Tay-Sachs disease is a strange medical condition which, although strange to the majority of the population, appear to be ethnic groups in which it has a high prevalence.
It is a genetic disease that affects the nervous system, causing the accumulation of lipids present in the nerve cells and eventually damaging it.
We are finding out what causes this disease, what are its main symptoms, how it is treated and how it can be diagnosed, as well as in which populations people with Tay-Sachs disease are more likely to be found.
What is Tay-Sachs disease?
Tay-Sachs disease, also known as GM2 gangliosidosis and lysosomal storage disease, is a life-threatening medical, neurodegenerative, and genetic disease that typically affects children at an early age. Its form of transmission is from parents to children, that is, it is hereditary, specifically of the autosomal recessive type. In fact, we have seen that certain populations, such as Ashkenazi Jews and the Amish community, are prone to cases of this disease.
It is a rare disease, which occurs when the body cannot break down fat, causing it to build up to toxic levels in the nervous system of the affected person, causing progressive degeneration of that system. The child loses muscle control, suffers from visual loss and paralysis until he finally dies.
Tay-Sachs disease is caused by a defective gene on chromosome 15 and is inherited autosomal and recessively. If both parents have a defective copy of the gene, there is a 25% chance that their child will have the disease.
To manifest it, he must have inherited both copies of the defective gene, One from the father and one from the mother. If you only inherited one defective chromosome, you will not develop the disease, but you will be a carrier.
This gene under non-pathological conditions encodes the alpha subunit of the enzyme hexosaminidase A or Hex-A, a protein that helps break down gangliosides, especially GM2. These gangliosides are a group of lipids found in nervous tissue.
Hex-A is normally found in the lysosomes of nerve cells, Organelles that break down large molecules for recycling. Without the enzyme, gangliosides build up in neurons and gradually damage them.
It should be noted that although people who have both copies of the defective gene will be the ones who will manifest Tay-Sachs disease, without being able to synthesize hexosaminidase A, carriers may have altered levels of this enzyme. Yes, they do produce it and therefore do not suffer from the symptoms, but they only synthesize half the normal amount of Hex-A.
Anyone can carry the defective gene that causes Tay-Sachs disease. However, we have seen that there are some populations that have more cases of this disease because the defective gene is more prevalent in their ethnic groups.
One case of this is the Ashkenazi Jewish population, in which one in 27 members carries the gene that causes this disease. Among the populations where the defective gene is most widespread, we have:
- Jewish communities in Central and Eastern Europe, especially Ashkenazi.
- Franco-Canadian communities in Quebec.
- The Amish of the Old Order of Pennsylvania.
- Louisiana Cajun community.
There are three types of Tay-Sachs disease: infantile, juvenile and adult. These forms vary in their appearance and symptomatology, however, it must be said that juvenile and adult are extremely rare.
The most common form is the infantile form, which results in very early mortality. The disease already causes damage when the fetus is still in the womb, and symptoms are usually visible when the baby is 3 to 6 months old. In most cases, the child dies around the age of 4 or 5.
Among the symptoms that can be found in this disease we have:
- Loss of muscle tone
- Loss of motor skills: the baby does not roll over, crawl or sit.
- slow growth
- Delay in intellectual and social development
- Dementia (loss of brain function)
- Increased startle reflex: you jump when you hear loud noises.
- Cherry red spots on the eyes
Cases of this disease have been documented in adults, but it is very rare and has a very late start. It is not detectable until the age of 20 or 30 and, in general, its symptoms are less severe than in children, although it can lead to a high degree of disability in the patient.
To confirm that this is a Tay-Sachs case, the first thing to do is find out if there is a history of the disease in both parents, In addition to whether they are from one of the four most common ethnic groups of the defective gene.
On top of that, they do tests of the level of enzymes in the child’s blood and body tissues, To check the hexosaminidase levels. An eye exam will also be done to see if cherry red spots appear on the macula.
There is currently no effective treatment to cure Tay-Sachs disease. Unfortunately, if a baby is diagnosed with this disease, he is expected to live no more than 5 years. however, investigated the use of ganglioside synthesis inhibitors and hex-A enzyme replacement therapies as potential treatments for this rare disease.
It has also been the subject of research on gene therapy. One of them would be, by genetic engineering, to include in the DNA of the child with the defective gene a gene which resolves the abnormal synthesis of the enzyme Hex-A. It is still a very experimental and very controversial technology, in addition to being quite expensive.
The surest way to ensure that Tay-Sachs disease will not be affected is if two people who carry the defective gene do not have children in common. Genetic tests can detect whether you are a carrier or not, In addition to whether there were any cases of children who died in the family at an early age.
In the event that both members of the couple have the defective gene, they should know that they have a 25% chance of having a child with the disease.
If the mother is already pregnant, the amniotic fluid can be analyzed to determine whether or not the baby will have the disease. If you have inherited two defective copies of the gene, it is confirmed that you may have the disease and it is the parents’ decision to terminate the pregnancy.
In fertilization therapies, it is possible to make a preimplantation genetic diagnosis to make sure the baby does not get sick. It involves fertilizing the eggs extracted from the mother and, once they have very primitive embryos, selecting those that do not have a copy of the defective gene.
This same method has been used for other diseases of genetic origin, such as cystic fibrosis, sickle cell anemia and Huntington’s disease, but it must be said that it is a very expensive method in which it is necessary, a technology very invasive medical.
- Kwon JM. (2016) Neurodegenerative Disorders of Childhood. A: Kliegman RM, Stanton BF, St. Geme JW, Schor NF, eds. Nelson Handbook of Pediatrics. 20th ed. Philadelphia, PA: Elsevier; Chapter 599.
- Nussbaum RL, McInnes RR, Willard HF (2016). The molecular, biochemical and cellular basis of genetic diseases. In: Nussbaum RL, McInnes RR, Willard HF, eds. Thompson and Thompson Genetics in Medicine. 8th ed. Philadelphia, PA: Elsevier: Chapter 12.
- Wapner RJ, Dugoff L (2019). Prenatal diagnosis of congenital disorders. A: Resnik R, Lockwood CJ, Moore TR, Greene MF, Copel JA, Silver RM, eds. Maternal-Fetal Medicine by Creasy and Resnik: Principles and Practice. 8th ed. Philadelphia, PA: Elsevier; chapter 32.