Recessive neurodegenerative disease of the Belgian Shepherd, described mainly in the Malinois variety, combining very early-onset cerebellar ataxia and spongy degeneration of white and grey matter. Signs appear around 4 weeks of life and progress rapidly to death or euthanasia within a few weeks. Histologically, bilateral-symmetrical vacuolation of the neuropil is observed in the cerebellum, brainstem and ventral horn of the spinal cord. It is the canine homologue of human EAST syndrome.

Specific to the Belgian Shepherd, particularly the Malinois variety, although the variant has also been detected in heterozygosity in Tervueren and Groenendael. Reliable population frequency data not published; most cases are concentrated in working Malinois lines.

- Cerebellar ataxia with onset at ~4 weeks of age\n- Hypermetria and intense action tremors\n- Vacillation and frequent falls\n- Progressive loss of coordination\n- Bilateral-symmetrical signs\n- Rapid progression to death or euthanasia within a few weeks

Kleiter and colleagues (2011) first described spongy degeneration with cerebellar ataxia (SDCA) in the Malinois as a recessive disorder. The genetic heterogeneity observed in clinically overlapping cases led Mauri and colleagues (2017) to identify, by linkage mapping and whole-genome sequencing, a missense variant in KCNJ10 (c.986T>C; p.Leu329Pro) in the C-terminal cytoplasmic domain of the potassium channel Kir4.1. The variant segregated with the phenotype in four families and one isolated case, and was confirmed by Van Poucke and Stee in 2017. The existence of clinically similar cases without this variant prompted the search for a second locus, giving rise to the designation SDCA1 versus SDCA2 (ATP1B2).

- Test breeding animals before mating, especially in Malinois lines with neurological history\n- Do not cross two carriers: 25% risk of affected homozygotes\n- A carrier may be crossed with a clear animal; offspring intended for breeding must be tested\n- Exclude carriers in lines with high prevalence and replace them with clear offspring without narrowing the gene pool\n- Remember that not all cases of cerebellar ataxia in the Malinois are explained by SDCA1: also consider SDCA2 (ATP1B2)

The differential diagnosis within the Belgian Shepherd includes SDCA2 (mutation in ATP1B2, similar phenotype but with seizures and central blindness), other juvenile-onset cerebellar ataxias and toxic or infectious processes. Histopathology shows bilateral-symmetrical vacuolation of the neuropil directed at cerebellar nuclei, cervical ventral horn and brainstem. SDCA1 is a canine model of human EAST syndrome (epilepsy, ataxia, sensorineural deafness and tubulopathy).

1. Mauri N et al. 2017, una variante missense en KCNJ10 en pastores belgas afectados por degeneración esponjosa con ataxia cerebelar (SDCA1) (PMID 28007838)
2. Kleiter M et al. 2011, degeneración esponjosa con ataxia cerebelar en cachorros Malinois: descripción inicial (PMID 21488963)
3. OMIA:002089 SDCA1 (KCNJ10)