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Tay-Sachs Disease

Cell Bio Presentation by Chelsea Weidman, Jenelle Noble, Emily Guilmette, Joshua Hagan, and Alex Soto

Alex Soto

on 23 October 2012

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Transcript of Tay-Sachs Disease

by: Chelsea Weidman, Jenelle Noble, Emily Guilmette, Joshua Hagan, and Alex Soto Tay-Sachs Disease Introduction Causes Symptoms Who Gets It? What is Tay-Sachs disease? Treatments There is currently no known cure for Tay-Sachs Disease. Diagnosis The diagnosis of Tay-Sachs relies on the demonstration of absent to near-absent HEXA enzyme activity in the serum or white blood cells of a symptomatic individual in the presence of normal or elevated activity of the hexosaminidase B (HEXB). Description General symptoms include :
¬ hearing loss
¬ blindness
¬ intellectual/mental disorders
¬ dementia
¬ paralysis
¬ ataxia (loss of muscle control)
¬ inability to swallow
¬ seizures
¬ exaggerated startled reflex to loud noises Tay-Sachs disease is especially prevalent among people of Ashkenazi (eastern and central European) Jewish heritage as well as in French-Canadians, Amish in Pennsylvania, and the Cajun population of Louisiana. Sources "Tay-Sachs Disease." A Diagnosis and Treatment. N.p., n.d. Web. 18 Oct. 2012. <http://www.mayoclinic.org/tay-sachs-disease/>.
"Tay-Sachs Disease Prevention." Tay-Sachs Disease Prevention. N.p., n.d. Web. 18 Oct. 2012. <http://www.news-medical.net/health/Tay-Sachs-Disease-Prevention.aspx>.
"Health Guide." Tay-Sachs Disease. N.p., n.d. Web. 18 Oct. 2012. <http://health.nytimes.com/health/guides/disease/tay-sachs-disease/overview.html>.
"Tay-Sachs Disease." - Genetics Home Reference. N.p., n.d. Web. 17 Oct. 2012. <http://ghr.nlm.nih.gov/condition/tay-sachs-disease>.
Kaback, Michael M. "Summary." Hexosaminidase A Deficiency. U.S. National Library of Medicine, 03 Nov. 1999. Web. 18 Oct. 2012. <http://www.ncbi.nlm.nih.gov/books/NBK1218/>.
"NINDS Tay-Sachs Disease Information Page." Tay-Sachs Disease Information Page: National Institute of Neurological Disorders and Stroke (NINDS). N.p., n.d. Web. 18 Oct. 2012. <http://www.ninds.nih.gov/disorders/taysachs/taysachs.htm>.
"Learning About Tay-Sachs Disease." Learning About Tay-Sachs Disease. National Human Genome Research Institute, 17 Mar. 2011. Web. 16 Oct. 2012. <http://www.genome.gov/10001220>.
"HEXA." - Hexosaminidase A (alpha Polypeptide). U.S. National Library of Medicine, Sept. 2008. Web. 16 Oct. 2012. <http://ghr.nlm.nih.gov/gene/HEXA>.
"HEXA." HEXA. N.p., n.d. Web. 20 Oct. 2012. <http://www.bio.davidson.edu/courses/molbio/molstudents/spring2003/holmberg/hexa.html>.
There are, however, treatments whose foci are patient comfort, early diagnosis, prevention as well as family support and counseling Post-diagnosis measures include :
¬ Medication - to help reduce symptoms such
as seizures.
¬ Physical therapy - which aid in delaying the
loss of function in muscles
and joints.
¬ Familial support - for individuals facing a
debilitating disease such
as Tay- Sachs, receiving
support from close family
members (whether it be
emotional, physical, etc.)
may ease the individual's
emotional pain, and
reduce physical
discomfort. Pre-diagnosis measures include :
¬ Prenatal diagnosis - should one of the parents be a known
carrier of the allele for the disease,
prenatal diagnosis may help prepare the
parents in dealing with a diagnosed child.
This however, comes with a caveat as
some believe that prenatal diagnosis
could potentially lead to an increase in
abortions of diagnosed fetuses.
¬ Mate screening - The organization Dor Yeshorim also
known as The committee for The
Prevention of Jewish Genetic Diseases
offers genetic screening amongst the
Jewish community.Testing is
anonymous and only the patient
knows his or hers identification
number which is the only
thing that can link them
to their diagnosis. The mutation that causes the disease is found in 1 in 27 individuals with backgrounds previously listed, 1 in 50 among Irish-Americans, and 1 in 250 of the general population. In order for someone to inherit the disease, both parents need to be carriers of the recessive gene.
Even so, there is only a 25% chance that the child will get the disease.
There is a 50% chance that the child will be a carrier for the gene and a 25% chance that the child will not have any trace of the mutated gene. Although individuals who carry a recessive gene for Tay-Sachs only have half of the normal hexosaminidase enzyme function, they typically do not display any signs or symptoms and are not adversely effected. Tay–Sachs, a hereditary disease, is attributed to a lack of hexosaminidase-A (Hex-A) enzyme activity, which breaks down ganglioside GM2 found in nerve tissue.
Without Hex-A, a dangerous build up of ganglioside GM2 in the brain occurs which the nerve cells are unable to break down. Purpose? The purpose of the this presentation is to fully elaborate on Tay-Sachs disease, and its prevalence among the Jewish community, following the outlined points : Description
Who it effects & why? Treatments
Conclusion/Questions Who were Tay and Sachs? The disease is named for Warren Tay, and ophthalmologist who first described the cherry-red spot on the retina which is the specific phenotype for the disease; and Bernard Sachs, a neurologist who first described the changes in the brain and the prevalence among Ashkenazi Jews. Molecular genetic testing of HEXA, the only gene in which mutations cause HEXA deficiency, is clinically available. This is used primarily to:
a) distinguish pseudodeficiency alleles from disease-causing mutations in healthy
individuals with apparent deficiency of HEXA enzymatic activity.
b) identify the specific disease-causing mutations in an affected individual to allow
for genetic counseling of at-risk family members. If Tay-Sachs disease is suspected, the doctor will perform a physical examination and take a family history. Additional tests may include:
¬ Enzyme analysis of blood or body tissue for
HEXA levels
¬ Eye examination (reveals a cherry-red spot in the
macula) Infants with Tay-Sachs disease appear to develop normally for the first few months. Then, as nerve cells become distended with fatty material, a relentless deterioration of mental and physical abilities occurs. Infantile (6 months) symptoms include :
¬ developmental issues
¬ slowing of muscle movement/motor skills
¬ death by age 4-5 years MOST COMMON Tay-Sachs disease is a fatal genetic lipid storage disorder in which harmful quantities of a fatty substance called ganglioside GM2 build up in tissues and nerve cells in the brain. Signs and symptoms that appear in childhood, adolescence, or adulthood are usually milder than those seen with the infantile form as well as have more variable neurologic findings. Physical characteristics in juveniles, adolescents, and adults include :
¬ muscle weakness
¬ ataxia
¬ problems with moment
¬ speech difficulties Neurological characteristics include :
¬ progressive dystonia
¬ spinocerebellar degeneration
¬ motor neuron disease
¬ bipolar form of psychosis (sometimes
in individuals with adult-onset
Tay-Sachs) Tay-Sachs is caused by mutations in the HEXA gene. This gene provides instructions for making Alpha subunit of the HEXA enzyme.
¬ 1 Alpha subunit + 1 Beta subunit (from HEXB) = 1 functioning enzyme. This functioning enzyme plays a large role in the brain and spinal cord as it aids break down of ganglioside GM2.
The HEXA gene is located on the long arm (q) of chromosome 15. With the mutation, the activity of the HEXA enzyme is disrupted, which prevents the enzyme from breaking down ganglioside GM2. This leads to toxic levels of ganglioside GM2 accumulating, particularly in the neurons in the brain and spinal cord and results in the destruction of those neurons which produces the individual's symptoms. More than 120 mutations in the HEXA gene have been identified as the causes of Tay-Sachs.
¬ The mutations reduce or eliminate the HEXA enzyme.
¬ Infantile Tay-Sachs is caused by the most known HEXA gene mutations and result in completely nonfunctional
HEXA enzymes.
¬ Late Onset Tay-Sachs is caused by HEXA gene mutations that reduce the activity of HEXA enzymes,
which causes the delay and lessens the severity of symptoms. Everyone has 2 copies of the HEXA gene.
¬ A carrier has 1 copy of the active gene and 1 copy of the inactive gene and is healthy because
enough HEXA enzyme is produced to prevent abnormal build up of ganglioside GM2. The prognosis for a child with classic Tay-Sachs disease is death, usually by age 4 or 5 years. Because the chronic form of Tay-Sachs was discovered near the end of the 2000s, prognosis for this type of the disease was, as of 2004, not completely known. A few variations from this classical progression of Tay-Sachs disease are possible :
¬ Juvenile - symptoms appear between ages two and five; the disease progresses more slowly,
with death by about 15 years.
¬ Chronic - symptoms may begin around age five or may not occur until between 20
and 30 years of age. The disease is milder. Speech becomes slurred. The
individual may have difficulty walking due to weakness, muscle
cramps , and decreased coordination of movements. Some
individuals develop mental illness. Many have changes in
intellect, hearing, or vision. A fatty substance or lipid that is part of normal metabolism. An oval-shaped highly pigmented yellow spot near the center of the retina of the human eye. Loss of brain function that occurs with certain diseases. It affects memory, thinking, language, judgment, and behavior. A neurological movement disorder, in which sustained muscle contractions cause twisting and repetitive movements or abnormal postures. Spinocerebellar degeneration is a form of ataxia which is defined by a patient experiencing a progressive loss of skeletal muscle control, although their mental acuity generally remains unaffected. A serious and incurable form of progressive neurodegeneration, in which over time the nerves in the spine and brain progressively lose function. Why The Prevalence? In order for HEXA to degrade ganglioside GM2, it must first create a complex with GM2 activator protein.
Once bound, the complex hydrolyzes GM2 ganglioside by removing a beta-1,4-linked N-acetylhexosamine residue from the GM2 ganglioside transforming it into GM3 ganglioside.
The alpha-subunit is very important in the degradation because the alpha-subunit is the specific region that hydrolyzes the lipid.
The beta-subunit region is not capable of this specific action. But both subunits are vital to the function of HEXA. If one subunit is malfunctioning, HEXA cannot form the hydrolyzing complex with GM2 activator protein.
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