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.
Down Syndrome Mutation. Down Syndrome is caused by a trisomy. Another name for down syndrome is Trisomy 21. When a child receives its chromosomes pairs from their parents and a trisomy occurs...you receive 3 chromosomes instead of the two that are normally in a pair. When this happens on the 21st chromosome, it will most likely result in down syndrome. The mutation is a trisomy.