UC Davis

The use of genetically variant peptides (GVPs) from human hair shaft proteins as a protein-based human identification method has been a validated and discriminating method for the identification of human hair shafts since 2016, with current research showing it can distinguish between identical twins, can produce high random match probabilities (RMP) regardless of hair pigmentation status, age, hair location on the body, and after single harsh chemical treatments. GVPs are a type of single amino acid polymorphism (SAP) found in proteins. These SAPs are classified as GVPs if they are genetically inherited, which can be associated with genetically inherited single nucleotide polymorphisms (SNP) present in at least one percent of the global population. Using GVPs, scientists can infer genotypes, estimate random match probability, and characterize the origin population. This is a complementary human identification method to nuDNA and mtDNA typing. This study exposed human hair shafts from three individuals to oxidative chemistries, specifically to 12 repetitive treatments of Clairol Professional BW 2 powder lightener mixed with Salon Care Professional 50 volume crème developer, and followed by Clairol Professional Beautiful Collection “moisturizing semi-permanent color” in the shade BO1N “Light Natural Blonde.” The protein modifications of interest included cysteic acid, deamidation, and oxidation and di-oxidation of methionine, which are all involved in characterizing oxidative damage to hair. The protein modifications behaved as expected across all subjects and like previous research on oxidative damage and degradation of human hair shafts. The number of GVPs initially increased due to the opening of the matrix from cysteic acid formation and peaked at 4 treatments for all 3 samples. GVPs then decreased as the number of treatments increased to 8 and 12. This was consistent with past oxidative chemistry research on single hairs. The unique GVPs ranged from 4 in the U1.003 control to a maximum of 84 in the U1.016 4-treatment sample. This research supports the findings in previous GVP studies and provides additional validation that protein-based human identification methods can be useful in a forensic context.