in Human Identity Testing, 51 J. Forensic Sci. 253 (2006).
20. Cole, supra note 1, at
59 (emphasis in original).
21. Id.
22. For the full quotation, see id.
23. If a tumor-suppressor gene has been inactivated by a gross
deletion of a portion of the chromosome containing the gene, it is likely that
any nearby STRs also will be missing. If
the patient’s normal cells are heterozygous—the two chromosomes have two
different alleles at the same STR marker locus—then there has been a loss of
heterozygosity (LOH) in the diseased cells. Only the one remaining allele shows up when the tumor cells are
typed. Thus, by comparing cells from a
heterozygous patient’s normal tissue to those from the same patient’s tumors,
clinicians may be able to learn something about the progression of the cancer. For an interesting example, see James R. Davie et al., Univ. of Pittsburg Sch. of Med., Molecular Diagnostics: Case 287—Medicolegal Case of 56 Year Old
Female with One Lymph Node Metastasis and Two Oral Squamous Cell Tumors
(2001), http://path.upmc.edu/cases/case287.html (link). LOH also can be used as a research tool to
infer the location of previously unknown tumor-suppressor genes. P. Bennett, Demystified . . .
Microsatellites, 53 Molecular
Pathology 177, 181–82 (2000).
24. Even the direct test generally will not be useful for general population
screening because each Mendelian disease is rare, diminishing the predictive
value of a positive test result, and there may be many disease-causing
mutations in the population, diminishing the predictive value of a negative
result.
25. See, e.g.,
John M. Butler, Forensic DNA Typing: Biology, Technology, and Genetics of STR
Markers (2d ed. 2005).
26. Today, NDIS contains STR profiles of about 4.7 million convicted
offenders. NDIS Statistics,
http://www.fbi.gov/hq/lab/codis/clickmap.htm (link)
(last visited Sept. 9, 2007). If the
12-allele frequency in the population were, say, 5%, we would expect to find
slightly less than 10% of the people in this database with either or one or two
copies of this allele. (This
relationship assumes that the population is in Hardy-Weinberg equilibrium. This is not correct for the mixture of the
major population groups reflected in NDIS, but it is reasonable as a first
approximation for the rough calculation here. See Committee on DNA
Technology in Forensic Science: An Update, National Research Council, The
Evaluation of Forensic DNA Evidence 92 (1996). It also assumes that the general population
and the convicted-offender population in the database have the same STR allele
frequencies.) VHL is rare—fortunately,
there are only about 7,000 people in the United States who are afflicted with
the condition. For the sake of argument,
let us assume that fully 10% of them are convicted offenders whose STR profiles
are in the database. Finally, assume
that notwithstanding the high mutation rates of STRs, every one of these 7,000
people are descendants of a common ancestor who had the 12-allele near the
mutant VHL allele, so that they too have this association. If we were to use the 12-allele to predict the
VHL allele for everyone in the database, we would identify some 10% of 4.5
million, or 450,000 people as positive for VHL. Of these 450,000 positive predictions, we would be correct in only 700
cases. For any particular positive
prediction, the probability of the VHL mutation is only 700/450,000 =
0.001. This probability is known as the
“positive predictive value” (PPV) of the screening test. The real PPV will be even closer to zero
because the correlation between the marker and the gene within the family will
not be perfect. So despite the high
correlation in the family study, the STR locus has essentially no predictive
value in the general population.
27. As a result, it is not easy for “the medical community [to]
ultimately choose[] to use forensic STRs or some other genetic test to screen
for any particular disease.” Cole, supra note 1, at 59. Geneticists
cannot simply take a CODIS STR locus that may have shown some correlation with
some disease in a family study and use it as a screening test that will reveal
which convicted offenders have the disease. And, the idea that they can use “some other genetic test to screen” is
quite impossible—the only genetic data in the database records are the alleles
at the 13 STR loci. Of course, one could
go back to the stored DNA samples and retype them with the “other
genetic test.” That is why sample
retention poses a scientifically real privacy risk, as Cole clearly recognizes.
28. Id.
29. The STRs are sufficiently common that many individuals in the
population with a particular STR allele would not carry the gene mutation. In other words, the population correlation
between the STR type and a disease-related gene is likely to be weak. Furthermore, even if the correlation were
strong, the individual gene to which the STR is linked would contribute a small
fraction to the occurrence of the polygenic, environmentally influenced
disease.
30. See, e.g., Keith Wailoo &
Stephen Pemberton, The Troubled Dream of Genetic Medicine: Ethnicity and Innovation in Tay-Sachs, Cystic
Fibrosis, and Sickle Cell Disease 1 (2006).
31. NCFDNA, supra note 4, at 60.
32. Cole, supra note 1, at 62.
33. See, e.g., S.K. Dey &
Sujoy Ghosh, PCR-Based Detection of Parental Origin of Extra Chromosome 21
in Down Syndrome, 5 Int’l J. Hum.
Genetics 183 (2005).
34. “Trisomy” refers to the presence of an extra chromosome (or part
of one) in an individual’s cells. Only
five to ten percent of the babies with Trisomy 18 or 13 survive the first year
of life. There are a few reports of survival
into the teens, Lucile Packard Children’s Hospital, Medical Genetics: Trisomy 18 & 13, http://www.lpch.org/DiseaseHealthInfo/HealthLibrary/genetics/trisomy.html
(link) (last visited Sept. 10, 2007), but these
children are exceedingly unlikely to be swept into an offender database, and
even if that were to occur, their physical condition would be obvious without
genetic testing. See also Nat’l Library of
Med., Medline Plus, Medical
Encyclopedia, http://www.nlm.nih.gov
/medlineplus/ency/article/001660.htm (link) (discussing Trisomy 13); id., http://www.nlm.nih.gov
/medlineplus/ency/article/001661.htm (link) (discussing Trisomy 18).
35. See Nat’l
Library of Med, Medline Plus, Medical Encyclopedia, http://www.nlm.nih.gov/medlineplus/ency/article/000997.htm
(link) (discussing Down syndrome).
36. Cole, supra note 1, at 54.
37. Cole, supra
note 1, at 62 (internal quotations removed).
38. STRs also are not likely to be used in inferring the probable racial
or ethnic group of the source of a crime-scene sample because there are other
loci that are much more informative of ancestry. See,
e.g., Mark Shriver et al., Letter to the Editor, Getting the Science
and the Ethics Right in Forensic Genetics, 37 Nature Genetics 449, 449 (2005). These “ancestry informative markers” have
been used in rare cases in which police have turned to geneticists to evaluate
the probable race of a serial rapist or other unidentified criminal.
39. Mark Benecke, Coding or Non-Coding, That Is the Question, 3
EMBO Reports 498, 500 (2002).
40. Cole, supra note 1, at 55.
41. He merely notes that “[p]rivacy advocates
contend that ‘DNA samples can provide insights into personal family relationships,
disease predisposition, physical attributes, and ancestry.’” Id. at 55.
42. Virtually all close relatives have an unusually high number of
matching alleles. In particular, ignoring
mutations, a child is identical by descent with one parent at one allele at
every locus, and siblings have a 25% chance of matching by descent at both
alleles at each locus. But a nonrelative
occasionally can be the source of an equally good or better partial match. This has a small probability in each case,
but in a large database, there are a vast number of opportunities for
coincidental partial matches to occur.
43. In repeated searches for matches in a simulated database of 50,000
unrelated individuals and a profile of one child, researchers found that the
profile of the true parent emerged as the most likely candidate only about half
the time. Frederick R. Bieber et al., Finding Criminals Through DNA of Their
Relatives, 312 Science 1315,
1315 (2006). The larger the database,
the more opportunities there are for nonrelatives to emerge, by chance, as good
partial matches.
44. See
Cole, supra note 1, at 60 (citing commentary).
45. D.H. Kaye & Michael E. Smith, DNA Identification
Databases: Legality, Legitimacy, and the
Case for Population-wide Coverage, 2003 Wis.
L. Rev. 413, 432 n.59 (link). As previously indicated, this is much less of an issue in a
convicted-offender database. To test for
marital infidelity, for example, the investigators would need to have the
profiles of the child and the putative mother and father. All three profiles are not likely to be in
the database. In contrast, this privacy
concern is more significant when DNA typing is done in mass disaster cases to
identify the remains of missing people. In that situation, investigators compare suitable alleles in the remains
to those of known family members.
46. Cole, supra
note 1, at 62.
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