Lecture 26 Flashcards
What are the three most common chromosomal trisomies?
1) Down’s syndrome (trisomy 21)
2) Edward’s syndrome (trisomy 18)
3) Patao syndrome (trisomy 13)
What percentage of chromosomal abnormalities are present in miscarriages (SABs - Spontaneous Abortion), conceptuses (the embryo in the uterus, especially during the early stages of pregnancy) and liveborns respectively?
50%, 5% & 1%
Which is more harmful in general: A sex chromosome abnormality or an autosomal chromosome abnormality?
An autosomal chromosome abnormality
What is a requirement for a chromosome test to be done on a cell?
It must be nucleated (RBCs have no nucleus)
What are the most common cell types that undergo chromosomal testing?
Blood lymphocytes, amniocytes, fibroblasts and bone marrow cells
What is the most frequently used stain for chromosomal testing?
Giemsa stain
How are lymphocytes chromosomally tested?
1) A blood sample is added to culture media
2) Red blood cells are removed
3) T-cell division is stimulated
4) The cells are “frozen” in metaphase
5) The cells are lysed and dropped onto slides for analysis
What is Fluorescence in situ hybridization (FISH) used for?
To identify trisomies (extra chromosomes) or microscopic deletions in interphase or metaphase cells
What can be used to uncover complex chromosomal rearrangements?
Chromosomal paint - refers to the hybridization of fluorescently labeled, chromosome-specific, composite probe pools to cytological preparations; Usually used for cancer cells
What is Comparative genomic hybridization (CGH) used for?
To identify subtle chromosomal deletions and duplications
What is Comparative genomic hybridization (CGH)?
Comparative genomic hybridization is a molecular cytogenetic method for analyzing copy number variations relative to ploidy level in the DNA of a test sample compared to a reference sample, without the need for culturing cells (ratio between actual DNA and test DNA should always be 1:1 if they are normal)
What is the proper way to assign Cytogenetic nomenclature?
1) # of chromosomes or chromosomal units
2) Sex chromosome complement
3) Any structural or numeric variation not otherwise specified
What is SAB?
Spontaneous abortion or miscarriage
What is IUGR?
Intrauterine growth retardation (restriction)
What is MCA?
Multiple congenital anomalies
What is SS?
Short stature
What is ID?
Intellectual disabilities
What is LD?
Learning disabilities
What is ADHD/ADD?
Attention deficit hyperactivity disorder/Attention deficit disorder
What are signs of a prenatal chromosomal abnormality?
1) IUGR
2) MCA
3) hydrops/edema
What are signs of an infantile/childhood chromosomal abnormality?
1) MCA
2) unusual facial features
3) SS
4) ID
5) LD
6) ADHD
What are signs of an adulthood chromosomal abnormality?
1) LD
2) infertility
3) SABs
4) stillbirths
What is the anatomy or phenotype of a cytogenetic variation?
Fools Believe Genes are Disposable
F - Facial Features (dysmorphic)
B - Birth defects and physical variations
G - Growth retardation including head growth
D - Developmental problems
When does Trisomy 21 (Down’s Syndrome) become more common?
Non-disjunction that results in Down’s syndrome is associated with increasing maternal age.