DNA on the Shroud of Turin: Distinguishing endogenous versus exogenous DNA

In the late 1990s it was reported that human DNA existed on the Shroud of Turin, and although in a generally degraded state, certain regions were sufficiently intact to clone and sequence three genes from bloodstained fibers: human betaglobin, amelogenin X and amelogenin Y. An unknown variable in such studies is the extent of contamination by exogenous DNA, transferred to the Shroud by persons or objects that have come in contact with cloth. Indeed, the abovementioned genes are not exclusive to blood cells, but are also found within other cell types, including skin cells. Here, a simple experimental approach is described for distinguishing endogenous versus exogenous DNA, which may help establish that DNA in the blood areas of the Shroud of Turin originated from white blood cells (lymphocytes) present on the cloth. Human DNA on the Shroud In the 1990s, Garza-Valdes reported in the book “The DNA of God” the cloning and sequencing of three human gene segments from blood remnants on the Shroud: the betaglobin gene (which encodes a portion of the hemoglobin protein), located on chromosome 11; and the amelogenin-X and amelogenin-Y genes, found on the X and Y sex chromosomes, respectively (1). One issue that persists in DNA analysis of objects that have been handled by numerous individuals is contamination. Garza-Valdez stated in his book, “obviously there was the possibility of contamination and possibility that blood from someone other than the crucified victim happened to fall on the part of the Shroud from which the sample was taken. But it is certainly more likely that the blood came from the Man on the Shroud, rather than a bystander, in view of the fact that the sample was taken from the back of the head, from the area where the crown of thorns would have damaged the head of the victim” (1). Unlike hemoglobin protein, whose expression is primarily restricted to red blood cells, hemoglobin (betaglobin) DNA is contained within essentially all cell types throughout the body, including skin cells. Realistically, a person would not have to bleed on the Shroud to transfer betaglobin DNA, but merely to touch it. Or to touch an object, which then came in contact with the cloth, or with threads taken from it. Or perhaps even to touch an object, which then comes in contact with an object that contacts the sample. The average human being sheds approximately 400,000 skin cells per day, a portion of which contains DNA that may be transferred by contact, referred to as touch DNA (2-4). The vast majority of cells in the outermost layer of skin have undergone a process known as keratinization, which includes hardening and loss of their nuclei. Small amounts of DNA fragments are believed to be