NORD gratefully acknowledges Kathleen Renna, BS, Scientific Program Analyst, Division of Genomics and Society, National Human Genome Research Institute and Camilo Toro, MD, NIH Undiagnosed Diseases Program, National Human Genome Research Institute, National Institutes of Health, for assistance in the preparation of this report.
Tay-Sachs disease is a rare, neurodegenerative disorder in which deficiency of an enzyme (hexosaminidase A) results in excessive accumulation of certain fats (lipids) known as gangliosides in the brain and nerve cells. This abnormal accumulation of gangliosides leads to progressive dysfunction of the central nervous system. Tay-Sachs disease is categorized as a lysosomal storage disease. Lysosomes are the major digestive units in cells. Enzymes within lysosomes break down or “digest” nutrients, including certain complex carbohydrates and fats (like glycosphingolipids). When one of these lysosomal enzymes (such as hexosaminidase A) is missing or ineffective, glycosphingolipids start to build up in the lysosome. If there is too much accumulation of these materials in the lysosome, the cells in the nervous system degenerate and die, triggering an inflammatory response that amplifies damage in surrounding tissue.
The most common form of Tay-Sachs disease is the Infantile form, which can present around 6 months of age as reduced vision and an exaggerated startle response and eventually progress to a gradual loss of skills and seizures by age 2 and early death, usually by the age of 5. There is also a juvenile version of the disease beginning at about the age of 5 years of age and adult forms of Tay-Sachs disease also known as late-onset Tay Sachs disease (LOTS) beginning in the late teens and beyond. All three forms of Tay-Sachs disease are inherited in an autosomal recessive manner and the age of onset is a function of the amount, if any, of residual enzyme activity.
Infantile Tay-Sachs Disease
The infantile form of Tay-Sachs disease is characterized by complete or almost complete lack of hexosaminidase A enzyme activity. The disorder often progresses rapidly, resulting in significant cognitive and physical deterioration.
Infants may appear completely unaffected at birth. Initial symptoms, which usually develop between 3 and 6 months, can include mild muscle weakness, twitching or jerking of muscles (myoclonic jerks) and an exaggerated startle response, such as when there is a sudden or unexpected noise. The startle response may be partly due to an increased sensitivity to sound (acoustic hypersensitivity).
Between six and 10 months, affected infants may fail to gain new motor skills. They may no longer make eye contact and there may be unusual eye movements. They may be listlessness and irritable. As affected infants age, they may experience slow growth, progressive muscle weakness and diminished muscle tone (hypotonia). Affected infants may also exhibit gradual loss of vision, involuntary muscle spasms (myoclonus), slow, stiff movements (spasticity) and the loss of previously acquired skills (i.e., psychomotor regression) such as crawling or sitting up.
A characteristic symptom of Tay-Sachs disease is the development of a macular “cherry red” spot. This ophthalmological finding emerges from abnormal accumulation of pale undigested material in the macula which contrasts to the thin foveal transparent background exposing the normal rich choroidal vasculature. This characteristic finding occurs is approximately 90% of individuals with infantile Tay-Sachs disease.
As affected infants age, more serious complications may develop including seizures, difficulty swallowing, loss of vision, paralysis and progressive hearing loss. Additional cognitive deficits may include confusion, disorientation and/or deterioration of intellectual abilities. Eventually, infants may become unresponsive to their environment and surroundings. By three to five years of age, life-threatening complications begin to occur such as aspiration pneumonia leading to respiratory failure.
Juvenile (Subacute) Tay-Sachs Disease
The onset of juvenile Tay-Sachs disease can be anywhere between 2 and 10 years of age. One of the first signs is often clumsiness and incoordination. This occurs because affected children have issues controlling their body’s movements (ataxia). Children tend to experience a progressive loss of speech, life skills and intellectual abilities. Affected individuals may or may not develop a cherry-red spot in the eyes. Degeneration of the optic nerves (optic atrophy) may occur. Some children may have retinitis pigmentosa, a progressive loss and degeneration of the cells in the retina where shapes and colors are first encoded. Affected children become less responsive to their environment and surroundings. Life-threatening complications usually occur around 15 years of age.
Late-Onset Tay-Sachs Disease
The presentation and symptoms associated with late-onset Tay-Sachs disease vary greatly. Onset of the disease may vary from the late teens to any time in adulthood. This variability may occur even within affected members of the same family. For example, in a given family one person may have symptoms in their 20s, while another reaches into their 60s or 70s with relatively milder minor symptoms. The disorder progresses much slower than the infantile or juvenile forms of the disease.
Initial symptoms associated with late-onset Tay-Sachs disease may include progressive muscle weakness and wasting (neurogenic atrophy), incoordination and clumsiness from cerebellar dysfunction (ataxia) or acute psychiatric presentation. As affected individuals age, muscle twitching (fasciculation), cramps, weakness and muscle wasting progresses affecting preferentially the quadriceps and hip flexor muscles, and later, the triceps muscles. Patients need to lock their knees in hyperextension to be able to stand and support their weight. Failure to do so results in falls and eventually leads to the need for a device to assist with walking. Patients may exhibit tremors and progressive slurred speech (dysarthria). Difficulties swallowing (dysphagia) may emerge late in the disease. Some affected individuals experience acute psychiatric manifestations (mania, acute depression or psychosis) that may require emergency psychiatric care. Over time, cognitive difficulties including executive dysfunction and some memory difficulties might emerge.
Tay-Sachs disease is caused by a change (mutation) in the hexosaminidase subunit alpha (HEXA) gene. Genes provide the instructions for the basic structure of proteins, all of which that play a critical role in many functions and structure of the body. When a mutation occurs in a gene, the protein product may be faulty, inefficient or absent. Depending upon the functions of the protein, this can affect many organ systems of the body, including the brain.
The HEXA gene encodes the structure of the protein HEXA which is a subunit of the enzyme hexosaminidase A. More than 80 different mutations of the HEXA gene have been identified in individuals with the disease. Inheriting two mutated copies of the HEXA gene (homozygotes) causes deficiency of the hexosaminidase A enzyme, which is necessary to breakdown GM2-ganglioside (a glycosphingolipids) within cells of the body. Failure to breakdown GM2-ganglioside results in its abnormal accumulation in brain and nerve cells eventually resulting in the progressive deterioration of the central nervous system.
In infantile Tay-Sachs disease, there is a complete lack of hexosaminidase A. In juvenile and late-onset Tay-Sachs disease, there minimal but still some residual hexosaminidase A enzyme activity which explains why these disorders might be less severe and progress at a slower pace than infantile Tay-Sachs disease.
Tay-Sachs disease is inherited as an autosomal recessive disease. Recessive genetic disorders occur when an individual inherits two copies of an abnormal gene, one from each parent. If an individual inherits one normal copy of the gene from one parent and an abnormal (mutated) copy of the gene from the other parent, that person will be a carrier for the disease but will not develop the disease. The risk for two carrier parents to both pass the altered gene and have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive the normal genes from each parent is 25%. The risk is the same for males and females.
Tay-Sachs disease affects males and females in equal numbers. Tay-Sachs disease used to be considered a prototypical disease of Jewish people of Ashkenazi descent. Community counselling and carrier screening efforts in these communities have succeeded in reducing disease prevalence to figures roughly equivalent to those of non-Jewish populations. Increased prevalence of Tay Sachs disease is also reported in other ethnic groups including those living in the Cajun community of Louisiana and southeastern Quebec. In the general population, the carrier rate for Tay-Sacks disease is approximately 1 in 250-300 people.
The diagnosis of Tay-Sachs disease may be confirmed by a thorough clinical evaluation and specialized tests such as blood tests that measure the enzyme activity levels of hexosaminidase A. Molecular genetic testing for mutations in the HEXA gene can confirm a diagnosis of Tay-Sachs disease. With the advent of more widely available gene panels and exome and whole genome sequencing, more patients are initially diagnosed by molecular testing followed by enzymatic confirmation.
It is possible that a diagnosis of Tay-Sachs disease may be suspected before birth (prenatally) based upon specialized tests, such as amniocentesis and chorionic villus sampling (CVS). During amniocentesis, a sample of fluid that surrounds the developing fetus is removed, while CVS involves the removal of tissue samples from a portion of the placenta. These samples are studied to determine hexosaminidase A activity. Absence or greatly reduced activity suggests a diagnosis. Prenatal diagnosis is also possible through molecular genetic testing of tissue samples obtained through CVS or amniocentesis, particularly if the disease-causing mutation(s) in the HEXA gene are known in the family.
Carrier testing for Tay-Sachs disease can be accomplished from a blood sample and determines whether an individual carries one disease-causing copy of the HEXA gene. Relatives of individuals with Tay-Sachs disease can be tested to determine whether they are carriers. Couples who are planning to have a child and have any Jewish ancestry (not just Ashkenazi) are encouraged to undergo carrier screening before proceeding with a pregnancy.
For couples that find that they are carriers, there are several options available for starting a family. These options include assisted reproductive technologies (ART) such as in vitro fertilization (IVF) and adoption. Couples are encouraged to consult with a genetic counselor to discuss these options.
Genetic counseling is available to assist families in testing decisions, interpreting test results and understanding health insurance coverage. Families are strongly encouraged to seek out a genetic counselor, particularly before carrier screening, to be most informed when making genetics healthcare decisions. For assistance finding a genetic counselor, visit: https://findageneticcounselor.nsgc.org/?reload=timezone
There is no approved treatment for Tay-Sachs disease. Treatment is directed toward the individual symptom management. Treatment may require the coordinated efforts of a team of specialists. Pediatricians, neurologists, speech pathologists, specialists who assess and treat hearing problems (audiologists), eye specialists and other health care professionals may need to collaborate to develop a plan for an affected child’s treatment.
Because of the potential for feeding difficulties, infants should be monitored for nutritional status and proper hydration. Nutritional support and supplementation may be necessary. Occasionally, the insertion of a feeding tube may be required to help prevent food, liquid or other foreign material from accidently going into the lungs (aspiration).
Anticonvulsants may be used to treat seizures in some people with Tay-Sachs disease, but may not be effective in all people. The types and frequency of seizures can change over time in some individuals which will require a change in medication type or dosage.
Genetic counseling is recommended for affected individuals and their families. Psychosocial support is recommended for the entire family.
Enzyme replacement therapy (ERT) has been considered and developed for lysosomal storage disorders. In Tay-Sachs disease, enzyme replacement therapy involves replacing a missing or deficient hexosaminidate A. An inability to find a way for the deliver the replacement enzyme (a large molecule) to cross the blood-brain barrier limits this strategy.
Chaperone therapy is also being studied for the therapy of Tay-Sachs disease. This type of therapy involves very small molecules called chaperones that attach to newly synthetized hexosaminidase A enzymes. This approach seeks to protect degradation of the abnormal hexosaminidase A inside the cells before it is degraded, thus allowing the hexosaminidase A, albeit deficient, to exert its activity for a longer time-period. A chaperone called pyrimethamine has been studied as a treatment for Tay-Sachs disease. Affected individuals who took the medication showed increased activity of hexosaminidase A. However, increased activity did not lead to any noticeable improvement in symptoms and was accompanied by undesirable side effects.
Substrate reduction therapy for Tay-Sachs disease seeks to decrease the overall burden of substrate (ganglioside) that needs degradation by reducing its synthesis. In the case Tay-Sachs, substrate reduction requires some degree of penetration into the central nervous system across the blood-brain barrier as the burden of disease is in the brain and spinal cord. Such strategy is currently under clinical investigation. [ClinicalTrials.gov Identifier: NCT04221451]
Gene therapy is also being studied as another possible approach to therapy for some lysosomal storage disorders. In gene therapy, the defective gene present in a patient is replaced with a normal gene to enable the production of active enzyme and prevent the development and progression of the disease. Given the permanent transfer of the normal gene, which can produce active enzyme at all sites of disease, this form of therapy is theoretically most likely to lead to a “cure.” The Tay-Sachs Gene Therapy (TSGT) Consortium is a collaborative group of scientists seeking to translate information from animal model studies into clinical trials.
Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government website.
For information about clinical trials being conducted at the National Institutes of Health (NIH) in Bethesda, MD, contact the NIH Patient Recruitment Office:
Toll-free: (800) 411-1222
TTY: (866) 411-1010
Email: [email protected]
Some current clinical trials also are posted on the following page on the NORD website:
For information about clinical trials sponsored by private sources, contact: www.centerwatch.com
For more information about clinical trials conducted in Europe, contact: https://www.clinicaltrialsregister.eu/
Please note that some of these organizations may provide information concerning certain conditions potentially associated with this disorder.
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