Children whose seizures have some of these features are less likely to have the syndrome of Childhood Absence Epilepsy. 1  An absence seizure with mild clonic components involves mild, often subtle twitching of the eyelids, the corners of the mouth, and sometimes the arms.
1 Trisomy 21 â More than 90% of Down syndrome cases are caused by trisomy 21. 2  An extra chromosome (chromosome 21) originates in the development of either the sperm or the egg. 3  When the egg and the sperm unite to form the fertilized egg, three (rather than two) chromosomes 21 are present.
Â· just now. 1  Down syndrome is caused by a problem with a babyâs chromosomes that happens long before the baby is born. 2  Down syndrome is a chromosomal disorder where an extra copy of chromosome 21 is made, the term is called trisomy 21. 3  It is caused by trisomy, having 3 of the same chromosomes (chromosome 21) One usually have 2 of the same chromosomes, but down syndrome has 3. i a chromosomal disorder caused by the presence of all or part of an extra 21st chromosome. one extra chromosome.