Improved STR typing of telogen hair root and hair shaft DNA

Abstract

Today the STR typing of telogen hair and hair shafts is regarded as a challenge. The small DNA quantity in the hair is highly degraded. Another problem are PCR inhibitors in the hair. In particular hair pigments, the melanins, are known to inhibit PCR. Hairs are exposed to sunlight and partly to chemical oxidation processes, which make them even more difficult to analyze. To increase the chances of a correct typing of hair, the small amount of DNA must be successfully isolated and the inhibitors have to be removed or neutralized. Furthermore, miniSTR typing improves the analysis of stains with degraded DNA like it is the case with hair. We introduce a nonorganic extraction method and in addition a miniSTR concept which is promising in typing stains with little and degraded DNA, especially hairs. The miniSTR concept including five database STRs (SE33, VWA, TH01, FGA, D3S1358) and the gender typing system Amelogenin was optimized for the amplification of hair DNA. Compared to commercial STR kits, this approach resulted in considerably higher success rates.

Sequencing of mtDNA in Shed Hairs: A Retrospective Analysis of Material from Forensic Cases and a Pre-Screening Method

“…In a previous study based on 11 STR loci, analysis of telogen hair roots from forensic cases resulted in full DNA profiles for 65% of the sampled hairs [6]. Moreover, an assay utilising six miniSTR loci revealed complete DNA profiles for 41% of hairs found at crime scenes [24]. In addition to its higher evidence value a significant advantage of nDNA analysis is that the profiles obtained can be compared with those in national databases.…”

“…If the hair is totally dissolved and the disulphide bonds within the hair are broken an efficient amplification of DNA in hair is possible. Large variations are seen with some types of hair being resistant to proteinase K but that lyses well when dithiothreitol (DTT) is added to the extraction solution [5,6,[23][24][25]. Previously it has been suggested that dark, highly melanised hairs inhibit PCR [26].…”

“…In order to allow or optimise nDNA analysis of challenging samples, reduced-size STR assays have been developed that can be applied in the analysis of shed hairs [6,23,24]. In a previous study based on 11 STR loci, analysis of telogen hair roots from forensic cases resulted in full DNA profiles for 65% of the sampled hairs [6].…”

Scope of X-Chromosomal MiniSTRs: Current Developments

“…As reported in the literature, the amplicon size of a miniSTR is below 200bp, above which chances of getting a complete profile from a degraded sample diminish significantly [42]. Others have suggested that the optimum product size is below 150bp [26].…”

“…Since then, a number of other studies have demonstrated that successful analysis of degraded DNA specimens from mass disasters or compromised forensic evidence improves with smaller-sized PCR products [8,10,12,14,[27][28][29][30][31]. The TIMELINE (Figure 1) shows the progress of ChrX miniSTRs over the years [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]. …”