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.
Most people have 46 chromosomes in each cell. Children with Down syndrome have 47 chromosomes. They have an extra copy of chromosome 21. Normally, we inherit 23 chromosomes from our mother and 23 chromosomes from our father (for a total of 46).