Let's talk about Congenital Myotonia - Written by Stephanie Trout
- Danielle Bagozzi
- Nov 12
- 9 min read
This article is meant to open a dialogue and educate Nigerian Dwarf breeders about congenital myotonia (CM) by first discussing what is CM, what testing is available for CM, and what do the testing results mean. I will share a conversation with a breeder of Nigerian Dwarf and Nubian goats on how they managed G6-Sulfatase deficiency (G6S), an undesirable genetic disease in Nubians, in their herd and how their management parallels with potential management for CM. Lastly, I will share my recent experience with CM in my own herd and final thoughts.
What is Congenital Myotonia?
Summary of Congenital Myotonia: It is a heritable neuromuscular disorder characterized by a slow relaxation of skeletal muscles following voluntary contraction. The sudden muscle stiffness often causes the animal to fall over briefly. This is a characteristic trait of the Myotonic goat, also known as Fainting Goats, a meat breed known for heavy muscling.
Physical Characteristics of the Trait (Phenotype): Affected goats become stiff and immobile, and often fall over briefly, following sudden forceful movements or when startled.
Mode of Inheritance: Autosomal recessive
Alleles: N = Normal, CM = Myotonia Congenita
Breeds appropriate for testing: Myotonic or Tennessee Fainting Goat and their crosses, Nigerian Dwarf Goat
Genetic Testing Results (Genotype) Interpretation:
N/N – Goats are NORMAL and do not have this inherited neuromuscular disorder and will never transmit the CM allele to their offspring.
N/CM - Goats will not be affected by this inherited neuromuscular disorder but CARRIER the CM allele. Offspring from NORMAL to CARRIER mating’s have a 50% chance of being a CARRIER. Mating between two CARRIERS are predicted to produce 25% NORMAL, 50% CARRIER and 25% AFFECTED offspring.
CM/CM - Goats are expected to be AFFECTED by neuromuscular disorder and will transmit the CM allele to all of their offspring.
Information Adapted from University of California, Davis, Veterinary Genetics Lab
Where to test: Currently there are two labs that offer the test through a hair sample: UC Davis VGL in California and InfogeneNZ in New Zealand (note prices on the website are not in US dollars, the price in US dollars will appear at check out).
Conversation with LeRoy Satter owner of Till-Riv Farm
Thank you for participating in the article on congenital myotonia (CM) and helping to educate Nigerian Dwarf breeders on the similarities with managing G6S in Nubians.
To start, how long have you bred Nubians and Nigerian Dwarf Goats?
Leroy: I started with Nubians in 2008 and added Nigerians in 2017.
How long had you been breeding Nubians when you learned of G6S?
Leroy: Probably 2 years.
For those that do not know what G6S is, here is a summary of genotypes and impacts adapted from University of California, Davis, Veterinary Genetics Lab https://vgl.ucdavis.edu/test/g6-s-goat
Summary: G6-Sulfatase deficiency is an inherited autosomal recessive metabolic defect that occurs in Nubian goats and related crosses. Affected goats exhibit delayed motor development, growth retardation, and early death.
Physical Characteristics of the Trait (Phenotype): Goats affected by G6-Sulfatase deficiency exhibit delayed motor development, growth retardation, and early death.
Mode of Inheritance: Autosomal recessive
Alleles: N = Normal, G = G6-Sulfatase deficiency
Breeds appropriate for testing: Nubian and breeds derived from Nubian stock
Genetic Testing Results (Genotype) Interpretation:
N/N - Goats are NORMAL and will not have G6-Sulfatase deficiency and will never transmit this G6-Sulfatase deficiency variant to their offspring.
N/G - Goats will not be affected by G6-Sulfatase deficiency but are CARRIERS.
G/G - Goats are AFFECTED G6-Sulfatase deficiency, a condition leading to delayed development and early death. If bred they will transmit the G allele to all of their offspring.
How did you learn G6S had entered your herd?
Leroy: I had always run DNA on my bucks, both to ensure accuracy of my pedigrees and so that it is on file if I collect semen from them. With Nubians G6S test was and is an option when you order DNA test through ADGA so I had always checked the box to test for it unless I personally knew that both parents were NORMAL. My experience was after I had purchased a young buck from a breeder who was known worldwide. I was excited to use him and never considered that it was possible for that breeder to sell a possible carrier without disclosure. Shortly after he arrived, I started using him, mainly on my best does and taking reservations on kids. By the time DNA and G6S results came back approximately half of my herd was pregnant to him. He tested positive for being a CARRIER (N/G). At that time, there was an option to check when ordering the DNA, as to whether you wanted the test results to be kept private or to be publicly available. When I contacted the breeder, the response I got was “Oh well, most of my good ones are”. I then had to contact everyone that had reservations on those kids to inform them that no kids sired by him would leave my farm until DNA was run on them and they would be informed of the results so they could decide if they still wanted the kid or not. I chose to wether the CARRIER bucks and keep the CARRIER does in my herd for the genetics I sought for my breeding program.
How did you manage G6S within your herd?
Leroy: Since I had done the testing, I knew who the CARRIERS were in my herd. All CARRIERS were bred to known NORMALS. The resulting kids were all tested so that I knew their status. After several generations, I was able to remove the gene from my herd but still retain the genetics that I had wanted to add to it.
When you think of G6S do you see similarities/differences in the current discussion of CM in Nigerian Dwarf Goats?
As a breeder of Nigerian Dwarf Goats, what are your thoughts on how to manage CM?
Leroy: I feel like it should be managed exactly as the G6S was handled. At one point that gene was very common in the Nubian breed as the most widely known buck, that ended up in almost all pedigrees, was a CARRIER. By testing and managing the gene, it has been pretty much eliminated. I think CM needs to be addressed, listed as an undesirable trait and tested for if the breeder wishes to do so. I think ADGA should offer the test and maintain a database, but also offer the option of maintaining the privacy of the results if requested to do so. Otherwise, many breeders may choose not to test their herds if they do not want to make it public. I definitely do not want this to become a mandatory test in any way. Continued discussion and testing will eventually decrease to almost eliminating the gene as we have seen in the number of G6S positive animals with informed breeding decisions
through testing.
Thank you for all of the information and sharing your experience. Last, question/thought: Since this gene when expressed as AFFECTED causes myotonia, non-life-threatening
condition, but an undesirable trait in dairy goat, and is known in at least one prominent line within the Nigerian Dwarf herd book, to assist with removing the stigma of the conversation, would you agree management of the gene is based upon having knowledge to ensure crosses will not produce AFFECTED animals? Essentially, designating CM as an undesirable genetic trait is about bringing awareness to breeders, creating open conversations, knowledge, and thus removing the stigma.
Leroy: Totally agree with that! If they had removed the G6S CARRIERS from the Nubian herd book, there would be no Nubians left…almost ALL Nubians in existence trace back to known CARRIERS somewhere in their pedigree. We need to control this trait through genetic testing and management.
Three Hearts Farm and the Trout Family’s personal experience with Congenital Myotonia
Like many breeders our goals are to continually improve the herd through genetics and well thought out crosses. When we decided to bring in a new buck, we started researching pedigrees, websites, and ADGA National Show results. One buck kept coming up during the searches that had been exported to Australia and we started looking for farms that had does bred to him by AI for the 2022 kidding season. We found an upcoming breeding with a dam that had the qualities we were also searching for to improve within our herd. Fast forward to 2022 and the arrival of our new buck kid and the excitement of the breeding season. We were pleased with our first crop of kids and even more pleased with our first fresheners, as was our linear appraiser. Then within months we learned that our buck’s sire had tested positive as a CARRIER for CM. To be honest we were taken back by the information. We learned there was a test in New Zealand and decided to test him along with four of our other bucks on the farm, from a total of five different farms.
I will be honest and say I held my breath when opening the results hoping he would be negative. But after opening the results and having three out of five come back as CARRIERS I sat in shock and disbelief. I had not expected the CARRIER results on the other two bucks (one was a great grandson of the CM CARRIER sire to our other buck and the other did not have the known CARRIER buck in his lines at all). In researching our unrelated CARRIER buck’s lineage to find shared lines we had to go back multiple generations to ancestors that are foundation animals in the Nigerian Dwarf breed.
Two of the CARRIER bucks were foundation bucks for our herd. I wondered how this would impact the herd, our farm, and our daughters' hard work. Then we started thinking of the offspring we had sold out of our bucks and the breeders that bred the CARRIER bucks. We made the only decision we felt was right and contacted all breeders of the bucks, an individual that had used one of our bucks for breeding, and owners of offspring from our CARRIER bucks. What I learned in my communications was that our “clients”, like us up until recently, had never heard of myotonia in Nigerian Dwarf Goats and their first question was: What does this mean for our goats? It was a question that we as a family had been discussing and researching since our results.
I want to start this part of the article off by saying everyone has to make their own decision and this only represents what we have decided to do with our breeding program:
We educated our clients and ourselves about CM. As stated in the beginning of the article, CM is a not life-threatening neuromuscular disorder and by testing breeding animals we can prevent AFFECTED animals from being produced (CARRIER to CARRIER mating resulting in CM/CM animals). Having a CARRIER is just that, a CARRIER, with no signs of Myotonia, but this is also the reason why genetic testing is so important to us because there are no outward signs. Knowledge of the status of the animal assists in breeding decisions in the same way when breeding for a higher rear udder height or more milk production. This is another tool for informed decisions that in many ways is easier than trying to breed for a higher rear udder height.
We also reminded ourselves of why we had the CARRIER genetics to begin with, because we believed in the lines and they are proven in the Nigerian Dwarf herd book through show wins, linear appraisal scores, and milk records. The line of the buck that started this discussion for us is sought after in the Nigerian Dwarf community. We plan to continue to use the lines within our herd through educated breeding decisions (NORMAL to CARRIER or NORMAL to NORMAL) and through education of our
clients and fellow breeders. This management plan ensures only CARRIERS or NORMAL animals will be produced in our herd moving forward and allows the lines to continue as part of our herds future.
I think it is important to say we hold no negative feelings towards the breeders that we purchased our boys from as the first test for CM in the US only recently became available in October 2024. Many breeders, like us, are just learning about CM, and many will learn, like we did, that they have unknowingly bred CM CARRIER animals in their herd. Part of educating is to have awareness that CM exists, and this is another question to ask when
researching for new lines and talking to breeders: Do you test for myotonia and/or have you ever produced an offspring with myotonia?
Final Thoughts
Congenital Myotonia is in the Nigerian Dwarf breed and is an undesirable genetic disorder for a dairy goat. This is likely a gene defect that entered the breed during its foundation and is present in the current genetic pool including animals with outstanding dairy performance. Like G6S this is an easily managed genetic disorder that can be managed through genetic testing and in no way should impact which animals are eligible for registration in the
ADGA herd book. This article is meant to bring the topic public and remove the stigma of CM through education. We are all stewards of the Nigerian Dwarf breed and as stewards we should share information and continually try to improve the breed. To quote a familiar saying, “Knowledge is Power”. If you have read to this point, thank you for taking the time to educate yourself about Congenital Myotonia. I encourage everyone to continue engaging in an open and transparent dialogue about CM in the Nigerian Dwarf breed.
Feel free to click the file below and download it at your convenience for your records.