Down syndrome is caused by all except:
Correct Answer: Deletion of 21
Description: Three cytogenetic variants cause Down syndrome:
Trisomy 21
Chromosomal translocation
Mosaicism
Trisomy 21 accounts for nearly 95% of all patients with Down syndrome.
It is now generally accepted that there are at least three forms of Down syndrome:
One in which there is the typical trisomy 21 with 47 chromosomes (accounting for about 95% of cases)
Another termed the translocation type, in which there appear to be only 46 chromosomes, although the extra chromosome material of number 21 is translocated to another chromosome of G or D group, either 21/22 translocation or 21/21 translocation (about 3% of cases)
Another that is the result of chromosomal mosaicism (about 2%)
Rajendran R. Shafer's textbook of oral pathology. Edition 7. Page 729
Category:
Pathology
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