Trisomy 18, also known as Edwards syndrome, occurs when there is an extra copy of chromosome 18. It can be caused by nondisjunction during meiosis I or II. Symptoms include clenched hands, crossed legs, and low birth weight. Prognosis is poor, with 50% of full-term babies being stillborn and 90% of infants dying within 6 months. It can be tested for prenatally using ultrasound, CVS, or amniocentesis.

1. Trisomy 18
Nicholas Cherney

2.  Discovered by John H. Edwards
 Extra chromosome or piece of chromosome
 Can be full, partial, or mosaic
 Second most common trisomy after trisomy
21 (Down’s Syndrome)
 Much more common in females than males
◦ 80%
About Trisomy 18

3.  Edwards Syndrome
 Trisomy E
Other Names

4.  Trisomy is a type of aneuploidy.
 Caused by nondisjunction in either
meiosis I or meiosis II
◦ Translocation
 Common way of expressing an individual
with Edwards Syndrome is 47, XX, +18
◦ Normal would be 46, XX
Trisomy 18

5. Karytotype

6. Nondisjunction

7.  Full trisomy 18 is when an individual has 3 copies
of chromosome 18.
◦ ~95%
 Mosaic trisomy 18 arises when there is an extra
copy of chromosome 18 present in some cells.
◦ ~5%
 Partial trisomy occurs when part of chromosome
18 is translocated to another chromosome
◦ Balanced or unbalanced
◦ Extremely rare
Types of trisomy 18

8. Partial Trisomy

9. Balanced vs Unbalanced

10.  Clenched hands with crossed fingers
 Crossed legs
 Rocker-bottom feet
 Low birth weight
 Low-set ears
 Poorly developed fingernails
 Small head and jaw
 Abnormally shaped head
 Small sternum
 Many others
Symptoms

11. Signs

12.  Currently there are no treatments
 Each case is treated differently depending
on the specific needs of the individual
Treatment

13.  Majority die during fetal stage and are
spontaneously aborted (miscarried)
 Occur in about 1 in 5,000 live births.
 50% of full term babies will be still born.
◦ Males having higher rates than females.
 90% of infants die within 6 months
Prognosis

14.  Because trisomy 18 is caused by
nondisjunction (or translocation) it cannot
be passed to offspring.
◦ Exception: partial trisomy 18
Inheritance

15.  Ultrasound
◦ Maternal polyhydramnio
 CVS (chorionic villi sampling)
◦ 10-12 weeks of pregnancy
◦ Removal of a piece of the chorionic villi
 Amniocentesis
◦ 15-18 weeks of pregnancy
◦ Withdraw of small volume of amniotic fluid
 Blood test
Tests

16.  How does trisomy 18 occur? (2 ways)
 Briefly explain the 2 in-utero tests for
trisomy 18.
 How can trisomy be inherited?
Quiz

17.  http://www.slh.wisc.edu/cytogenetics/cases/aug1997/karyo.dot
 http://rarediseases.info.nih.gov/GARD/Disease.aspx?PageID=4&DiseaseID=6321
 http://www.chromosome18.org/TheConditions/OtherConditions/tabid/518/Default.aspx
 http://www.trisomy18.org/site/PageServer?pagename=whatisT18_whatis
 http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002626/
 http://ghr.nlm.nih.gov/condition/trisomy-18
 http://ghr.nlm.nih.gov/chromosome=18
 http://www.emedicinehealth.com/trisomy_18_edwards_syndrome/page6_em.htm
 http://ghr.nlm.nih.gov/condition/trisomy-18#diagnosis
 http://drugline.org/medic/term/meiotic-nondisjunction/
References