Spongy cerebellar degeneration with cerebellar ataxia (SDCA1) in Belgian shepherds

Spongy cerebellar degeneration with cerebellar ataxia  (SDCA1) is a neurodegenerative disease that affects dogs of Belgian shepherd breed. The disease is caused by point mutation c.986T>C in KCNJ10 gene. This gene encodes potassium channels (K+ channels) that are present in central nervous system, eyes, internal ear and kidneys. Function of K+ channel in cerebellar cortex altered due to this mutation results in extracellular accumulation of potassium, reduction of membrane potential and subsequent occurrence of neurological attacks. The mutation was found in the Belgian Shepherds Malinois and Tervueren. In other varieties of Belgian Shepherd, this mutation has not been found so far. However detection of such mutation in future is not excluded.  The estimated frequency of mutant allele in the Malinois population is 2.9%. The occurrence of this mutation in breeds that were cross-bred with Belgian shepherds in the past, for example in some lineages of Dutch shepherds, cannot be excluded.

The first signs appear before the age of two months. It is reported that the signs can be usually observed between 4.5 and 8.5 weeks of age. The affected dogs show a characteristic gait with hind limbs held wide apart to maintain the stability and improve the coordination of leg movement. There can be observed further signs such as stumbling, tremor, loss of stability, jumping about, staggering and falling. In some dogs, muscular spasm may occur triggered by stress situations or exercise activities. The prognosis usually leads to euthanizing of the affected dog.

SDCA1 is a recessively inherited disease. The disease develops in dogs which inherit the mutated gene from each parent.  These dogs are designated as P/P (positive/positive). The carriers of the mutated gene are designated as N/P (negative/positive). The carriers inherited the mutated gene from one parent only and are without clinical signs. However, they pass the disease on to their offspring.  When mating two heterozygotes (N/P), there will be theoretically 25% of the offspring healthy, 50% of the offspring will be carriers and 25% of the offspring will inherit the mutated gene from both parents and will be affected by SDCA1.  Mating one healthy dog (N/N) with a carrier of this mutation (N/P) will theoretically produce 50% carriers and 50% healthy offspring.  If a carrier (N/P) is mated with an affected dog (P/P), there will be theoretically 50% affected dogs and 50% carriers.

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References:

Kleiter, M., Högler, S., Kneissl, S., Url, A., & Leschnik, M. (2011). Spongy degeneration with cerebellar ataxia in Malinois puppies: a hereditary autosomal recessive disorder?. Journal of veterinary internal medicine, 25(3), 490-496.

Mauri, Nico, et al. "A Missense Variant in KCNJ10 in Belgian Shepherd Dogs Affected by Spongy Degeneration with Cerebellar Ataxia (SDCA1)." G3: Genes| Genomes| Genetics (2016): g3-116.

Van Poucke, M., Stee, K., Bhatti, S. F., Vanhaesebrouck, A., Bosseler, L., Peelman, L. J., & Van Ham, L. (2017). The novel homozygous KCNJ10 c. 986T> C (p.(Leu329Pro)) variant is pathogenic for the SeSAME/EAST homologue in Malinois dogs. European Journal of Human Genetics, 25(2), 222-226.

Stee, K., Van Poucke, M., Pumarola, M., Geerinckx, L., Van Soens, I., Bhatti, S.F.M., Peelman, L., Cornelis, I.: Spinocerebellar ataxia in the Bouvier des Ardennes breed is caused by a KCNJ10 missense variant. J Vet Intern Med:, 2022. Pubmed reference: 36426918