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Tay Sachs Disease

Tay-Sachs disease (TSD) is an inherited disorder that tends to affect people of central and northern European Jewish (Ashkenazi) or French-Canadian ancestry. The faulty gene targets the nervous system. Symptoms first appear at around six months of age in a previously healthy baby. Over a short period of time, the baby stops moving and smiling, becomes paralysed and eventually dies. Most children with TSD die before their fifth birthday. There is no cure.

Causes

Tay-Sachs disease (also known as GM2 gangliosidosis) is an autosomal recessive disorder in which the enzyme hexosaminidase A is virtually absent or deficient. This enzyme is necessary for metabolism of gangliosides, water-soluble glycolipids found primarily in central nervous system (CNS) tissues. Without hexosaminidase A, accumulating lipid pigments distend and progressively destroy and demyelinate CNS cells.

Tay-Sachs disease appears in fewer than 100 neonates born each year in the United States. However, it strikes persons of Eastern European Jewish (Ash­kenazi) ancestry about 100 times more often than the general population, occurring in about 1 in 3,600 live births in this ethnic group. About 1 in 30 Ashkenazi Jews, French Canadians, and American Cajuns are heterozygous carriers. If two such carriers have children,each of their offspring has a 25% chance of having Tay-Sachs disease.

Signs and symptoms

A neonate with classic Tay-Sachs disease appears normal at birth, although he may have an exaggerated Moro reflex. By age 3 to 6 months, he becomes apathetic and responds only to loud sounds. His neck, trunk, arm, and leg muscles grow weaker, and soon he can't sit up or lift his head. He has difficulty turning over, can't grasp objects, and has progressive vision loss.

By age 18 months, the infant is usually deaf and blind and has seizures, generalized paralysis, and spasticity. His pupils are dilated and don't react to light. Decerebrate rigidity and a vegetative state follow. The child suffers recurrent bronchopneumonia after age 2 and usually dies before age 5. A child who survives may develop ataxia and progressive motor retardation between ages 2 and 8.

The "juvenile" form of Tay-Sachs disease generally appears between ages 2 and 5 as a progressive deterioration of psychomotor skills and gait. Patients with this type can survive to adulthood.

Diagnosis

Examination of the eyes of a child with Tay-Sachs disease will reveal a characteristic cherry-red spot at the back of the eye (in an area called the retina). Tests to determine the presence and quantity of hexosaminidase A can be performed on the blood, specially treated skin cells, or white blood cells. A carrier will have about half of the normal level of hexosaminidase A present, while a patient with the disease will have none.

Treatment

Tay-Sachs disease has no known cure. Supportive treatment includes tube feedings of nutritional supplements, suctioning and postural drainage to remove pharyngeal secretions, skin care to prevent pressure ulcers in bedridden children, and mild laxatives to relieve neurogenic constipation. Anticonvulsants usually fail to prevent seizures. Because these children need constant physical care, many parents have full-time skilled
home nursing care or place them in long-term special care facilities.

Prevention

There is no known way to prevent this disorder. However, genetic testing can detect carriers of the gene for this disorder and is recommended prior to conception for couples from at risk populations. Prenatal diagnosis is possible from amniotic fluid studies.