Aneuploidy Flashcards
what is normal conceptus
haploid gametes produces diploid normal conceptus - spermatozoon plus ovum = conceptus
what is chromosome abnormality
Aneuploidy = chromosome segregation goes wrong = 2 types, 2n +1 or 2n-1
describe aneuploidy
trisomy/monosomy
describe haploidy
one set of chroms
describe polyploidy
more than 2n chroms (triploidy, tetraploidy etc)
describe chromosome rearrangements
could be translocations, deletions, inversions, duplications
what is maternal age effect in human reproduction
direct correlation between age and female repro
females become pregnant at any age = risk of chrom problem but risk goes up as age
what is paternal age effect in human reproduction
limited study
associations = older = more likely to produce autistic children and also children with more gene defects
name origins of chromosome abnormalities
gametogenesis errors
fertilization
Embryogenesis
describe gametogenesis - origin of chromosome abnormality
= m1 and m2
oogenesis
spermatogenesis
describe fertilization - origin of chromosome abnormality
dispermic fertilization
digynic fertilization after icsi
parthenogenic activation/chimera
describe embryogenesis - origin of chromosome abnormality
mitotic error
describe female - divisions involved in formation of embryo
Prophase: after DNA replication, homologous chromosomes pairing, synapsis and recombination, and arrest at the diplotene (dictyate) stage.
Oocyte remain arrested until puberty-follicular growth -LH surge triggers ovulation and resumption of m1 in preovulatory follicle
ovulated egg arrest at MII stage until fertilization - complete MII division
describe male - divisions involved in formation of embryo
Mammalian spermatogenesis is an androgen-dependent developmental process. It is driven by interactions between germ cells and somatic cells. Generates a continuous supply of functional sperm and it begins at puberty
describe meiosis 1 - non disjunction
one of mechanisms where chrom segregate goes wrong
= trisomy and monosomy
describe normal chrom segregation in meiosis 1 and after fertilization
normal, before = each cell has one set chrom and one set chrom in polar body (opp = switch chrom)
after fert = 2n (chromosomes can differ, what is in polar bodies vs oocyte)
describe nondisjunction chrom segregation in meiosis 1 and after fertilization
before = can result in disomic (2 chroms in oocyte, none in polar body), or nullsomic (all chroms in polar body)
after fert = trisomy or monosomy
describe predivision of one univalent in meiosis 1 and after fertilization
before = instead of dividing at same time = sister chromatids separate early = 23 +1/2 (one full plus half in oocyte, and half in polar body) or 22+ 1/2 (half in oocyte, 1+1/2 in polar body)
after = trisomy or monosomy
describe predivision of both univalent in meiosis 1 and after fertilization
before = leads to balanced m2 oocyte but still mistake tho
after = balanced egg, 2n
what is pssc
premature separation of sister chromatids
describe meiosis 1 errors
recomb failure
premature homologue separation
true nondisjunction
premature sister chromatid separation
describe meiosis 2 errors
Nondisjunction
premature sister chromatid separation
describe Aneuploidy in humans: estimated levels at different stages - eggs
eggs or polar bodies
karyotyping = 19902, 10-35%
fish = 1990s-present, 20-70%
cgh, snp array, cgh array= 2000s-present, 30-70%
ABNORMALITIES IN EGGS QUITE HIGH
describe aneuploidy in sperm
non disjunction - due to mistake in reduction division
if pssc = disomic 2, normal 1 and nullsomic 1 spermatozoa
if true nondisjunction = disomic 2 and nullsomic 2 spermatozoa
describe Aneuploidy in humans: estimated levels at different stages - sperm
karyotyping 1980s-1990s, 1-4%
fish = 1990s-present, 1-3%
low in sperm = 1-4%
millions of sperms in ejaculate so much study large numbers of sperm cells in one person
(opposite problem for egg, )
name all techniques used to detect chromosome abnormality in eggs, sperm and embryos
- Karyotype
- Fluorescence in situ hybridization (FISH)
- Whole chromosome painting (SKY)
- Comparative genome hybridization (CGH), Array CGH, SNP array (chip based)
- Next Generation Sequencing (NGS)
describe metaphase karyotype -gen
5-10ml blood, and will process culture, arrest cells at metaphase stage then see of any issues
gold standard even now
describe metaphase karyotype -sperm
studying sperm not easy =
take hamster egg and human sperm and inject and wait for it to condense and see when reach metaphase and then can do G-banded human sperm chromosome spread after ICSI of hamster oocytes= can see sperm chroms since hamsters ones have diff shapes and sizes
describe karyotype of pb and m2 oocyte
m2 oocyte metaphase shows extra marker = tetrads
2nd polar body karyotype = except haploid cells, very different to get good spread, not best for clinical cases in eggs
what is fish - describe
most common for sperm
want to find out if 1 or 2 copies of chrom 2 =
probe dna complementary to chrom 2 (somewhere on whole chrom) then label with fluorescent dye, = red fluorochrome then denature and hybridize and do metaphase spread = lights up chroms
describe interphase nucleus
most cases = count colour = know which fluorochrome attached to each chrom e
Especially in preimplantation embryo
describe fish on sperm
label x and y diff colours and see for diff chromosomes
one = abnormal see x and y = xy18, should be haploid tho, if sperm fertilize normal egg = get xxy aneuploidy
name and describe Four methods used for detection of chromosomal copy number variation
fish
comparative genome hybridization
array cgh (chip based, need to analyze chromosome complement in sample)
snp microarray
what is principle of cgh/acgh
Biopsies cells - dna and then do whole genome amplification
label control dna with red
label biopsy dna with green = unknown
combine and gives yellow
2 results possible =
metaphase cgh = see if colours correct, yellow = normal, more red = 2:1 monosomy, 2:3 more green = trisomy
or do array cgh= use computer to analyze
describe fertilization errors - dispermic
3 pronuclei
sperm brings abnormality or fertilized by 2 sperms = triploidy, 3 sets chroms
describe fertilization errors - digynic triploidy
especially with icsi
separation of polar body = instead of becoming diff cell= retained 3rd pronuclei
describe mitotic error during embryogenesis
affects chrom composition
describe chromosome compositions in preimplantation embryos - 3 types
Normal = all euploid
Abnormal = all aneuploid
Mosaic = mix of both
describe chromosome compositions in preimplantation embryos -DESCRIBE abnormal
Aneuploid = trisomy/monosomy
polyploid = more than 2n
haploid = one set of chroms
chaotic = random loss or gain of chroms
what does mitotic error do
generated mosaic embryo
Embryo develops fast after fertilized = 70-100 cells after 5 days
not proper cell cycle checkpoint = leads to mosaic, could also happen at later stages
more normal blastocyst cells if error early
what is mosaicism
Mosaicism is the presence of one or more genetically distinct cell lines within an individual/embryo.
how to generate mosaicism = 2 ways
Post zygotic error in an originally diploid zygote
Post zygotic error in an originally aneuploid zygote
describe Post zygotic error in an originally diploid zygote - trisomy 21
non disjunction during division = leads to 45,-21 and 47+21 and 2 46, n normal
monosomy lost
so embryo has normal and abnormal for trisomy 21, 46n, 47+21 MIX OF CELLS
describe Post zygotic error in an originally aneuploid zygote
starts with 47+21 abnormal zygote trisomy 21
during division = anaphase lag so loss of one chrom so it corrects itself
Embryo mix of 46 n and 47+21
explain uniparental disomy conceptus
Abnormal oocyte + normal gamete from other parent = trisomy conceptus
if corrects early = gets rid of one chrom- could get rid of one from dad, so now the 2 chroms are both from mom
depends on which chrom= if has imprinted genes = can cause issues for implantation and live birth
how can we analyze embryos - diagnosing chromosome composition
spreading of nuclei on glass slide = interphase nucleus and label and see if normal or abnormal
can also use fish
describe fish results - analyzing embryos
large portion of embryos mosaic like 47%
describe mosaicism throughout preimplantation development
randomly took human embryos (must ask patients first, ethics board, after ivf, hard to do), frequency of mosaic embryos heavily increased as move to blastocyst
2 or more distinct cell lines = mosaicism but the embryos make normal babies
describe type of mosaicism
2-4 cell = mostly diploid aneuploid and diploid chaotic, continues untill morula
but by time reach blastocyst = diploid polyploid or diploid aneuploid
describe proportions of polyploid cells in blastocysts - good quality
polyploid cells important for invasion of endometrium during implantation
normal = have fewer percentage of polyploid cells
describe proportions of polyploid cells in blastocysts - poor quality
higher % of polyploid cells
if fetus tetra or triploid = miscarriage
still do not know what % is normal or abnormal
describe Mixoploidy in Blastocysts of Domestic Species
Present in many animals - domestic species
Mechanism of mitotic error in embryos - what causes gains and losses
non disjunction
anaphase lag
Chromosome demolition
chromsome replication
Mechanism of mitotic error in embryos - what causes losses alone
anaphase lag
Chromosome demolition
Mechanism of mitotic error in embryos - what causes gain and loss for same chromosome
non disjunction
describe overall chromosome abnormality in embryos from older women
were much higher than younger patients
when is mosaicism present
mosaicism is present throughout the pre-implantation development
describe chaotic embryos
chaotic embryos are higher in poor quality embryos compared to good quality embryos
what increases with advanced maternal age
Aneuploidy rate increases with advanced maternal age
when does chromosome mosaicism have effects
only during preimplantation embryo dev and it has no clinical implications post implantation
describe significance of abnormal cells - 4
Abnormal cells are lethal - could be but depends on % of polyploid, most cells with chaotic = arrest
Abnormal cells are loss = not necessarily true, depends on % cells left
Abnormal cells become allocated to te = yes, did mouse studies, if make chimera (tetra + normal cells) = all tetra goes to te
Abnormal cells co exist
describe pathogenesis of chromosomal mosaicism and its effect on early human dev - gen
~15 weeks amniocentesis or chorionic villi sample and see what cells are like
describe pathogenesis of chromosomal mosaicism and its effect on early human dev - 3 types
fetus mosaic placenta normal
confined placental mosaicism = fetus fine but issues with pregnancy
both fetus and placenta mosaic
describe pathogenesis of chromosomal mosaicism and its effect on early human dev - post zygotic trisomic rescue through placental mosaicism
postzygotic chromosome loss = leads to 2 possibilities
non mosaic trisomic fetus + mosaic placenta with confinement of diploidy to trophoblast
or
trisomic placenta and non moasic diploid fetus
happens in embryos but corrected *uniparental disomy = baby has some issues but mostly fine - diploid baby
what will post fertilization mitotic error result in
in constitutional chromosomal mosaicism - the mechanism by which it arises is not fully understood.
what does distribution of mosaicism in conceptus depend on
timing, cell lineage(s) involved, cell viability, and chromosome involved
describe origin of mosaicism - 2
meiotic or mitotic origin
Meiotic mosaicism often have adverse effect on the conceptus such as trisomy zygote rescue, due to the presence of uniparental disomy in the embryo/fetus and/or due to dysfunction of a trisomic placenta
what can mosaicism be
tissue specific
normal karyotype in lymphocytes does not exclude the presence of mosaicism elsewhere in the conceptus
what is main cause of infertility
due to pregnancy wastage due to chrom abnormality
describe chromosomal imbalance and pregnancy loss - reasons
Trisomies
Monosomies
Triploidies
Multiple Aneuploidies
Tetraploid and structura
describe trisomy 16
most common trisomy observed in product of conception studies
never seen in live born
advanced mat age, always loss, non viable
describe trisomy 21 and 22
next most common 2 = equally as common
describe survivable chromosomal imbalance
only a few full non-mosaic aneuploidies are observed in live-born apart from sex chromosome abnormalities
For example:
Trisomy 21, Trisomy 13,
Trisomy 18…
describe trisomy 21
diagnose by checking blood = use peripheral blood standard
47, xy+21
down syndrome
most still birth or features of down syndrome
describe trisomy 21 - medical issues
many issues
cannot see what problems embryo will have even tho can see chrom abnormality
Gastrointestinal obstruction -3%
Respiratory infections = Common
Leukemia = 15-20 X
Congenital heart defect - 40%
Moderate to severe mental retardation - 100%
Development: Early intervention program
describe trisomy 18
47,xy+18 edwards syndrome
possible live birth, most lost
under 46 = probably die or sex chrom issue, above 46= bad news generally
describe trisomy 18 - medical features
exhibiting characteristic facial features, short sternum, overlapping fingers with clenched fists, and clubfoot
probably wont live long
describe trisomy 13
47, xy,+13
patau syndrome
live birth
autosomal trisomies = severe
describe trisomy 13 - medical features
holoprosencephaly = defects, probbaly never take babies home, 6m-12m
Defect of the brain, affects facial features, causing closely spaced eyes, and sometimes cleft lip and palate
name sex chromosome abnormalities - 4
- Turnersyndrome(XO)
- Klinefeltersyndrome(XXY)
- TripleXormore(XXX/XXXX..)
- XYY
what is only monosomy to go to live birth
TURNER SYNDROME XO
what are some effects of turner syndrome
short stature-broad chest
-low hairline
-low set ears
-small fingernails
-characteristic facial features
-poor breast development
-ear infections and hearing loss
-high waist to hip ratio (hips are not much bigger than the waist)
Approx. 99%of all fetuses with Turner syndrome results SA - first trimester
-Affects 1 in every 2,500 girl
describe turner syndrome
only about 1%, 45x survive, 99% do not survive (lost through spont abort)
Hook and Warburton hypothesis that most surviving ones are ‘cryptic’ mosaics Rescue cell line may have viable karyotype= cells correct = possibility of normal cells somewhere, in some cells but not all, peripheral blood shows xo thp
what is klinefelter syndrome
47, xx7
probable cause =
xx oocyte + y sperm
or x oocyte + xy sperm
what is klinefelter syndrome - x inactivation
Most genes from the extra X undergo inactivation, but some escape and serve as the putative genetic cause of the syndrome
what is klinefelter syndrome - who it affects
Affects one in 660 men
what is klinefelter syndrome - phenotype
from “near-normal” (no intellectual issues) to a significantly affected individual
what is klinefelter syndrome - syndrome characterized by
varying degrees of cognitive, social, behavioral, and learning difficulties and in adulthood additionally primary testicular failure with small testes, hypergonadotropic hypogonadism, tall stature, and eunuchoid body proportion
what is klinefelter syndrome - when diagnosed
Most of them diagnosed later in life – mostly during fertility work up
what is klinefelter syndrome - infertility
47,XXY is identified in 11% of azoospermic men and in 3% of infertile men and thus represents the most common genetic cause of infertility
no sperm in ejaculate, maybe one = if mosaic = find some sperm
what is klinefelter syndrome medical treatment
Medical treatment is mainly testosterone replacement therapy to alleviate acute and long-term consequences of hypogonadism
most only realize when trying to make fam
describe 47, XYY male fertility
Most males with 47,XYY syndrome have normal sexual development and are fertile
some may be fine, fertile no repro issues
describe 47, XYY male - who
Affects -1 in 1,000 newborn boy
describe 47, XYY male - syndrome associated with
an increased risk of learning disabilities, delayed development of speech and language skills. Delayed development of motor skills (such as sitting and walking), weak muscle tone (hypotonia), hand tremors or other involuntary movements
describe 47, XYY male - small percent
A small percentage of males with 47,XYY syndrome are diagnosed with autistic spectrum disorders
describe 47, XYY male twin brothers
two twin brothers. The shorter has a normal XY chromosome complement. The taller one has an XYY complement
What is the possible mechanism in generating this extra Y-chromosome in non mosaic males? -47, XYY
parental nondisjunction at m2 resulting in extra y chromosome
yy sperm + x oocyte = xyy male
describe Post zygotic error in an originally diploid zygote - triple xxx
non disjunction = 45,x 47,xxx 46,xx 46,xx
cell lines survive = individual is mix of alll
