Overview 

Tay-Sachs disease is a rare genetic disorder found more commonly in niche communities. It is mainly a disease affecting children, commonly characterised by the clinical manifestations of cherry red spots in the eye and lack of growth and development. However, in rare cases, it can manifest in adults as a late-on-set form, with symptoms like loss of movement and stimulatory senses. 

Introduction 

Tay-Sachs disease is a rare genetic autosomal recessive disorder also known as hexosaminidase A deficiency (HEX A)and is considered a type of GM2 gangliosidosis. Patients with Tay-Sachs disease are associated with progressive neurological impairment and pass away before the age of 5. There are three general forms: classic, juvenile and late-onset. The sooner the disease manifests, the more severe the condition is, significantly decreasing life expectancy. 

Tay-Sachs disease in adults is considered the late-onset form of the disease, in which the disease is much rarer and less aggressive compared to its other forms. The disease can manifest much later in the person's life, which can develop starting from early adolescence up to 20 to 30 years into adulthood. Since the mutation for the late-onset form is not as significant, the patient will still possess a certain degree of activity from hexosaminidase A activity, ranging from 5% to 20% of the regular activity.¹

Causes 

Tay-Sachs disease is caused by a genetic mutation which leads to a deficiency in the beta-hexosaminidase A enzyme (HEX A). This enzyme, along with beta-hexosaminidase B, plays a vital role in the degradation of the GM2 ganglioside.¹ Gangliosides are glycosphingolipids found in the membrane of neuronal cells and they are responsible for various functions within the central nervous system.² In a regular person, these gangliosides are catabolised by Hex A through hydrolysis. However, a patient with Tay-Sachs disease will have mutations in the gene encoding for the Hex A enzyme.³ This results in a conformational change, affecting its functionality and impacting the degradation of GM2. The absence of Hex A results in the accumulation of GM2 in the lysosome, which brings cytotoxic effects in the neurons, which can lead to neuronal death.⁴

Symptoms 

Tay-Sachs disease in adults leads to various clinical symptoms and the severity of the illness also affects the presentation of symptoms. Since the form of Tay-Sachs disease developed by adults would be considered as the late-onset form, these symptoms are usually not as extreme. These symptoms include:

• Loss of coordination and muscle weakness⁵
• Tremors 
• muscle spasms 
• Difficulty in breathing⁶, swallowing⁵ and speaking⁶
• Inability to move 
• Mental and psychiatric disorders¹

Children manifesting Tay-Sachs disease also present similar symptoms as adults, but also some additional clinical presentations including:

• Loss of sensory stimulation, such as vision and hearing
• Cherry red spots in the eyes⁷
• Amplified response to loud noises
• Seizures
• Absence of development and growth¹

Risk Factors

Since Tay-Sachs disease is caused by genetic changes, communities that are more populated with these alterations are more likely to pass on the genes to the offspring, which increases their likelihood of having Tay-Sachs disease. These communities include:

• Jewish communities in Eastern and Central Europe⁸
• French-Canadian communities in Quebec⁹
• Cajun community in Louisiana¹⁰
• Old Order Amish community in Pennsylvania¹¹

However, the mutation that causes Tay-Sachs disease would still occur, though rarely, in the global population. 

Diagnosis

Diagnosis usually begins with recognising the various clinical characteristics of the Tay-Sachs disease, such as looking for cherry red spots in the eyes. They are usually followed by a blood test to test for the activity of the Hex A enzyme. The MUGS assay can also be used to determine the Hex A activity as well but is often not used as a first line of testing.¹²

During pregnancy, mothers can do different tests to check whether the baby could develop any genetic conditions.¹³ Amniocentesis, where a small sample of amniotic fluid is taken, is one of the options for testing, furthermore, chorionic villus sampling, in which a small tissue sample is taken from the placenta is another type of genetic test. There are other genetic tests available to help rule out any potential genetic conditions as well. 

Treatments and Preventions

There is currently no definitive cure for Tay-Sachs disease. Since adults with Tay-Sachs disease usually have the less severe form, treatments are available to help manage and alleviate the symptoms and to assist with their daily lives. An example would be taking medications to help with mental health and muscle spasms, using devices that can help them with mobility, such as a wheelchair, to make navigation and travelling more convenient when by themselves and also speech therapy to improve their communication. 

There are also a few different therapies being looked into nowadays to target Tay-Sachs disease, including:

• Gene therapy - One of the more promising potentials in combating the mutations in Tay-Sachs disease is gene therapy, which involves repairing the broken gene that results in the disorder.¹⁴
• Enzyme replacement therapy - This therapy involves the use of chaperon molecules, which play a role in stabilising the enzymes by mediating the disrupted folding of the protein structure caused by the mutation, which can increase the activity of Hex A to break down GM2.¹⁴
• Substrate reduction therapy - Substrate reduction therapy aims to decrease the levels of GM2 to compensate for the diminished activity of the Hex A enzyme.¹⁵ 

Although no prevention can take place, if parents are planning on pregnancy and are concerned with the risks of Tay-Sachs disease, they can talk to healthcare providers to learn more about genetic testing. They could also book genetic counselling appointments with healthcare professionals, which allows the parents to discuss the potential genetic risks of different genetic conditions and provide some professional insight. 

Living With Tay-Sachs Disease 

When living with someone with Tay-Sachs disease, there are a range of supportive treatments to assist with their daily lives to alleviate their symptoms and feel more comfortable. An example would be breathing techniques, as patients experience difficulty in using the muscles in the respiratory system. Along with a buildup of excess mucus, this can easily result in lung infections and breathing difficulties if not managed properly, so exercises that help keep the airway open would help. Swallowing is another major consequence of Tay-Sachs, so patients would require help with food and hydration. People around the patient would need to assist to ensure proper nutrient uptake and might need a feeding tube to help with feeding. As mentioned previously, there are also medications available to help with seizures and spasms, which could improve their lifestyle quality. If there are any uncertainties, it is vital to seek guidance from healthcare providers or care teams who have more experience in the field. 

Summary

Tay-Sachs disease is a rare genetic disorder that causes a mutation in the beta-hexosaminidase A-encoding gene, which causes a build-up in GM2 ganglioside which results in neurological damage. In adults, the clinical symptoms include muscle weakness, psychiatric disorders, and difficulties in swallowing and breathing. There is currently no cure for Tay-Sachs disease, but supportive therapies and treatments are available to help patients manage their symptoms and to prove the patient's quality of life.