Prenatal Genetics - Nagl Flashcards
Define:
Euploid
Haploid
Diploid
Polyploid
Aneuploid
- Euploid: normal number of chromosomes
- Diploid: 2n (46 chromosomes)
- Haploid: n (23 chromosomes)
- Polyploid: Integer multiple deviation of the haploid number (example: triplod = 69, tetraploid = 92)
- Aneuploid: non-integer multiple deviation of the haploid number (example: trisomy = 47, monosomy = 45)
Is triploidy viable?
No. Lethal in virtually all cases. Exact prognosis depends on the parental origin of the extra set of chromosomes
Describe the features of a digynic triploidy.
Describe the features of a diandric triploidy.
Digynic triploidy
- Extra set of chromosomes of maternal origin
- Usually has small placenta, severe growth restriction
- Usually spontaneously abort early in pregnancy
Diandric triploidy
- Extra set of chromosomes of paternal origin
- Enlarged placenta, fetus usually not growth restricted
- Risk of severe early onset preeclampsia, hyperthyroidism, theca lutein cysts, and gestational trophoblastic disease
What is advanced maternal age for a singleton pregnancy?
For a twin pregnancy?
35 for single
33 for twins
What is the most common trisomy?
Give some of the deficiencies seen with this condition
What is the usual life expectancy for this disorder?
Trisomy 21 (Down syndrome)
- cognitive deficiencies
- vision problems
- hearing loss
- thyroid dysfunction
- increased risk of early onset dementia or cancer
- congenital amonalies (heart malformations, GI malformations)
Life expectancy: ~45 years
What is Edwards Syndrome?
Give some clinical features of this disease
What is the life expectancy of children born with this disease?
Trisomy 18
- Severe psychomotor delay
- Growth restriction
- Microcephaly
- Micrognathia
- Distinctive hand clawing/positioning
- Rocker bottom feet
- Congenital anomalies (heart, omphalocele, clefting, clubfoot)
Life expectancy: <1 year (this is a lethal chromosome disorder)
What is Patau Syndrome?
Give some clinical features
What is the life expectancy?
Trisomy 13
- Severe psychomotor delays
- Microphthalmia
- Polydactyly
- Congenital anomalies (oral clefting, holoprosencephaly, brain, heart, diaphragmatic hernias)
Life expectancy: <1 year (lethal chromosome disorder)
What is another name for Monosomy X?
Give some clinical features
Turner Syndrome
- Growth retardation
- Infertility (though 5% may experience spontaneous menstruation)
- Hearing loss
- Possible cognitive diability
- Congenital anomalies (heart, cystic hygroma, horseshoe kidney, other renal abnormalities)
What is the chromosome abnormality of Klinefelter Syndrome?
XXY (XYY and others also possible)
- Tall/lean build
- Infertility
- Slightly delayed motor and language milestones
- Possible cognitive disabilities
- Increased risk of extragonadal germ cell tumors, male breast cancer, and autoimmune disorders
Define: reciprocal translocation
Chromosome material is exchanged equally or unequally
Define: Robertsonian translocation
The short arms (p) of two chromosomes are lost and the remaining long arms (q) are joined, forming a single chromosome
What is a balanced translocation? Is the phenotype normal or abnormal?
What is an unbalanced translocation? Is the phenotype normal or abnormal?
Balanced: chromosome segments are not lost or duplicated. Phenotype tends to be normal.
Unbalanced: chromosome segments are duplicated or deleted. Phenotype is often unusual.
What is more common: duplication or deletion?
Deletion
What is the first trimester screen?
Who should get it?
Routine risk assessment (not diagnostic) of fetal Down syndrome, trisomy 13 and trisomy 18. It includes blood testing and ultrasound imaging.
Indicate for all pregnant patients
What is the cell-free fetal (cff) DNA / Non-invasive prenatal screening (NIPS) test?
Who should get it?
Non-routine screening test (not diagnostic) for Down Syndrome, trisomy 13, trisomy 18, and sex chromosome abnormalities. The test screens small amounts of fetal DNA found in maternal blood.
Performed on high-risk pregnant patients
What is the maternal serum quad screen test?
What does it look for?
Who should get it?
Risk assessment test (not diagnostic) of Down Syndrome, trisomy 18, neural tube defects, and abdominal wall defects (gastroschisis)
Tests for:
- alpha-fetoprotein
- hCG
- urine unconjugated estriol
- inhibin-A
Indicated for all pregnant patients
Name (3) diagnostic tests used to screen for prenatal chromosome abnormalities
- Chorionic Villus Sampling (CVS)
- Amniocentesis
- Cordocentesis/Percutaneous Umbilical Blood Sampling (PUBS)
Cordocentesis/Percutaneous Umbilical Blood Sample (PUBS):
- When is it used?
- How is it done?
- Used when amniocentesis fails, yields ambiguous results, or other findings (fetal plasma or blood cell abnormalities and infections) require additional confirmation
- Sample of fetal blood is obtained from the umbilical vein under ultrasound guidance
When is amniocentesis indicated?
How it is performed?
What does it screen for?
Indicated for pregnancies with increased risk of aneuploidy or chromosomal abnormalities
A sample of amniotic fluid (containing free/floating fetal cells) is obtained via trans-abdominal biopsy
Detects:
- Fetal aneuploidy
- Chromosomal abnormalities
- Single gene disorders
- Abnormal biochemical levels
- AChE for detection of neural tube defects and abdominal wall defects
Fetal alcohol syndrome is associated with maternal consumption of how many drinks per day?
8-10
However, effects have been reported with lower levels (don’t drink at all, please)
Is cocaine found in the breast milk of mothers who use it?
What kind of fetal abnormalities are associated with mothers who use cocaine during pregnancy?
Yes
- Growth retardation
- Premature birth
- Placental abruption
- Abnormal behavioral characteristics
- CV and respiratory problems
- Structural malformations (controversial)
Maternal use of Isoretinoin is assocated with several fetal abnormalities. Name a few.
Should mothers taking this medication breast feed?
Associated with:
- CNS abnormalities
- Craniofacial abnormalities
- Heart defects
- Cognitive deficiencies
Breast milk: excess retinoic acid in the milk are unlikely, but it may contribute to suppressed bone growth and staining of the teeth. Caution is recommended.
Maternal use of Valproic acid is associated with what fetal abnormalities?
Should these mothers breastfeed?
Associated with:
- Neural tube defects
- Oral clefts
- Craniofacial abnormalities
- Heart defects
- Cognitive deficiencies
Valproic acid can be excreted into breast milke, but adverse effects are uncommon. Caution is recommended.
Discuss the risk of maternal SSRI use to the developing infant
- Generally not associated with increased risk of congential anomalies
- SSRI use in the third trimester can cause withdrawal symptoms in the neonate (irritability, tremors, poor feeding/sleeping, arrhythmia, pulmonary depression, fetal distress)
- SSRIs are excreted into the breast milk, but studies on the risks of this are inconclusive
What is multifactorial inheritance?
Give some examples relevant to fetal/neonate development
a.k.a. complex inheritance
Type of non-mendelian inheritance involving a trait or phenotype that resuts from an unclear/complex combination of genetic and environmental factors. May cluster or aggregate in families
Examples: pyloric stenosis, spina bifida, diabetes mellitus, mental illness
What is the inheritance pattern of Fragile X Syndrome?
Describe the biomolecular defect seen in this disease
Describe some clinical features
X-linked recessive
Abnormal repeats within the X chromosome
Clinical features:
- Mild to profound mental retardation
- Behavioral anomalies and autistic tendencies
- Macrocephaly and subtle facial characteristics
- Increased risk of premature ovarian cancer (females)
- Increase risk of adult-onset cerebellar ataxia/intention tremors
Fragile X Syndrome is often misdiagnosed as what?
What features of a family pedigree should arouse your suspicion of Fragile X?
Parkinson’s Disease
Worrisome pedigreee features:
- Siblings with autistic tendencies
- Relatives with Parkinson’s Disease Diagnosis
- Female relatives with ‘early menopause’
- Relatives with developmental delay or intellectual under-achievement
What genetic defect, previously considered solely a ‘white people disease’ should always be considered in genetic screening?
Cystic fibrosis
