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Questions and Answers
A neonate is diagnosed with Patau syndrome. Genetic analysis reveals a robertsonian translocation. Which parent is most likely a carrier of the translocation, and what is the implication for future pregnancies?
A neonate is diagnosed with Patau syndrome. Genetic analysis reveals a robertsonian translocation. Which parent is most likely a carrier of the translocation, and what is the implication for future pregnancies?
- Either parent could be a carrier, and genetic counseling is recommended to assess the recurrence risk in future pregnancies. (correct)
- Neither parent is a carrier, as robertsonian translocations arise spontaneously and do not affect future pregnancy outcomes.
- The mother is likely a carrier, and future pregnancies have a 50% chance of also resulting in a trisomy.
- The father is likely a carrier, and future pregnancies are unaffected as the translocation originated in the father's germline.
A fetus is suspected of having Patau syndrome based on first-trimester screening. If confirmatory genetic testing demonstrates Trisomy 13, what would be the most likely findings on a detailed ultrasound?
A fetus is suspected of having Patau syndrome based on first-trimester screening. If confirmatory genetic testing demonstrates Trisomy 13, what would be the most likely findings on a detailed ultrasound?
- Microcephaly, holoprosencephaly, and polydactyly. (correct)
- Cystic hygroma, coarctation of the aorta, and horseshoe kidney.
- Omphalocele, diaphragmatic hernia, and clubfoot.
- Chorioid plexus cysts, clenched fists, and rocker-bottom feet.
During a prenatal screening, a 38-year-old woman's first-trimester serum markers reveal low levels of both β-hCG and PAPP-A. Nuchal translucency is also increased. Which of the following chromosomal abnormalities is most likely, and what is the primary mechanism behind this condition?
During a prenatal screening, a 38-year-old woman's first-trimester serum markers reveal low levels of both β-hCG and PAPP-A. Nuchal translucency is also increased. Which of the following chromosomal abnormalities is most likely, and what is the primary mechanism behind this condition?
- Turner syndrome, resulting from monosomy X due to meiotic nondisjunction in the paternal gamete.
- Patau syndrome, resulting from trisomy 13 due to nondisjunction during maternal meiosis. (correct)
- Down syndrome, resulting from trisomy 21 due to robertsonian translocation.
- Edwards syndrome, resulting from trisomy 18 due to post-zygotic mosaicism.
A newborn presents with cyclopia and a proboscis. Which of the following underlying conditions is most likely contributing to these congenital anomalies, and what is the embryological basis?
A newborn presents with cyclopia and a proboscis. Which of the following underlying conditions is most likely contributing to these congenital anomalies, and what is the embryological basis?
An infant is diagnosed with Patau syndrome and exhibits severe cardiac defects, including both a ventricular septal defect (VSD) and an atrial septal defect (ASD). How does trisomy 13 disrupt normal cardiac development to cause these defects?
An infant is diagnosed with Patau syndrome and exhibits severe cardiac defects, including both a ventricular septal defect (VSD) and an atrial septal defect (ASD). How does trisomy 13 disrupt normal cardiac development to cause these defects?
When counseling parents about Patau syndrome after a prenatal diagnosis, what information should be emphasized regarding survival rates and long-term morbidity?
When counseling parents about Patau syndrome after a prenatal diagnosis, what information should be emphasized regarding survival rates and long-term morbidity?
A newborn presents with polydactyly and rocker-bottom feet. What is the underlying mechanism by which Trisomy 13 causes polydactyly?
A newborn presents with polydactyly and rocker-bottom feet. What is the underlying mechanism by which Trisomy 13 causes polydactyly?
A fetus is diagnosed with Patau syndrome. The parents inquire about the likelihood of future pregnancies being affected. If the Patau syndrome is due to nondisjunction, what is the recurrence risk in future pregnancies?
A fetus is diagnosed with Patau syndrome. The parents inquire about the likelihood of future pregnancies being affected. If the Patau syndrome is due to nondisjunction, what is the recurrence risk in future pregnancies?
In second-trimester screening for Patau syndrome, why might a quadruple screen be less reliable compared to first-trimester screening?
In second-trimester screening for Patau syndrome, why might a quadruple screen be less reliable compared to first-trimester screening?
An ultrasound reveals a two-vessel umbilical cord during a routine prenatal visit. What is the most appropriate next step in evaluating potential underlying issues?
An ultrasound reveals a two-vessel umbilical cord during a routine prenatal visit. What is the most appropriate next step in evaluating potential underlying issues?
Flashcards
Trisomies
Trisomies
Extra copies of autosomal chromosomes, including Patau (13), Edwards (18), and Down (21).
Nondisjunction
Nondisjunction
Failure of chromosomes to separate properly during meiosis, leading to an extra chromosome copy.
Robertsonian Translocation
Robertsonian Translocation
Attachment of a chromosome or large segment to another, causing genetic imbalance.
First Trimester Ultrasound
First Trimester Ultrasound
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Nuchal Translucency (NT)
Nuchal Translucency (NT)
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Chorionic Villus Sampling (CVS)
Chorionic Villus Sampling (CVS)
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Amniocentesis
Amniocentesis
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Patau Syndrome
Patau Syndrome
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Holoprosencephaly
Holoprosencephaly
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Polydactyly
Polydactyly
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Study Notes
Trisomies Overview
- Extra copies of autosomal chromosomes
- Patau syndrome is Trisomy 13
- Edwards syndrome is Trisomy 18
- Down syndrome is Trisomy 21
- Increased maternal age and nondisjunction are common among all three
- Robertsonian translocation is a less common cause (~5%)
- Risk factor of multiple children in the family with trisomy is a Robertsonian translocation
- Trisomy 13 and 18 are more severe with malformations
- Infants with Trisomy 13 and 18 rarely survive past one year
- Down syndrome patients can survive into middle age or older
General Perinatal Workup for Aneuploidy
- First trimester ultrasound (10-14 weeks) for gestational age, placental, and fetal development
- Nuchal translucency (NT) should be combined with serum screening tests to diagnose chromosomal abnormalities
- Umbilical cord assessment looks for two vessel umbilical cord, suggesting chromosomal abnormalities or congenital anomalies
- Second and third trimesters include assessment of fetal growth and anatomy to detect structural abnormalities
Non-Routine Perinatal Testing
- Chorionic Villus Sampling (CVS) is performed early in pregnancy to take placental tissue for genetic testing
- Benefits of CVS include early detection and earlier family decision-making
- Risks of CVS include miscarriage, bleeding, infection, and placental damage
- Amniocentesis is done later via transabdominal needle aspiration of amniotic fluid for genetic analysis
- Risks of amniocentesis include miscarriage, infection, and leakage of amniotic fluid
Perinatal Screening Tests
- Indicated for all women, those with family history, or concern for aneuploidy or neural tube defects
- Key serum markers include beta-hCG, PAPP-A, maternal serum AFP, unconjugated estriol, and inhibin A
β-hCG
- Produced by the Placenta
- Elevated in Down syndrome
- Low in Patau and Edwards syndromes
PAPP-A
- Pregnancy-associated plasma protein A
- Typically low in trisomies
AFP
- Maternal serum alpha-fetoprotein
- Low in trisomies
uE3
- Unconjugated estriol
- Decreased in trisomies
Inhibin A
- Elevated in Down syndrome
- Normal or low in other trisomies
Patau Syndrome (Trisomy 13)
- Most severe trisomy
- Incidence is 1 in 10,000–20,000 live births
- High rate of fetal loss with only 1 in 40 conceptions reaching full term
- Average life expectancy around 13 days
- Some children survive past one year with profound disabilities
Genetic Basis
- Most common cause is nondisjunction during maternal meiosis
- Maternal age ≥ 35 years is a major risk factor
- Robertsonian translocation occurs in ~4% of cases
- Chromosome 13 may fuse with chromosome 14 or 22
Neurological and Craniofacial Anomalies
- Microcephaly is a small head due to underdevelopment of the brain
- Holoprosencephaly is the failure of brain hemispheres to divide properly
- Scalp defects (cutis aplasia) are areas of missing skin on the scalp
- Cyclopia means one central eye
- Microphthalmia means small eyes
- Proboscis is flesh tissue above the eye in place of a nose
Cardiac Anomalies
- Ventricular Septal Defect (VSD) is a hole in the wall between the ventricles
- Atrial Septal Defect (ASD) is a hole in the wall between the atria
Renal Anomalies
- Polycystic kidneys involve multiple cysts in the kidneys
- Horseshoe kidney is when the kidneys fuse together
Limb Abnormalities
- Polydactyly is extra fingers/toes
- Rocker-bottom feet have a prominent heel and convex sole
Mnemonic
- Patau = Polydactyly helps to remember one of the hallmark features
Perinatal Screening
- First Trimester: Increased nuchal translucency and low β-hCG and PAPP-A
- Second Trimester: β-hCG, AFP, and estriol may be low or normal, making the screening less reliable
- Diagnosis requires karyotyping or FISH to confirm Trisomy 13
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