When Harry Eastlack was 5 years old, he broke his left leg while out playing with his sister. The fracture failed to set properly, and soon his hip and knee had stiffened up as well. Examining the boy, doctors found ominous bony growths on the muscles of his thigh. Within a few years, bony deposits had spread throughout Harry’s body, infiltrating his chest, neck, back and buttocks. Surgeons tried to cut the excess bone away, only to watch it grow back thicker and more invasive than before.
By his mid-20s, his vertebrae had fused together, his torso been thrust rigidly forward and his back muscles replaced with solid bone. Finally, even his jaw locked up, and he died of pneumonia in 1973, just shy of his 40th birthday.
Fun fact: the gene that causes this disease is ACVR1, which lies in a region of extended haplotype homozygosity and extreme population differentiation suggestive of recent positive selection in non-African populations.