Tay-Sachs disease (TSD) is a rare inherited disorder that progressively destroys the brain and nervous system. The body progressively loses basic functions, leading to deafness, blindness, and paralysis. Individuals with TSD usually do not live beyond five years of age. Infection is a common cause of death in TSD patients.
TSD is caused by mutations in the HEXA gene. This gene contains instructions for making the hexosaminidase A enzyme, which plays an important role in maintaining the central nervous system. The central nervous system, which controls many of the bodily functions, is eventually destroyed by TSD. Because it affects the nervous system, TSD is classified as a neurological disease.
TSD is named after British ophthalmologist Warren Tay and American physician Bernard Sachs, who independently described the symptoms of what would later be known as infantile TSD. In 1881, Tay described eye defects, which are characteristic of TSD, in an infant with a progressive neurological disease. In 1887, Sachs presented his observations of a disease that was prevalent among German immigrants of Jewish heritage.
TSD is a recessive genetic condition, which means that the mutation must be inherited from both parents for the disease to occur. People who have inherited the mutation from only one parent do not have TSD, but are called "carriers" because they may pass the disease on to their children. Historically, certain populations (such as French Canadians and those of Ashkenazi Jewish descent) had a higher proportion of carriers and thus a higher incidence of TSD.
TSD was among the first genetic diseases for which genetic screening was available. The accuracy of the TSD screening test, combined with professional counseling, has significantly lowered the incidence of TSD among formerly high-risk populations. Presently, the rates of TSD in the Ashkenazi Jewish and French Canadian populations are similar to those of the general population.
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types of the disease
Tay-Sachs disease (TSD) is classified into various forms based on when the symptoms first appear.
Infantile TSD (or early-onset TSD): The vast majority of TSD occurs early in life. Though nerve damage may begin before birth, the symptoms generally develop when the infant is three to six months old. The symptoms progress very quickly in infantile TSD, and patients rarely survive beyond five years of age.
Children with early-onset TSD may make very little eye contact with others. Other eye problems are common, including twitchy eyes and difficulty focusing on objects.
As symptoms progress, they may include limp and floppy muscles, decreased alertness, decreased playfulness, difficulty sitting up, poor motor skills, decreased hearing, gradual loss of vision, and an abnormally large head (macrocephaly). During the last stage of the disease, the child typically becomes blind, deaf, mentally impaired, paralyzed, and unresponsive. The patient may have difficulty swallowing or breathing and may have seizures.
Juvenile onset TSD: The symptoms of TSD sometimes develop during childhood. These patients typically die between the ages of 10 and 15.
Symptoms of juvenile-onset TSD are generally similar to early-onset TSD. However, symptoms of juvenile-onset TSD do not develop until the patient is between three and 10 years of age.
Late-onset TSD (LOTS) or adult-onset TSD: In extremely rare cases, TSD may not develop until the patient is an adolescent or adult. Although the nerve damage continues throughout life, the damage may progress relatively slowly and symptoms may be mild. Those with late-onset TSD may have normal life expectancies.
Symptoms of late-onset TSD may develop when the patient is an adolescent or in his/her mid 30s and may be milder than other forms of TSD.