Presentation on theme: "Down Syndrome This PowerPoint file contains a number of slides that may be useful for teaching of genetics concepts. You may use these slides and their."— Presentation transcript:
1 Down SyndromeThis PowerPoint file contains a number of slides that may be useful for teaching of genetics concepts.You may use these slides and their contents for non-commercial educational purposes.This set of slides contains information on:Clinical features of Down SyndromeKaryotypes of Trisomy 21Meiotic Non disjunctionFISH images
3 Down syndrome 1 in 700 live births >60% spontaneously aborted 20% stillbornFacial appearance permits diagnosisMarked muscle hypotonia as babySingle palmar crease may be presentLearning difficulty (IQ usually <50)Congenital heart malformations (40%)Many other associated features
4 Three different patterns of chromosomes can cause Down syndrome 95% people have three separate copies of chromosome 21 - trisomy 214% have the extra copy of chromosome 21 because of a Robertsonian translocationNon-disjunction1% have mosaicism with normal and trisomy 21 cell lines (and usually have much milder features because of the presence of the normal cells); - occurs postzygotically
5 Trisomies appear to be associated with an increase in maternal age eggs held at crossing-over stage in meiosis from approx 6 months gestationso “wear and tear” with increasing maternal age in machinery for cell division thought to be a major component (plus other factors)The trisomy 21 type of Down syndrome is the result of an error in meiosis, and has a recurrence risk of about 1 in 100.
6 three separate copies of chromosome 21 Trisomy 21: 47,XX,+21three separate copies of chromosome 21
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