Storage lysosomal disease of the English Springer Spaniel due to deficiency of the lysosomal enzyme alpha-L-fucosidase, which prevents the degradation of fucosides and causes their accumulation in neurons and other tissues. It affects mainly the central nervous system, with progressive neurodegeneration and systemic signs. The disease is lethal and is inherited in an autosomal recessive manner. It is associated with a 14-base-pair deletion in the FUCA1 gene.

Affected breed: English Springer Spaniel, especially in British and Australian conformation lines. No recent large-scale carrier figures are published; the spread of the genetic test has markedly reduced cases.

- Onset between 12 and 18 months of age
- Progressive neurological deterioration: ataxia, behavioural change, deafness, blindness
- Loss of learned behaviour and lethargy
- Difficulty swallowing in advanced stages
- Rapidly progressive course towards death or euthanasia

Canine fucosidosis was characterised biochemically as a model of the human disease in English Springer Spaniel colonies, especially in British and Australian show lines. In 1996, two independent groups cloned the cDNA of canine alpha-L-fucosidase and identified the same causal mutation: a 14-bp deletion at the 3' end of exon 1 of FUCA1, which introduces a frameshift and two premature stop codons. These findings allowed the development of a PCR test to distinguish carriers, homozygotes and clear dogs.

- Test all breeding English Springer Spaniels with the FUCA1 test
- Do not mate two carriers: 25% risk of lethal affected homozygotes
- A carrier may be mated to a clear animal; offspring intended for breeding must be tested
- Progressively replace carriers with clear offspring so as not to lose genetic diversity
- Exclude affected animals from breeding

Differential diagnosis with other canine lysosomal diseases with neurodegeneration of the young adult (GM1/GM2, leukodystrophies) and with toxic-metabolic processes. Measurement of alpha-L-fucosidase activity in leukocytes or cerebrospinal fluid and the genetic test are confirmatory. Vacuoles in lymphocytes on the blood smear may be informative.

1. Occhiodoro T, Anson DS (1996) Isolation of the canine alpha-L-fucosidase cDNA and definition of the fucosidosis mutation in English Springer Spaniels. Mamm Genome 7(4):271-274. PMID: 8661697
2. Skelly BJ et al. (1996) The molecular defect underlying canine fucosidosis. J Med Genet 33(4):284-288. PMID: 8730282
3. OMIA:000396-9615. Fucosidosis, alpha in Canis lupus familiaris. https://omia.org/OMIA000396/9615/