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The classic exhortation primum non nocere (first, do no harm) is as pertinent to clinical genetics as it is to medicine in all specialties. Attention to this principle arises particularly in the context of predictive genetic diagnosis, possible for a rapidly escalating number of neurodegenerative disorders (e.g. Huntington disease, frontotemporal dementia, Machado–Joseph disease), cardiovascular and other serious disorders including multiple endocrine neoplasia type 2B, and breast, colon, and other malignancies. Published recommendations and guidelines³⁵⁴ urge rigorous pretest and post‐test genetic counseling. Many factors impact the attempt at risk communication and prediction. Patients who attend for genetic counseling invariably have their own, possibly tentative idea, about their personal risks. Their perception of risks will vary according to their family history, educational level, socioeconomic status, psychological state of mind, life experience, gender, health status, language ability, culture, IQ, and comprehension of mathematics.^355–359 Those who initially thought their personal risks or risks of having an affected child were 50 percent and are informed that the risk only approximates 10 percent may be relieved and not even opt for any testing. Others may be startled to hear that all couples face a 3–4 percent risk on average for bearing a child with a birth defect, intellectual disability, or genetic disorder.

The inherent harm that could potentially be done by predictive testing is the potential for demoralization and depression with possible suicidal consequences (see later discussion). Extreme caution is recommended in considering predictive testing for a disorder without curative, let alone meaningful, palliative treatment. Although for certain dominant disorders some 50 percent of individuals at risk may receive good news, the other 50 percent face, effectively, a death sentence. A single consultation is inadvisable for a couple (or individual) considering predictive testing. During the counseling session with full information transfer, an assessment of emotional health should be made. For many, a consultation with a psychologist or psychiatrist would be wise before a follow‐up visit to determine the decision to test or not, and to obtain informed consent.

Many at risk of developing Huntington disease choose not to be tested. In a study of 733 individuals who did not wish to learn if they harbored this fatal flaw, 66 percent pointed to lack of a cure or treatment, and 66 percent to the inability to undo information provided.³⁶⁰ Only 12–17 percent of those at risk in North America and Europe pursue testing.^360–364 Family and extended family repercussions may occur as a consequence of a choice not to be tested in the face of a 50 percent risk.^365–367 Some family members may hold the untested who proceed to have children morally irresponsible.

There is of course the right of every person not to know their genetic status as potential carrier of a serious genetic disorder. It is not the duty of a counselor to state or hint that it is a moral imperative to have a predictive test. Rather, the responsibility is to provide a perspective on the testing, the various options, and the disparate pros and cons.

Predictive testing of children younger than 18 years of age is proscribed except in life‐threatening disorders (e.g. long QT syndrome, multiple endocrine neoplasia type 2B). Given the remarkable pace of advances in human genetics, it may well be possible in the foreseeable future to develop a therapy that enhances the extant biologic mechanism already in place that delays the manifestations of later onset disease for decades after birth. No life should be ruined by severe depression or suicide only to discover later that a critical palliative remedy has emerged.

No longer hypothetical is the prenatal diagnosis request by a pregnant mother for fetal Huntington disease without the knowledge of her at‐risk partner who does not wish to know his genetic status. In preserving the partner's autonomy and recognizing maternal rights, we have in the past honored such requests. Mothers have, in these circumstances, faced with an affected fetus, elected to terminate the pregnancy, invoking miscarriage as the reason to her unknowing partner. Distressing as it is to contemplate such a marital relationship, textured on the one hand by extreme care and on the other hand by deceit born of sensitivity, consider our report of symptomatic juvenile Huntington disease at 18 months of age and diagnosed at the age of 3 years.³⁶⁸ These cases pose challenging ethical, moral, and legal questions, but both prenatal and preimplantation genetic testing (see Chapter 2) are now well accepted in the Western world.^369–371 Certainly rigorous recommendations and guidelines are in place for the prenatal diagnosis and the preimplantation genetic testing for Huntington disease,³⁶⁹ which would apply equally to other neurodegenerative disorders and serious/fatal adult‐onset disorders.

In general, the post‐prenatal testing behavior of the mother is not likely to escape the average paternal observer. In a study of 54 women whose fetal risks of being affected were 50 percent (that included spouses of an affected partner), after an initial unaffected pregnancy, 10 percent chose not to have prenatal testing in a subsequent pregnancy.³⁷²

Prenatal diagnosis is not recommended for couples who do not intend to terminate a pregnancy if the fetus is affected.³⁷³ A contrary view holds that diagnosis of a fetal genetic disorder may well inform the subsequent management of labor and delivery. Continuation of that pregnancy would likely remove the autonomous right of that child to decide to be tested or not.³⁷⁴ In a review of 15 such pregnancies, one guideline was to recommend that couples should not disclose the diagnosis in order to protect the confidentiality and autonomy of the future child.³⁷⁴

Clearly, there are extraordinarily difficult circumstances related to planned childbearing in the face of 50 percent risks for a neurodegenerative disorder coupled with a wish not to know. In these special circumstances, predictive testing can be regarded as acceptable only if performed with extreme care, concern, and professionalism.

Preconception care should begin during visits to the family physician after menarche. Reiterated and expanding discussions on personal health habits that will affect both the adolescent herself and a future child, provide a basis for promoting good health behavior, while a solid grounding in knowledge about the hazards of smoking, drugs, alcohol, sexually transmitted diseases, and nutrition is provided. Early adolescence is also a vital period during which to inculcate the importance of genes and the wisdom of assimilating and updating information on family history. Linkage of family history to the common experience of physical and mental handicap, outlined in the context of personal risk in childbearing, provides a compelling and cogent framework on which physicians, teachers, and parents can build.

This preparatory background may help educate all women about the importance of planning pregnancy. Over 50 percent of pregnancies in the United States are not planned and are often unintended.³⁷⁵ Physicians also need to reorient their practices so that women of childbearing age understand that to optimize the chance of having a healthy child,³³⁵ prenatal care is best initiated before conception and not after the second missed menstrual period, as is still anachronistically practiced so widely.