Monitoring Needle Sharing

In yet another application of the capability to perform mixture detection with STRs, a laboratory method was described by Shrestha et al. (2000) using the CODIS STR marker D8S1179 (called D6S502 in the paper) to differentiate between single and multi-person use of syringes by intravenous drug users.

D.N.A. Box 7.2 Natural mixtures and chimeric individuals

In May 2002, the New England Journal of Medicine published a report of the genetic analysis of a phenotypically normal chimeric individual who was unexpected identified because histocompatibility testing of family members suggested that she was not the biological mother of two of her three children (Yu et al. 2002). The doctors examining this chimeric individual proposed that her condition had arisen because two fertilized eggs, destined originally to be fraternal twins, had fused to form a zygote that possessed DNA of two different types. Thus, from a genetic perspective she was both her children's mother and their aunt.

Among the various genetic tests performed on this chimeric individual was analysis of 22 STR loci. All of the CODIS core loci except CSF1PO were examined in this study. This unusual patient possessed some differences in her STR profiles among various tissues tested. While the buccal and blood samples tested matched exactly, a mixture containing another type was present as the minor component in the thyroid, hair, and skin cells of this chimeric patient.

While chimeric individuals such as the one described above are most likely extremely rare in the general population, it is possible in theory for DNA testing from different tissues of a chimeric individual to not match one another and thus lead to a false exclusion. This situation may increase in frequency with the rise of in vitro fertilization since multiple eggs are sometimes fertilized in order to increase the success rate of the procedure.

Sources:

Yu et al. (2002) New England Journal of Medicine, 346, 1545-1552. David Baron, 'DNA tests shed light on hybrid human', National Public

Radio-Morning Edition, August 11, 2003 (http://www.npr.org). Pearson, H. (2002) Human genetics: dual identities (see http://www.

nature.com/nsu/nsu_pf/020429/020429-13.html)

Monitoring needle sharing can help determine the source of spreading blood-borne pathogens among drug users.

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