hen you meet identical four-year old twins Addi and Cassi Hempel, you might notice something about the way they walk. They used to run around like other toddlers, but now they are more wobbly, more uncertain, and walk with their legs somewhat wide apart, as if aboard a boat. They can sway in any direction, losing their balance. They fall more often than they should.
They will notice you, and smile. They don't say words but they talk, a rhythmic, nonsensical babble from which a crystal-clear sound occasionally escapes: "ice cream," "paddycake," "four." Their heads have a slight bobble, and they sometimes can't angle their eyes downward, so they fall again.
1 Neurons affected by both diseases experience dramatic accumulations of autophagic vacuoles and lysosomes, and cells affected by both disorders have enlarged endosomes, a feature seen in only a small number of disorders, says Nixon.
The ...
