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.
The extra copy of the # 21 chromosome is what causes the health problems that are associated with Down syndrome. In translocation Down syndrome, the extra 21 chromosome may be attached to the #14 chromosome, or to other chromosome numbers like 13, 15, or 22.In some cases, two #21 chromosomes can be attached to each other.Three to 4 percent of babies born with Down syndrome have translocation Down syndrome.n translocation Down syndrome, the extra 21 chromosome may be attached to the #14 chromosome, or to other chromosome numbers like 13, 15, or 22.