What Is Tay-Sachs Disease?

Introduction

Tay-Sachs disease is a genetic disorder that affects the brain's nerve cells. Individuals who have this disorder lacks a type of protein that is needed to break down fatty substances in the brain. Without this protein, fatty substances accumulate in the brain to toxic levels, which affect the normal functioning of the nerve cells. Children with Tay-Sachs eventually lose muscle control as the disease progresses. It also leads to paralysis, blindness, and death. 

This disorder is usually diagnosed early in the baby's life, which is around 3 to 6 months, but may also show later before the child reaches 10. A rarer type of Tay-Sachs may also occur in adults called as "adult onset". However, the condition may be quite difficult to diagnose. 

Causes

The main cause of Tay-Sachs disease is a defect in the HEXA gene. Normally, humans have two Tay-Sachs genes called HEXA. Tay-Sachs disease occurs when a child does not have two working HEXA genes due to gene mutations. A child becomes a carrier of the disorder if he or she has one working HEXA gene and one defective gene.

Carriers usually do not have symptoms of the disorder. However, when two carriers have children, each of their children is at risk of having a 25 percent chance of developing the disease. A child will become a carrier if only one of his or her parents passes a defective gene. The child will then have the potential to pass the disorder to his or her offspring.

Symptoms

Tay-Sachs symptoms usually show 3 to 6 months after birth. A child with the disorder tends to have muscle weakness, myoclonic twitches (sudden muscle contractions), increased startle response, and hypotonia (low muscle tone). When the child reaches 6 to 10 months, he or she may be unable to sit.

During an eye exam, there would be a decrease in the child’s eye movement and attentiveness. A characteristic cherry-red spot in the eye is also seen during the exam. Lesser response and lesser movements are expected when the child reaches 8 to 10 months. Upon reaching their first birthday, they will experience loss of vision and bouts of seizures. The size of their head usually becomes larger as they reach 24 months. They would also have difficulty swallowing and eventually become unresponsive leading to a vegetative state. Death occurs when they reach 2 to 4 years old, and is often caused by pneumonia.

Other forms of Tay-Sachs disease are:

• Juvenile - Individuals with this form of Tay-Sachs begin with ataxia (trouble walking) and poor coordination. Its symptoms are the same with the classic Tay-Sachs disease, but the characteristic cherry-red spot in the eye is uncommon. Children usually reach their teenage years, but often die sooner because of infections.

• Adult-onset - Its symptoms include muscle wasting and weakness, speech difficulty, cognitive impairment, and dementia. Life expectancy usually varies.

• Chronic - This form of Tay-Sachs develops before the child reaches 10 years old. It usually affects verbal and cognitive abilities later in life.

Risk Factors

Tay-Sachs is more common in people who have an Ashkenazi Jewish descent. According to statistics, one in 30 Ashkenazi Jews are carriers of the defective HEXA gene. Old Order Amish groups in Pennsylvania, French Canadians, and Cajuns are also known to have carriers of the defective gene.

In some studies, people of Irish descent have a one in 50 chance of becoming a carrier of the defective Tay-Sachs gene. 

Diagnosis

• Blood Test - A blood test is usually carried out to determine the level of hexosaminidase-A. Patients with Tay-Sachs often do not have this protein, while others only have a reduced level of HEXA in their blood.

• Eye Exam - An eye examination is conducted to check the presence of the characteristic cherry-red spot in the eye, specifically the macula, which is a part of the retina.

• Genetic Testing - It is used to screen family members and relatives of children with the disorder to find out if they are carriers.

Prenatal tests include amniotic fluid analysis, chorionic villus sampling (CVS), and genetic embryo profiling before implantation. These tests can be quite complicated, so genetic testing and counseling are highly recommended when planning for pregnancy.  

Treatment

Currently, there is no cure for Tay-Sachs disease. However, the symptoms can be managed through supportive treatments, which include:

• Medications - Symptoms can be reduced by using prescription medications, which include anticonvulsants or anti-seizure agents.

• Physical Therapy - Tay-Sachs is a progressive disease. Thus, children with the disorder may need physical therapy to maintain the flexibility of their joints and enhance their movement. Physical therapy can effectively delay the loss of muscle function and joint stiffness.  

• Respiratory Support - Most children with Tay-Sachs disease are prone to having lung infections. They may frequently experience breathing problems and mucus buildup in the lungs. A chest physiotherapy may help to get rid of accumulated mucus in their lungs. Feeding tubes may also be utilized since children often have a difficulty swallowing. 

• Speech-language Pathologist: Speech therapists can help provide ways to help children keep their suck-swallow reflex and at the same time help figure out the right time to use feeding tubes.

• Play and Stimulation: Music, play, and stimulations such as music and textures can help children interact with the world. 

• Neurology Care: Neurologists are able to help children and their parents when it comes to managing bouts of seizures. Anti-seizure medications are usually given along with instructions on what to do when children are having seizures. 

There are still other treatment options being developed by scientists for this medical condition. The use of gene therapy and enzyme replacement therapy are said to eventually help in treating the progression of the disease. 

Prevention

People can undergo a blood test to see if they are carriers of the defective HEXA gene. If a couple is planning for a pregnancy, but discovers that they are both carriers, a genetic counselor can guide them through different options to effectively reduce the risk of having children with Tay-Sachs disease.