Criminal Justice Section  


Criminal Justice Magazine
Winter 2005
Volume 19 Number 4

Mitochondrial DNA

By Paul C. Giannelli

Paul C. Giannelli, is the Albert Weatherhead III and Richard W. Weatherhead Professor of Law at Case Western Reserve University Law School in Cleveland, Ohio, and coauthor of SCIENTIFIC EVIDENCE (LEXIS 3d ed., 1999). He is also a contributing editor to Criminal Justice magazine and a member of its editorial board.

Mitochondrial DNA
Most DNA cases involve nuclear DNA (nuc-DNA), with PCR-STR being the current technology of choice. This type of testing has been supplemented with mitochondrial DNA (mtDNA) analysis. The latter will not replace STR testing because it is not as discriminating, nor suitable for database searches under current protocols. Nevertheless, it can be used where nuclear DNA testing is not possible—typically, on hair shafts without root cells, bones, teeth, and some degraded samples. Mitochondrial DNA is found outside the cell nucleus and is inherited maternally.
Cases admitting mitochondrial DNA have begun to be reported. Some courts have admitted mtDNA evidence under the Frye general acceptance test. (E.g., Magaletti v. State, 847 So. 2d 523, 528 (Fla. App. 2003) (“[T]he mtDNA analysis conducted [on hair] determined an exclusionary rate of 99.93 percent. In other words, the results indicate that 99.93 percent of people randomly selected would not match the unknown hair sample found in the victim’s bindings.”); People v. Holtzer, 660 N.W.2d 405, 411 (Mich. App. 2003); People v. Klinger, 713 N.Y.S.2d 823 (Nassau Cty. Ct. 2000).)
Other courts have reached the same result under Daubert’s reliability standard. (E.g., United States v. Coleman, 202 F. Supp. 2d 962, 967 (E.D. Mo. 2002) (hair sample; “Dr. Melton testified that ‘at the most,’ seven out of 10,000 people would be expected to have that exact sequence of As, Ts, C, and Gs.”), aff’d, 349 F.3d 1077 (8th Cir. 2003); State v. Pappas, 776 A.2d 1091, 1095 (Conn. 2001); State v. Underwood, 518 S.E.2d 231, 240 (N.C. App. 1999); State v. Council, 515 S.E.2d 508, 518 (S.C. 1999).)
In United States v. Beverly, 369 F.3d 516 (6th Cir. 2004), the Sixth Circuit wrote:

The scientific basis for the use of such DNA is well established. Any issues going to the conduct of the specific tests in question were fully developed and subject to cross-examination. There was no error in finding that the testing methods, and Dr. Melton’s testing in particular, were sufficiently reliable to be admissible. Finally, the mathematical basis for the evidentiary power of the mtDNA evidence was carefully explained, and was not more prejudicial than probative. It was made clear to the jury that this type of evidence could not identify individuals with the precision of conventional DNA analysis. Nevertheless, any particular mtDNA pattern is sufficiently rare, especially when there is no contention that the real culprit might have been a matrilineal relative of the defendant, that it certainly meets the standard for probative evidence . . . .
(Id. at 531.)

In State v. Scott, 33 S.W.3d 746, 758-59 (Tenn. 2000), the Tennessee Supreme Court ruled that the state’s DNA admissibility statute, Tenn. Code Ann. § 24-7-117(b), obviated the need for a judicial determination of the admissibility of mtDNA evidence.
There are important differences between nuclear DNA and mtDNA—in particular, how statistical estimates are developed:

If there is a match, the matching sequence is then compared to profiles in the FBI’s mtDNA database to determine whether the sequence appears in the database, and a simple “counting method” is used to indicate the number of times the sequence appears in the database. There are presently 4,142 profiles in the FBI’s mtDNA database. For example, if the subject sequence appears in the database twice, the lab will report that two matches were observed out of 4,142 profiles currently in the database. Because mtDNA is maternally inherited and because all matrilineal decedents will share the same mtDNA, traditional random match probability used in nucDNA analysis cannot be calculated. Instead, the counting method is used, and a ninety-five percent confidence interval is applied. If, as in this case, the matching sequence derived from the mtDNA analysis is not found in the FBI database, an exclusionary rate is calculated to say that “X” percent of the population may be excluded as potential donors of the unknown sample.
(Magaletti, 847 So. 2d at 527.)

Because mtDNA presents new and complex issues, the defense should seek expert assistance. In Scott, the defense counsel offered the testimony of other attorneys:
[C]ounsel offered expert testimony from witnesses who stated that expert assistance in this area was absolutely crucial to competent representation given that the subject matter was inordinately complex and beyond the common understanding of most attorneys. One of the appellant’s experts further opined that it was doubtful that the appellant’s attorney could even know the relevant issues involved in DNA analysis without some type of expert assistance.
(33 S.W.3d at 753-54.)

The court cited the complexity of the procedure and then commented on several peculiarities in the case:

[A]ppellant also established that because the DNA examinations from the FBI and LabCorp reached inconsistent results regarding the donor of the hair samples, expert assistance was especially needed to help determine whether the samples were contaminated and why the appellant was apparently excluded as a donor in one test involving PCR analysis. Finally, counsel demonstrated that he needed expert assistance to understand why some reports mentioned that the samples of blood from the appellant’s clothing contained the DNA of an unidentified third person.
(Id. at 754.)

As this passage indicates, LabCorp’s analysis excluded the defendant as a possible source while the FBI’s mtDNA testing included him. (See generally Paul C. Giannelli, Ake v. Oklahoma: The Right to Expert Assistance in a Post-Daubert, Post-DNA World, 89 CORNELL L. REV. 1305 (2004).)

Scott also highlights one of the potential problems with mtDNA—contamination. “The State’s expert admitted that all who handle mtDNA must be cognizant of the greater potential for contamination and that in any mtDNA laboratory, the contamination controls must be heightened. The potential for contamination seems to be greatest when the mtDNA is exposed to other organic materials or fluids.” (33 S.W.3d at 757.) The issue was important because the DNA of an unidentified third person appeared in the analysis. The court observed: “When questioned about this anomaly [unidentified third person] at trial, the [LabCorp] scientist testified that the samples could have been contaminated.” (Id. at 750.)
Of course, contamination is a concern with nuclear DNA as well. An FBI article cautioned:
Contamination occurs when the evidence comes in contact with another individual’s body fluids through actions, such as sneezing, coughing, or touching. Contamination becomes a critical issue because today, laboratories use the polymerase chain reaction (PCR) technique to replicate DNA. . . . But, the PCR process cannot distinguish between DNA from a suspect and another source. Therefore, any substantial contamination to the DNA material will result in a confusing result.
(John E. Smialek et al., The Microscopic Slide: A Potential DNA Reservoir, FBI LAW ENFORCEMENT BULL. 18, 19 (Nov. 2000).)

Chain of custody
Concerns about contamination led the National Academy of Science to comment: “Given the great individuating potential of DNA evidence and the relative ease with which it can be mishandled or manipulated by the careless or the unscrupulous, the integrity of the chain of custody is of paramount importance.” (NATIONAL RESEARCH COUNCIL, THE EVALUATION OF FORENSIC DNA EVIDENCE 25 (1996).) Similarly, the Federal Judicial Center’s manual noted that “[i]t is especially important that the laboratory follow procedures for ensuring that the known sample is not mislabeled as, or mixed with, the crime sample. These errors can lead to false positive results that incriminate the wrong suspect.” (FEDERAL JUDICIAL CENTER, REFERENCE MANUAL ON SCIENTIFIC EVIDENCE 293 (1994).)
Several cases have also addressed the issue. In Smith v. State, 702 N.E.2d 668, 673 (Ind. 1998), the Indiana Supreme Court observed: “Two of the State’s experts agreed that contamination can be a problem in some situations, for example if someone sneezed onto the sample. However, they also testified that simply breathing on or touching the sample is unlikely to have much of an impact because the DNA present in the sample will overpower the small amount of contamination.” In State v. Morel, 676 A.2d 1347, 1356 (R.I. 1996), the Rhode Island Supreme Court noted that “in the preservation and testing of DNA evidence, careful attention and proper handling of the crime sample by police and scientists are crucial in defending chain-of-custody issues and in ensuring that laboratory mislabeling and inadvertent contamination have not occurred.”
The Scott case raised a different chain of custody issue. The court wrote:

[W]e can find no evidence whatsoever to show how the hairs came to be mounted on the slides. We also can find no evidence to show who mounted the hairs on the slides or whether the hairs were mounted in a manner sufficiently free of contamination or alteration. Although the hairs were apparently mounted on glass slides by someone with the FBI, no one was able to establish this important “link” in the chain of custody.
(Scott, 33 S.W.3d at 761.)

Postconviction testing
The advent of mtDNA analysis is a two-edged sword. Although it gives the prosecution a powerful tool, it also may be used to exonerate a person who has been wrongfully convicted on the basis of traditional hair evidence. Microscopic hair examinations were often misused in the past; examiners frequently overstated the conclusions that could be reached using this type of examination. (See Paul C. Giannelli, Splitting Hairs in the Shadow of the Gallows, 17:4 CRIM. JUST. 30 (Winter 2003).)
In one study comparing the results of microscopic hair comparisons and mitochondrial DNA analysis at the FBI laboratory, the former were wrong 10 percent of the time—and this was when the conclusion was limited to an “association” (“consistent with” testimony). (Max M. Houch & Bruce Budowle, Correlation of Microscopic and Mitochondrial DNA Hair Comparisons, 47 J. FORENSIC SCI. 964, 966 (2002) (“Of the 80 hairs that were microscopically associated, nine comparisons were excluded by mtDNA analysis.”).)
If hair or other evidence still exists, it may be suitable for mtDNA testing even though STR testing is not possible.

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