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Disease Profile


Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.


Age of onset





Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable


Other names (AKA)

MHAC; Hydranencephaly and microcephaly


Congenital and Genetic Diseases


Microhydranencephaly is a developmental abnormality that affects the brain. Signs and symptoms may include extreme microcephaly, scalp rugae (a series of ridges), profound developmental delay and severe intellectual disability. Imaging studies of the brain generally reveal incomplete brain formation and severe hydrocephalus (accumulation of fluid in the brain). In most cases, the underlying cause is unknown. Rarely, the condition is caused by changes (mutations) in the NDE1 gene and is inherited in an autosomal recessive manner. Treatment is based on the signs and symptoms present in each person.[1][2][3]


Microhydranencephaly is a developmental abnormality that affects the brain. Signs and symptoms can vary but generally include:[3][2][1]

  • Extreme microcephaly
  • Scalp rugae (a series of ridges)
  • Profound developmental delay
  • Severe intellectual disability
  • Spasticity

Imaging studies of the brain generally reveal incomplete brain formation and severe hydrocephalus (accumulation of fluid in the brain).[3][1]

This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

Medical Terms Other Names
Learn More:
Percent of people who have these symptoms is not available through HPO
Agenesis of corpus callosum
Involuntary writhing movements in fingers, hands, toes, and feet
Autosomal recessive inheritance
Cerebellar hypoplasia
Small cerebellum
Underdeveloped cerebellum

[ more ]

Generalized myoclonic seizure
Increased reflexes
Hypoplasia of the brainstem
Small brainstem
Underdeveloped brainstem

[ more ]

Intellectual disability, progressive
Mental retardation, progressive
Progressive mental retardation

[ more ]

Intellectual disability, severe
Early and severe mental retardation
Mental retardation, severe
Severe mental retardation

[ more ]

Large ears
Abnormally small skull
Decreased circumference of cranium
Decreased size of skull
Reduced head circumference
Small head circumference

[ more ]

Multiple joint contractures
Fewer and broader ridges in brain
Profound global developmental delay
Prominent nasal bridge
Elevated nasal bridge
High nasal bridge
Prominent bridge of nose
Prominent nasal root
Protruding bridge of nose
Protruding nasal bridge

[ more ]

Bulging eye
Eyeballs bulging out
Prominent eyes
Prominent globes
Protruding eyes

[ more ]

Deliberate self-harm
Self mutilation

[ more ]

Short stature
Decreased body height
Small stature

[ more ]

Skeletal muscle atrophy
Muscle degeneration
Muscle wasting

[ more ]

Sloping forehead
Inclined forehead
Receding forehead

[ more ]

Spastic tetraplegia
Talipes equinovarus
Club feet
Club foot

[ more ]



In many cases, the exact, underlying cause of microhydranencephaly is unknown. There are reports of families in which the condition is caused by changes (mutations) in the NDE1 gene. In these rare cases, more than one family member (often a pair of siblings) had the condition.[1][3]


A diagnosis of microhydranencephaly is generally suspected based on the presence of characteristic signs and symptoms. Additional testing can then be ordered to confirm the diagnosis. This generally consists of imaging studies to evaluate the brain for structural abnormalities and severe hydrocephalus (accumulation of fluid in the brain).[2]

Testing Resources

  • The Genetic Testing Registry (GTR) provides information about the genetic tests for this condition. The intended audience for the GTR is health care providers and researchers. Patients and consumers with specific questions about a genetic test should contact a health care provider or a genetics professional.


    Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

    Organizations Supporting this Disease

      Learn more

      These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

      In-Depth Information

      • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
      • Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
      • PubMed is a searchable database of medical literature and lists journal articles that discuss Microhydranencephaly. Click on the link to view a sample search on this topic.


        1. Guven A, Gunduz A, Bozoglu TM, Yalcinkaya C, Tolun A. Novel NDE1 homozygous mutation resulting in microhydranencephaly and not microlyssencephaly. Neurogenetics. August 2012; 13(3):189-194.
        2. Behunova J, Zavadilikova E, Bozoglu TM, Gunduz A, Tolun A, Yalcinkaya C. Familial microhydranencephaly, a family that does not map to 16p13.13-p12.2: relationship with hereditary fetal brain degeneration and fetal brain disruption sequence. Clin Dysmorphol. July 2010; 19(3):107-118.
        3. Marla J. F. O'Neill. MICROHYDRANENCEPHALY. OMIM. April 2014; https://omim.org/entry/605013.

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