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.
A patient with trisomy 21 has three copies of chromosome 21. Down syndrome is classified as a genetic â¦ disorder and it includes a combination of characteristic facial features, often some degree of mental retardation, and sometimes heart defects. Many people with Down syndrome also have hearing and vision problems.