SDCA2 is a highly variable disease in terms of disease onset, disease severity, and brain lesions identified. Symptoms appear in puppies around 4 to 6 weeks of age. The main symptoms are a broad, atactic gait, which is mainly noticeable in the rear extremities, loss of balance and poor coordination of movements (stumbling, tumbling, falling, trembling). A swaying, wide-legged gait can be observed in the affected puppies. In this way, the dogs try to gain stability and to improve their coordination. The prognosis worsens and usually ends with euthanasia of the affected puppy.

The disease is caused by a mutation in the ATP1B2 gene (expressed predominantly in the brain, particularly in the cerebellum). This genetic defect disrupts the functioning of potassium channels in the central nervous system and is associated with neurological disorders such as cerebellar dysfunction (disorders of movement) and epilepsy.

The cerebellum is important for balance and coordination. Together with the cerebrum, it coordinates the muscles and thus the movements. It also makes a significant contribution to maintaining muscle tension in the body. While the cerebrum is primarily responsible for conscious movements, the cerebellum controls movement sequences that have already been learned. The mutation affects a different gene than SDCA 1, but also results in potassium channel dysfunction like type 1. SDCA2, like SDCA1, is also an autosomal recessive disease. The birth of affected puppies can be safely ruled out if care is taken when mating that at least one of the two breeding animals is free of the genetic defect.

Die Mutation betrifft ein anderes Gen als SDCA 1, führt aber ebenso zu einer Störung der Kaliumkanäle wie Typ 1. SDCA2 ist, wie SDCA1, ebenso eine autosomal rezessiv vererbte Krankheit. Die Geburt von betroffenen Welpen kann sicher ausgeschlossen werden, wenn bei Verpaarungen darauf geachtet wird, dass mindestens eines der beiden Zuchttiere frei von dem Gendefekt ist.

Genetic scheme of the animals involved in the study and their relationships

Filled symbols represent animals with cerebellar dysfunction. Numbers indicate dogs from which samples were available. Six dogs affected by SDCA1 (KCNJ10:c.986T>C) are outlined in red. Four affected siblings from family 6 who did not carry the previously identified KCNJ10 variant are indicated by blue outlines. 251 other Malinois, 25 Groenendael, two Laekenois, 35 Tervueren and 503 dogs of genetically different other breeds were genotyped in the study. The variant for SDCA2 was not found outside the Belgian Shepherd Dog population, but was also present in a heterozygous state in 38 Malinois, one Groenendael and seven Tervueren dogs. Statistics from our database.

The data is updated regularly:

Case study "I-litter THE FLYING EAGLES"

After a 'normal' birth with 12 puppies, of which one was born dead, the remaining puppies initially developed evenly. At two weeks, two of them had extreme abdominal pain and flatulence and needed urgent veterinary treatment. At the age of four weeks, two puppies from the litter showed unusual behavior: because they bumped into walls and objects, they seemed blind, but the symptoms subsided the next day. Just two days later, four puppies again showed abnormalities - one more pronounced, the other three less pronounced. The severely affected puppy again ran in circles and against walls and objects.

The following day, the symptoms worsened and the disorientation was accompanied by loud and tormented wailing. It was not possible for the puppy to find peace and he kept running into walls and all sorts of objects. The movement sequences were also completely disturbed. The other three puppies show a similar, but much less pronounced, conspicuous behavior. All four puppies were taken to the veterinary clinic and initially admitted with suspected poisoning. The most affected pup had to be euthanized two days later after becoming progressively weaker and exhibiting persistent epileptic seizures. The body was handed over to pathology. However, the condition of the three other affected and treated puppies improved, which initially strengthened the assumption of poisoning. However, ophthalmological examinations confirmed that all three were blind. Nevertheless, it was expected that after recovering, they would also be able to see normally again. Due to the suspected poisoning, the puppies had to be weaned immediately and switched to puppy food.

At the age of 4.5 weeks the other three puppies could be brought back home. All ten remaining puppies developed severe diarrhea due to the abrupt change in feeding, which worsened despite the administration of medication. The first autopsy report of the euthanized puppy initially reaffirmed the suspicion of poisoning. At 5 weeks, two of the three puppies previously treated clinically deteriorated again: they refused to eat and their movements became more and more disturbed. As a result, both had to be euthanized. Their bodies were handed out to the University of Bern for research purposes.
In the sixth week, the last remaining of the previously affected puppies developed epileptic seizures and showed increasingly atactic movement patterns. That night, after screaming loudly, he lay on his side, a pool of blood in front of his nose. He died on the way to the clinic. Apart from the severe diarrhea when the food was changed, the other 7 puppies developed normally and appeared perfectly healthy. The research department of the University of Bern phoned the breeder two days before the puppy was handed over: Poisoning was ruled out and the cause of her suffering was determined to be a form of Belgian ataxia, which was known, but for which no "material" for research had been available up to that point. Thanks to the help and the submission of blood samples from all siblings in the litter, as well as the parents and many relatives, research on this form of ataxia could be restarted. Sometime later the genetic test for SDCA2 was developed and made available.

Neuropathology Report:


Link zum Video
With the help of the breeder Christa Wermelinger, this form of ataxia could be researched and the genetic test for SDCA-2 developed. Thank you, Christa, for your commitment!!!




Reference:

Nico Mauri, Miriam Kleiter, Elisabeth Dietschi, Michael Leschnik, Sandra Högler, Michaela Wiedmer, Joëlle Dietrich, Diana Henke, Frank Steffen, Simone Schuller, Corinne Gurtner, Nadine Stokar-Regenscheit, Donal O’Toole, Thomas Bilzer, Christiane Herden, Anna Oevermann, Vidhya Jagannathan and Tosso Leeb: A SINE Insertion in ATP1B2 in Belgian Shepherd Dogs Affected by Spongy Degeneration with Cerebellar Ataxia (SDCA2); G3: GENES, GENOMES, GENETICS Early online June 15, 2017; https://doi.org/10.1534/g3.117.043018