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Trisomy 18 and Trisomy 13

by Brian Alverson, MD
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    00:01 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.

    00:35 This is due to 3 copies of chromosome 18 in the cells of the body.

    00:41 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.

    02:18 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.

    02:27 One of the key findings is micrognathia.

    02:30 These children have very small jaws and it may lead to an upper respiratory distress.

    02:36 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.

    03:16 The most common cardiac defect is the VSD or the ventricular septal defect.

    03:21 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.

    03:36 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.

    04:29 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.

    05:05 They can develop a severe cleft lip and palate.

    05:09 They often have polydactyly which is an extra finger or digit.

    05:13 They may have severe cardiac or renal malformations.

    05:17 There?s a lot of similarities between Trisomy 13 and Trisomy 18.

    05:21 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.


    About the Lecture

    The lecture Trisomy 18 and Trisomy 13 by Brian Alverson, MD is from the course Pediatric Genetics. It contains the following chapters:

    • Trisomy 18 (Edwards Syndrome)
    • Trisomy 13 (Patau Syndrome)

    Included Quiz Questions

    1. Rocker bottom feet
    2. Polydactyly
    3. Death in the second year of life
    4. Mild cognitive disability
    5. Macrocephaly
    1. …chromosome 18
    2. …chromosome Y
    3. …chromosome X
    4. …chomosome 12
    5. …chromosome 21
    1. 95% of cases are due to a Robertsonian translocation
    2. Severe intellectual disability
    3. Congenital malformations
    4. Greatly reduced life expectancy
    5. More common in females than males
    1. Micrognathia
    2. Low birth weight
    3. Low set ears
    4. Microcephaly
    5. VSD
    1. Congenital hydrocephalus is common
    2. Patients can have scalp defects
    3. Life expectancy is 7 to 10 days
    4. Patients can have cardiac and renal malformations
    5. It is due to trisomy 13

    Author of lecture Trisomy 18 and Trisomy 13

     Brian Alverson, MD

    Brian Alverson, MD


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