Figure 2. The macular cherry-red spot on the eye is an indicator of Tay-Sachs disease, an autosomal recessive disease that affects the nervous system.

polypeptide chain of amino acids base pairs two nucleotides (either DNA or RNA) linked by weak bonds endoplasmic reticulum network of membranes within the cell

Golgi network system in the cell for modifying, sorting, and delivering proteins the neuron swelling observed by Sachs and the cherry-red spot described by Tay. The cherry-red spot is due to the white appearance of swollen neurons of the retina surrounding the normally red fovea centralis (central depression in retina and site of maximum vision acuity) in the back of the eye (Figure 2).

Newborns with Tay-Sachs disease appear normal at birth. By six months of age, parents begin to notice that their infant is becoming less alert and is less responsive to stimuli. The affected infant soon begins to regress and shows increasing weakness, poor head control, and inability to crawl or sit. The disease continues to progress rapidly through the first years of life, with seizures and increasing paralysis. The child eventually progresses to a completely unresponsive vegetative state. Death is often caused by pneumonia because of the child's weakened state. Some forms of Tay-Sachs disease are much milder with onset of the disease later in childhood or even adulthood. We now know that these forms of the disease are caused by less severe mutations in the HEXA gene.

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