Trisomy 18 and Trisomy 13

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.