Description
Tay-Sachs disease (TSD) is a rare fatal genetic disorder of the central nervous system. Infants with the disorder appear to develop normally for the first few months of life, then at about the age of six months of age, a deterioration of mental and physical abilities begins. The child stops smiling, crawling or turning over, loses their ability to grasp or reach out, and gradually becomes blind and paralysed. It affects both male and female babies.
TSD is most common amongst descendants of Central and Eastern European (Ashkenazi) Jews and some French Canadians. TSD is caused by inheriting a ‘double-dose’ of a fault in a gene which codes for the Hex-A enzyme. Every person has two copies of this gene in each cell of their body. A person will only be affected by TSD if they have a fault (mutation) in both copies of the Hex-A gene. This can only happen if one faulty copy is inherited from each parent. About one in every 26 Ashkenazi Jews and 1 in every 40 French Canadians carries one copy of the faulty gene and one regular copy of the gene. In the general population, however, only about one in 300 people carry a faulty copy of the Hex-A gene. Carriers are not themselves affected by the disease.
If both parents carry a copy of the faulty gene then there is a 1-in-4 (25%) chance that the child will inherit the faulty Hex-A gene from both parents. This child will be affected by Tay-Sachs disease. The chance remains the same for each pregnancy.
A simple blood test can distinguish Tay-Sachs carriers from non-carriers and genetic counselling is available for those in high-risk groups such as those mentioned above.
TSD is one of a group of genetic diseases known as storage diseases which are caused by the abnormal accumulation of certain waste products in the cells or tissues of the affected person.
Types
- Infantile Tay-Sachs: The most common and severe form. Infants appear healthy at birth, but symptoms usually begin between 3 to 6 months of age.
- Juvenile Tay-Sachs: Symptoms typically emerge between ages 2 and 10. It leads to issues with coordination, muscle control, and swallowing, followed by cognitive and speech decline.
- Late-Onset/Adult Onset Tay-Sachs: The rarest and mildest form, which appears in the late teen years or adulthood. Adult onset progresses more slowly than other forms. and is characterised by unsteadiness of gait and progressive neurological deterioration.
Symptoms
The symptoms of TSD in a young baby include:
- movement problems – loss of ability to smile, reach out, hold onto objects, crawl, turn over or sit up
- vision and hearing impairment
- exaggerated reactions to loud noises
- seizures.
Treatment
There is currently no cure or effective treatment for TSD, patients receive supportive care to manage symptoms and improve quality of life. This may include nutritional support and mediccation to treat seizures.
Outlook
The disease tends to progress rapidly, and life expectancy for children with TSD is around five years of age.
Further Information and Support
Rare Find Foundation – Australia
www.rarefindfoundation.org
Childhood Dementia Inititiaive – Australia
www.childhooddementia.org
National Tay-Sachs & Allied Diseases Assocation – USA
www.ntsad.org
National Institute of Neurological Disorders and Stroke – USA
www.ninds.nih.gov/Disorders/All-Disorders/Tay-Sachs-Disease-Information-Page
National Institute of Health – USA
www.nlm.nih.gov/medlineplus/ency/article/001417.htm
Reviewed by Dr Carolyn Ellaway, Clinical Geneticist, The Children’s Hospital at Westmead, Australia
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