Tay-Sachs disease

Tay-Sachs disease is a rare and usually fatal genetic disorder that causes progressive damage to the nervous system.

Introduction

Tay-Sachs disease is a rare and usually fatal genetic disorder that causes progressive damage to the nervous system.

In the most common form of the condition, symptoms usually begin at around six months of age, when a previously normal child's development begins to slow and they gradually lose their ability to move.

The most noticeable early symptoms include a child being excessively startled by sudden noises and red dots appearing near the middle of the eyes.

The child will then develop problems such as muscle weakness, increasing loss of vision, loss of hearing and seizures.

Most children with the condition die by the age of three to five years.

Less common forms of Tay-Sachs disease can begin later in childhood or even early adulthood. These usually progress less rapidly than the disease seen in very young children. However, only in rare cases is life expectancy not affected.

Read more about the symptoms of Tay-Sachs disease.

What causes Tay-Sachs disease?

Tay-Sachs disease is caused by two genetic mutations. This happens when the instructions found in cells become "scrambled" in some way, causing one or more processes of the body to not work properly.

In Tay-Sachs disease, a genetic mutation in the HEXA gene results in the body not producing an enzyme called Hexosaminidase-A (Hex-A). Without this enzyme, a fatty substance called GM2 ganglioside builds up in the cells of the brain and nerves, causing them to stop working normally and eventually destroying them.

Both parents have to be carriers of a HEXA mutation to be at risk of having a child with Tay-Sachs disease. If both parents are carriers, each child they have will have a 25% chance of developing the condition.

Read more about the causes of Tay-Sachs disease.

Testing for Tay-Sachs disease

Screening for Tay-Sachs disease is recommended for people in high-risk groups before planning a family. In the UK, this includes people of Ashkenazi Jewish descent and anyone with a history of the condition in their family.

Screening can take place at two points, either before or after a baby is conceived. If the condition is diagnosed in an unborn baby, the parents can decide whether to continue with the pregnancy or not.

Read more about testing for Tay-Sachs disease.

How is Tay-Sachs disease treated?

There is currently no cure for Tay-Sachs disease, so treatment involves making the child feel as comfortable as possible by treating the associated symptoms.

Research is being carried out into possible cures for Tay-Sachs disease, but this is still at an early stage.

Read more about treating Tay-Sachs disease.

Symptoms

In the most common form of Tay-Sachs disease, classic infantile Tay-Sachs disease, a baby will develop normally until they are around three to six months old.

One of the first noticeable signs of the condition is the appearance of a red dot at the back of their eyes. You may also notice that their vision seems poor or that they are excessively startled by noises and movement.

It is likely that your baby will be much slower in reaching developmental milestones, such as learning to crawl.

Additional symptoms usually develop after about eight months of age and quickly become more severe. They include:

  • increasing muscle weakness that progresses to paralysis (inability to move body parts)
  • increasing loss of vision
  • loss of hearing
  • difficulties swallowing (dysphagia)
  • muscle stiffness (spasticity)
  • lack of interest in the world around them
  • repeated fits (seizures)

Due to the increasing damage to the nervous system, children with Tay-Sachs disease become increasingly vulnerable to infection, particularly lung infections. Many children with the condition die from a complication of an infection such as pneumonia.

Most children with infantile onset Tay-Sachs disease die at around four years old because of complications from repeated infections.

Rarer forms of Tay-Sachs disease

There are two much rarer forms of Tay-Sachs disease, which are described below.

Juvenile form

In the juvenile form, the symptoms do not usually begin until a child is 2 to 10 years old.

Initially, the child will have problems with speech and motor skills, such as balance, walking and holding objects. Some children may also develop problems with vision.

As the condition progresses, the child will have repeated fits and experience an increasing loss of mental abilities such as memory, thinking and understanding. This is known as dementia. Dementia is usually associated with ageing but it can affect people of all ages, although it is rare in children.

Children with the juvenile form of Tay-Sachs disease will usually die in the second or third decades of life due to a complication of an infection.

Late-onset form

The symptoms of late-onset Tay-Sachs disease develop later in life, usually during the teenage years or even early adulthood.

Symptoms include:

  • slurred speech
  • loss of balance and co-ordination
  • uncontrollable shaking of the hands (tremor)
  • muscle cramps and twitching
  • muscle weakness

Around one in three people with late-onset Tay-Sachs disease will also develop psychosis. Psychosis is a mental health condition where a person is unable to tell the difference between the real world and their imagination. They may see or hear things that aren't there (hallucinations) or believe things that aren't true (delusions).

Unlike other forms of the condition, late-onset Tay-Sachs disease doesn't always shorten life expectancy.

Causes

Tay-Sachs disease is caused by a genetic mutation in the HEXA gene.

This mutation affects the production of an enzyme called Hexosaminidase-A (Hex-A). Enzymes are proteins that the body uses for chemical reactions.

The Hex-A enzyme plays a vital role in helping to remove a fatty substance called ganglioside from nerve cells. Without the Hex-A enzyme, ganglioside will build up inside these cells and they gradually stop functioning.

In most cases of Tay-Sachs disease, this enzyme is completely absent. However, in the rarer forms of the condition that develop later in life, the enzyme is present but its function is severely limited. This means it takes longer for ganglioside to damage the nerve cells.

The build-up of ganglioside in the nerve cells can have a catastrophic effect on many bodily functions, including vision and hearing, speech, physical movement and mental functions.

How the mutation is inherited

All the genes in your body come in pairs. You receive one half of the pair from your mother and the other half from your father.

Mutations in the HEXA gene that causes Tay-Sachs disease do so in an autosomal recessive manner. This means that a child with the condition received two copies of the mutated gene: one from their mother and one from their father.

If you only receive one copy of the mutated gene from one of your parents, you will not develop Tay-Sachs disease. However, you will be a carrier of the mutated gene.

If you are a carrier of a HEXA mutation and you have a baby with a partner who is also a carrier of a HEXA mutation, there is:

  • a 25% chance that the baby will receive a pair of normal genes and will not develop the condition
  • a 25% chance that the baby will receive a pair of mutated genes and will develop Tay-Sachs disease
  • a 50% chance that the baby will receive one normal gene and one mutated gene, and will become a carrier of a HEXA mutation but will not develop the condition

It's estimated that around 1 in 250 people are carriers of the HEXA mutation.

Diagnosis

Tests can be carried out to check if you are a carrier of Tay-Sachs disease or to diagnose the condition after birth.

Preconception screening

Screening for the HEXA mutation that causes Tay-Sachs disease is recommended if you are planning to start a family and you are in a high-risk group for developing the disease.

In the UK, two main groups of people are thought to have a high risk of developing the condition:

  • people of Ashkenazi Jewish descent – this applies to most people of Jewish descent in the UK
  • people with a known history of Tay-Sachs disease in their family

Screening involves checking yourself and your partner for the HEXA mutation using a blood test. If you both test positive, you have a 25% chance of conceiving a baby who develops Tay-Sachs disease.

Antenatal screening

It is also possible to test a foetus for Tay-Sachs disease during pregnancy (antenatal screening) using tests such as:

  • chorionic villus sampling (between weeks 10 and 13 of pregnancy) – where a sample of cells is taken from the placenta to be tested
  • amniocentesis (between weeks 15 and 20 of pregnancy) – where a needle is used to remove amniotic fluid for testing

If a diagnosis of Tay-Sachs disease is confirmed, you can choose to terminate or continue the pregnancy.

Tests after birth

A diagnosis of Tay-Sachs disease would be strongly suspected if a young baby develops symptoms that are closely associated with the condition, such as an exaggerated response to sudden noises and red spots at the back of the eyes.

Blood tests can also be carried out to check if the body is producing the Hexosaminidase-A (Hex-A) enzyme (see causes of Tay-Sachs disease for more information).

If there is any doubt about the diagnosis, it can usually be confirmed by taking a blood sample and extracting DNA from it to check for the HEXA mutation.

Receiving the diagnosis

Being told that your baby has a fatal and incurable condition is a devastating experience, and it's likely you will experience profound feelings of grief, bereavement and even guilt.

The UK-based charity Genetic Alliance UK also provides information and services for people who have been affected by genetic conditions such as Tay-Sachs disease, as do organisations such as Climb.

You may also find it useful to read more about caring for a child with a terminal illness.

Treatment

There is currently no cure for Tay-Sachs disease, so the aim of treatment is to make living with the condition as comfortable as possible.

Treatment usually focuses on:

  • preventing problems with the lungs and airways
  • relieving any feeding or swallowing problems (dysphagia)
  • using medication to help control or relieve symptoms such as fits and muscle stiffness

Your child's care plan

Due to the rarity of Tay-Sachs disease, it's likely that you will be referred to a specialist centre that has experience of treating children with complex health needs.

Children with Tay-Sachs disease can have complex needs. They will therefore need to be treated by a team of different specialists working together. These types of teams are called multidisciplinary teams (MDTs).

After the initial diagnosis, you and your child will probably need to spend some time at the specialist centre so that a detailed treatment plan can be drawn up.

Once your child's symptoms stabilise, your MDT may be able to speak to your doctor or your local clinical commissioning group (CCG) so that any necessary treatment can be given where you live. This will mean that hopefully you and your child will only have to visit the centre occasionally.

Problems with the lungs and airways

Children with Tay-Sachs disease are more vulnerable to developing problems with their lungs and airways. This is because:

  • food or liquid can fall into the lungs and trigger an infection – this type of infection is called aspiration pneumonia
  • increasing muscle weakness can result in poor cough reflexes and a build-up of mucus in their lungs (congestion)

Children with Tay-Sachs disease are prone to drooling and the excessive production of saliva can further disrupt breathing.

These difficulties are described in more detail below.

Aspiration pneumonia

Aspiration pneumonia can be very difficult to prevent in children with Tay-Sachs disease, even if the care they receive from their parents and health professionals is of the highest standards.

Antibiotics are the most common form of treatment for aspiration pneumonia. Depending on the severity of the symptoms, the child may be given antibiotic tablets or injections. In particularly severe cases where airways become inflamed and swollen, a tube may be required to help keep the airways open.

Congestion

Congestion of the lungs with mucus can usually be treated with a type of therapy known as physical therapy of the chest, or chest PT for short.

Chest PT involves several techniques, such as using your hands to pat your child's chest to help encourage their cough reflex. Only attempt chest PT if you have been properly trained by a qualified healthcare professional. Performing the technique incorrectly could damage your child's lungs.

Drooling and saliva

Two medications used to reduce the production of saliva and control the symptoms of drooling are:

  • hyoscine skin patches – originally designed to treat motion sickness, these patches have the useful side effect of causing dryness of the mouth
  • trihexyphenidyl or glycopyrrolate – these medications are available in oral form and cause dryness of the mouth

Feeding and swallowing difficulties

Feeding young babies with initial symptoms of Tay-Sachs disease can be difficult because they often lack a suck reflex. This means they have problems latching on to a nipple or the teat of a bottle.

There are a number of things you can do to help, such as helping your baby close their lips around the nipple or teat, or stroking their cheek towards their lips to encourage their suck reflex.

For more information and advice about feeding, you can download a home care manual produced by the support group National Tay-Sachs and Associated Diseases (NTSAD).

As your child gets older and moves onto solid food, they may require a feeding tube. There are two main types of feeding tube:

  • a tube that is passed down the nose and into the stomach (nasogastric tube)
  • a tube that is surgically implanted directly into the stomach (percutaneous endoscopic gastrostomy, or PEG tube)

PEG tubes are often recommended for children with Tay-Sachs disease because they are designed for long-term use, but general anaesthetic is required to fit them.

See treating dysphagia for more information and advice.

Other symptoms

Medication such as gabapentin and lamotrigine can be useful in preventing seizures, but this can become more difficult as the condition progresses and higher doses may be required.

Problems with muscles, such as stiffness and cramping, can be relieved using medications designed to relax the muscles (muscle relaxants), such as diazepam.

Resuscitation

As your child gets older, it's highly likely that they will experience repeated lung infections, which will damage their lungs and prevent them from breathing. This is known as respiratory arrest.

Respiratory arrest can be treated, but often with a low chance of success. In such circumstances, you and your partner may decide that you do not wish your child to be treated and that you would prefer them to die peacefully in their sleep.

If this is the case, you will need to make what is known as a do not attempt resuscitation (DNAR) order. Once the order is made, it will be placed with your child's medical records. However, it can be withdrawn at any time should you change your mind. This is a very difficult decision and there is no right or wrong choice.

Some parents decide that even if treatment prolongs their child's life by just a few days or months, it is still precious time they get to spend with their child.

Other parents feel that attempting to resuscitate their child will just prolong the inevitable and that treatment should be withdrawn. Discuss the issue carefully with your partner, family and loved ones.

Content supplied by NHS Choices