A central feature of MEN2B is overgrowth of nerve cells.

Underneath mucous membranes like the lips and cheeks, nerve cells overgrow into little balls called "neuromas."

Nerve balls in a lip will enlarge the lip. Thus, people with MEN2B have large lips.

When a nerve ball is half in and half out of the lip, it produces a bump on the lip. (Think of an ice cube floating in water.) People with MEN2B have bumpy lips.

The photograph below was taken in 1865 (probably February):

(There are better photographs, but this is the best one from the Library of Congress' collection.)

Photographs show that Lincoln had lumpy lips for at least 7 years. They also show lumpy lips in his sons Eddie, Willie, and Tad -- all of whom died before age 20.

The lips on Lincoln's son Robert are normal. He lived to 82.

An 1865 plaster cast of Lincoln's face shows more clearly the lumpiness of his lower lip.