7.4: Genetic Counseling and Testing
- Page ID
- 228146
\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)
\( \newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\)
( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\)
\( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)
\( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\)
\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)
\( \newcommand{\Span}{\mathrm{span}}\)
\( \newcommand{\id}{\mathrm{id}}\)
\( \newcommand{\Span}{\mathrm{span}}\)
\( \newcommand{\kernel}{\mathrm{null}\,}\)
\( \newcommand{\range}{\mathrm{range}\,}\)
\( \newcommand{\RealPart}{\mathrm{Re}}\)
\( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)
\( \newcommand{\Argument}{\mathrm{Arg}}\)
\( \newcommand{\norm}[1]{\| #1 \|}\)
\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)
\( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\AA}{\unicode[.8,0]{x212B}}\)
\( \newcommand{\vectorA}[1]{\vec{#1}} % arrow\)
\( \newcommand{\vectorAt}[1]{\vec{\text{#1}}} % arrow\)
\( \newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vectorC}[1]{\textbf{#1}} \)
\( \newcommand{\vectorD}[1]{\overrightarrow{#1}} \)
\( \newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}} \)
\( \newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}} \)
\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)
\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)- Define genetic counseling.
- Explain the role of genetic counseling in supporting families and children with genetic conditions.
- Distinguish between genetic screening and diagnostic testing during pregnancy.
- Describe common prenatal screening and diagnostic procedures.
- Identify the benefits and limitations of genetic testing for early detection and intervention planning.
- Discuss ethical considerations regarding prenatal genetic testing, including privacy, consent, and family decision-making.
Genetic counseling is a professional service that provides individuals and families with information about the genetic basis of health conditions and how they may be passed down through generations. For children, genetic counseling can play a critical role in identifying potential genetic disorders early, which can lead to timely interventions and improve long-term health outcomes. Genetic counselors, trained in genetics and counseling, work closely with parents and caregivers to explain genetic risks, inheritance patterns, and the available options for testing and management (National Society of Genetic Counselors [NSGC], 2020).
From the perspective of the developing child, genetic counseling is essential for:
- Early Diagnosis and Intervention: Identifying genetic disorders early can lead to immediate interventions, which may reduce developmental delays or other complications.
- Managing Family Planning: Counseling can help parents understand how a genetic condition might impact future children and offer support for family planning decisions.
- Understanding Genetic Risks: Counseling helps families understand genetic risks in a way that is comprehensible and meaningful, especially when considering how these risks may affect their child’s development.
Types of Prenatal Genetic Testing
Genetic prenatal testing can be broadly classified into screening tests and diagnostic tests.
Screenings
Screening tests assess the likelihood of a genetic condition, while diagnostic tests confirm whether the condition is present.
- First Trimester Screening: This test combines blood tests and an ultrasound to assess the risk of chromosomal abnormalities, such as Down syndrome (trisomy 21), trisomy 18, and trisomy 13. The blood test measures the levels of certain substances in the mother's blood. At the same time, the ultrasound looks for specific markers in the fetus, such as the nuchal translucency (fluid at the back of the neck), which may indicate an increased risk of Down syndrome.
- Integrated Screening: A combination of first and second trimester screening tests, integrated screening involves measuring blood markers at both stages of pregnancy. It provides a more accurate risk assessment for conditions such as Down syndrome, trisomy 18, and neural tube defects like spina bifida.
- Non-Invasive Prenatal Testing (NIPT): NIPT is a blood test that analyzes small fragments of fetal DNA found in the mother's blood. It is highly accurate for detecting conditions like Down syndrome, trisomy 18, and trisomy 13. NIPT can be done as early as the 10th week of pregnancy and is considered more accurate than other screening tests. However, it is still a screening test, and a positive result requires confirmation through diagnostic testing.
Diagnostic Tests
Diagnostic tests provide definitive results and are used when a screening test indicates an increased risk of a genetic condition or when there is a family history of certain disorders. These tests involve taking a sample of fetal cells and examining them for genetic abnormalities.
Figure \(\PageIndex{1}\): Amniocentesis. Image by BruceBlaus is licensed CC BY-SA 4.0
- Amniocentesis: Performed between the 15th and 20th week of pregnancy, amniocentesis involves taking a sample of amniotic fluid from the sac surrounding the fetus. The fluid contains fetal cells that can be analyzed for chromosomal abnormalities, such as Down syndrome, and genetic disorders, such as cystic fibrosis. Amniocentesis is highly accurate, with a diagnostic accuracy rate of about 99.4% for detecting chromosomal abnormalities (American Pregnancy Association, 2020).
- Chorionic Villus Sampling (CVS): CVS is performed between the 10th and 13th week of pregnancy and involves taking a small sample of cells from the placenta (chorionic villi). These cells are tested for genetic conditions such as Down syndrome, cystic fibrosis, and Tay-Sachs disease. CVS has a slightly higher risk of complications compared to amniocentesis, but offers the advantage of being performed earlier in the pregnancy.
- Cordocentesis (Percutaneous Umbilical Blood Sampling): This is a rare test performed after the 18th week of pregnancy. It involves obtaining a sample of the fetus's blood from the umbilical cord. It is typically used to diagnose blood disorders, such as anemia or infections. However, this test is more invasive and is usually reserved for specific cases.
Benefits of Genetic Testing
Prenatal genetic testing can detect a range of genetic disorders early in pregnancy, including conditions that may affect the child’s long-term health. Early identification of disorders allows parents and healthcare providers to plan for the child’s care, provide early interventions, and/or make decisions about the pregnancy and how to proceed. This may involve decisions about continuing the pregnancy, preparing for the birth of a child with special needs, or making informed choices about healthcare and future treatments.
For families with a known genetic condition or family history, prenatal genetic testing provides information to make informed decisions about future pregnancies. If a genetic condition is detected, parents may consider options such as preimplantation genetic diagnosis (PGD) with in vitro fertilization (IVF) or consider adoption.
Ethical Considerations in Genetic Testing
Genetic prenatal testing raises important ethical issues, particularly regarding the privacy of results and the rights of children as they grow older. Initially, parents control the genetic information, but as children mature, they may gain the ability to understand and decide how their genetic data is shared. Ethical concerns arise when parents withhold information from the child's early years, as the child may later seek or be exposed to this information. When children reach an age where they can comprehend their genetic results, the question becomes whether they should have the right to consent to disclosing this information, especially if it relates to life-altering conditions. Balancing the child’s right to privacy with the parents’ role in decision-making is crucial, and genetic counselors can help guide families through these complex conversations while prioritizing the child's emotional and psychological well-being.
References, Contributions and Attributions
American Pregnancy Association. (2020). Amniocentesis: What to expect. Retrieved from https://americanpregnancy.org
National Society of Genetic Counselors. (2020). Genetic counseling and testing: Guidelines and ethical considerations. Journal of Genetic Counseling, 28(5), 532-540.