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.
Down syndrome is a condition in which a person has an extra chromosome. Chromosomes are small âpackagesâ of genes in the body. They determine how a babyâs body forms during pregnancy and how the babyâs body functions as it grows in the womb and after birth. Typically, a baby is born with 46 chromosomes.Babies with Down syndrome have an extra copy of one of these chromosomes, chromosome 21. A medical term for having an extra copy of a chromosome is âtrisomy.â Down syndrome is also referred to as Trisomy 21.ypically, a baby is born with 46 chromosomes. Babies with Down syndrome have an extra copy of one of these chromosomes, chromosome 21. A medical term for having an extra copy of a chromosome is âtrisomy.â Down syndrome is also referred to as Trisomy 21.