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.
Typically, a baby has 46 chromosomes. Babies with Down syndrome have an extra copy of one of these chromosomes, chromosome 21. This extra copy changes the bodyâs and brainâs development and can cause mental and physical problems for the baby.ome examples of physical problems associated with Down syndrome include a birth defect of the heart or problems with the stomach, hearing, skeleton, intestines, thyroid, or eyes. People with Down syndrome usually have an IQ in the mild-to-moderate range of intellectual disabilities.