TWINS... a word that can make anyone who thought they were ready to be parents think twice…literally.
With a new age of medical science comes the opportunity to store stem cells for later use. The question is, should you store stem cells for each twin? Hematopoietic, or blood borne stem cells, are the basis of the components for your blood. Erythrocytes, leukocytes, and thrombocytes are all formed from these precursor cells that can be found in abundance inside a newborn's umbilical cord blood. These cells are unique to the individual, due to a group of genes called Human Leukocyte Antigen or HLA. The HLA system encodes for the proteins on the surface of cells that are responsible for the body’s immune system.
Responsible for the immune system, the HLA system is the major cause of organ transplant rejection (Brown, 2014). Any cell displaying some other HLA type is "non-self" and is seen as an invader by the body's immune system, resulting in the rejection of the tissue bearing those cells. This is why stem cells are important, because the body will not reject its own cells with corresponding HLA typing.
Twins are a very unique case, and it has been shown that approximately 3 out of every 100 births results in twinning (Fierro). The actual science behind twins is unique in itself for what kinds of twins are produced. There are two main categories of twins, dizygotic and monozygotic. Dizygotic, or fraternal, twins are the result of 2 separate eggs being fertilized by two separate sperm. This results in twins who are as genetically similar as a sibling. They will look similar like any other pair of siblings but they are still very unique in terms of genetics.
Monozygotic, or identical, twins are quite different from dizygotic twins. Identical twins are formed as a result of a single egg and a single sperm forming one zygote. The zygote then “collapses” to form separate embryos. These embryos then develop into an almost exact phenotypic copy of one another. A misconception of identical twins is that they are genetically the exact same, when in actuality they are not (Daily, 2013). After the embryos have split from one another, they are then subjugated to random sporadic mutations, like any other child without a twin, that change the genetic code of each child.
Another cause of twins being different genetically is that the environments they are subjected to are different, resulting in epigenetic modification (Hunter, 2014). Within the shared placenta, some areas may have a slightly different temperature or may have a higher or lower concentration of certain molecules, and this can result in activation or deactivation of certain genetic loci, such as the HLA markers.
Since stem cell transplants are dependent upon an individual’s HLA typing, it is important to find a suitable match. It is more likely to find a suitable donor from a sibling or even better a twin, than from a donor list. However, the best option is to use the owner’s personal stem cells, because while twins are very closely related at a genetic level, they are still not exact copies of one another. The HLA typing of one twin may be different at key markers, causing rejection of the graft. That is why it is best to have options when dealing with an illness that requires stem cell grafting.
Twins are far more likely to have the same HLA markers with each other than with another sibling, but they still can differ. That is why the decision of banking a set of twin’s cord blood is a decision that requires forethought and knowledge of the implications of only banking one.
