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Flashcards in Embryology Deck (26)
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What are the proportions of minor and major mal-developments?

Minor - 15%
Major - 3%


List broad causes of mal-development.

Genetic - 30%
Environmental - 15%
Multifactorial - 45%


List some external causes of mal-development.

- teratogens
- infectious agents
- physical agents
- chemical agents


List some infectious agents and the problems they cause.

1. Rubella virus - cataracts, glaucoma, heart defects, deafness
2. Herpes simplex virus - microphthalmia, microcephaly
3. HIV - microcephaly, growth restriction
4. Syphilis - mental retardation, deafness
5. Zika virus - microcephaly


List some physical agents and the problems they cause.

X-rays and other ionising radiation - microcephaly, spina bifida, cleft palate, limb defects


List some chemical agents and the problems they cause.

1. Thalidomide - limb defects, heart malformations
2. Lithium - heart malformations
3. Amphetamines - cleft lip and palate, heart malformations
4. Cocaine - growth restriction, microcephaly, behavioural abnormalities
5. Alcohol - FAS, maxillary hypoplasia, heart defects


What would happen if a teratogenic event occurred in the first few weeks of development?

The foetus would be miscarries, as the teratogen would completely derange development.


What is mosaicism?

Chromosomal abnormality which means cells in an individual have a different genetic makeup.


What is chimerism?

Chromosomal abnormality in which multiple different zygotes fuse - the individual has 2 different genetic makeups.


List some conditions associated with extra XY chromosomes.

XXY (Klinefelter's syndrome) - decreased fertility
XXXY, XXYY - severe forms of KS
XYY - variable effects
XXX - limited effects, some mental change
XXXX, XXXXX - more severe effects


List some conditions associated with extra autosomes.

Chr. 21 (Down syndrome) - heart problems determine survival
Chr. 18 (Edward's syndrome) - most die before birth
Chr. 13 (Patau syndrome) - most die before birth


List some conditions associated with too few XY chromosomes.

X0 (Turner's syndrome) - short stature, infertile


List some conditions associated with too few autosomes.

NO complete losses are viable.
Partial chromosome losses are often characterised (e.g. translocations such as XX male).


Give an example of a gene found in both humans and mice.

KIT receptor - mutation in this causes piebaldism (unusual distribution of pigments in the skin/fur).


What is Holt-Oram syndrome?

A condition associated with a range of heart and hand defects:
- atrial septation defects
- lack of symmetry in the hands
- structure of the heart doesn't develop properly
This is due to a mutation in TBX5.


What is achondroplasia?

Means 'lack of cartilage'.
There is a defect in the conversion of cartilage to bone, and therefore a lack of bone growth. This is due to a gain of function mutation in FGFR3.


What is polydactyly?

An extra digit present on the hand or foot.
Forelimb buds appear at day 27/28 and hindlimb buds at day 29. The digits are fully formed by day 56.
In some instances, webbing between the fingers may remain - this indicates that the extra digit has formed too close to another digit.


What is clefting of the lip/palate?

Facial structures generally develop laterally and move medially as development progresses. This means clefting occurs in the midline.
A cleft palate is more severe, as there is a connection between the mouth and nasal cavity, meaning there may be problems with breathing, eating and drinking. Food or liquid could end up in the sinus cavities. A cleft palate MUST be repaired immediately, whereas a cleft lip can be repaired for cosmetic outcome and psychological health.
Surgery is done early, as babies heal well and there is little scarring.


What is spina bifida?

Means 'twin spine'.
1-2 per 1,000.
The parts of the body below the lesion are generally affected.


What are the 3 types of spina bifida?

1. Spina bifida occulta - the spine forms incorrectly, although the CNS is unaffected. There may be a patch of hair over the affected area.
2. Meningocele - a fluid-filled swelling.
3. Myelomeningocele - a nervous tissue-filled swelling (the most severe form).


How does development of spina bifida occur?

It occurs within 4 weeks of fertilisation. There is a protrusion of CNS tissue, which prevents the spine from covering that area (the posterior neuropore structure does not completely seal). Neuralation is faulty.


What decreases incidence of spina bifida?

Folic acid decreases incidence by 70%. It should be given 3 months prior to conception, as the egg does most of its development before it is selected as the main follicle in these 3 months.


What is anencephaly?

Means 'no head'.
1-8 per 10,000.
Female babies are more commonly affected.


How does development of anencephaly occur?

A similar cause to spina bifida (incomplete anterior neuropore closure) is implied. The anterior neuropore develops at the head of the foetus, whilst the posterior neuropore develops at the tail end. Anencephaly has the potential to occur around 23 days post-fertilisation.


What is thalidomide and what does it affect?

Thalidomide was a drug given to pregnant women in the 50s for treatment of hyperemesis gravidarum.
Primarily, limbs are affected, but there is also eye, heart, alimentary and urinary defects, as well as blindness and deafness.
It must NOT be given to women of reproductive age.


How does thalidomide prevent limb development?

Use sonic hedgehog (shh) proteins to replicate normal limb development. It could then be observed that a thalidomide isoform stopped blood vessel development, resulting in cell death. Short exposure results in a truncated limb, whilst long exposure can cause complete loss.