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In this lecture, I will discuss Trisomy 18 and Trisomy 13.
00:06
For Trisomy 21, you can see one of the other lectures.
00:09
So, here?s a great way to remember.
00:12
These are also called Edwards and Patau Syndrome
and just as a mnemonic, at 13 you enter puberty,
so Trisomy 13 P-Puberty, P-Patau.
00:23
At 18, you can vote in an election, so 18 E-Edwards. That?s a way to remember.
00:31
Okay, let?s start with Edwards Syndrome or Trisomy 18.
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This is due to 3 copies of chromosome 18 in the cells of the body.
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It?s associated with characteristic dysmorphic features,
which we?ll go through, severe intellectual disability,
congenital malformations and a greatly reduced life expectancy.
00:52
Half of these patients will die
within the first week and most within the first year.
00:57
This affects about 1 in 8,000 live births.
01:01
It?s less common than Trisomy 21 but more common than Trisomy 13.
01:07
It affects females more than males
and 95% of these fetuses are spontaneously aborted.
01:14
How does this happen?
More than 90% of the time,
it?s a freak meiotic nondisjunction of the maternal chromosomes.
01:23
Essentially one egg has an extra gene, an extra chromosome in it
and then the sperm goes and fertilizes that egg and then the patient has 3.
01:34
This risk increases with advanced maternal age, just like Down syndrome.
01:38
A small percentage of the time,
this can be a result of a Robertsonian translocation.
01:44
For more on Robertsonian translocations, please review the Trisomy 21 lecture.
01:49
But generally,
the idea is that the translocated spouse has 6 potential gametes
that may arise and they may either have a normal child,
a balanced carrier or a patient with the Trisomy 18.
02:06
The other eggs are not viable.
02:10
So the options are you have a normal child,
a balanced carrier child or Trisomy 18 child.
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What does Trisomy 18 look like?
They have low birth weight.
02:23
They may have a prominent occiput like you can see in this patient here.
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One of the key findings is micrognathia.
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These children have very small jaws
and it may lead to an upper respiratory distress.
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They can have microcephaly despite the prominent occiput
and you?ll see they have low set and malformed ears.
02:43
These infants often have clenched overlapping fingers
like you can see in this picture.
02:50
That?s often will show up in our test,
clenched, overlapping fingers are consistent with Trisomy 18.
02:55
Another one that shows up on the test is what we call ?Rocker-bottom? feet.
02:59
This is feet that are round on the bottom
as if the patient were standing up, they could rock.
03:04
These patients will have severe intellectual disability.
03:08
They will have digestive tract abnormalities of a variety of types
and they often have either cardiac or renal malformations.
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The most common cardiac defect is the VSD or the ventricular septal defect.
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So what are the therapies we can provide to these children?
Well generally, the therapy relates to the defect that is in play.
03:31
So patients most commonly die of cardiopulmonary arrest.
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They simply aren?t capable of maintaining their respiratory
and cardiac effort.
03:41
This is common and remember half of these patients
will die on their first week of life.
03:47
What?s key to provide to some these families
is simply an acceptance that this infant is really not going to be viable.
03:54
We have to provide hospice so infants can die comfortably
and we have to provide grief counseling for parents.
04:02
It?s important provide them with support group services
and it?s also important to do parental chromosome studies.
04:10
The reason is if this a Robertsonian translocation,
there is an increased risk substantially of future children
also having this problem
and they may want to do pre-selection of eggs in the future.
04:24
Let?s switch gears now to Trisomy 13 which is Patau Syndrome.
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This is due to 3 copies of chromosome 13.
04:33
It results also in severe intellectual disability,
multiple congenital malformations
and a greatly reduced life expectancy. This affects 1 in 9500 births.
04:45
It happens in females more than males
and about 60% of these fetuses
will spontaneously abort in the second trimester.
04:53
What are the features?
As you can see here, these patients may have holoproesencephaly.
04:59
They can develop scalp defects.
05:02
They may have very small eyes or microphthalmia.
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They can develop a severe cleft lip and palate.
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They often have polydactyly which is an extra finger or digit.
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They may have severe cardiac or renal malformations.
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There?s a lot of similarities between Trisomy 13 and Trisomy 18.
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These children really don?t do very well.
05:25
The average of survival is 7-10 days and so again, family support
and counseling is very important and once again
chromosomal studies of the parents are indicated.
05:38
If they have a Robertsonian translocation,
we need to counsel them about the risk to future infants.
05:44
So that?s my review of Trisomy?s 18 and 13.
05:49
Thanks for your attention.