Introduction

Tay-Sachs disease is a rare, autosomal recessive-inherited (a person has the condition if they inherit a copy of the faulty gene from both parents), neurodegenerative disorder caused by a genetic mutation. It is characterised by the progressive destruction of the nervous system in the brain and spinal cord leading to severe disability and premature death. 

Because of this devastating impact of the disease on affected individuals and their families, there is an urgent need for effective prevention and treatment strategies. 

By identifying the carriers and offering a prenatal diagnosis, genetic testing has the potential to significantly reduce the incidence of Tay-Sachs disease. However, there are complexities of genetic testing which include accuracy, ethical implications, and accessibility. 

In this review, we try to explore the available genetic tests and their effectiveness in predicting disease and advanced therapeutic approaches.

Understanding tay-sachs disease

Tay-Sachs disease is classified as an autosomal-recessive lysosomal storage metabolic disorder, caused by β-hexosaminidase A (HexA) enzyme deficiency due to mutations, resulting in the accumulation of GM2 ganglioside in the lysosomes of the nerve cells.¹ 

These gene mutations cause the devastating neurodegenerative disorder, characterised by the progressive destruction of nerve cells in the brain and spinal cord. The infantile form of Tay-Sachs disease is the most severe, rapidly affecting the nervous system. This accumulation of harmful substances leads to severe physical and mental deterioration, ultimately resulting in premature death. The incidence rate of Tay-Sachs disease is 1/100,000 live births.²

Clinical symptoms

Tay-Sachs disease is inherited in an autosomal recessive pattern, meaning that both parents must carry a copy of the defective gene for a child to be affected. The infantile form of Tay-Sachs disease is characterised by very low HexA activity levels, rapidly manifesting with mental and motor developmental delay.³ 

The neurodegenerative symptoms in infants are the inability to sit or hold their head unsupported, ocular movement abnormalities, hypotension, dysphagia, muscle spasms, and hypomyelination. The symptoms of Tay-Sachs disease may occur a few months after birth and most patients with infantile disease do not survive past 4 years of age.^4,5,6 

Pathophysiology

The accumulation of GM2 ganglioside within the nerve cells disrupts normal cell function and leads to progressive cell death. As the disease progresses, affected individuals experience a decline in motor skills, vision, hearing, and cognitive abilities. Seizures, blindness, and paralysis are common symptoms in the later stages of the disease.

Types of genetic tests

Carrier screening

Tay-Sachs disease is inherited in an autosomal recessive pattern, meaning parents can carry a copy of the defective gene for a child to be affected. While carriers themselves are typically unaffected, they can pass the gene on to their offspring. If both parents are carriers, there is a 25% chance of having a child with Tay-Sachs disease.⁷ 

The carrier screening involves testing individuals to determine if they carry one copy of the defective HexA gene. It originated as measuring Hex A activity because below-normal levels indicate carrier status. Individuals of Ashkenazi Jewish ancestry have the highest risk, because of the 1 in 31 carrier frequency. It is beneficial for couples from any background with a family history of Tay-Sachs disease or related disorders.⁸  

Prenatal diagnosis

Prenatal diagnosis offers the possibility of determining if an unborn child is affected, and involves testing foetal cells for the presence of the defective HexA gene. In the event of unknown mutational status, enzyme analysis must be performed in conjunction with DNA-based assays to enhance diagnostic accuracy.

These tests can be performed in both direct specimens as well as cultured cells from chorionic villi sampling or amniocentesis.

• Chorionic villus sampling (CVS): This procedure can be performed as early as 10 to 12 weeks of pregnancy. A small sample of placental tissue is taken for genetic analysis
• Amniocentesis: Typically performed between 15 and 18 weeks of pregnancy, amniocentesis involves collecting a sample of amniotic fluid, which contains foetal cells⁹

Newborn screening

Babies born with Tay-Sachs disease develop the symptoms in the first 3 to 6 months of life, then within months to a few years, the ability to see, hear, and move is severely affected. Children with this condition usually do not live past 5 years of age. Early identification of Tay-Sachs disease through newborn screening allows for immediate initiation of supportive care and counselling. As far as we know, there is no cure for Tay-Sachs disease, but early diagnosis can help families with the challenges ahead. Public health initiative of newborn screening is aimed at identifying certain metabolic, hormonal, or genetic disorders in newborns before symptoms appear. While not universally implemented for Tay-Sachs disease, its inclusion in newborn screening panels can offer significant benefits.¹⁰

Advances in genetic testing technology

Ongoing advancements in genetic testing technology hold promise for improving the accuracy, efficiency, and accessibility of Tay-Sachs disease testing.

• Non-invasive prenatal testing (NIPT): While primarily used for detecting chromosomal abnormalities, NIPT is continually evolving and may eventually include testing for Tay-Sachs disease
• Whole exome and genome sequencing: These comprehensive genetic analyses can identify rare or novel mutations associated with Tay-Sachs disease, expanding our understanding of the disease's genetic basis
• Preimplantation Genetic Diagnosis (PGD): This advanced technique involves screening embryos created through in vitro fertilisation (IVF) for genetic abnormalities, including Tay-Sachs disease. Couples at risk can select unaffected embryos for implantation

Challenges and limitations in screening for Tay-Sachs disease

• False positives: Newborn screening tests may produce false positive results (the test is positive, but the child doesn’t have the condition), leading to unnecessary anxiety and further testing
• Limited treatment options: Currently, there is no curative treatment, which may limit the immediate impact of early diagnosis¹¹
• Costs: Expansion of newborn screening panels for rare conditions like Tay-Sachs disease can increase costs

What needs to be carefully done in the process of predicting the disease?

• Ensuring equitable access to genetic testing for all populations is crucial
• Privacy and confidentiality: Protecting genetic information is essential to prevent discrimination and misuse
• Reproductive decision-making: Providing comprehensive genetic counselling to support individuals and couples in making informed reproductive choices is vital¹¹

What are the options for parents if there is a positive prenatal diagnosis?

Couples may encounter challenging decisions, as the main objective of prenatal diagnosis is to prevent the birth of affected children. By offering couples the knowledge and options to make informed decisions, genetic testing can significantly reduce the incidence of Tay-Sachs disease. The options for the parents include:

• Termination of pregnancy: This is a personal and sensitive choice made by couples while consultation with healthcare providers
• Continuing the pregnancy: Parents can prepare for the challenges of caring for a child with Tay-Sachs disease by seeking support from medical professionals, genetic counsellors, and relevant organisations¹²

Genetic counselling

Genetic counselling plays a vital role in supporting individuals and couples undergoing genetic testing for Tay-Sachs disease. Genetic counsellors provide information about Tay-Sachs disease, inheritance patterns, and testing options. They offer guidance in making informed decisions, as well as explore the ethical, legal, and social issues related to genetic testing.¹³

Development of new treatments and therapies

While genetic testing primarily focuses on prevention, research into treatments for Tay-Sachs disease is ongoing. Promising areas of investigation include:

Gene therapy

Gene therapy involves correcting the mutated HexA gene by cell engineering; attempts began in the mid-1990s. This involves developing approaches for GM2 gangliosidoses gene therapy using adeno-associated virus-based vectors. The aim is to deliver a functional copy of the HexA gene to affected cells, potentially halting or reversing the disease progression. Early clinical trials show promising results.^11,14

Enzyme replacement therapy

Enzyme replacement therapy is an option for the treatment of lysosomal storage diseases. Many somatic symptoms are decreased, but it is less effective in preventing neurodegeneration since IV administration doesn’t allow the enzyme molecule to cross the blood-brain barrier.¹⁵

Substrate reduction therapy

Substrate reduction therapy utilises small molecules to slow the glycolipid biosynthesis.¹⁶

Bone marrow transplantation

Application of bone marrow transplantation following substrate reduction therapy led to an increase in HexA activity in leukocytes and plasma 23 months after transplantation. The main problem is that it does not prevent the development of neurological dysfunction.¹¹

Conclusion

Predicting a disease plays a crucial role in preventing genetic disorders, and significant progress is being made toward developing promising solutions for rare genetic conditions. Genetic testing tools remain essential for the effective management and prevention of Tay-Sachs disease. Continued research and advancements offer hope for better diagnostic methods, enhanced treatments, and, ultimately, a potential cure for this devastating condition.

FAQs

Can you live with tay-sachs disease?

This condition is fatal, usually, the infant dies around 3 to 5 years of age.

Is there a cure for tay-sachs disease?

Currently, there is no complete cure for this condition, but research shows promising results.

Is tay-sachs 100 per cent fatal?

Late onset of this condition does not directly affect the life expectancy of adults.