Download Tay-Sachs Disease

Tay-Sachs Disease
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What is it?
A degenerative neurological disorder where virtual absence of
activity of a lysosomal enzyme, hexosaminidase A
Biochemistry
Characterized by deficiency of alpha subunit of hexosaminidase
A
A deficiency of this enzyme results in accumulation of Gm2
gangliosides in neurons causing a severe neurologic
degenerative disease resulting in blindness, loss of neurologic
function, and death between ages 2 and 4 years.
Who is affected?
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3% of Ashkenazi Jews are carriers of Tay-Sachs disease
Less than 0.3% of the general population are carriers of TaySachs
The frequency of matings between two carriers and thus the
risk of having a Tay-Sachs child is 1 in 1,000 in the Ashkenazi
Jewish population.
Whereas, in a non-Ashkenazi Jewish population the probability
is 1 in 360,000.
Why are Ashkenazi Jews
Carriers of Tay-Sachs Disease?
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Balanced Polymorphism:
One copy of the Tay-Sachs gene protects individuals
against tuberculosis.
TB was prevalent within the Eastern European Jewish
population, due to living conditions.
The mortality was so high that the gene pool was very
small, increasing the risk of carrying the Tay-Sachs
disease for Ashkenazi Jews.
***The Tay-Sachs gene increases the risk for breast
cancer and Gaucher’s disease.
Genetics
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The inheritance pattern of Tay-Sachs is autosomal
recessive.
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Three mutations account for 98% of Tay-Sachs
disease in Ashkenazi Jews.
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Therefore, definitive DNA diagnosis is available
Screening for Tay-Sachs
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The screening for Tay-Sachs disease is a controversial
issue.
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Screening has reduced the incidence of Tay-Sachs in the
Ashkenazi Jewish population by 95%.
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In the Ashkenazi Jewish population, you can only screen
for Tay-Sachs prior to marriage.
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Abortions are rare in the Askkenazi Jewish population.
Screening for Tay-Sachs
Disease
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There are several screening techniques available.
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One screening involves an inexpensive test to measure
the heat-labile hexosaminidase activity in the blood.
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Carrier status can be confirmed by definitive measure of
hexosaminidase activity in white blood cells.
Ethical Considerations
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The information obtained from genetic screening for
Tay-Sachs is only beneficial when the information is
presented to potential parents in a meaningful way.
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Misinformation can cause loss of self-esteem by carrier
and social stigmatization and discrimination.
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Early screenings only effective when it is used in a
reasonable fashion and information is used
appropriately by those who are screened.