This is a chapter taken from the book. I am including it on this website because I so often see the term "lethal white" being used inappropriately in reference to Double Merle.
Please feel free to share this page anytime you see the phrase being used incorrectly!!
I would like to address the use of the term "Lethal White" in regards to a dog expressing pigment deleted to white from Merle combinations mentioned on page 88. I often see confusion in the use of this term when referring to canines.
Lethal White is a condition found in equines, it refers to a white pattern called "Frame Overo" caused by the "Ile118Lys - EDNRB" mutation. Inherited as a single mutation it causes pigment loss, producing white markings on certain areas of the horse. When inherited as Homozygous - 2 copies of the mutation - it is linked to a fatal condition known as Lethal White Overo or (LWO). The foal is almost pure white in appearance and will suffer intestinal abnormalities caused by undeveloped nerves of the digestive system. These foals usually die within 2 - 3 days and are typically euthanized.
Using the term "Lethal White" in relation to dogs is an incorrect usage of the term.
There are 4 known canine traits that are embryonic lethal when inherited as homozygous -
Merle is not one of them.
"Panda White Spotting" - P - KIT mutation; present in the German Shepherd breed. This mutation is rather recent and traced back to a female born in 2000. In the homozygous state, the Panda mutation is an early embryonic lethal.
"Natural Bobtail" - NBT - C189G mutation; present in many breeds. In the homozygous state, the NBT mutation is an early embryonic lethal. https://academic.oup.com/jhered/article/100/2/236/851021
"Harlequin" - H - PSMB7 mutation; present in the Great Dane breed. In the homozygous state, the H mutation is an early embryonic lethal.
"Hairless" - HR - FOXI3 mutation; present in Chinese Crested, Mexican Hairless Dog and Peruvian Hairless Dog breeds. In the homozygous state, the HR mutation is an early embryonic lethal. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5182420/