Developmental and epileptic encephalopathy 1 (DEE1) is a seizure disorder characterized by a type of seizure known as infantile spasms. The spasms usually appear before the age of 1. Several types of spasms have been described, but the most commonly reported type involves bending at the waist and neck and extending the arms and legs (sometimes called a jackknife spasm). Each spasm lasts only seconds, but they occur in clusters several minutes long. Although individuals do not usually have spasms while they are sleeping, the spasms commonly occur just after awakening. Infantile spasms usually stop by age 5, but many children then develop other types of seizures that recur throughout their lives.
Early in life, babies with DEE1 stop developing normally and begin to lose skills they have acquired (developmental regression), such as sitting, rolling over, and babbling. Most affected individuals also have intellectual disability throughout their lives.
Most babies with DEE1 have characteristic results on an electroencephalogram (EEG), a test used to measure the electrical activity of the brain. The EEG of these individuals typically shows an irregular pattern known as hypsarrhythmia, and this finding can help differentiate infantile spasms from other types of seizures. [from
MedlinePlus Genetics]