Anomalous Amelogenin Results

While amelogenin is an effective method for sex-typing biological samples in most cases, the results are not full proof. A rare deletion of the amelogenin gene on the Y chromosome can cause the Y chromosome amplicon to be absent (Santos et al. 1998). In such a case, a male sample would falsely appear as a female. It appears that this deletion of the Y chromosome amelogenin region is more common in Indian populations (Thangaraj et al. 2002) than those of European or African origins. A study of almost 30 000 males in the Austrian National DNA database revealed that only six individuals lacked the amelogenin Y-amplicon (Steinlechner et al. 2002). These individuals were verified to be male with Y-STRs and amplification of the SRY region (see Chapter 9).

Amelogenin X allele dropout has also been observed in males. In this case only the amelogenin Y-amplicon is present (Shewale et al. 2000). This phenomenon was observed only three times out of almost 7000 males examined and likely results from a rare polymorphism in the primer binding sites for the amelogenin primers used in commercial STR kits. A different set of amelo-genin primers targeting the same 6 bp deletion on the X chromosome amplified both the X and Y alleles of amelogenin (Shewale et al. 2000).

STRBASE: A DYNAMIC SOURCE OF INFORMATION ON STR MARKERS

The rapid growth of the human identification applications for STR loci insures that static written materials, such as this book, will quickly become out-of-date. New alleles are constantly being discovered (including 'off-ladder' microvariant alleles), additional STR markers are being developed, and population data increases with each month of published journals. Indeed, a growing list of publications describing the application of STR loci to forensic DNA typing has exceeded 2000 references.

The growth of the World Wide Web now permits dynamic sources of information to be widely available. Several years ago a web site was created to enable forensic scientists to keep abreast with the rapidly evolving field of DNA typing. In anticipation of the impact of STR markers on DNA typing and the need for a common source of information that could evolve as the process improved, an internet-accessible informational database was created in early 1997. STRBase was officially launched in July 1997 and is maintained by the DNA Technologies Group of the National Institute of Standards and Technology (Butler et al. 1997, Ruitberg et al. 2001). STRBase may be reached via the World Wide Web using

Figure 5.12

Homepage for STRBase, an internet-accessible database of information on STR markers used in forensic DNA typing. STRBase may be accessed via the URL: http:// www.cstl.nist.gov/biotech /strbase/ and contains among other things a comprehensive listing of all papers relating to STR typing for human identity testing purposes now numbering over 2000 references.

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Stammering Its Cause and Its Cure

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