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Reproductive System > Prenatal Genetics > Flashcards

Prenatal Genetics Flashcards

1
Q

What are 2 examples of abnormalities in chromosome number?

A

Triploidy (3n)

Aneuploidy

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2
Q

Triploidy

Definition

Prevalence

Prognosis

A
  • Euploid complement of standard diploid (2n) chromosome number
  • 3rd extra set of chromosomes (46 –> 69)
  • 1-3% of pregnancies
  • Lethal in virtually all cases
  • Prognosis depends on parent of origin
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3
Q

What is Digynic Triploidy?

A
  • Extra chromosome set of maternal origin
  • Small placenta
  • Fetus exhibits severe growth restriction
  • Spontaneous abortion early in pregnancy
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4
Q

What is Diandric Triploidy?

What are women at risk for?

A
  • Extra chromosome set of paternal origin
  • Enlarged placenta
  • Fetus is NOT growth restricted
  • Partial Hydatidiform mole
  • Women at risk for:
    • Severe early onset preeclampsia
    • Hyperthyroidism
    • Multiple theca lutein cysts
    • Gestational trophoblastic disease
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5
Q

What is Aneuploidy?

A
  • Any other chromosome # that is not an exact multiple of haploid (n)
  • Most common type of human chromosome disorder (5%)
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6
Q

What are some pathologic examples of aneuploidy? (5)

A
  • Trisomy 21 (Down Syndrome)
  • Trisomy 18 (Edwards Syndrome)
  • Trisomy 13 (Patau Syndrome)
  • Monsomy X (Turner Syndrome)
  • XXY Syndrome (Klinefelter Syndrome)
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7
Q

Trisomy 21 (Down Syndrome)

Clinical Manifestation

A
  • 1:800 live births
  • Cognitive deficiencies
  • Vision problems
  • Hearing loss
  • Thyroid dysfunction
  • Increased risk for early onset dementia or cancer
  • Congenital anomalies (heart malformations, GI abnormalities)
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8
Q

Trisomy 18 (Edwards Syndrome)

Clinical Manifestation

A
  • 1:3,000 live births
  • Severe psychomotor delays
  • Growth restriction
  • Microcephaly
  • Micrognathia
  • Distinctive hand/finger posturing
  • Congenital anomalies (heart malformations, Omphalocele, oral clefting, clubfoot)
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9
Q

Trisomy 13 (Patau Syndrome)

Clinical Manifestation

A
  • 1:10,000 live births
  • Severe psychomotor delays
  • Micropthalmia
  • Polydactyly
  • Congenital anomalies (oral clefting, holoprosencephaly, brain abnormalities, heart malformations, diaphragmatic hernia)
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10
Q

Monosomy X (Turner Syndrome)

Clinical Manifestation

A
  • 1:2,500 live born females
  • Growth retardation
  • Infertility
  • Hearing loss
  • Possible cognitive disabilities
  • Congenital anomalies (heart malformations, cystic hygromas, horseshoe kidney & other renal abnormalities)
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11
Q

XXY Syndrome (Klinefelter Syndrome)

Clinical Manifestation

Risk

A
  • Tall/lean build
  • Infertility
  • Slightly delayed motor & language milestones
  • Possible cognitive disabilities
  • Increased risk
    • Extragonadal germ cell tumors
    • Male breast cancer
    • Autoimmune disorders
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12
Q

Risk for aneuploidy ________ with maternal age.

A

Increases

  • Singleton pregnancy (_>_35 YO)
    • Risk of Down Syndrome = 1:385
    • Risk of any aneuploidy = 1:204
  • Twin pregnancy (_>_33 YO)
    • Risk of Down Syndrome = 1:347
    • Risk of any aneuploidy = 1:176
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13
Q

Translocation

Definition

Balanced vs. Unbalanced

A
  • Structural breakage & rearrangement of chromosome material
  • 1:375 live births
  • Spontaneous or transmitted from parent to offspring
  • Balanced
    • Exchange of chromosome segments
    • Not deleted (lost) or duplicated (gained)
    • Carriers
    • Normal phenotype
    • 5-10% risk of passing on unbalanced
    • Low risk (1%) vs. high risk (>20%)
  • Unbalanced
    • Chromosome segments that are deleted or duplicated
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14
Q

Deletion

Definition

Phenotype

A
  • Loss of segment of a chromosome (any length/size)
  • 1:7,000 live births
  • Chromosomal imbalance (partial monosomy)
  • Phenotype results from haploinsufficiency
    • Inability of a single copy of a genetic unit to perform the function of 2 copies
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15
Q

Duplication

Definition

A
  • Gain of a segment of a chromosome (any length/size)
  • Less common than deletions
  • Chromosomal imbalance (partial trisomy)
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16
Q

What tests are done to screen for maternal serum and/or fetal ultrasound markers?

A
  • 1st trimester screen
  • Cell-free fetal DNA/Non-invasive Prenatal Screening (NIPS)
  • Maternal Serum Quad Screen
17
Q

What is the 1st trimester screen for pregnant patients?

What are the indications?

A
  • Routine test
  • Risk assessment
    • Down Syndrome
    • Trisomy 13
    • Trisomy 18
  • **Indicated for ALL pregnant patients regardless of fetal aneuploidy risk **
18
Q

What is the Cell-free DNA/Non-invasive Prenatal Screening (NIPS)?

What are the indications?

A
  • Non-routine test
  • Risk assessment
    • Down Syndrome
    • Trisomy 13
    • Trisomy 18
    • Sex chromosome abnormalities
  • Indicated for high-risk pregnant patients
    • Advanced maternal age
    • Previous pregnancy or + FaHx of aneuploidy
    • Abnormal fetal ultrasound
    • Screening blood test suggestive of chr abnormality
19
Q

What is the Maternal Serum Quad Screening test for pregnant patients?

A
  • Routine test
  • Risk assessment
    • Down syndrome
    • Trisomy 18
    • Neural tube defects (spina bifida, anencephaly)
    • Abdominal wall defects (Gastroschisis)
  • **Indicated for all pregnant patients regardless of fetal aneuploidy risk **
20
Q

What are 3 examples of Genetic Diagnostic Testing?

A
  • Chorionic Villus Sampling
  • Amniocentesis
  • Cordocentesis/Percutaneous Umbilical Blood Sampling (PUBS)
21
Q

Chorionic Villus Sampling

Definition

Indications

Procedure

A
  • Prenatal diagnosis of fetal aneuploidy, other chromosome abnormalities & single gene disorders
  • Does not screen for neural tube defects
  • Indications
    • Advanced maternal age
    • FaHx
    • Abnormal 1st trimester screen
  • Available to all pregnant patients
  • **Sample of placental chorionic villi obtained by transabdominal or Transcervical biopsy **
22
Q

Amniocentesis

Definition

Indications

Procedure

A
  • Prenatal diagnosis of fetal aneuploidy, other chromosome abnormalities, single gene disorders, abnormal biochemical levels
  • Amniotic fluid AFP analysis & AChE to detect:
    • Open neural tube defects
    • Abdominal wall defects
  • Indications
    • Advanced maternal age
    • FaHx or abnormal screen
    • Available to all pregnant patients
  • Sample of amniotic fluid obtained via transabdominal biopsy
  • Floating fetal cells used for culture, chromosomal & DNA analysis
23
Q

**Cordocentesis/Percutaneous Umbilical Blood Sampling (PUBS) **

Indications

Procedure

A
  • Follow-up
    • Amniocentesis fails or is ambiguous
    • Biochemical tests of fetal plasma/blood cells or infection need to be confirmed
  • Sample of fetal blood directly from umbilical vein
  • Ultrasound guidance or infusion of blood products
24
Q

Development vs. Dysmorphism

A
  • Development – cellular pathways responding to environmental & genetic signals
  • Dysmorphism – morphological, developmental abnormalities of 1 or more tissues or organ systems due to environmental or genetic factors
25
Q

How can environmental factors alter fetal development?

What are the risk factors?

What are some examples?

A
  • Environmental agents or maternal infections can be teratogenic
  • Ability to alter fetal gene products & cellular communication
  • Increased risk
    • Birth defects, unusual facial characteristics, growth retardation, miscarriage, preterm birth, hearing loss, vision loss, cognitive deficiencies, behavior abnormalities
  • Maternal teratogen exposure
    • Alcohol, smoking, illicit drugs, prescription medications, radiation
26
Q

How does Alcohol act as a teratogen?

A
  • Maternal consumption of 8-10 drinks/day
  • Affects cellular pathways
    • Central nervous system
    • Craniofacial structures
27
Q

How do illicit drugs (cocaine) act as teratogens?

A
  • Fetal growth retardation
  • Premature growth
  • Neonatal complications
    • Abnormal behavioral testing
    • CV or respiratory problems
  • Vasoconstrictive problems
  • Skeletal abnormalities
  • Genitourinary abnormalities
  • **Cocaine excreted into breast milk **
28
Q

How does Retinoic Acid (Isotretinoin) act as a teratogen?

A
  • Accutane - oral medication for severe acne
  • CNS abnormalities
  • Craniofacial abnormalities
  • Heart defects
  • Cognitive deficiencies
  • Retinoic acid is a natural component in breast milk (suppresion of bone growth, teeth stain)
29
Q

How does Valproic Acid act as a teratogen?

A
  • Oral anticonvulsant medication
  • Neural tube defects
  • Oral clefts
  • Craniofacial abnormalities
  • Heart defects
  • Cognitive deficiencies
  • Valproic acid can be excreted into breast milk
30
Q

How do Selective Serotonin Reuptake Inhibitors (SSRIs) act as teratogens?

A
  • Example: Zoloft
  • Overall risk not above general population
    • Cardiac malformations
    • Neural tube defects
  • SSRIs in 3rd trimester: withdrawal symptoms
    • Irritability
    • Tremors
    • Poor feeding & sleeping
    • Arrhythmia
    • Pulmonary depression
    • Fetal distress
  • **SSRIs are excreted into breast milk **
31
Q

**Multifactorial Inheritance **

Definition

Risk Assessment

A
  • Complex inheritance – trait/phenotype that results from an unclear combination of genetic & environmental factors
  • Affected individuals may cluster in families
  • Relatives likely to share predisposing alleles
  • Risk assessment: population-based incidence of trait & degree of relationship w/i family of affected & non-affected individuals
32
Q

**Multifactorial Inheritance **

Examples

A
  • Pyloric stenosis
  • Spina bifida
  • Oral clefts
  • Diabetes Mellitus
  • Mental illness
33
Q

What are Single Gene Mendelian Disorders?

A
  • Inherited in patterns of Mendelian inheritance
    • Autosomal dominant
    • Autosomal recessive
    • X-linked
  • Ancestry-based carrier screening offered to women of reproductive age
34
Q

Single Gene Mendelian Disorders

  • Euro/Caucasian (Northern)
  • Euro/Caucasian (Southern)
  • French Canadian
  • African American
  • Asian
  • Latino
  • Ashkenazi Jewish
A
35
Q

Aside from common ancestry-related diseases, additonal disorders such as _________________ are becoming more prevalent in carrier screening discussion with patients.

A

**Fragile X Syndrome **

36
Q

Fragile X Syndrome

Clinical Manifestation

Risk

Inheritance

A
  • Mild to profound mental retardation, behavioral abnormalities, autistic tendencies, macrocephaly & other subtle facial characteristics
  • Increased risk
    • Premature ovarian failure among females
    • Adult-onset cerebellar ataxia/intention disorders
  • Abnormal repeats of DNA code w/i X chromosome
  • X-linked pattern of inheritance
  • Carrier mothers asymptomatic
    • Sons (50% affected)
    • Daughters (50% asymptomatic carriers)

Reproductive System (35 decks)

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