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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®

MECP2-related severe neonatal encephalopathy

Reviewed October 2011

What is MECP2-related severe neonatal encephalopathy?

MECP2-related severe neonatal encephalopathy is a brain disease characterized by small head size (microcephaly), poor muscle tone (hypotonia) in infancy, movement disorders, rigidity, and seizures. This condition primarily affects males. Infants with MECP2-related severe neonatal encephalopathy appear normal at birth but then develop severe brain dysfunction (encephalopathy) within the first week of life. These individuals experience poor feeding and frequent vomiting leading to a failure to gain weight and grow at the expected rate (failure to thrive). Males with MECP2-related severe neonatal encephalopathy have mild to severe intellectual disability. Affected individuals have breathing problems, with some having episodes in which breathing slows or stops for short periods (apnea). Most males with this condition do not live past the age of 2 due to respiratory failure.

How common is MECP2-related severe neonatal encephalopathy?

It is estimated that 1 in 50,000 to 100,000 males are affected with MECP2-related severe neonatal encephalopathy.

What genes are related to MECP2-related severe neonatal encephalopathy?

Mutations in the MECP2 gene cause MECP2-related severe neonatal encephalopathy. The MECP2 gene provides instructions for making a protein called MeCP2 that is critical for normal brain function. Researchers believe that this protein has several functions, including regulating other genes in the brain by switching them off when they are not needed. The MeCP2 protein likely plays a role in maintaining connections (synapses) between nerve cells. The MeCP2 protein may also control the production of different versions of certain proteins in nerve cells. Although mutations in the MECP2 gene disrupt the normal function of nerve cells, it is unclear how these mutations lead to the signs and symptoms of MECP2-related severe neonatal encephalopathy.

Related Gene(s)

Changes in this gene are associated with MECP2-related severe neonatal encephalopathy.

  • MECP2

How do people inherit MECP2-related severe neonatal encephalopathy?

More than 99 percent of MECP2-related severe neonatal encephalopathy cases occur in people with no history of the disorder in their family. Many of these cases result from new mutations in the MECP2 gene.

A few families with more than one affected family member have been described. These cases helped researchers determine that MECP2-related severe neonatal encephalopathy can have an X-linked pattern of inheritance. A condition is considered X-linked if the mutated gene that causes the disorder is located on the X chromosome, one of the two sex chromosomes. One copy of the altered gene in each cell is sufficient to cause the condition. Females with these same mutations typically have a similar disorder called Rett syndrome.

Where can I find information about diagnosis or management of MECP2-related severe neonatal encephalopathy?

These resources address the diagnosis or management of MECP2-related severe neonatal encephalopathy and may include treatment providers.

  • Cincinnati Children's Hospital: MECP2-Related Disorders (
  • Gene Review: MECP2-Related Disorders (
  • Genetic Testing Registry: Severe neonatal-onset encephalopathy with microcephaly (
  • Johns Hopkins Children's Center: Failure to Thrive (

You might also find information on the diagnosis or management of MECP2-related severe neonatal encephalopathy in Educational resources and Patient support.

General information about the diagnosis ( and management ( of genetic conditions is available in the Handbook. Read more about genetic testing (, particularly the difference between clinical tests and research tests (

To locate a healthcare provider, see How can I find a genetics professional in my area? ( in the Handbook.

Where can I find additional information about MECP2-related severe neonatal encephalopathy?

You may find the following resources about MECP2-related severe neonatal encephalopathy helpful. These materials are written for the general public.

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

What other names do people use for MECP2-related severe neonatal encephalopathy?

  • severe congenital encephalopathy due to MECP2 mutation
  • severe neonatal encephalopathy due to MECP2 mutations

For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines ( and How are genetic conditions and genes named? ( in the Handbook.

What if I still have specific questions about MECP2-related severe neonatal encephalopathy?

Ask the Genetic and Rare Diseases Information Center (

What glossary definitions help with understanding MECP2-related severe neonatal encephalopathy?

apnea ; cell ; chromosome ; congenital ; disability ; encephalopathy ; failure to thrive ; gene ; hypotonia ; inheritance ; microcephaly ; muscle tone ; mutation ; neonatal ; pattern of inheritance ; protein ; respiratory ; sex chromosomes ; syndrome

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


  • Francke U. Mechanisms of disease: neurogenetics of MeCP2 deficiency. Nat Clin Pract Neurol. 2006 Apr;2(4):212-21. Review. (
  • Gonzales ML, LaSalle JM. The role of MeCP2 in brain development and neurodevelopmental disorders. Curr Psychiatry Rep. 2010 Apr;12(2):127-34. doi: 10.1007/s11920-010-0097-7. Review. (
  • Kankirawatana P, Leonard H, Ellaway C, Scurlock J, Mansour A, Makris CM, Dure LS 4th, Friez M, Lane J, Kiraly-Borri C, Fabian V, Davis M, Jackson J, Christodoulou J, Kaufmann WE, Ravine D, Percy AK. Early progressive encephalopathy in boys and MECP2 mutations. Neurology. 2006 Jul 11;67(1):164-6. (
  • Schüle B, Armstrong DD, Vogel H, Oviedo A, Francke U. Severe congenital encephalopathy caused by MECP2 null mutations in males: central hypoxia and reduced neuronal dendritic structure. Clin Genet. 2008 Aug;74(2):116-26. doi: 10.1111/j.1399-0004.2008.01005.x. Epub 2008 May 8. Review. (
  • Villard L. MECP2 mutations in males. J Med Genet. 2007 Jul;44(7):417-23. Epub 2007 Mar 9. Review. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: October 2011
Published: February 1, 2016