The third chapter of a two hour program. (running time 08:57) Tay Sachs disease results from a single base pair change causing the malfunction of a critical protein that breaks down fat in the brain. As fat builds up, and crushes critical cells in a child's brain, they lose motor skills, the ability to talk, swallow, and see. This chapter explores two couples with children with this devestating disease and poses the question of whether or not people should be tested as carriers for such diseases before having children.