Lysosomes serve as waste disposal and recycling centers. Enzymes inside them break large molecules into smaller subunits that the cell can use as building material or eliminate. In some people, a genetic mutation causes a deficiency or malfunction in one of the lysosomal enzymes. As a result, molecules that would normally get broken down accumulate instead. The result can be deadly. For example, cells continually make, use, and break down gangliosides, a kind of lipid. This lipid turnover is especially brisk during early development. In Tay-Sachs disease, the enzyme responsible for ganglioside breakdown misfolds and is destroyed. Most commonly, affected infants seem normal for the first few months. Symptoms begin to appear as gangliosides accumulate to higher and higher levels inside their nerve cells. Within three to six months the child becomes irritable, listless, and may have seizures. Blindness, deafness, and paralysis follow. Affected children usually die by age five (Figure 4.19). The mutation can be detected in prospective parents by genetic screening, and in a fetus by prenatal diagnosis. Researchers continue to explore options for treatment. Potential therapies involve blocking ganglioside synthesis, using gene therapy to deliver a normal version of the missing enzyme to the brain, or infusing normal blood cells from umbilical cords. All treatments are still considered experimental, and Tay–Sachs is still incurable.