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Disease Profile

Hydrocephalus due to congenital stenosis of aqueduct of sylvius

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.

1-9 / 100 000

US Estimated

Europe Estimated

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)

Hydrocephalus, X-linked; HSAS1; Aqueductal stenosis, X-linked;


Congenital and Genetic Diseases; Nervous System Diseases


Hydrocephalus due to congenital stenosis of aqueduct of sylvius (HSAS) is a form of L1 syndrome, which is an inherited disorder that primarily affects the nervous system. Males with HSAS are typically born with severe hydrocephalus and adducted thumbs (bent towards the palm). Other sign and symptoms of the condition include severe intellectual disability and spasticity. HSAS, like all forms of L1 syndrome, is caused by changes (mutations) in the L1CAM gene and is inherited in an X-linked recessive manner. Treatment is based on the signs and symptoms present in each person.[1][2]


Males with hydrocephalus due to congenital stenosis of aqueduct of sylvius (HSAS) are typically born with severe hydrocephalus and adducted thumbs (bent towards the palm). Other signs and symptoms may include:[1][2]

  • Seizures
  • Severe intellectual disability
  • Spasticity

Of note, HSAS is one form of L1 syndrome, which is an inherited condition that primarily affects the nervous system. Other forms include MASA syndrome, X-linked complicated hereditary spastic paraplegia type 1, and X-linked complicated corpus callosum agenesis. All of the different forms of L1 syndrome may be observed in affected people within the same family.[1] GeneReviews offers more specific information about the signs and symptoms associated with each form of L1 syndrome. Please click on the link to access this resource.

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:
80%-99% of people have these symptoms
Aqueductal stenosis
Paralysis or weakness of one side of body
Too much cerebrospinal fluid in the brain
Increased intracranial pressure
Rise in pressure inside skull
Intellectual disability, severe
Early and severe mental retardation
Mental retardation, severe
Severe mental retardation

[ more ]

Involuntary muscle stiffness, contraction, or spasm
30%-79% of people have these symptoms
Adducted thumb
Inward turned thumb
5%-29% of people have these symptoms
Absent septum pellucidum
Agenesis of corpus callosum
Coarse facial features
Coarse facial appearance
Joint stiffness
Stiff joint
Stiff joints

[ more ]

Involuntary, rapid, rhythmic eye movements
Squint eyes

[ more ]

Percent of people who have these symptoms is not available through HPO
Corticospinal tract hypoplasia
Intellectual disability
Mental deficiency
Mental retardation
Mental retardation, nonspecific

[ more ]

Increased size of skull
Large head
Large head circumference

[ more ]

Spastic paraplegia
X-linked recessive inheritance


A diagnosis of hydrocephalus due to congenital stenosis of aqueduct of sylvius is typically suspected based on the presence of characteristic signs and symptoms on physical examination and/or brain imaging (i.e. CT scan, MRI scan). Identification of a change (mutation) in the L1CAM gene can be used to confirm the diagnosis.[1]

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.


    The treatment of hydrocephalus due to congenital stenosis of aqueduct of sylvius (HSAS) is based on the signs and symptoms present in each person. For example, hydrocephalus is typically treated with shunt surgery. Special education and early intervention may be recommended for children with intellectual disability. Although intervention is rarely necessary for adducted thumbs (bent towards the palms), tendon transfer surgery or splinting may be suggested in some cases.[1][2]


    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.

      Where to Start

      • Genetics Home Reference (GHR) contains information on Hydrocephalus due to congenital stenosis of aqueduct of sylvius. This website is maintained by the National Library of Medicine.
      • The National Organization for Rare Disorders (NORD) has a report for patients and families about this condition. NORD is a patient advocacy organization for individuals with rare diseases and the organizations that serve them.

        In-Depth Information

        • GeneReviews provides current, expert-authored, peer-reviewed, full-text articles describing the application of genetic testing to the diagnosis, management, and genetic counseling of patients with specific inherited conditions.
        • 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. 
        • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
        • PubMed is a searchable database of medical literature and lists journal articles that discuss Hydrocephalus due to congenital stenosis of aqueduct of sylvius. Click on the link to view a sample search on this topic.


          1. Stumpel C & Vos YJ. L1 syndrome. GeneReviews. March 5, 2015; https://www.ncbi.nlm.nih.gov/books/NBK1484/. Accessed 4/24/2015.
          2. L1 syndrome. NORD. August 2012; https://www.rarediseases.org/rare-disease-information/rare-diseases/byID/1097/viewAbstract.
          3. L1 syndrome. Genetics Home Reference. March 2008; https://ghr.nlm.nih.gov/condition/l1-syndrome.

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