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Dandruff derives from the horny layer of the skin which consists mainly of nuclei-free, keratinized corneocytes. Nevertheless, due to incomplete differentiation processes during epidermopoesis, a considerable portion of cells within the aggregates contains nuclei. This was shown by microscopic examination. DNA of those parakeratotic cells could be partially degraded.

To test the suitability of DNA from dandruff particles for forensic application, a study of 35 subjects and material from two crime cases (masks from bank robberies) has been carried out using several different STR polymorphisms (HUMTH01, HUMVWA, HUMFES, HUMFGA and HUMAMELOGENIN).

DNA was extracted from dandruff particles using Chelex, supplemented with proteinase K (300mg/ml final conc.) and dithiothreitol (30mM final conc.) providing complete dissolution of cell aggregates. In addition, Chelex was supplemented with Tween^® 20 (0.5% v/v final conc.) to provide wetting of the partly hydrophobic surface of dandruff. PCR amplification products were separated and visualized by polyacrylamide gel electrophoresis and silver staining.

Due to the large variety of the morphological appearance of dandruff particles and the unknown proportion of parakeratotic cells within the aggregates, the DNA content of a dandruff particle is hardly to be quantitated. It has been estimated that dandruff of about 0.5mm in diameter could contain between 500 and 1000 horny cells with a parakeratotic level of about 25%. This would correspond with a range of 0.8 to 1.5 ng DNA per dandruff.

In practice, DNA genotyping from five dandruff particles of each subject revealed that in

About 90% of the samples STR analysis for all tested polymorphic loci could be easily performed.

About 5% of the samples showed weak signals, but fragments could be identified;

Only 6% of the samples failed in STR analysis.

Same results were obtained for multiplex application (HUMVWA & HUMFES).

A titration study (one to ten dandruff particles extracted in 200ml Chelex) was performed to estimate the minimum amount of dandruff material for reliable STR genotyping. Using 15ml of the 200ml extract for amplification, two dandruff particles were sufficient for reproducible results. In addition, DNA profiles from only one dandruff particle could be obtained if extraction volume was reduced to 100ml Chelex.

These results clearly demonstrate that DNA genotyping of human dandruff is possible. Therefore, dandruff can be considered as an additional or alternative stain in forensic casework.