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Thursday, July 10, 2014

Tay Sachs Disease

Tay Sachs disease is a type of degenerating neurological disease caused by a deficiency of the enzyme protein hexosaminidase A. Because the enzyme is deficient, a lipid molecule called GM2 ganglioside builds up inside the lysosomes of cells. It's for this reason that doctors categorize it as a type of lysosomal storage disease.

The disease occurs when parents that are BOTH carriers of the genetic mutation have a baby. The most common carriers are Ashkenazi Jews, French Canadians and Louisiana Cajuns (1 in every 27), though carrier frequencies are also high in Irish Americans (1 in 50) and the general population (1 in 250). 

The disease typically occurs acutely in infancy, but there are three documented presentations: acute, subacute and late onset. 

The classic presentation, the acute (infantile) form, involves progressive motor weakness with loss of milestones and myoclonic jerking beginning at 3 months of age. 98% of patients develop seizures, and death typically occurs within the first few years of life. The severity is due a complete absence of the hexosaminidase A enzyme.

The subacute (juvenile) form will present as late as 9 years old, and is characterized by seizures, choreiform movements, speech problems and incontinence.  These children will typically develop dementia and won't live past the teenage years. 

Late onset Tay Sachs (LOTS, adult) cases have been reported in older patients, and usually involve subtle disturbances in speech, mood and psychological state. 

Pediatricians should suspect Tay Sachs Disease in any Jewish patient or patient of Jewish descent with delayed milestones and myoclonic jerks before the age of 1. Close inspection of the eye will typically reveal a cherry-red colored spot on the macula of the retina, which is only present in a few childhood diseases (Krabbe, Canavan, Alexander, and Gaucher diseases). A blood test will officially confirm the diagnosis. 

The differential diagnosis of neurologic progression in pediatric patients involves neurodegenerative disorders (spinal muscular atrophy/SMA, amyotrophic lateral sclerosis/ALS, Friedreich ataxia/FA and leukodystrophy)

Management of the disease involves maintaining nutrition, respiratory function and motor function while minimizing infectious diseases and seizures. Later forms benefit from both speech and physical therapies. All patients and their families should be referred to a certified genetic counselor for counseling. 

The prognosis for Tay Sachs disease is very poor. One retrospective study followed 97 infants diagnosed with Tay Sachs disease and noted that death occurs before the age of 5 in nearly all patients. Milestones such as head control, transferring objects from hand to hand and sitting without suport were acheived by the babies in over half the cases, but all lost their abilities by 1 year of age. The median lifespan of the infants was only 47 months.

Tay Sachs Disease. Dynamed Database. Updated May 12 2014. Accessed July 10, 2014.