TBL 6 Flashcards
down syndrome
- Trisomy 21 accounts for 95% of Down Syndrome cases
risk increase with maternal age
Ovum is the source of 95% of trisomy cases,
nonisjunction during gamete formation
karyotype: 47,XX,+21
Clinical Features of Down Syndrome
12 to 14 characteristics that can
develop in Down Syndrome → affected individuals
express 6 to 8 characteristics on average.
flat facial profile, oblique
palpebral fissures, epicanthic folds, palmar crease,
clinodactyly.
Approximately 40% of the patients have congenital heart
disease.
* Children with Down Syndrome also have a high risk of
developing leukemia.
* Virtually all patients with trisomy 21 older than age 40
develop neuropathologic changes characteristic of
Alzheimer disease.
mosaic down syndrome
1%
mitotic nondisjunction of chromosome 21 during embryogenesis.
symptoms are milder
Trisomy 18 - Edwards Syndrome
- Trisomy 18 is the second most common autosomal trisomy after 21 → incidence
is 1:8,000. - In individuals with Edwards Syndrome, death usually occurs by age 1.
- Clinical presentation includes hypertonia, prenatal growth deficiency,
characteristic fist clench, rocker-bottom feet, receding jaw, and low set ears.
Trisomy 13 - Patau Syndrome
- Clinical features include
microcephaly, sloping forehead,
characteristic fist clench, rocker-
bottom feet, polydactyly, cleft lip
and palate. - 50% of children die within the
first month, 90% within the first
year.
Klinefelter Syndrome can result from
nondisjunction that can take place both in meiosis I
and meiosis II of maternal oogenesis or during meiosis I of paternal
spermatogenesis
clinical presentation of Klinefelter Syndrome
Classically, KS patients are of male appearance with very small, firm
testes, gynecomastia and tall stature with long legs and a relatively short
trunk.
* Infertility is almost always observed in KS men, frequently leading to its
diagnosis.
Klinefelter Syndrome
Klinefelter syndrome (KS) is the most frequent sex chromosome disorder
of the male population, accounting for almost _________
males and the most frequent form of male hypogonadism.
1 in every 650 newborn
- 90% of cases result from 47,XXY
Male hypogonadism –
Male hypogonadism – two or more X chromosomes + one or more Y
chromosomes
example of monosomy
turner syndome
Turner Syndrome (TS) is one of the most common sex
chromosome abnormalities, affecting approximately ______
live-born girls
1 in 2000
- Hypogonadism in phenotypic females
prognosis of turner
Most cases of Turner syndrome are non-viable and end in
spontaneous abortion, though if the baby is born, the prognosis
is excellent.
- Complete or partial monosomy of the X chromosome:_____ % are___
~57% are 45,X
balanced vs unbalnced chromosomes
Structural rearrangements are classified as
balanced, if the genome has the normal
complement of chromosomal material, or
unbalanced, if there is additional or missing
material.
robersonian traslocation
About 4% of Down syndrome cases result from a
translocation of the long arm of chromosome 21 onto
another chromosomes (22 or 14) → Robertsonian
Translocation
* Unlike standard trisomy 21, shows no relation to
maternal age
high risk to passing on if carrier, especially in female carrier
Oncogenic Chromosome Translocations
what is the chromosome called
what does it cause
9 chrom gene goes on chrom 22
The most well studied is the Philadelphia chromosome (Ph1)
which is a result of a translocation between chromosome 9
and 22 → causing chronic myelogenous leukemia (CML)
proto-oncogene abl1 (tyrosine
kinase that activates signal pathways)
moves to chrom 22q to chrom 9 q and get inserted infront of bcr
abl1-bcr always turned on so can lead to continued cell proliferation, inhibition of cell differentiation,
and cell death.
examples of translocations
robertsonian down syndrome and ocogenic translocation
what does oncogenic chromosome translocation cause
chronic myelogenous mutation
examples of chromosome deletions
digeorge syndrome and cri-du-chat
digeorge syndome’s deletion
deletion within 22q11.2 (distal) on chromosome 22
due to unequal crossing over
cri-du-chat deletion
deletion of small terminal portion of chromosome 5 p arm
clinical presentation of cri-duchat
microcephaly, epicanthal folds, low-set ears, micrognathia (low set, small jaw ), cat-like cry, intellectual disability
due to haploinsuffiency (not enough gene to have enough product)
Amniocentesis or chrionic villus sampling (CVS) :
Fetal cells obtained from
amniotic fluid or chorion of placenta
Nuchal translucency (NT) scan -
measures the clear (translucent) space in the tissue at the back of your baby’s neck (11 – 14 week ultrasound)
- NIPGD: Noninvasive prenatal genetic diagnosis -
Fetal cells and DNA obtained
from maternal circulation
primary oocytes are surrounded by granulosa cells and called _____
primordial follicle
then that become primary follicle then secondary follicle then enlarges to mature (graafian) follicle
what happens when the oocyte exits from dictyate arrest
LH cause resume in meiosis 1. nucleus breaks down and chrom line up at metaphase 1. Homologs go to opposite poles. one set of homolgs in oocyte and the other in polar body
what happens during meosis 11 in oocyte
mature egg is arrested in meta II and trasported to oviduct during ovulation
only comples meiosos II when fertilized
types of chromosome rearrangement
aneuploidy, deletions, duplications, rearrangements (translocation)n
whats a normal karyotype
46, XX. 46, XY
