Progeria

Progeria is an extremely rare disease of childhood that is characterized by extremely premature aging. It affects 1 in 4 million newborns. When a child is born it looks normal until about a year. Their growth rate slows down, and they are shorter and weigh less than other kids their age, but still have the same intelligence. Other symptoms include baldness, aged looking skin, pinched nose, small face, stiffness of joints, hip dislocation, and severe progressive heart disease. The most severe type is Hutchinson-Gilford progeria syndrome. There is no treatment or cure, but the children can get heart surgery to slow down heart complications. The average age of death is 13, and is usually caused by heart attack or stroke.

Researchers have found that Hutchinson-Gilford progeria is caused by a tiny mutation in a single gene called lamin A (LMNA). Parents and other siblings are usually never affected by the disease. They found that the mutation happens in the sperm prior to conception. In almost all cases this arises from the substation of one base pair among 25,000 DNA base pairs that make up the LMNA gene. The LMNA gene codes for lamin A and lamin C which are known to stabilize the inner membrane of the cell's nucleus. The progeria gene causes the LMNA to produce an abnormal form of the lamin A protein. This destabilizes the cell's nuclear membrane and is harmful to tissues that are usually subjected to instances physical force (cardiovascular and musculoskeletal). This is why they are so small and have heart issues. Also, the LMNA gene is also responsible for at least 6 other genetic disorders, including muscular dystrophy. 

"Progeria" by See SourceMinor edit by Mikael Häggström - The Cell Nucleus and Aging: Tantalizing Clues and Hopeful Promises. Scaffidi P, Gordon L, Misteli T. PLoS Biology Vol. 3/11/2005, e395 http://dx.doi.org/10.1371/journal.pbio.0030395. Licensed under CC BY 2.5 via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Progeria.png#/media/File:Progeria.png

Resources:
http://www.genome.gov/11007255