Illustration of Tay-Sachs disease, a genetic disorder that progressively destroys brain neurons. It is caused by a mutation in the HEXA gene of chromosome 15 leading to deficiency of hexosaminidase A. Neurons become swollen with lamellar inclusions due to accumulation of gangliosides in lysosomes with subsequent neuronal degeneration. Tay-sachs is most commonly seen in infants, manifesting in muscle weakness and decreased motor function, vision and hearing loss, and intellectual disability. All patients with Tay-Sachs disease have a ''cherry-red'' spot in the eye retina, easily observable by a physician using an ophthalmoscope, in the back of their eyes.