Case 7 Flashcards
(20 cards)
Give the karyotype of a boy with Mosaic DS. Give two causes of this condition.
46XY / 47XY+21 1.
1) Non disjunction of chromosome 21 during meiosis which leads to the fertilised egg being trisomy 21.
This is followed by trisomy rescue during embryonic development (when non disjunction leads to loss of the extra chromosome 21 in one cell line) leading to some cells being normal. –> Trisomy rescue is quite rare. 2.
2) Normal fertilised egg but non disjunction during mitosis in embryonic development leads to trisomy 21 in some cells.
What is the most common cause of Downs Syndrome?
Trisomy 21.
Non disjunction of chromosome 21 during meiosis leads to an extra chromosome 21 in the gamete.
At fertilisation the zygote will have trisomy 21.
What is a Barr body?
What does one barr body indicate?
What does two barr bodies indicate?
Barr bodies are the inactive X chromosomes found on the periphery of the cell.
One barr body indicates 2 X chromosomes ( normal female 46XX).
Two barr bodies means that they have 47 chromosomes. (47XXX)
What is the function of BMP-4?
BMP-4 is a is part of the TGF-Beta family which is released from the dorsal part of notocord.
It causes differentiation of the ectoderm germ layer into the epidermis etc.
(The TGF-Beta family of proteins regulate cell differentiation)
What is the function of Sonic hedgehog protein?
SHH is expressed in the notochord. It induces patterning of somites and neural patterning.
What three things does the Ectoderm differentiate into?
1) The OUTER ECTODERM which gives rise to Hair, epidermis, nails, sebaceous glands, lens, cornea, olfactory epithelium
2) The NEURAL CREST CELLS : PNS, adrenal medulla, Schwann cells, dentine of teeth, melanocytes, neuroglial cells, dorsal root ganglia and facial cartilage.
3) The NEURAL TUBE: Brain, retina, spinal cord, motor neurones and the neural pituitary.
What are risks of a women having a baby with downs syndrome with increasing age?
From PCS3:
20 years-1 in 1450
30 years-1 in 940
40 years-1 in 85
49 years-1 in 25
From NHS Choices:
20 years of age has a risk of one in 1,500
30 years of age has a risk of one in 800
35 years of age has a risk of one in 270
40 years of age has a risk of one in 100
45 years of age has a risk of one in
50 or greater
Note! Big increase in risk from age 30 –> 40.
How does the body deal with genes that have duplicated?
The body can deal with duplication’s by down regulating expression of the duplicated gene.
How is hPL linked to gestational diabetes?
hPL is a diabetogenic which decreases sensitivity to insulin.
It maintains the concentration gradient of glucose so that the fetus receives an adequate supply.
As a result, high levels of hPL can lead to increased blood sugar levels in the mother.
When is Amniocentesis usually carried out?
During weeks 15-20 of pregnancy. during the second trimester of pregnancy.
Number of pregnancies, miscarriages and births are coded for. What goes G mean? P mean? Extra notations?
G gravity= the number of pregnancies the woman has had including current pregnancies
P parity= the number of times a woman has given birth to a foetus with gestational age 24 weeks +
Extras e.g. +2= indicates the number of miscarriages/terminations that she has had
So if this woman is G3P0+2 … G3 = on 3 pregnancies with none carried to full term +2 = 2 miscarriages/terminations therefore she must currently be pregnant with her third child.
Mutation or deletion of SNRPN gene (15q11-13) inherited by Maternal UPD will produce what chromosome disorder?
Prader Willi Syndrome
What percentage of pregnancies end in miscarriage?
15%
Give features of dark bands (3)
Dark band:
Condensed chromatin
AT rich
Gene poor
Give features of light bands (4)
Light band:
Less condensed chromatin
Transcriptionally active
Gene rich
GC rich
What is the notochord?
The notochord is a flexible rod of mesoderm which signals the ectoderm to thicken into the neural plate.
It then stimulates the neural plate to fold upwards into the mesoderm forming the neural groove.
The neural groove then comes together to form the neural tube which later develops into the CNS and the Brain
What are the 3 main consequences of fertilisation?
- Restoration of diploid number
- Sex determination
- Induction of cleavage
Name the different layers of the egg that the sperm goes through in order to fertilise it.
Sperm (only capacitated ones) penetrates corona radiata
Sperm penetrates zona pellucida (this requires the acrosome reaction in which proteolytic enzymes digest the zona pellucida)
Zona reaction occurs (sperm touches the oocyte surface and so lysosomes are released from cortical granules- cortical reaction)
Fusion of cell membranes
Head and tail of sperm enter cytoplasm of oocyte (the head forms the male pronucleus)
What is the differnece between ‘fertilisation age’ and ‘gestational age’?
Gestational age is a measure of the age of a pregnancy from the woman’s last menstrual period (LMP).
The fertilization age is the time from the fertilization. It usually occurs within a day of ovulation, which occurs on average 14.6 days after the beginning of the preceding menstruation (LMP).
e.g. 3-4 weeks gestational age = 1-2 weeks fertilisational age.
Ventricular septal defect (VSD) is the most common congenital heart defect, what condition is it most likely to be associated with?
Congenital rubella
Down Syndrome
Foetal alcohol syndrome
Maternal diabetes
Foetal alcohol syndrome
VSD is associated with foetal alcohol syndrome.
PDA is associated with congenital rubella.
ASD (ostium primum type) is associated with Down syndrome.
Transposition of great vessels is associated with maternal diabetes.
