Barclay's Protomorphosis Syndrome
Barclay's Protomorphosis Syndrome (also known as the intron virus) was an artificial disease accidentally created by Dr. Beverly Crusher aboard the  in 2370. 

Attempting to cure Lieutenant Reginald Barclay of his Urodelan flu, Dr. Crusher used synthetic T-cells to activate the gene that would fight off the infection. However, an anomaly in Barclay's genetic structure caused the T-cell to mutate and activate all of Barclay's dormant genes, including his introns. The T-cells then became airborne, spreading throughout the ship like a virus and causing the crew to "de-evolve." The syndrome was cured by using amniotic fluid from Alyssa Ogawa to create a retrovirus, eliminating the effects.

Initial symptoms of the disease included abnormal behavior, irritability, hyperactivity or decreased activity, chills, fever, and paranoia. Later, the newly activated introns transformed the crewmembers into many different earlier lifeforms from their respective homeworlds. ()

Examples of transformation
 Reginald Barclay: a 'partial' spider-like creature
 : in initial stages of transformation when killed
 Livingston: a jellyfish-like creature
 Alyssa Ogawa: an ape-like creature
 Jean-Luc Picard: in early stages of transformation into an early primate, possibly a lemur or pygmy marmoset
 William T. Riker: an early hominid (australopithecine)
 Spot: an iguana
 Deanna Troi: an amphibious humanoid
 Worf: a large predator, weighing two hundred kilograms with an exoskeleton, capable of spewing acid

See also
Genetic reversion

de:Barclay'sches Protomorphosesyndrom
es:Síndrome Barclay de Protomorfosis
Medical conditions