Genetics Case Study Case Study

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Genetics Case Study

Genetic Case Study: The Rita and Peter Trosack and Tay-Sachs Disease

Genetic testing is becoming a much more common practice in medicine today. This presents a unique set of challenges for medical professionals in virtually all specialties. The practical aspects of determining which test to order, and in interpreting the result accurately in the context of the family history, can be difficult.

Additionally, the ethical conundrums that frequently present themselves when genetic risk assessment and/or genetic testing is being considered can be daunting. These challenges present real concerns for medical professionals and patients alike.

Included in this paper is a review of some of the practical and ethical complexities associated with genetic testing. Pretest and posttest genetic counseling is also emphasized as an important and essential process in today's medical practice.

The Interdisciplinary Team

The interdisciplinary team members should include an obstetrician, a genetic counselor, a psychologist/psychiatrist, geneticist and a neurologist. Each of these team members would play an essential role in the Trosacks' care. The obstetrician would attend to the pregnancy of Rita Trosack, the genetic counselor would give advice on the prenatal genetic testing; the psychologist would attend to the psychosocial concerns of testing, while the geneticist would inform the Trosacks on the social, ethical and legal implications of their choices for themselves and the baby. The pediatric neurologist would help with the care of the baby once it is born.

Each team member was chosen for the contribution they would provide in helping the Trosacks understand the implications of genetic testing for themselves and the baby. The burden on the Trosacks is quite large in this case and would extend to other family members who are feeling the psychological effects of a positive prenatal test for Tay- Sach's disease.

Due to the complexities involved in genetic testing in addition to the far-reaching effects of a genetic test result for both the patient and his/her family, genetic counseling is an integral part of the genetic testing process. Genetic counseling is defined as a communication process that deals with human problems associated with the occurrence or risk of occurrence of a genetic disorder in a family. The genetic counseling process includes information gathering, establishing or verifying diagnosis, risk assessment, information giving, and psychosocial counseling.

Teaching Plan In the case of the Trosacks, with Peter's paternal grandparents having one daughter and one son dying of unknown causes, the probability that the Tay-Sachs gene is in his family is high. Rita also has paternal grandparents who had a son that died of unknown causes. Genetic diagnosis: Both Peter and Rita carry the recessive allele for the Tay Sachs gene and both alleles appeared in the fetus. Tay-Sachs disease is an autosomal recessive lysosomal storage disorder with progressive neuronal accumulation of GM2 ganglioside caused by mutations in the HEXA gene resulting in a defect of hexosaminidase A (Hex A). There are 3 clinical types: infantile (acute), juvenile (subacute), and adult-onset (chronic).

The geneticist would disclose the following about the carrier frequency of Tay Sachs in Irish-American and Polish-American populations. From data collected in a North American Tay-Sachs disease (TSD) heterozygote screening program, the TSD carrier frequency among 46,304 Jewish individuals was found to be .0324 (1 in 31 individuals). This frequency is consistent with earlier estimates based on TSD incidence data. TSD carrier frequencies were then examined by single country and single region of origin in 28,029 Jews within this sample for whom such data were available for analysis. Jews with Polish and/or Russian ancestry constituted 88% of this sample and had a TSD carrier frequency of .0327. No TSD carriers were observed among the 166 Jews of Near Eastern origins. Relative to Jews of Polish and Russian origins, there was at least a twofold increase in the TSD carrier frequency in Jews of Austrian, Hungarian, and Czechoslovakian origins (Petersen et al., 1983).

Additionally, previous reports have found that non-Jewish-Americans with ancestry from Ireland have an increased frequency of heterozygosity for Tay-Sachs disease, although frequency estimates are substantially different. In a recently published study, the frequency of heterozygosity for Tay Sachs disease (TSD) among Irish-Americans was determined, who were referred for determination of their heterozygosity status and who had no known family history of Tay Sachs disease or of heterozygosity for these conditions. Of 610 nonpregnant subjects with Irish background, 24 TSD heterozygotes were identified by biochemical testing, corresponding to a heterozygote frequency of 1 in 25 (4%; 95% CI, 1/39D1/17).

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Samples from 21 Irish heterozygotes were analyzed for HEXA gene mutations. Two (9.5%) Irish heterozygotes had the lethal 11 IVS-9 GR A mutation, whereas 9 (42.8%) had a benign pseudodeficiency mutation. No mutation was found in 10 (47.6%) heterozygotes (Branda 2004).

Treatment: Once a genetic test result is obtained, the psychosocial implications of this result should be further explored. During the posttest genetic counseling process, one must keep in mind that the actual patient reaction may be different than expected. For example, one might imagine that a positive test (showing increased risk) may be a "bad" outcome, whereas a negative test may be a "good" outcome. In clinical practice, this is not always the case. Many patients who have strong family histories of potentially hereditary conditions feel relieved and empowered by a positive genetic test. This positive test for a first family member provides answers to why there is a high frequency of disease in the family and also can be used as a tool for at risk family members to determine their actual level of risk. In contrast, in families where a known disease-causing mutation has previously been identified, patients who do not carry the familial mutation may feel survivor guilt. As part of posttest genetic counseling, the patient should be encouraged to discuss his/her reaction to the test result. The disclosure of genetic test results to family members and their reactions should also be discussed since the disclosure process can be distressing for many individuals. Throughout this process, the patient should feel supported, and referrals to a support group, psychologist, or psychiatrist should be offered if indicated (Ensenauer, 2005).

Prognosis. Hex A is composed of one a subunit and one b subunit. Mutations in the HEXA gene encoding the a subunit cause TSD. In the absence of Hex A activity, the glycolipid GM2 ganglioside accumulates in cells of the central nervous system. This, in turn, leads to cellular dysfunction and death, paralleled clinically by a loss of neurological functions. An infant with TSD typically develops normally for several months before beginning to decline and losing developmental milestones; paralysis and death between the ages of 2 and 6 years ultimately result (Gravel et al., 2001).

Ethical Considerations of Genetic Testing (Ensenauer, et al. 2005)

Ethics in medicine is generally associated with terms referring to the end of a patient's life, such as advance directives or futility. In the field of clinical genetics, however, a variety of additional ethical implications have evolved to become an increasingly substantial part of practice. Of general debate have been ethical issues associated with prenatal diagnosis, assisted reproduction including PGD, diagnostic genetic testing in minors, and population-based testing including expanded newborn screening.

In addition, genetic testing has been discussed in the context of discrimination by insurers and employers. In all of these circumstances, careful consideration needs to be given to the application of the general principles of medical ethics: autonomy, beneficence, nonmaleficence, justice, and confidentiality.

Autonomy

Autonomy is synonymous with the right to choose. In a physician-patient relationship, this principle dictates that adequate and sufficient information is provided in a nondirective manner to allow the patient to make an informed, reasonable, and independent decision on whether or not to proceed with testing. This particularly raises issues regarding the limits of parental autonomy of making decisions on behalf of their children.

Prenatal Testing. Informed prenatal testing allows a pregnant woman to have reproductive choices and thus increases her autonomy. Prenatal diagnosis has the potential of providing early detection of abnormalities in the offspring, reassuring and reducing anxiety, preparing for optimal management immediately after birth, and allowing for prenatal treatment in some cases. Alternatively, prenatal testing also allows couples to make choices about continuation of pregnancies affected with severe medical complications. The availability of new genetic technologies for disorders of variable severity may raise ethical questions. Preimplantation genetic diagnosis as a new complementary approach to prenatal testing also entails ethical implications, eg, regarding questions of sex selection or HLA matching to conceive a child who may serve as a stem cell donor for a sibling afflicted with a disease such as leukemia.

Beneficence and Nonmaleficence

The principles of "doing good" and "not doing harm" imply that informed consent is provided and that this process fully appreciates disclosure of benefits and all possible risks, in order to allow an informed decision by the patient.

Informed Consent Issues in Research. The discovery of genes associated with disease.....

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