Specific Melanin Content in Human Hairs and Mitochondrial DNA Typing Success

Abstract

This study investigated whether a difference exists in the ability to obtain quality mitochondrial DNA (mtDNA) sequence data from hair shafts due to specific melanin content differences. Eumelanin, the pigment in darker hairs, protects nuclear DNA in the skin by absorbing and scattering UV radiation. In contrast, sensitized pheomelanin, the predominate melanin in red hairs and some blond hairs, is unable to prevent DNA damage in skin upon exposure to UV radiation. It has been reported in the literature that darker hairs (predominate eumelanin content) have a higher mtDNA sequencing success rate than lighter colored hairs. However, others have reported to the contrary when different methodologies are used. In this study, 2-cm hair fragments were cut from dark brown, red, and gray white hairs and typed using standard casework mtDNA sequence analysis methods. All 30 hair fragments produced quality mtDNA sequence data on first attempt from the second half of hypervariable region 1. These results are likely due to the apparent shielding of mtDNA by the hard protein of the hair shaft fiber from radiation-induced damage, regardless of melanin type, after 10-months minimal solar exposure. Nonetheless, this study may serve as a guide for future quantitative studies that investigate hair mtDNA photodamage in circumstances of increased solar, chemical, environmental, or mechanical damage.

Degeneration of Nuclei and Mitochondria in Human Hairs

“…It may in fact be more proper to state that nuDNA loses its nucleus rather than nuclei lose their DNA in keratinizing tissues. MtDNA in hair shafts is easily recovered several centimeters distal to the location in the keratinized hair shaft where mitochondria are no longer visible (6). Thus it appears that the mitochondrion provides no additional protection for mtDNA in the keratinized hair shaft.…”

“…Although the hairs were from only one individual, that individual's hairs were included in a recent mtDNA study using five persons with red hair, five persons with dark brown hair, and five persons with gray hair (6). When hair pieces were cut from the same position in those hair shafts, and cut with the same length and diameter, no significant differences could be seen in recovered mtDNA amounts when using PCR product gels (6). One would expect that the greatest individual variable in hair root cell ultrastructure would include the amount and type of melanosomes rather than the number of nuclei or mitochondria.…”

“…The ability to recover mitochondrial DNA (mtDNA) from small pieces of hair is probably possible due to the high copy number of mtDNA molecules per cell (1)(2)(3)(4)(5)(6). Nuclear DNA (nuDNA) is more difficult to recover from hair shafts and efforts in that regard continue (7).…”

Forensic Science

“…81 Success rates with amplifying mtDNA from human hairs were correlated to specific melanin content. 82 The performance of mtDNA minisequencing assays was explored, 83 and a comprehensive phylogenetic tree of global human mitochondrial DNA variation was developed. 84 Nonhuman DNA Typing Systems.…”

“…Denaturing high-performance liquid chromatography was used for comparative analysis of the HV1 and HV2 regions . Success rates with amplifying mtDNA from human hairs were correlated to specific melanin content . The performance of mtDNA minisequencing assays was explored, and a comprehensive phylogenetic tree of global human mitochondrial DNA variation was developed …”