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in this lecture I will discuss trisomy
18 and trisomy 13 for trisomy 21 you can
see one of the other lectures so here's
a great way to remember these are also
called Edwards and potala syndrome and
just as a mnemonic at 13 you enter
puberty so trisomy 13 P puberty P Patel
at 18 you can vote in an election so 18
e Edwards yeah it's a way to remember
okay let's start with Edward syndrome or
trisomy 18 this is due to three copies
of chromosome 18 in the cells of the
body it's associated with characteristic
dysmorphic features which will go
through severe intellectual disability
congenital malformations and a greatly
reduced life expectancy half of these
patients will die within the first week
and most within the first year this
affects about one in eight thousand live
births it's less common than trisomy 21
but more common than trisomy 13
it affects females more than males and
95% of these fetuses are spontaneously
aborted so how does this happen well
more than 90 percent of the time it's a
freak mitotic nondisjunction of the
maternal chromosomes so 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 three this risk increases
with advanced maternal age just like
Down syndrome a small percentage of time
this can be a result of a Robert Sounion
translocation for more on Robertson and
translocations please review the tries
only 21 lecture but generally the idea
is that the translocated spouse has six
potential gametes that may arise and
they may either become a have a normal
child a balanced carrier or a patient
with the trisomy 18 the other patients
are the other eggs are not viable so
options are you have a normal child a
balanced carrier child or a trisomy 18
care child so what does trisomy 18 look
like well they have low birth weight
they may have a prominent occiput like
you can see in this patient here one of
the key findings is micrognathia these
child children have very small jaws and
it may lead to an upper respiratory
distress they can have microcephaly
despite the prominent occiput and you'll
see they have low set and malformed ears
these infants often have clenched obrah
overlapping fingers like you can see in
this picture that's often will show up
on a test clenched overlapping fingers
are consistent with trisomy 18 another
one that shows up on the test is what we
call rocker-bottom feet this is feet
that are round on the bottom as if if
the patient we're standing up they could
rock these patients will have severe
intellectual disability they will have
digestive tract abnormalities of a
variety of types and they often have
either cardiac or renal malformations
the most common cardiac defect is the
VSD or ventricular septal defect so what
are the therapies we can provide to
these children well generally the
therapy relates to the defect that is in
play so patients most commonly died of
cardiopulmonary arrest they simply
aren't capable of maintaining their
respiratory and cardiac effort this is
common and remember half of these
patients will die in their first week of
life what's key to provide to some of
these families is simply an acceptance
that this infant is really not going to
be viable we have to provide hospice so
that infants can die comfortably and we
have to provide grief counseling for
parents it's important to provide them
with support group services and it's
also important to do parental chromosome
studies the reason is is if this is a
Robert Sounion 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
let's switch gears now to trisomy 13
which is potala syndrome this is due to
three copies of trys chromosome 13 it
results also in severe intellectual
disability multiple congenital
malformations and a greatly reduced life
expectancy this affects 1 in 9,500
births
itta happens in females more than males
and about 60% of these fetuses will
spontaneously abort in the second
trimester so what are the features as
you can see here these patients may have
holo prose encephalo they can develop
scalp defects they may have very small
eyes or micro opthalmic they can develop
a severe cleft lip and palate they often
have polydactyly which is an extra
finger or digit they may have severe
cardiac or renal malformations so
there's a lot of similarities between
trisomy 13 and trisomy 18 these children
really don't do very well the average
age of survival is seven to ten days and
so again family support and counseling
is very important and once again
chromosomal studies of the parents are
indicated if they have a Robert Sounion
translocation we need to counsel them
about the risk to future infants so
that's my review of trisomies 18 and 13
thanks for your attention
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