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Lethal guinea pigs

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CavySpirit

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LETHAL guinea pigs
or
"Why you'd better know what you are doing if you breed."

This reference thread presents information about lethal guinea pigs. This information is also available in Russian.

A number of breeders specialize in breeding dals and roans knowing that they will get a certain percentage of lethals, which they kill.

People who breed indiscriminantly (no clue about breeds and genetics) could end up with lethal babies. Buy a guinea pig from a pet store that turns out to be pregnant and there may be a possibility of a lethal baby. At Cavy Spirit, we've received a couple of those phone calls, "my guinea pig just had babies and one is blind..."

You can discuss lethals on this thread. Relevent reference information will be pulled out and added to this thread.

A lethal guinea pig is a seriously deformed guinea pig which is caused by breeding roan or dalmation varieties to each other. Lethal guinea pigs are always white.


Originally Posted by Salana

Roan or dalmatian guinea pigs have one copy of the "roan gene", technically the roan allele, and one copy of the normal allele of this gene. (One from mom, one from dad.) Whether the pig gets spots or mixed white and colored hairs depends on other genes that aren't important. Each pig passes on half its genes to its children, so each baby has a 50% chance of getting the roan allele from Mom and 50% chance of getting the normal allele from Mom. If Dad is also a roan (or dal), each baby obviously has a 50% chance of getting a roan allele from him and a 50% chance of getting normal.

Now, some pigs can have the gene without showing it, for instance my sow Suzi has no white and black hairs mixed together, and the black patches on her head are too large and in the wrong place to be dalmatian spots. However, she gave birth to a lethal (she was pregnant when I got her--another good reason to avoid pet stores!). The enormous amount of white hair she had (due to other genes, which don't cause problems) completely obscured any signs of her having the roan gene. So any white pig, or any pig with large amounts of white could be carrying the gene.

Basically, if both parents are roan (I can't see your picture, so I can't see whether the mother is or not) then each baby has a 1 in 4 chance of getting two roan alleles and being a lethal white, and a 3 in 4 chance of being a perfectly healthy roan or non-roan (normally colored). All lethals that I know of have the following problems:
  • blindness
  • one or more missing incisors
  • complete lack of hair color
Other problems that I have known lethals to have include:
  • deafness
  • missing eyes
  • missing incisors
  • deformed molars
  • teeth that grow in and fall out randomly
These are all problems that long-lived lethals have...most of them are worse off and die shortly after birth. Nobody knows exactly why some live and some die, although there may be digestive problems involved (a related disorder in rats causes the affected rats to be missing nerves in their large intestines) and the tooth problems have to be caught and managed quickly. I have a lethal, Einstein, who had his first molar trim at 3 weeks of age and had already been syringe-fed for a week at that point. Einstein is now a year and a half old, and I know of two lethals older than him.

If you wind up with a lethal (or more than one), I hope you'll do the right thing and take care of them as long as they live. It's a commitment of time (syringe feeding, vet trips) and money (Oxbow's Critical Care food, tooth trims) that most people who get into breeding without doing research aren't prepared to make.

Here's the thread of Einstein's medical history and vet visits. Even non-GL-members can read it. http://www.guinealynx.info/forums/viewtopic.php?t=7156
In addition to the deformities that Salana mentions, lethals frequently have internal organ deformities as well, especially GI tracts. This has been confirmed by necropsies. If a lethal has these kinds of internal problems, no matter the care they receive, they may be bound to die a potentially slow and painful death. Yet, you can't know ahead of time if your lethal is one that can be saved and might make it with proper care or vet treatment.
 
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salana

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List of known lethals

I am going to make a list of all the lethals I know about from forums, known deformities, age they lived to, and cause of death if known, along with any other pertinent information and links to relevant threads if available.

Symphony (alanas)--blind, underformed eye sockets, deaf, two top incisors, had one litter with near-toxemia afterwards, alive at 3 years
Sullivan (Gainesville Guinea Pig Rescue)--blind, missing one eye, head tilt, two top incisors, alive at 3(?) years
Piggly and Wiggly (LobsterOverlord on GuineaPigCages and GL) -- sibling sisters born February 2005. Piggly - blind, half-sized eyes, top incisors only, slight tilt to head, 2/3 size of sister. Wiggly - bottom incisors only, sticking straight out, noticable head tilt.
Tobby (critterluv02 on GL)--blind, deaf, one deformed eye, teeth OK, alive at 9 months GL thread
Gen (breeder in Moscow)--deaf, normal molars, born with one top incisor, other top incisor grew in later, apparently not blind (can follow moving objects, has pupil response to light) but has white-reflecting eyes, alive at 1 year 3 months Cavy Compendium thread
Dazzoowozzie (luvpigpigs on GL, Compendium)--deaf, blind in one eye (reflects white) but other (reflects light pink) may have some sight, no incisors, molars very small, early chlamydia infection from bad pet store/distributor, alive at 2 months Compendium thread GL thread
Einstein (Salana on GL, Pigloo, GuineaPigCages)--blind, deaf, no incisors, molar problems, lost 2 molars, gradual decline in weight after 2nd molar lost, died at 2 years almost 7 months from lack of intestinal villi (causing malabsorption)
CottonBall (vince on GL)--top incisors only, no molar problems, sudden seizure and death at 3 months: GL Thread
Stevie (Kallie on GL)--blind, deaf, no front teeth, died at 1.5 years related to tooth problems
Claude (chii on GL, Pigloo)--blind, deformed eyes, died at 3.5 years from unknown causes
Patrick (Erin8607 on GL, Pigloo, GuineaPigCages)--blind, deaf(?), one normal incisor and one sideways one, deformed sinuses, died at 5 months from complications from sinus deformity Patrick
Goobber (scooter's pet on GL, CG)--blind, deaf, unknown tooth problems, died at 1 year from bordetella, had 1 litter of 3 stillborn pups
Rio (Jin on CG, GL)--blind, deaf(?), one incisor that grew in at 1 year of age and later fell out, died at 3(?), cause unknown
Paisley (littlemisspvc on GL)--blind, deaf, two top incisors, died at 9 months from pneumonia GL thread 1 GL thread 2
Pearl (angelscavies on GL, GuineaPigcages)--
Breezy (alibee on GL)--blind, deaf, digestive problems, neurological problems, died at 3 weeks GL thread
unnamed sow (Malibu on GL)--not thriving despite all teeth, died at ~7 months GL post
Malteser (DarkRain on CG)--blind, possibly deaf, no front teeth, died at 1 week
unnamed boar (Joanna on GL)--one top incisor GL thread
unnamed sow (cutr on Compendium)--blind, deaf, one upper incisor, never sick, died suddenly of unknown causes at 2 years, mother was Himalayan
Baby #2 and Baby #3 (HappyBuds fostering for ladyveg, on GL)--siblings, no front teeth, mother had barely noticeable roaning, died at 1 week and 2 weeks

Secondhand reports:
Breeder boar--unknown deformities, alive at 7 years at last report, sired many litters
3 breeder sows--unknown deformities, each had 1 litter with dal boars, total of 7 dal pups and no lethals
Unnamed boar--unknown deformities, died at 14 months from a fall GL post

Thanks to momof911kids for helping me find all this info! Members of other forums, please let me know if there are posts about lethals.
 
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salana

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How does the roan gene make lethals?

While mammal embryos are developing, they have a "tube" down their backs called the neural tube. A stripe along this tube is called the neural crest, and all neurons (nerve cells) start out in the neural crest. Pigment (color) cells are a special kind of neuron.

Normally, at certain points in their development, embryos make various proteins that act as signals to the neural crest to release the neurons, which then travel across the body and fill it with nerves and pigment cells. If the genes for any of these proteins are changed, though, the protein won't work. Different broken proteins cause different problems, but basically, some types of neurons don't leave the neural crest and spread throughout the body. In guinea pigs these include pigment cells and the nerves that make up the back of the eye, and possibly sometimes nerves in the digestive system that stimulate the muscles to keep it moving.

After doing a lot of reading, I think the protein that's broken in lethal white guinea pigs is called MITF (microphthalmia-inducing transcription factor). MITF is associated with similar disorders in hamsters and mice, causing white hair, small or missing eyes, and skeletal deformities including tooth problems. MITF is also associated with other processes in the body, like bone formation and growth, and deformed MITF can screw with that process, resulting in the teeth deformities most lethals have.

Deafness in lethals may be a result of neurons never getting to the inner ear, or it could be related to the lack of pigment. If the inner ear has no pigment cells, the nerve cells related to hearing can die off. This is seen in other animals, such as cats, where white cats can be deaf. Dalmatian dogs with white ears are much more likely to be deaf than ones with spotted or patchy ears.

A single deformed copy of the MITF gene causes roan or dalmatian markings in pigs. The protein-making process works on both copies of the gene, so the pieces of MITF floating around are half good and half bad. The good ones trigger normal neuron movement from the neural crest, but there's only half as much of it as in a pig with two good copies of the gene. So about half as many pigment cells get out in time to make it all over the body. Therefore, the white hairs of roans and dals are, like the white hairs of lethals, not attached to pigment cells. The white hairs of other pigs are attached to pigment cells that don't make any pigment for other reasons. Since the two openings in the neural tube are in the head and butt, pigment cells that got a late start or didn't get very far cluster in the head and butt, making them solid colored instead of roaned. (This also helps roans to be able to see and hear.)

A roan with solid-colored head and butt:
doomroan040222.jpg


For more info on neuron migration from the neural crest, try this site. It focuses on rats, who have a different "lethal white" gene and therefore different symptoms, but the process shown is the same. Plus, it has pictures!
 

salana

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"But she doesn't look roan!"

Sometimes lethals pop out of sows that don't have any roaning whatsoever. Or the mother may be roan, but you know who the father is and he doesn't look roan. There are basically two possibilities.

New mutation in roan gene: Your baby lethal just happened to be so unlucky that he got a deformed copy of the roan gene from one parent, and then when he should have gotten a normal copy from the other parent, somehow in the DNA copying process, there was an error and now that one doesn't work either. This is probably not that common, but mutations are known to happen.

Roaning is hidden in the parent(s): You might not have looked close enough to see that Dad has a spot on his back where five white hairs are mixed in with his 50 million black hairs. Or Mom has other genes causing white hair, and roaning has no visible effect. For example:
suziveggies031127.jpg

We know (or suspect, because it could have been a new mutation that caused Einstein to be a lethal) Suzi is a roan/dalmatian. However, most of her hair is white because of other genes, specifically the spotting gene, which is the normal gene that causes white patches on guinea pigs. Even if her pigment cells are in the roan pattern, the ones that are there don't give her hair any color, so you can't see the characteristic mixed white and colored hairs that produce the roan pattern.

Breeders warn each other against breeding the roan gene into lines of guinea pigs with the spotted gene (most pigs with white spots, e.g. tortoiseshell and white, black and white, etc.) as this apparently often produces guinea pigs who are nearly all white with patches around the eyes and possibly on the butt. So if you get a pregnant sow who's mostly white with eyepatches, be on the lookout for lethal babies!

Himalayan and all-white pigs can also easily hide that they have a deformed copy of the roan gene and could produce lethal pups, since they're all or mostly white. Some scumbag breeders even take pride in producing "white roans" for whatever reason, even though they look no different from a normal white pig.
 
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