Molecular mechanism

Acral Mutilation Syndrome (AMS) is a neurological condition that causes acral analgesia, typically presents at a young age. Proprioception, motor abilities, and spinal reflexes are unaffected, but intermittent prescence of intense licking, biting, and self-mutilation of the feet can occur (Plassais et al., 2016). The condition is inherited as an autosomal recessive condition however not every homozygous carrier of the mutation, an at risk dog, shows clinical signs of the disease. Plassais et al., (2016) first sequenced and identified the gene variant, chr4.g.70,875,561C\u0026gt;T, in 300 affected dogs and confirmed it was not present on the 900 unaffected dogs from 130 breeds.

Frequency not yet studied although in 250 clinically affected dogs across four sporting breeds they were distinctly genomically different from 900 unaffected dogs across 130 breeds (Correard et al., 2017).

Molecular mechanism

Centronuclear Myopathy (CNM) is an inherited neuromuscular disorder characterised by progressive skeletal muscle weakness, hypotonia and muscle atrophy, with clinical signs typically developing from approximately one month of age, although onset may occasionally be delayed until six months of age (Walmsley et al., 2016). Disease severity is variable, ranging from reduced exercise tolerance and gait abnormalities to marked muscle atrophy and collapse (McKerrel \u0026amp; Braund, 1987; Blot et al., 2002). Some affected dogs develop oesophageal muscle weakness, resulting in difficulty swallowing and an increased risk of sudden death, while clinical signs may also be exacerbated by exposure to cold temperatures (McKerrel \u0026amp; Braund, 1987).
Centronuclear Myopathy is inherited as an autosomal recessive condition. Pelé et al., (2005) identified a SINE insertion (PTPLA.9459_9460ins236) in exon 2 of the PTPLA (HACD1) gene on canine chromosome 2 (CFA2) as the causative variant. A worldwide survey of 7,426 Labrador Retrievers identified all 80 clinically affected dogs as homozygous for the variant, while none of the 1,172 heterozygous dogs developed disease, supporting its role as the causative mutation (Maurer et al., 2012). The carrier frequency was reported to be particularly high in the UK (19%), highlighting the importance of genetic testing to identify carriers and inform breeding decisions (Maurer et al., 2012).

Molecular mechanism

Degenerative Myelopathy (DM) is a progressive neurodegenerative disease of the spinal cord that typically affects dogs older than 8 years of age. The condition is characterised by progressive muscle atrophy and weakness of the limbs, advancing to tetraparesis (Awano et al., 2009) and eventually respiratory muscle failure (Nardone et al., 2016). DM is inherited as an autosomal recessive condition with variable expression between breeds. Missense mutation (c.118G\u0026gt;A; p.E40K) in exon 2 of the SOD1 gene on canine chromosome 31 (CFA31) was identified as the primary genetic risk factor by Awano et al., (2009). However, some dogs homozygous for the variant remain clinically unaffected, demonstrating incomplete penetrance. The SOD1.118G\u0026gt;A risk allele has been identified in 222 dog breeds; however, in Bernese Mountain Dogs a second disease-associated allele, SOD1.52A\u0026gt;T, has been identified and was concluded to be limited to this breed (Zeng et al., 2014). Consequently, the genetic test is offered in two versions: one for Bernese Mountain Dogs and one for all other breeds.

Molecular mechanism

Exercise-Induced Collapse (EIC) is characterised by transient episodes of muscle weakness and collapse triggered by strenuous exercise in otherwise healthy young dogs. Clinical signs typically develop within 2 minutes of completing 5–15 minutes of intense exercise and include hindlimb weakness, incoordination and an unsteady gait, which may progress to collapse, extensor rigidity, loss of consciousness and, in rare cases, death. Most dogs recover completely within approximately 30 minutes (Taylor et al., 2008; Patterson et al., 2008).
In retriever breeds, EIC is inherited as an autosomal recessive condition. Patterson et al., (2008) identified a missense mutation (c.767G\u0026gt;T; p.Arg256Leu) in exon 6 of the DNM1 gene on canine chromosome 9 (CFA9) as the causative variant. The variant has been reported in Labrador Retrievers, Chesapeake Bay Retrievers and Curly Coated Retrievers, allowing genetic testing to identify affected and carrier dogs. In a Midwestern US population of Labrador Retrievers, the variant was reported at a relatively high frequency, with 37% of dogs identified as carriers and 3% as homozygous affected, highlighting the importance of genetic testing to inform breeding decisions (Patterson et al., 2008). Although Border Collies can exhibit similar clinical signs, no causative variant has yet been identified for this breed; therefore, this genetic test is not applicable to Border Collies (Norton et al., 2021).

Molecular mechanism

Familial Nephropathy - Cocker Type, also known as Alport syndrome, is an inherited renal disorder affecting English Cocker Spaniels and also English Springer Spaniels but the Springer id a different variant. The condition is inherited as an autosomal recessive trait and is associated with mutations in the COL4A4 gene. Type IV collagen is a major structural component of the glomerular basement membrane (GBM), where it contributes to the integrity of the glomerular filtration barrier. Mutations affecting type IV collagen can cause structural abnormalities of the GBM and progressive loss of renal function, with Alport syndrome also associated with abnormalities affecting the eye and ear (Savige et al., 2013; Miner 2012).

In English Cocker Spaniels, Davidson et al., (2007) identified a single-nucleotide substitution at base 115 of COL4A4, resulting in a premature stop codon in exon 3. The variant segregated with clinical status in affected dogs and obligate carriers. A different COL4A4 mutation was subsequently identified in English Springer Spaniels by Nowend et al. (2012), involving a single-nucleotide substitution at base 2806 that also results in a premature stop codon.

The c.115T variant has been reported at a frequency of 0.9% in English Cocker Spaniels in Brazil (Andrade et al., 2020). Genetic testing can identify dogs carrying the known disease-associated variants, supporting informed breeding decisions to reduce the risk of producing affected offspring. This genetic test is for the Cocker Type only.

Molecular mechanism

Hereditary Nasal Parakeratosis (HNPK) is an inherited skin disorder characterised by the development of crusting and fissuring of the nasal planum from a young age. Affected dogs are otherwise healthy, with the condition primarily affecting the nasal epidermis. Histopathological examination reveals marked parakeratotic hyperkeratosis, characterised by retention of nuclei within the stratum corneum and accumulation of proteinaceous fluid within the superficial epidermal layers (Jagannathan et al., 2013).
HNPK is inherited as an autosomal recessive condition (Page et al., 2003). Jagannathan et al., (2013) identified a missense mutation (c.972T\u0026gt;G; p.Asn324Lys) in the SUV39H2 gene on canine chromosome 2 (CFA2) as the causative variant in Labrador Retrievers.

Molecular mechanism

Hyperuricosuria and Hyperuricemia (HUU) is an inherited metabolic disorder characterised by impaired uric acid transport, resulting in increased urinary excretion and blood concentrations of uric acid. Affected dogs are predisposed to the formation of ammonium urate uroliths within the urinary tract, although not all dogs carrying the causative variant will develop the disease (Bannasch et al., 2008). Clinical signs are associated with stone formation and may include haematuria, pollakiuria, dysuria and urethral obstruction, while severe obstruction can result in systemic illness including anorexia, vomiting, collapse and metabolic disturbances (Bartges et al., 1999; Bartges and Callens, 2015).
Hyperuricosuria and Hyperuricemia is inherited as an autosomal recessive condition; however, the SLC2A9 variant represents a genetic risk factor for urate urolithiasis rather than a definitive predictor of clinical disease. Bannasch et al., (2008) identified a missense mutation (c.616G\u0026gt;T; p.Cys188Phe) in the SLC2A9 gene on canine chromosome 3 (CFA3) as the causative variant. The variant is fixed in Dalmatians, with all dogs reported to be homozygous, but has also been identified at lower frequencies in several other breeds, including Labrador Retrievers, Bulldogs, German Shepherd Dogs and Pomeranians (Bannasch et al., 2008; Karmi et al., 2010; Cosgrove et al., 2015).

Molecular mechanism

Progressive retinal atrophy (PRA) encompasses a genetically heterogeneous group of inherited retinal degenerative disorders characterised by the progressive loss of photoreceptor function, ultimately resulting in irreversible blindness. Although the clinical presentation is broadly similar across affected breeds, with initial degeneration of rod photoreceptors causing night blindness followed by cone degeneration and progressive loss of daylight vision, numerous genetically distinct forms of PRA have been identified (Miyadera et al., 2012; Mowat et al., 2024). Advances in canine molecular genetics have demonstrated that variants in multiple genes involved in photoreceptor development, maintenance and function can produce clinically similar retinal phenotypes. Consequently, breed-specific genetic testing is required, as different forms of PRA are associated with different causative variants.

PRA-RPGRIP1 (CORD1/crd4): Progressive retinal atrophy associated with RPGRIP1 is inherited as an autosomal recessive condition. In Miniature Long-Haired Dachshunds, Mellersh et al., (2006) identified a 44-bp insertion in the RPGRIP1 gene that results in a frameshift and premature protein truncation. Although additional genetic factors may influence disease severity, this variant remains the primary genetic marker used for testing (Miyadera et al., 2012).

The expanding number of recognised PRA-associated variants highlights the marked genetic heterogeneity underlying inherited retinal degeneration in dogs. While many of these variants are breed-specific, others are shared across multiple breeds through historical founder events. Genetic testing enables accurate identification of affected and carrier dogs, supporting informed breeding decisions aimed at reducing disease prevalence while preserving genetic diversity. As additional causative variants continue to be identified, molecular testing will remain an important tool for improving the diagnosis, management and long-term control of progressive retinal atrophy in canine populations (Lewis \u0026amp; Mellersh, 2019; Mowat et al., 2024).

Molecular mechanism

Skeletal Dysplasia 2 (SD2) is an inherited mild form of disproportionate dwarfism in Labrador Retrievers, characterised by shortened limbs with a normal body length and width. Affected dogs have an average reduction in shoulder height of approximately 6 cm (Frischknecht et al., 2013). As shoulder height is influenced by both genetic and environmental factors, affected dogs cannot always be reliably identified by physical appearance alone (Frischknecht et al., 2013).
Skeletal Dysplasia 2 is inherited as a monogenic autosomal recessive condition. Frischknecht et al., (2013) identified a missense mutation (c.143G\u0026gt;C; p.Arg48Pro) in the COL11A2 gene on canine chromosome 12 (CFA12) as the most likely causative variant. The carrier frequency was estimated at approximately 12% in the European Labrador Retriever population at the time of variant discovery, highlighting the value of genetic testing to confirm the diagnosis and inform breeding decisions (Frischknecht et al., 2013).