What is (are) X-linked infantile spasm syndrome ?
X-linked infantile spasm syndrome 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 involves bending at the waist and neck with extension of the arms and legs (sometimes called a jackknife spasm). Each spasm lasts only seconds, but they occur in clusters several minutes long. Although individuals are not usually affected while they are sleeping, the spasms commonly occur just after awakening. Infantile spasms usually disappear by age 5, but many children then develop other types of seizures that recur throughout their lives.  Most babies with X-linked infantile spasm syndrome 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.  Because of the recurrent seizures, babies with X-linked infantile spasm syndrome stop developing normally and begin to lose skills they have acquired (developmental regression), such as sitting, rolling over, and babbling. Subsequently, development in affected children is delayed. Most affected individuals also have intellectual disability throughout their lives.