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 refers to certain characteristics that occur in children and adults who have an abnormal number of number 21 chromosomes. As humans, we have 46 chromosomes or 23 pairs of chromosomes. 22 pairs are considered autosomes, and the other pair are the sex chromosomes - either XY for a boy and XX for a girl.