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34 Cards in this Set

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Sample types for prenatal cytogenetic testing
Give:
1. risk of pregnancy loss
2. weeks
Chorionic villi
(1) 1% (2)10-12 weeks
Amniotic fluid (most common; can pick up more DNA)
(1) 0.5% (2) 15-18 weeks
Percutaneous umbilical cord
(1) 2% (2) later in pregnancy
Products of conception-->amnion, chorion, villi, and fetal tissue *presence of maternal tissue can cause errors
tissues commonly used for postnatal cytogenetic testing
1. peripheral blood
2. tissue: skin, pericardium, tendon
3. BM/core, LN, tumors
DO NOT FREEZE
Define:
1. Euploidy
2. aneuoploidy
1. Euploidy=loss or gain of entire chormosome set (46, 23, 69, etc)
2. aneuoploidy=loss or gain of less than an entire chromo set (tri or monosomy)
Define:
1. Euploidy
2. aneuoploidy
1. Euploidy=loss or gain of entire chormosome set (46, 23, 69, etc)
2. aneuoploidy=loss or gain of less than an entire chromo set (tri or monosomy)
Aneuplody and live birth
Types and proportions of aneuoploidies found between live and spontaneous birth are different. High degree of lethality even if compatible with birth.
At what phases of meiosis does:
1. recombination occur?
2. independant assortment of homologues occur?
1. recombination= prophase I
2. independant assortment= anaphase
Nondysjunction in meiosis I and II both end up with mono and trisomies, but how can you tell them apart?
M I-->tri of three different chromos
M II-->tri of two same chromos and one from other parent
Mitotic nondysjunction: Mosaicism
Three differnet cells lines: normal, trisomy, monosomy.
In many cases, monosomy does not survive. would have only two cells lines therefore: normal and trisomy.
At times, trisomy may not survive either. one cell line that is normal.
Extent is infuenced by survivability and timing.
Mosacism phenotypes: name two
Gonadal=only in gonads; pheno normal but increased repro risk
Generalized=distributed thorugh body or confined to particular tissue. Pheno can range from normal to non-mosaic pheno if almost all cells.
anaphase lag
Anaphase lag=one chromosome fails to migrate and is lost from the cell. Gametes are null and normal.
If occurs during meiosis II, will get mostly normal with one null.
If M I: two normal, two null.
anaphase lag
Anaphase lag=one chromosome fails to migrate and is lost from the cell. Gametes are null and normal.
If occurs during meiosis II, will get mostly normal with one null.
If M I: two normal, two null.
anuploidy
Loss or gain of less than an entire set of chormosomes (eu=23, 46, 69, etc)
Nondisjunction (gain and loss)
Anaphase lag (loss only)
Meiosis (all cells affected) vs Mitosis (mosaicism possible)
Most trisomies occur secondary to what?
maternal meiosis I errors
Abnormal recombination and its contribution to trisomies.

Monosomies are usally...
Among pregnancies with trisomy 16, 21, or a sex chromosome trisomy:
--the number of recombination events is decreased and sometimes completely absent
--the placement or distribution of recombination events is altered.

Monosomies are usually paternal. NO AGE ASSN.
Polyploidy
1. Tetraploidy
2. Failed cytokinesis
3. orgins of triploidy
1. tetraploidy--very lethal; less than 10 liveborn
2. 46 chr-->fertilization-->triploid pregenancy with 69 chr.
3. most common orgin of triploidy is two sperm in normal egg
Relative risk for common trisomies.
FOR COMMON TRISOMIES, RISK IS RELATED TO AGE
<35 years old = 1% (germline mosaicism?)
>35 years old = age related risk
Offer prenatal dx for all future pregnancies
FISH
used to detect common aneuploidies
20-35% of chr. abnormalities go undetected
Structural chromosomal abnormalities
--less common than numerical abnormalities
--more likely to occur during male meiosis
--more variable, many rearrangements are particular to a family or indiv.
--occur secondary to recombination between shared DNA sequences in nonallelic regions; high copy #, etc.
Parental karyotypes are always requested when a structural rearrangement is observed. Why?
--Given an inherited mutation no increased risk.
--Given a new mutation risk is minimally 6-7%.
--May actually be unbalanced and they can’t pick it up.
--Malsegregation
--counseling: emperic risk is 10% but changes with size, region, family history
Clinical:
Floppy baby, eyes are slanting, white spots in periphery of iris = brush field spots, Ear is overfolded, Excess nucal syndrome, Single transverse crease, = sandal gap. Also can be seen if normal.
Down's syndrome
Where did the extra chr 21 come from?
3-4% are due to unbalanced Robertsonian translocations

Approx. 40% of which are inherited from a carrier parent. BUT carrier parent would have 100% recurrence risk Robersonian.



about 1-2% are mosaic with a normal cell line: mos 46,XX/47,XX,+21
Either post-zygotic non-disjunction event or trisomy rescue
In general a milder phenotype but cannot predict on an individual basis
Clinical:
Growth retardation. Microcephaly. REMEMBER HAND FORMATION. CLENCHED HAND. Pointed ear and posteriorly rotated ears.
Trisomy 18
--mean life expectancy is 4d
--most males die in utero, most long term survivors are female
--from maternal meiotic nondysjunction, 85%
Clinical:
Growth retardation. Microcephaly. REMEMBER HAND FORMATION. CLENCHED HAND. Pointed ear and posteriorly rotated ears.

What are the other problems?
Trisomy 18
Growth deficiency
VSD, ASD, TOGV, TOF, coarctation, pulmonic stenosis; _complex heart defects_,
Hydronephrosis, Wilms tumor, polycystic kidneys, ectopic kidney; _renal probl._
Thyroid and adrenal hypoplasia
Meckels diverticulum, hernias, omphlalocele
Trisomy 18
Clinical:
Microcephaly, scalp defects, clefts, _microphthalmia_, _polydactyly_, cardiac defects, renal anomalies
Trisomy 13
86% due in first year; MLifeExpectancy 130d
75% trisomy 13 from nondisjunction
20% translocations can be roberstonian
13;14 balanced carrier has 1% risk of unbalanced offspring
The 13;14 Robertsonian translocation!!!!!! is the most common ranslocation
THE MOST COMMON AUTOSOMAL TRISOMY IN HUMANS.
Trisomy 16
do NOT survive to be liveborn
Clinical:
Short stature, Lymphedema- puffiness, Gonadal dysgenesis,Coarctation of the aorta-more common genearlly in males, Nuchal webbing, Short 4th metacarpals
Intelligence normal, but often problems with spatial perception
Infertility and streak gonads
Turner's Syndrome
50% are 45, X
ther remainder have other abnormalities
risk of gonadoblastoma if has Y cell line
remove ovaries.
Clinical:
Tall stature
Hypogonadism, Infertility-can present, 50% have Learning disabilities but normal IQ, Problems with socialization, Require testost supplem
Clinefelter syndrome 47, XXY
Clinical: female, Above average stature,
Normal phenotype, Most have learning disabilities, Behavior problems common
Trisomy X; 47 XXX
Clinical: Severe growth and mental retardation, Ocular hypertelorism-wide space btwn eyes, Cleft lip and palate, Cardiac anomalies
4p minus syndrome
Wolf-Hirschhorn syndrome
Clinical: High-pitched cry in infancy, Severe somatic and mental retardation

Microcephaly, increased inner canthal distance, downslanting palpebral fissures, epicanthal folds, ear anomalies, micrognathia-small jaw, round face, Congenital heart defects
5p deletion syndrome
cri-du-chat syndrome
Microdeletion syndrome
Average band size: approximately 3.5-5 Mb
Many deletions are submicroscopic
FISH techniques enable diagnosis
Most of these are multiple congenital anomaly syndromes caused by deletion of several genes
Velo-Cardio-Facial syndrome
cleft palate, dysmorphic faces, slender hyperextensible fingers, cardiac abnormalities, learning disabilites, hypocalcemia,
Prader-Willi syndrome--inherited from DAD!
chr 15
Short stature
Small hands and feet
Hypogonadism
Mental retardation, usually mild
hypotonia
_feeding problems_
microdeletion syndrome
_in later childhood, onset of excessive appetite and obesity_
Angelman Syndrome--inherited from MOM!
chr 15
Supravalvular aortic stenosis
Pulmonary artery stenosis
Mental retardation, friendly personality
Microcephaly
Short stature
Seizures
Frequent unprovoked laughter
Severe mental retardation
Ataxia