What is Tay-Sachs disease?
Tay-Sachs disease (Hexosaminidase A deficiency) is a progressive
fatal genetic condition that affects the nerve cells in the brain. It is the
severe form of a group of disorders caused by Hexosaminidase A deficiency.
People with Tay-Sachs lack a specific protein called hexosaminidase A. This
causes a fatty substance, GM2 ganglioside, to build up in the brain. It is this
accumulation that causes the symptoms of Tay-Sachs.
What causes Tay-Sachs?
All people have two copies of the Tay-Sachs gene (HEXA). Tay-Sachs
occurs when neither of a person’s HEXA genes is working properly because of a
mutation (harmful change). If a person has one working copy of the HEXA gene and
the other copy has a mutation in it, he/she is called a "carrier." Carriers
don’t show symptoms but when two carriers have children together each child (boy
or girl) will have a 25% (1/4) chance of developing Tay-Sachs. If only one
parent passes on the defective gene to the child (50% chance in each pregnancy),
the child will not develop the disease but will be a carrier and have the
potential to pass the disease on to his or her children.
Although anyone can be a carrier of Tay-Sachs disease, the
disease is much more common among people of Ashkenazi (Eastern European) Jewish
descent. One in every 30 people of Ashkenazi Jewish descent is a carrier. Other
populations with as many (or more) carriers include French Canadians, Cajuns
(from Louisiana) and Old Order Amish in Pennsylvania. Around 1 in every 300
people who are not of these backgrounds is a carrier for Tay-Sachs.
What are the symptoms of Tay-Sachs?
Symptoms of Tay-Sachs usually develop around 3-6 months of age
when the child starts to have muscle weakness, low muscle tone, an increased
startle response and sudden contractions of large muscles when falling asleep (myoclonic
jerks).
Between 6 and 10 months of age, a child will not meet motor
milestones and may lose the ability to perform tasks (such as sitting) that
he/she had previously learned. Decreased eye movement and contact as well as
attentiveness are also seen along with a specific change in the eye seen during
exam called a cherry-red spot.
After 8 to 10 months of age, a baby will move less and become
less responsive. Vision will be lost and many will have seizures by a year of
age. A person’s head size will start to grow around 18 months of age and when a
child is 2 years old, they typically have trouble swallowing and progress into
an unresponsive vegetative state. Age of death is usually between 2 and 4 years,
often from pneumonia.