Sandhoff disease is an inherited, lysosomal storage disorder caused by the absence or deficiency of two enzymes; hexosaminidase A and hexosaminidase B. These enzymes are located in lysosomes, which are structures in cells that normally break down certain substances and act as recycling centers. Without these critical enzymes, a fatty substance, called GM2 ganglioside, and other molecules accumulate at harmful levels and cause progressive destruction of the nerve cells. Symptoms of the condition vary based on the form of presentation.
The most common and severe form of Sandhoff disease appears in infancy. Infants with this disorder typically appear normal until the age of 3 to 6 months, when their development slows and muscles used for movement weaken. Affected infants lose motor skills such as turning over, sitting, and crawling. They also develop an exaggerated startle reaction to loud noises. As the disease progresses, children with Sandhoff disease experience seizures, vision and hearing loss, intellectual disability, and paralysis. An eye abnormality called a cherry-red spot is characteristic of this disorder. Some affected children also have enlarged organs (organomegaly) or bone abnormalities.
A milder, more rare form of Sandhoff disease occurs when a person has mutations that only cause a partial enzyme deficiency. Signs and symptoms vary widely and can begin in childhood or adolescence. Affected individuals may experience muscle weakness, difficulty coordinating movement, speech problems, recurrent respiratory infections, and seizures.
The late-onset form can be difficult to diagnose. Early signs can include clumsiness and muscle weakness in the legs. Over time, people with late-onset Sandhoff disease may require mobility assistance and experience speech and swallowing difficulties. About 40% of affected adults experience mental illness, such as bipolar disorder or psychotic episodes.
One large U.S. population study estimated that the carrier frequency for Sandhoff disease is approximately 1 in 300 in non-Jewish individuals and less common (1 in 500) in those of Jewish descent. Clusters of cases have been reported in certain regions, such as locales of Canada, Argentina, Lebanon, and Central America, suggesting that the carrier frequency may be higher in some specific isolated populations.
There is no specific treatment or cure for Sandhoff disease. Treatment includes supportive care for symptoms, such as medications to control seizures and nutritional and respiratory support.
Children with the severe infantile-onset form will typically experience recurrent seizures by age 2 and will eventually lose muscle function, mental function, and sight, becoming mostly non-responsive to their environment. Death usually occurs by age 3 and is generally caused by respiratory infections. Children with juvenile-onset Sandhoff disease will show similar health problems but at an older age and will also progressively decline. Though challenging and debilitating, the late-onset form does not always shorten life span.
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