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A Genetic Counselor's Perspective on Cord Blood Banking
Cord blood banking offers all expectant families a rare opportunity to help patients with a number of devastating diseases, whether those patients are within or outside their family. In those families that have a history of medical conditions that may have a genetic component, genetic counseling can help the expectant parents to determine the potential therapeutic value of their baby's cord blood.
Of particular interest to a genetic counselor are the thousands of patients diagnosed each year with conditions that can be treated by stem cell transplant, either currently or in clinical trials. But over 70% of patients will not find a suitable matched adult stem cell donor within their own family. Umbilical cord blood is an alternative source of stem cells for these patients. The first cord blood transplant took place in 1988, and since then over 25,000 cord blood transplants have been performed world-wide for about 80 diagnoses.
Family genetics are important in stem cell transplantation, because patients fare better when their donor is related. Stem cell transplants from a close relative have the advantage in that the recipient is able to tolerate a less perfect match to the donor, experiences less graft-versus-host disease, have greater likelihood of survival than with an unrelated donor, and have the ability to go back to the donor for more matching blood or tissues if needed.
Families with histories of genetic disease or potential risk for genetic disease will likely have the greatest interest in cord blood banking. These families need to first understand the inheritance of genetic markers in their family. For example, if an expectant mother is offering to bank her baby's cord blood as therapy for a relative, is that baby a close enough match to be a donor for the prospective patient, and is that baby a carrier and/or at risk for the disease? A genetic counselor can review the genetics of any conditions of concern, in each family, so that this information can be factored into the decision to save or use cord blood for therapy.
Leukemia is one of the main diagnoses for which patients receive stem cell transplants, and a growing percentage of these patients will receive a transplant using cord blood. Altogether, there does not appear to be a strong genetic component to leukemia. However, we could do better at identifying the occasional families where leukemia may have a genetic component and/or be associated with an inherited cancer predisposition syndrome. At least 55 cancer syndromes are now characterized, each with their own causal genes, and at least a dozen of them list leukemia within their spectrum of possible cancers. Currently, the overall odds of a person in the US having a stem cell transplant are 1 in 217 over a lifetime (Nietfeld et al. 2008), but this could increase if at-risk individuals were better identified and entered into the treatment pipeline earlier.
Some inherited conditions are genetically heterogeneous, meaning that they may be inherited in multiple ways. Thus for the same condition, some families can use relatives as transplant donors and some families cannot. This is the case in dominantly inherited conditions or some chromosomal conditions such as DiGeorge Syndrome or Diamond-Blackfan anemia, where some carriers of the condition are only mildly affected. The genetic testing registry is a helpful resource for more information.
Those families that carry recessively inherited genetic diseases such as Fanconi anemia, thalassemia, sickle cell anemia, adenosine deaminase deficiency (ADA-SCID) and Hurler syndrome, face a complex set of possible options. For some of these conditions, such as ADA-SCID and Hurler syndrome, a stem cell transplant from a donor is the only hope of long-term survival. For other conditions, such as sickle cell and thalassemia, the benefits of stem cell transplants must be weighed against the risks, and at present transplantation is reserved for the most severely afflicted patients. However, ongoing clinical trials are attempting to help a wider range of these patients by delivering stem cell transplants with reduced intensity chemotherapy (see ClinicalTrials.gov). Finally, gene therapy is the newest therapy for inherited disorders, such as sickle cell anemia and Fanconi anemia.
Ironically, the advent of gene therapy changes the prevailing wisdom regarding the advisability of cord blood storage in families affected by genetic diseases. Before, treatment with a stem cell transplant required a donor who was a close match but did not have the disease. The patient's own cord blood was considered useless because it carried the disease, and instead cord blood donations were encouraged from healthy volunteers. Now that correction of the patient's own genome is becoming possible for more disorders, it is actually advisable to save the cord blood of children in affected families, for potential use in gene therapy.
Cord blood banking is particularly valuable in cultures where intermarriage between relatives is practiced. The more families practice consanguineous marriage, the more likely their offspring will have common disease genes, conferring greater risk for birth defects, mental retardation, leukemias, any inherited diseases and especially those inherited diseases prevalent in that ethnic group. Some examples of well-known genetic diseases which have higher prevalence in certain ethnic groups are sickle cell anemia, thalassemia, Tay Sachs, and cystic fibrosis. The rate of consanguinity is 20-50% in about one billion of the world's population. One consequence is that the prevention and treatment of thalassemia has been declared a public health priority by the World Health Organization.
To summarize, directed donation or private storage of cord blood may provide the only opportunity for a biological life-saving link for individuals who know there is a history of disease in their family. I only hope that more medical providers besides myself will be questioned on the matter of cord blood banking and will bring this topic to light in their practices and when called upon to educate their communities.