Hydrocephalus due to congenital stenosis of aqueduct of sylvius

Alternate names

Hydrocephalus, X-linked; HSAS1; Aqueductal stenosis, X-linked; HSAS; HYCX; XLAS

Definition

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.

Cause

HSAS, like all forms of L1 syndrome, is caused by changes (mutations) in the L1CAM gene.

Inheritance

X-linked recessive inheritance

Hydrocephalus due to congenital stenosis of aqueduct of sylvius is inherited in an X-linked recessive manner.

• 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.

Signs and symptoms

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:

• Seizures
• Severe intellectual disability
• Spasticity

Clinical presentation

For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed.

80%-99% of people have these symptoms

• Aqueductal stenosis
• Hemiplegia/hemiparesis(Paralysis or weakness of one side of body)
• Hydrocephalus(Too much cerebrospinal fluid in the brain)
• Increased intracranial pressure(Rise in pressure inside skull)
• Intellectual disability, severe(Early and severe mental retardation)
• Spasticity(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)
• Holoprosencephaly
• Joint stiffness(Stiff joint)
• Nystagmus(Involuntary, rapid, rhythmic eye movements)
• Seizure
• Strabismus(Cross-eyed)

Diagnosis

• 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.

Treatment

• 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.

NIH genetic and rare disease info

• NIH info on Hydrocephalus due to congenital stenosis of aqueduct of sylvius

Hydrocephalus due to congenital stenosis of aqueduct of sylvius is a rare disease.

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