Human DNA methylation and microbiome analysis as potential tools to solve open issues in personal identification

The human microbiota is the totality of microorganisms present in the human body, it is different for each individual and is influenced by several factors (e.g. site of the body, sex, age, health conditions, lifestyle).Thanks to Next Generation Sequencing, the study of human microbiota have been applied to the forensic field through the development of the forensic microbiology, which involves the use of microorganisms asauxiliary tool in the resolution of forensic cases. More specifically, microbiome analysis can be applied to achieve personal identification since they are highly individual, relatively stable over time and easy to befound and collected on the crime scene from traces of saliva and the surfaces of objects that have been touched by a potential perpetrator. For these reasons, oral and skin microbiota can have important consequences in forensics for personal identification when it is not possible to obtain a full human STR profile, but the fundamental limitations to the application of forensic microbiology is the lack of reference databases. Also forensic epigenetics, the study of epigenetic variation to solve forensic issues, has gained ground inrecent years. One of the most studied epigenetic alterations is the DNA methylation, that is related to different disease, but also associated with aging. In fact, the methylation of specific CpG sites can be used to estimate the age of a DNA source, since their methylation levels are greatly correlated with chronological age. So DNA methylation levels can be considered as individual epigenomic variations that constitute an epigenetic fingerprint and for this reason it is gaining importance in the field of forensic genetics for the estimation of age. While there are several research that investigated the use of DNA methylation for age estimation from blood and saliva samples, few studies have been done to analyse bone samples that can help resolve forensic cases where only skeletal remains are available.