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It is possible that the main title of the report CDKL5 is not the name you expected. Please check the synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.


  • CDKL5 deficiency
  • CDKL5 disorder
  • STK9

Disorder Subdivisions

  • None

General Discussion

CDKL5 is a rare X-linked genetic disorder that results in early onset, difficult to control seizures, and severe neurodevelopmental impairment. CDKL5 stands for cyclin-dependent kinase-like 5, and is a gene located on the X chromosome.

Most of the children affected by CDKL5 suffer from seizures that begin in the first few months of life. Most cannot walk, talk or feed themselves, and many are confined to a wheelchair. Many also suffer with scoliosis, visual impairment, sensory issues and various gastrointestinal difficulties.

CDKL5 mutations were initially thought to be specifically associated with the Hanefeld variant of Rett syndrome, in which earlier seizures are a prominent feature. However, the characteristics of the disorder (phenotype) have been expanded to include early epileptic seizures and later onset intractable seizure disorders commonly including myoclonus without clinical features of Rett syndrome. More recent studies suggest that the predominant phenotype caused by CDKL5 mutations is the so-called epileptic encephalopathy, the onset of severe seizures in the first six months of life (often within the first 3 months), and poor subsequent neurocognitive development and commonly the presence of repetitive hand movements (stereotypies).

CDKL5 mutations have been found in children diagnosed with infantile spasms, West syndrome, Lennox-Gastaut syndrome, Rett syndrome, and autism. The full spectrum of CDKL5 disorders is unknown at this time. It is likely that there are many people affected by CDKL5 who have mild symptoms and no seizures.

The first report associated with an abnormality of the CDKL5 gene was in a child who had retinoschisis, severe intellectual disability and seizures. This patient had a deletion of the end of the CDKL5 gene, which overlaps with the end of the RS1 gene, the latter being associated with the eye abnormality in this patient. Subsequently, disruption of the CDKL5 gene due to X:autosome translocations disrupting the CDKL5 gene were reported in two patients with X-linked infantile spasm syndrome (ISSX). CDKL5 mutations were then linked with Rett syndrome by two groups. Weaving, et al reported a rare family in which one of identical twin sisters had atypical Rett syndrome with early onset seizures, while the other twin had autism and intellectual disability, but did not have Rett syndrome. They had a brother who had severe neonatal onset epileptic encephalopathy. Another female was reported by this group who had atypical Rett syndrome and early onset seizures and a different CDKL5 mutation, and Tao, et al reported two cases with a similar presentation and different mutations of the CDKL5 gene.


International Rett Syndrome Foundation
4600 Devitt Dr.
Cincinnati, OH 45246
Tel: (800)818-7388

International Foundation for CDKL5 Research
P.O. Box 926
Wadsworth, OH 44282
Tel: (630)926-1189
Fax: (734)426-7790

For a Complete Report

This is an abstract of a report from the National Organization for Rare Disorders (NORD). A copy of the complete report can be downloaded free from the NORD website for registered users. The complete report contains additional information including symptoms, causes, affected population, related disorders, standard and investigational therapies (if available), and references from medical literature. For a full-text version of this topic, go to and click on Rare Disease Database under "Rare Disease Information".

The information provided in this report is not intended for diagnostic purposes. It is provided for informational purposes only. NORD recommends that affected individuals seek the advice or counsel of their own personal physicians.

It is possible that the title of this topic is not the name you selected. Please check the Synonyms listing to find the alternate name(s) and Disorder Subdivision(s) covered by this report

This disease entry is based upon medical information available through the date at the end of the topic. Since NORD's resources are limited, it is not possible to keep every entry in the Rare Disease Database completely current and accurate. Please check with the agencies listed in the Resources section for the most current information about this disorder.

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Last Updated:  1/17/2012
Copyright  2012 National Organization for Rare Disorders, Inc.