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.
Greater than 90 percent of patients with Down syndrome have trisomy 21. A patient with trisomy 21 has three copies of chromosome 21. Down syndrome is classified as a genetic 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.