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Trisomy 18 2

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  • 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 EOther 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, XXTrisomy 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 rareTypes 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 othersSymptoms
  • 11. Signs
  • 12.  Currently there are no treatments Each case is treated differently depending on the specific needs of the individualTreatment
  • 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 monthsPrognosis
  • 14.  Because trisomy 18 is caused by nondisjunction (or translocation) it cannot be passed to offspring. ◦ Exception: partial trisomy 18Inheritance
  • 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 testTests
  • 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