Updated: Apr 13
Confused about which term to use, albino or leucistic? Join the flock.
This post becomes very technical, very quickly. Want a simplified summary?
Here it is:
You have likely been using the term leucistic incorrectly. See the goose above? Yes, I realize it is not completely white, but it is still exhibiting albinism. In fact, it is exhibiting ocular albinism type 3 or 4, or OCA3/4. Leucistic has become an umbrella term to cover cases of pale organisms that the spotter cannot properly label. Most of us are not geneticists, so we use a single word to simplify our descriptions.
What does all this mean? Nothing. Absolutely nothing. But you clicked on this crap, so that is on you...
However, if your curiosity is still piqued, you can read more about the differences between albinism and leucism below. I don't recommend it, and I wrote it. Just start using terms like abnormal or aberrant. Problem solved. Quit reading.
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What is albinism?
Albinism is a genetic mutation that affects or alters the processes of an animal's pigment genes. This general definition can be shared with dilution and melanism.
Albinism is quite complicated and does not simply follow the traditional definition of an all-white animal with red or pink eyes.
The various types of albinism exhibit some degree of pigment loss and some degree of ocular involvement, often ocular function issues. Some types of albinism affect an animal's ability to hear normally.
Currently, at least seven types of albinism are recognized by various official groups and researchers:
OCA1, or tyrosinase-related albinism, results from a genetic defect in an enzyme called tyrosinase. This enzyme helps the body to change the amino acid, tyrosine, into pigment. (An amino acid is a “building block” of protein.) There are two subtypes of OCA1. In OCA1A, the enzyme is inactive and no melanin is produced, leading to white hair and very light skin. In OCA1B, the enzyme is minimally active and a small amount of melanin is produced, leading to hair that may darken to blond, yellow/orange or even light brown, as well as slightly more pigment in the skin.
OCA2, or P gene albinism, results from a genetic defect in the P protein that helps the tyrosinase enzyme to function. People with OCA2 make a minimal amount of melanin pigment and can have hair color ranging from very light blond to brown.
OCA3 is rarely described and results from a genetic defect in TYRP1, a protein related to tyrosinase. People with OCA3 can have substantial pigment.
OCA4 results from a genetic defect in the SLC45A2 protein that helps the tyrosinase enzyme to function. People with OCA4 make a minimal amount of melanin pigment similar to people with OCA2.
OCA5–7 were recognized in humans in 2012 and 2013. They have reported mutations on three additional causative genes. As gene testing becomes available, and more people with these types of albinism are identified, the complete range of physical manifestations will be recognized and may overlap with other known types of OCA. Currently, these types of albinism are considered to be uncommon.
What is leucism?
Leucism by its original definition is an inherited disorder of the skin that causes the organism to be unable to create or support pigment cells.
However, over the years, the term was used to describe any unusually white organism without red/pink eyes. However, this widely used term is frequently used incorrectly for organisms that are actually albino or exhibit the physical traits of neural crest disorder.
It's okay, we feel this way too.
What is piebaldism?
Frequently, this American Robin may be referred to as partially leucistic. However, a better description would be progressive depigmentation or progressive piebaldism resulting from a mutation in certain genes. If you use leucistic to describe this bird though, the genetics police will not come and take your nocs away.
(Remind me: Why am I writing this post again? This isn't fun to write about...)
Piebaldism can be caused by mutations in the KIT and SNAI2 genes. Piebaldism may also be a feature of other conditions, such as Waardenburg syndrome; these conditions have other genetic causes and additional signs and symptoms. Mean anything to you? I did not think so.
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Does albinism and leucism vocabulary matter?
No. How you use these terms will not change your life. However, I want to inform you of the most correct terminology available. Then, I cannot be blamed if a snarky birder corrects you. That's right, Flocking Around will not be held responsible for birder snark.
Edit: Flocking Around is proposing a new, SINGLE term to describe all abnormally plumaged birds:
Yeah, those white birds are magic.