National Center for Advancing and Translational Sciences Genetic and Rare Diseases Information Center, a program of the National Center for Advancing and Translational Sciences

Hydrocephalus due to congenital stenosis of aqueduct of sylvius


Other Names:
Hydrocephalus, X-linked; HSAS1; Aqueductal stenosis, X-linked; Hydrocephalus, X-linked; HSAS1; Aqueductal stenosis, X-linked; HSAS; HYCX; XLAS See More
Categories:
This disease is grouped under:
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]
Last updated: 4/26/2015
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.
Last updated: 4/24/2015

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.

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Medical Terms Other Names
Learn More:
HPO ID
80%-99% of people have these symptoms
Aqueductal stenosis 0002410
Hemiplegia/hemiparesis
Paralysis or weakness of one side of body
0004374
Hydrocephalus
Too much cerebrospinal fluid in the brain
0000238
Increased intracranial pressure
Rise in pressure inside skull
0002516
Intellectual disability, severe
Early and severe mental retardation
Mental retardation, severe
Severe mental retardation
[ more ] 		0010864
Spasticity
Involuntary muscle stiffness, contraction, or spasm
0001257
30%-79% of people have these symptoms
Adducted thumb
Inward turned thumb
0001181
5%-29% of people have these symptoms
Absent septum pellucidum 0001331
Agenesis of corpus callosum 0001274
Coarse facial features
Coarse facial appearance
0000280
Holoprosencephaly 0001360
Joint stiffness
Stiff joint
Stiff joints
[ more ] 		0001387
Nystagmus
Involuntary, rapid, rhythmic eye movements
0000639
Seizure 0001250
Strabismus
Cross-eyed
Squint
Squint eyes
[ more ] 		0000486
Percent of people who have these symptoms is not available through HPO
Corticospinal tract hypoplasia 0007016
Intellectual disability
Mental deficiency
Mental retardation
Mental retardation, nonspecific
Mental-retardation
[ more ] 		0001249
Macrocephaly
Increased size of skull
Large head
Large head circumference
[ more ] 		0000256
Spastic paraplegia 0001258
X-linked recessive inheritance 0001419
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Last updated: 7/1/2020
Hydrocephalus due to congenital stenosis of aqueduct of sylvius is inherited in an X-linked recessive manner.[3] A condition is X-linked if the responsible gene is located on the X chromosome. The X chromosome is one of the two sex chromosomes (the other sex chromosome is the Y chromosome). Females have two X chromosomes in each cell and males have an X chromosome and a Y chromosome in each cell.

Although females have two X chromosomes, one of the X chromosomes in each cell is "turned off" and all of the genes on that chromosome are inactivated. Females who have a change (mutation) in a gene on one of their X chromosomes are called carriers of the related condition. Carrier females usually do not have symptoms of the condition because the X chromosome with the mutated gene is often turned off and they have another X chromosome with a working copy of the gene. Sometimes, the X chromosome with the working copy of the gene is turned off, which may cause symptoms of the condition. However, females with symptoms are usually much more mildly affected than males.

A male has only one X chromosome, so if he inherits a mutation on the X chromosome, he will have signs and symptoms (be affected).

Males with an X-linked recessive condition always pass the mutated gene to all of their daughters, who will be carriers. A male cannot pass an X-linked gene to his sons because males always pass their Y chromosome to male offspring.

Female carriers of an X-linked recessive condition have a 25% chance with each pregnancy to have a carrier daughter like themselves, a 25% chance to have a non-carrier daughter, a 25% chance to have an affected son, and a 25% chance to have an unaffected son. This also means that each daughter of a carrier mother has a 50% chance of being a carrier, and each son has a 50% chance of having the condition.
Last updated: 4/24/2015
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]
Last updated: 4/26/2015

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]
Last updated: 4/26/2015

If you need medical advice, you can look for doctors or other healthcare professionals who have experience with this disease. You may find these specialists through advocacy organizations, clinical trials, or articles published in medical journals. You may also want to contact a university or tertiary medical center in your area, because these centers tend to see more complex cases and have the latest technology and treatments.

If you can’t find a specialist in your local area, try contacting national or international specialists. They may be able to refer you to someone they know through conferences or research efforts. Some specialists may be willing to consult with you or your local doctors over the phone or by email if you can't travel to them for care.

You can find more tips in our guide, How to Find a Disease Specialist. We also encourage you to explore the rest of this page to find resources that can help you find specialists.

Healthcare Resources

Research helps us better understand diseases and can lead to advances in diagnosis and treatment. This section provides resources to help you learn about medical research and ways to get involved.

Clinical Research Resources

  • ClinicalTrials.gov lists trials that are related to Hydrocephalus due to congenital stenosis of aqueduct of sylvius. Click on the link to go to ClinicalTrials.gov to read descriptions of these studies.

    Please note: Studies listed on the ClinicalTrials.gov website are listed for informational purposes only; being listed does not reflect an endorsement by GARD or the NIH. We strongly recommend that you talk with a trusted healthcare provider before choosing to participate in any clinical study.

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

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.

Questions sent to GARD may be posted here if the information could be helpful to others. We remove all identifying information when posting a question to protect your privacy. If you do not want your question posted, please let us know.

  1. Stumpel C & Vos YJ. L1 syndrome. GeneReviews. March 5, 2015; http://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; http://ghr.nlm.nih.gov/condition/l1-syndrome.