User:KClaudio/Prenatal testing

Reviewing the article: Prenatal testing

This sandbox article aims to improve the article "Prenatal testing" in Wikipedia by reviewing its content, citations and adding information as needed. All changes are done here before editing the original article.

Plan to improve the article

• Verify citations and information. The section "Screening for aneuploidy" needs citations. Since incorrect information was found, it will be edited as appropriate (see Notes section).
• Add more information in the "Concerns from disability rights activists and scholars" section.
• Edit the section "False positives and false negatives" by checking the citations and add more as needed.
• Add pictures where needed to improve understanding of main concepts.
• Verify and extend the sections where more information is needed, especially from the ethical context.

Section: Screening for aneuploidy

Due to the detection of fetal cells and fetal DNA circulating in maternal blood, noninvasive diagnosis of fetal aneuploidy is becoming more promising.. The development of a variety of screening methods for fetal aneuploidy and other chromosomal aberrations is now a prominent research area because of the discovery of circulating fetal nucleic acid in maternal blood plasma. A meta-analysis that investigated the success rate of using fetal cell-free DNA from maternal blood to screen for aneuploidies found that this technique detected trisomy 13 in 99% of the cases, trisomy 18 in 98% of the cases and trisomy 21 in 99% of the cases . Failed tests using fetal cell-free DNA are more likely to occur in fetuses with trisomy 13 and trisomy 18 but not with trisomy 21 . Previous studies found elevated levels of cell-free fetal DNA for trisomy 13 and 21 from maternal serum when compared to women with euploid pregnancies . However, an elevation of cell-free DNA for trisomy 18 was not observed . The key problem with the use of cell-free DNA is that circulating fetal nucleated cells comprise only three to six percent of maternal blood plasma DNA . Therefore, two effective approaches have been developed that can be used for the detection of fetal aneuploidy. The first involves the measuring of the allelic ratio of single nucleotide polymorphisms (SNPs) in the mRNA coding region in the placenta. The next approach is analyzing both maternal and fetal DNA and looking for differences in the DNA methylation patterns .

Section: Purposes of prenatal testing

Qualifying risk factors (I deleted this part because did not contribute to main topic and the information is not clear)

Because of the miscarriage and fetal damage risks associated with amniocentesis and chorionic villus sampling (CVS) procedures, many women prefer to first undergo screening so they can find out if the fetus' risk of birth defects is high enough to justify the risks of invasive testing . Since screening tests yield a risk score which represents the chance that the baby has the birth defect, the most common threshold for high-risk is 1:270. A risk score of 1:300 would therefore be considered low-risk by many physicians. However, the trade-off between risk of birth defect and risk of complications from invasive testing is relative and subjective; some parents may decide that even a 1:1000 risk of birth defects warrants an invasive test while others wouldn't opt for an invasive test even if they had a 1:10 risk score.

Ethical issues of prenatal testing

• Eugenics-like practice?
• Accuracy of testing
• Value of the human life is subjected to health and autonomy
• Cure for disease
• What about genetic diseases with a late onset (i,e. Huntington's disease)
• Real value of the test (psychological stress and individual's values and beliefs)
• How to ensure that information about testing options is given in a non-directive, culturally appropriate, and supportive way.

Another important issue to address is the uncertainty of prenatal genetic testing. Uncertainty on genetic testing results from several reasons: the genetic test is associated with a disease but the prognosis and/or probability is unknown, the genetic test provides information different than the familiar disease they tested for, found genetic variants have unknown significance, and finally, results may not be associated with found fetal abnormalities. Richardson and Ormond thoroughly address the issue of uncertainty of genetic testing and explained its implication for bioethics. First, the principle of beneficence is assumed in prenatal testing by decreasing the risk of miscarriage, however, uncertain information derived from genetic testing may harm the parents by provoking anxiety and leading to the termination of a fetus that is probably healthy. Second, the principle of autonomy is undermined given a lack of comprehension resulting from new technologies and changing knowledge in the field of genetics. And third, the principle of justice raised issues regarding equal access to emerging prenatal tests.

Section: Concerns from disability rights activists and scholars

"Disability rights activists and scholars have suggested a more critical view of prenatal testing and its implications for people with disabilities. They argue that there is pressure to abort fetuses that might be born with disabilities, and that these pressures rely on eugenics interests and ableist stereotypes. This selective abortion relies on the ideas that people with disabilities cannot live desirable lives, that they are "defective," and that they are burdens, ignoring the fact that disability scholars argue that "oppression is what's most disabling about disability." Marsha Saxton suggests that women should question whether or not they are relying on real, factual information about people with disabilities or on stereotypes if they decide to abort a fetus with a disability."

Notes:

cfDNA is used to detect aneuploidy in maternal blood. The article mentions that fetal cell DNA is elevated in trisomies 13, 18 and 21, which increase the chances of detecting these aneuplodies in maternal blood. However, another article mentioned that the failure rate of the test in from 0.3% to 12%. They explain that although it is hard to point at the specific reasons, it is possible that maternal obesity and low placental mass may determine the fetal fraction in maternal blood. They mentioned that trisomies 18 and 13 only tend to present lower fetal fraction resulting in failed test.