Bone marrow transplants have some unique characteristics with respect to other types of organ transplants that must be taken into account if genetic testing is desired. These peculiarities are due to the function of the bone marrow.
The function of the bone marrow
Bone marrow is a soft, fatty tissue located inside the long bones, such as the shoulder blades, ribs, pelvis, or, most well-known, the vertebral spine. This tissue is responsible for the production of blood stem cells and the subsequent creation of red blood cells, lymphocytes and platelets. The genetic material is extracted from the nucleated blood cells produced by the marrow for genetic analysis in peripheral blood.
Bone marrow transplantation
Some diseases such as leukemias, lymphomas or thalassemias damage the bone marrow, requiring its replacement with stem cells from healthy bone marrow. This transplant implies that after the transplant the blood cells will be produced by the new tissue, therefore, they will have the characteristics of the new tissue. There are basically two types of bone marrow transplantation, autologous transplantation and allogeneic transplantation.
Autologous bone marrow transplantation
This type of transplant is performed with the patient’s own healthy bone marrow tissue, in other words, the stem cells are the same as the patient’s own and therefore the genetic material of the blood derived from the bone marrow is not modified.
Bone marrow allotransplantation
In this case, the new bone marrow tissue transplanted is from another person who is compatible with the recipient. This means that, in a person who has been transplanted from the bone marrow through an allotransplant, as the blood stem cells are foreign, the transplanted individual will have blood cells with the genetic material of the donor person. Therefore, if the DNA of the blood of the allotransplant recipient is analyzed, the DNA belongs to the transplanted tissue, that is, to the marrow donor, but not to the rest of the analyzed patient’s cells (such as the germ cells responsible for generating oocytes or spermatozoa).
Given that, as we have mentioned, genetic analysis is mostly performed through the DNA contained in blood cells, in individuals with bone marrow transplants this analysis is not possible by using a blood sample. In order to perform the analysis, it is necessary to obtain a DNA sample from non-blood cells. The most reliable option is the analysis of skin biopsies since the sample will contain good quality genetic material from the patient to be analyzed. It is recommended to accompany the biopsy sample with a blood sample to rule out possible interferences in the analysis.
If it is not possible to obtain a skin biopsy sample, it is possible to perform the analysis on saliva samples, in which buccal desquamation cells are analyzed. As with skin biopsy, it is advisable to accompany the sample with a blood sample, in order to assess whether the saliva sample also contains blood cells that may interfere with the results of the analysis. It should be taken into account that the lower the amount of cells to be analyzed from desquamation, the more likely it is to obtain inconclusive results due to blood cell interference.