Tay-Sachs
disease is a recessive genetic disorder
(see Causes) that is common amongst Ashkenazi
Jews. It appears in the early months of
life. It features a progressive degeneration
of all brain functions.
In the general population, one person in
35,000 is a carrier of the gene for Tay-Sach's
disease. Among Ashkenazi Jews, 1 person
in 30 is a carrier, and about 1 in 2,000
people will suffer from the disease.
Symptoms
Tay-Sach's
disease leads to blindness, deafness, progressive
dementia, seizures, paralysis and death,
usually before the age of three years.
Causes
The condition
is due to the absence of an essential enzyme
that breaks down a substance called ganglioside,
present mainly in the nervous system. It
is the accumulation of this material that
is so damaging.
A recessive
genetic disorder is one in which both father
and mother must carry the gene before the
child can develop the disease. Chromosomes
come in pairs, each member of a pair having
an almost identical set of genes.
Parents carrying
the mutated gene can only have it on one
of the gene pairs, the other gene being
normal. When sperms and eggs are formed,
only one of each chromosome pair enters
the sperm or egg.
So it is
pure chance whether the sperm and the egg
carry the mutated gene or the normal one.
For the disease to occur, a sperm carrying
the mutation (50:50 chance) must fertilise
an egg carrying the mutation (50:50 chance).
Prevention
Unfortunately,
there is no treatment for Tay-Sachs disease,
so it is very important for carriers or
possible carriers to have genetic counselling.
Carrier status can be found by a blood test.
Antenatal
diagnosis (testing before birth) by Chorionic
villus sampling can be done. If the diagnosis
is confirmed, termination of pregnancy can
be offered.
Some Jewish
communities have successfully organised
pre-marital counselling services and testing
in the hope of preventing the occurrence
of this disorder. As a result, the incidence
of Tay-Sachs disease dropped by 80 per cent
between 1970 and 1980.
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Tay-Sachs Disease
