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Infantile Spasm Syndrome-2, X-linked
X-linked early infantile epileptic encephalopathy (EIEE2) is characterized by intractable early-onset tonic seizures or
spasms. This disorder is genetically heterogeneous, with up to a fifth of cases resulting from mutations in the
CDKL5 gene. The majority of patients with CDKL5 mutations are female. Females with CDKL5 mutations typically
present with drug-resistant seizures that begin before 6 months of age, and more than 90% show a phenotype before
the end of the first year. Up to 70% of affected females develop infantile spasms (IS), often in conjunction with
hypsarrythmia, and in some cases, they are diagnosed with West syndrome.4,7,11 Some females also present with
autism, hypotonia, and developmental delay.1-5 Some of these patients have features reminiscent of Rett syndrome,
including breathing dysfunction, deceleration of head growth and stereotypic hand movements. However, unlike
those with Rett syndrome, patients with CDKL5 mutations do not demonstrate developmental regression with loss of
language and motor skills after normal development in the first year of life. An Angelman syndrome-like phenotype
has also been observed in some female patients.1,2,11,12 Male individuals with a CDKL5 mutation typically also
develop epileptic encephalopathy characterized by severe intractable seizures and intellectual disability in the
absence of other signs.