Rare diseases — Medical conditions you may never have heard of before

LIG4 syndrome is an exceptionally rare disorder caused by a genetic mutation that prevents the body from repairing damaged DNA.

Alkaptonuria is an unusual disorder caused by a defect in protein metabolism.

Capnocytophaga infections in humans are rare, especially in historically healthy individuals, but when it occurs, the disease can be deadly.

Argyria is caused by a buildup of silver in the body, which discolors the skin.

Tularemia, or "rabbit fever," is an infectious disease that normally affects animals but can spread to humans, sometimes via tick and deer fly bites.

Situs inversus is a rare genetic condition that causes the organs in the chest and abdomen to be located on the opposite side from where they're usually found, like a mirror image.

Frosted branch angiitis is a rare condition that makes the blood vessels that supply the retina look like the frosted branches of a tree.

As fatal familial insomnia progresses, patients completely stop sleeping and enter a coma-like state that results in death within months.

Angelman syndrome is a rare disease that disrupts the normal development and function of cells, particularly in the nervous system, leading to severe developmental delays and learning disabilities.

Patients with acromegaly make too much growth hormone, which causes them to grow disproportionately large bones, organs and tissues.