From MedlinePlus Genetics
CDKL5 deficiency disorder is characterized by seizures that begin in infancy, followed by significant delays in many aspects of development.

Seizures in CDKL5 deficiency disorder usually begin within the first 3 months of life, and can appear as early as the first week after birth. The types of seizures change with age, and may follow a predictable pattern. The most common types are generalized tonic-clonic seizures, which involve a loss of consciousness, muscle rigidity, and convulsions; tonic seizures, which are characterized by abnormal muscle contractions; and epileptic spasms, which involve short episodes of muscle jerks. Seizures occur daily in most people with CDKL5 deficiency disorder, although they can have periods when they are seizure-free. Seizures in CDKL5 deficiency disorder usually do not get better with treatment.

Development is impaired in children with CDKL5 deficiency disorder. Most have severe intellectual disability and little or no speech. The development of gross motor skills, such as sitting, standing, and walking, is delayed or not achieved. About one-third of affected individuals are able to walk independently. Fine motor skills, such as picking up small objects with the fingers, are also impaired; about half of affected individuals have purposeful use of their hands. Most people with this condition have vision problems (cortical visual impairment).

Other common features of CDKL5 deficiency disorder include repetitive hand movements (stereotypies), such as clapping, hand licking, and hand sucking; teeth grinding (bruxism); disrupted sleep; feeding difficulties; and gastrointestinal problems including constipation and backflow of acidic stomach contents into the esophagus (gastroesophageal reflux). Some affected individuals have episodes of irregular breathing. Distinctive facial features in some people with CDKL5 deficiency disorder include a high and broad forehead, large and deep-set eyes, a well-defined space between the nose and upper lip (philtrum), full lips, widely spaced teeth, and a high roof of the mouth (palate). Other physical differences can also occur, such as an unusually small head size (microcephaly), side-to-side curvature of the spine (scoliosis), and tapered fingers.

CDKL5 deficiency disorder was previously classified as an atypical form of Rett syndrome. These conditions have common features, including seizures, intellectual disability, and other problems with development. However, the signs and symptoms associated with CDKL5 deficiency disorder and its genetic cause are distinct from those of Rett syndrome, and CDKL5 deficiency disorder is now considered a separate condition.  https://medlineplus.gov/genetics/condition/cdkl5-deficiency-disorder