You are here: Home / Rare Disease Information / Rare Disease Database

Search Rare Diseases

Enter a disease name or synonym to search NORD's database of reports.

0-9 - A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z



You are reading a NORD Rare Disease Report Abstract. NORD’s full collection of reports on over 1200 rare diseases is available to subscribers (click here for details). We are now also offering two full rare disease reports per day to visitors on our Web site.

NORD is very grateful to Dr. Helen Leonard, Telethon Institute, Perth, Australia; Prof. John Christodoulou, NSW Centre for Rett Syndrome Research, Children's Hospital at Westmead, Sydney, Australia; and Dr. Katheryn Elibri Frame, International Foundation for CDKL5 Research, for assistance in the preparation of this report.

Synonyms of CDKL5

  • CDKL5 deficiency
  • CDKL5 disorder
  • STK9

Disorder Subdivisions

  • No subdivisions found.

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.

CDKL5 Resources

NORD Member Organizations:

(To become a member of NORD, an organization must meet established criteria and be approved by the NORD Board of Directors. If you're interested in becoming a member, please contact Susan Olivo, Membership Manager, at

Other Organizations:

The information in NORD’s Rare Disease Database is for educational purposes only. It should never be used for diagnostic or treatment purposes. If you have questions regarding a medical condition, always seek the advice of your physician or other qualified health professional. NORD’s reports provide a brief overview of rare diseases. For more specific information, we encourage you to contact your personal physician or the agencies listed as “Resources” on this report.

0-9 - A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z

NORD's Rare Disease Information Database is copyrighted and may not be published without the written consent of NORD.

Copyright ©2015 NORD - National Organization for Rare Disorders, Inc. All rights reserved.
The following trademarks/registered service marks are owned by NORD: NORD, National Organization for Rare Disorders, the NORD logo, RareConnect. .