Biometrics from the Isotopic Analysis of Amino Acids in Human Hair

Instrumental methods of analysis can provide elemental, proteomic and isotopic information about human hair samples, which, because of their objectivity, scientific foundation, and statistical nature, offer many advantages over forensic hair microscopy. The criminal justice system could benefit greatly from an objective instrumental method of analysis that could provide investigative leads about a suspect from a questioned hair sample. Such investigative leads could include a suspects age, sex, race, region-of-origin, genetic disorders, and disease state(s) or body mass index, among other traits. The technique of isotope ratio mass spectrometry (IRMS)which is already in use in many government forensic laboratories and has passed Daubert standards for admissibility in court on many occasionshas the potential to offer this solution. Here, we propose to collect and analyze hair samples from a cohort of >150 subjects across the US along with a detailed questionnaire from each participant about his or her physical traits, genetic disorders, diet, lifestyle, exercise and hair treatments. After washing and drying each hair sample, we will first collect bulk isotope ratio measurements for 13C/12C, 15N/14N, and 34S/32S. We will then pulverize the hair, perform acid hydrolysis, then measure the 13C/12C isotope ratios of at least 14 amino acids via liquid chromatography (LC)-IRMS. We will then use statistical analyses to evaluate and classify participants into selected groups based on the information from the questionnaires. Statistical techniques such as canonical discriminant analysis (CDA) have the ability to overlook the covariance of amino acid isotope ratios caused by different dietary habits between individuals and highlight the selective differences caused by the grouping factor(s). We have already shown this capability to be true for a cohort of 20 female subjects, wherein we were able to predict a subjects body mass index and age from their hair with accuracies exceeding 93% (based on original discriminant rules). Finally, we will use the analysis results to identify amino acids in hair that are specific markers for certain group classifications and thus point directly to physiological and biochemical reasons for the classifications. Unlike bulk isotope ratio approaches, our compound-specific approach has the potential to go beyond region-of-origin or geospatial movements of individuals to the provision of physical and characteristic traits about the individuals. This project has the ability to provide significant advances in the scientific understanding of factors that influence the isotopic composition of amino acids in human hair. This basic understanding can benefit the criminal justice system by offering a scientific, biochemical basis for the comparison of human hairs and for the provision of investigative leads for suspects. Although the primary intended benefit of this research project is for the criminal justice system, the methods and results of this work has broader impacts that could directly benefit other fields of study such as archaeological applicationsinvolving human ancestral habits/traits, ecological applicationsinvolving migration and dietary habits, and disease diagnosis and health monitoring. ca/ncf