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.
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
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
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
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
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