What is congenital aqueductal stenosis and hydrocephalus? (Part 1)

In yesterday's blog - as well as a blog I wrote last year - I touched on aqueductal stenosis. Today, I want to look at congenital aqueductal stenosis and how it causes hydrocephalus. This is a condition that is "near and dear" to me because I found out back in October that I suffer from the condition. Most likely, according to the neurosurgeon, that is what caused my hydrocephalus.

What is hydrocephalus due to congenital aqueductal stenosis (HSAS)?

Hydrocephalus due to congenital aqueductal stenosis (HSAS) is a form of L1 syndrome -- a group of conditions that primarily affects the nervous system and occurs almost exclusively in males. They (L1 syndrome disorders) can vary in severity and include, from most severe to least severe, x-linked hydrocephalus with aqueductual stenosis (HSAS), Spastic paraplegia 1, and x-linked complicated corpus callosum agenesis.

HSAS is an acronym for the characteristic features of the condition: a buildup of cerebrospinal fluid (CSF) in the brain (hydrocephalus) which is often present from birth, muscle stiffness or spasticity, adducted thumbs (meaning they are permanently bent inward toward the palms), and a narrowing (stenosis) of the aqueduct of Sylvius.

How is HSAS passed from parent to child?

HSAS is inherited in an X-linked recessive manner. This means the responsible gene is located on the X chromosome -- one of two sex chromosomes; the other sex chromosome is the Y chromosome. Females have two (2) X chromosomes in each cell while the male has an X chromosome and a Y chromosome in each cell.

One of the female's X chromosomes is "turned off" meaning all of the genes on that chromosome are inactive. If a female has a change (mutation) in the gene on one of their X chromosomes, she is considered to be a carrier but will not exhibit the symptom(s) associated with the mutation. In those rare cases, where the female does experience symptoms, they are generally milder than those experienced by the males. In contrast, a male has only one (1) X chromosome, so, if he inherits a mutation on that chromosome, he will be symptomatic.

Bibliography

National Institutes of Health (N.D.) Hydrocephalus due to congenital stenosis of aqueduct of Sylvius. Retrieved on February 7, 2018 from https://rarediseases.info.nih.gov/diseases/434/hydrocephalus-due-to-congenital-stenosis-of-aqueduct-of-sylvius

National Institutes of Health (2018). L 1 syndrome. Retrieved on February 7, 2018 from https://ghr.nlm.nih.gov/condition/l1-syndrome.

Online Mendelian inheritance in men (OMIM) (ND). MASA syndrome. Retrieved on February 7, 2018 from http://www.omim.org/entry/303350.