Multi-disease and coat panel aimed at the Portuguese Water Dog that groups four tests for hereditary conditions described in the breed: two forms of progressive retinal atrophy (eo-PRA and prcd-PRA), GM1 gangliosidosis and improper coat (absence of the typical coat). The panel allows ocular and neurometabolic conditions to be managed and the coat phenotype to be predicted. GM1 is a severe neurometabolic disease with a progressive course.

Applicable breed: Portuguese Water Dog. prcd-PRA and eo-PRA (CCDC66) are documented in the breed, and improper coat was initially described in it. There are no published estimates of carrier frequency in the breeding population for the four variants (limited data).

- Reduced night vision and progressive retinal atrophy (eo-PRA, prcd-PRA)
- Progressive early-onset neurological signs: ataxia, tremors, behavioural deterioration (GM1)
- Absence of the typical coat (improper coat): short hair, without beard or bushy eyebrows

The panel tests were developed independently. prcd-PRA was associated with the PRCD gene (Zangerl et al., 2006). The eo-PRA of the Portuguese Water Dog was described in 2020: a 1-bp insertion in CCDC66 (c.2262_c.2263insA) that truncates the protein and cosegregates perfectly with the disease (Murgiano et al., 2020). GM1 gangliosidosis of the Portuguese Water Dog was associated with a transition in GLB1 (c.179G>A, p.Arg60His) (Wang et al., 2000). Improper coat was linked to a 167-bp insertion in the 3’UTR of RSPO2, responsible for the furnishing pattern (Cadieu et al., 2009; Parker et al., 2010).

- Genotype breeding animals before mating
- For the recessive conditions (eo-PRA, prcd-PRA, GM1): do not mate carrier×carrier (25% risk of affected homozygotes); carrier×clear produces 0% affected and 50% carriers
- Given the severity of GM1, avoid mating two known carriers; consider avoiding the breeding of carriers in high-risk lines
- For improper coat: useful information to predict the coat of the offspring; it carries no disease risk
- After a confirmed clinical case, do not repeat the parental mating and communicate the status to the buyer

Complementary annual ocular examination (ECVO); differentiate eo-PRA (CCDC66, onset 2-3 years) from prcd-PRA (PRCD, onset 3-6 years or more) by age of onset and electroretinography, since their molecular basis and reproductive management differ. GM1 is confirmed by enzymatic assay of leukocyte β-galactosidase and neurological study; it has a poor prognosis. Improper coat is a coat characteristic, not a disease; its test guides the coat type of the litter.

1. Zangerl B, et al. Genomics. 2006. PMID: 16938425.
2. Murgiano L, et al. CCDC66 frameshift variant associated with a new form of early-onset progressive retinal atrophy in Portuguese Water Dogs. Sci Rep. 2020. PMID: 33273526.
3. Wang ZH, et al. Isolation and characterization of the normal canine beta-galactosidase gene and its mutation in a dog model of GM1-gangliosidosis. J Inherit Metab Dis. 2000. PMID: 11032334.
4. Cadieu E, et al. Coat variation in the domestic dog is governed by variants in three genes. Science. 2009. PMID: 19713490.
5. Parker HG, et al. An insertion in the RSPO2 gene correlates with improper coat in the Portuguese water dog. J Hered. 2010. PMID: 20562213.
6. Donner J, et al. Genetic prevalence and clinical relevance of canine Mendelian disease variants in over one million dogs. PLoS Genet. 2023. PMID: 36848397.
OMIA:000402-9615 (gangliosidosis GM1).