Progeria

You might remember this one from the Bollywood blockbuster Paa. Considering it's caused by the tiniest defect in a child's genetic code, its effect is devastating. On average, any child born with this disease will be dead by the age of 13, and the entire time they're alive, they will look almost 80 years old. 

Their bodies age faster causing striking--and saddening--physical changes that include premature baldness, thinning bones and heart disease. Currently progeria is one of the rarest diseases in the world with only 48 people on the entire planet reportedly living with it. What's odd is that there is actually one family that has five children suffering from this disease.