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

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

Neonatal Encephalopathy with Seizures (NEWS) is an inherited neurological disorder affecting Standard Poodles. It follows an autosomal recessive pattern of inheritance and is caused by a missense variant in the ATF2 gene on canine chromosome 36 (CFA36). The causative variant, c.152T\u0026gt;G (p.Met51Arg), was first identified by Chen et al., (2008) following linkage analysis that mapped the disorder to a 2.87 Mb region containing ATF2.
Affected puppies are typically smaller than their littermates at birth and fail to develop normally. Clinical signs begin at around 3 weeks of age and include weakness, tremors, ataxia, poor coordination, increased muscle tone, and reduced responsiveness. As the disease progresses, affected puppies develop severe seizures that become resistant to treatment, with most dying or being euthanised before 7 weeks of age (Chen et al., 2008; Yu et al., 2020).
Genetic testing can identify clear, carrier, and affected dogs, allowing breeders to avoid producing affected puppies while maintaining genetic diversity. In the original study by Chen et al., (2008), approximately 36% of Standard Poodles tested were carriers and 2.7% were genetically affected, highlighting the importance of testing within the breed.

Molecular mechanism

Osteochondrodysplasia, also known as pseudoachondroplastic dysplasia, is an inherited skeletal disorder affecting Miniature Poodles. Affected puppies develop skeletal abnormalities from an early age, including shortened and bowed limbs, enlarged joints, abnormal paw conformation, an undershot jaw, and a flattened rib cage. As the disease progresses, affected dogs commonly develop restricted mobility and secondary arthritis due to abnormal bone and cartilage development (Neff et al., 2012). The condition follows an autosomal recessive pattern of inheritance and is caused by a 130 kb deletion affecting the SLC13A1 gene on canine chromosome 14 (CFA14). The deletion, which removes all but the first exon of SLC13A1, was first identified by Neff et al., (2012) following a genome-wide association study and subsequent FISH analysis.

Genetic testing can identify clear, carrier, and affected dogs, enabling informed breeding decisions to prevent affected puppies while maintaining genetic diversity within the breed. Neff et al., (2012) reported an allele frequency of approximately 5% in Miniature Poodles in the United States, corresponding to an estimated carrier frequency of around 10%.

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-PRCD is an autosomal recessive form of progressive retinal atrophy caused by a missense variant in the PRCD gene. PRCD Zangerl et al., (2006) identified a c.5G\u0026gt;A (p.Cys2Tyr) variant that has been reported across numerous dog breeds. Affected dogs are born with normal vision but gradually develop night blindness, progressing to complete blindness as both rod and cone photoreceptors degenerate. Widespread genetic testing has substantially reduced the frequency of this variant in several breeds, although carriers and affected dogs continue to be identified (Zangerl et al., 2006; Lewis \u0026amp; Mellersh, 2019; Clark et al., 2023).
https://omia.org/OMIA001298/9615/

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).

Molecular mechanism

Von Willebrand Disease (vWD) is an inherited bleeding disorder caused by deficiency or dysfunction of von Willebrand factor (vWF), a plasma glycoprotein essential for normal platelet adhesion and blood clotting (Boudreaux, 2012). Affected dogs may experience prolonged bleeding following injury or surgery, spontaneous bleeding from the nose or gums, bruising, or blood in the urine (Thomas, 1996). Three recognised forms of the disease exist, which differ in severity: Type I is characterised by reduced concentrations of normal vWF and typically causes mild to moderate bleeding, Type II results from qualitative defects in the vWF protein and is associated with moderate to severe bleeding, while Type III is characterised by an almost complete absence of vWF and is the most severe form of the disease.
The genetics and inheritance of von Willebrand Disease vary according to the disease type and breed. Type I is associated with the VWF c.7437G\u0026gt;A splice-site variant and shows autosomal dominant inheritance with incomplete penetrance in some breeds, including Doberman Pinschers and Kromfohrländers, while autosomal recessive inheritance has been proposed in others (Gentilini and Turba, 2013; Segert et al., 2019). As a result, the Type I genetic test identifies dogs carrying the risk variant but should be interpreted alongside clinical findings and additional haemostatic testing where appropriate (Segert et al., 2019). The appropriate genetic test should be selected according to both the breed and the form of von Willebrand Disease being investigated. If you are unsure then please send us an email.

Molecular mechanism

Startgardt Disease (ABCA4-related Retinal Atrophy), is an inherited retinal degeneration affecting Labrador Retrievers. The condition is inherited as an autosomal recessive trait and is caused by a frameshift insertion, ABCA4:c.4176insC (p.Phe1393Leufs*1395), in exon 28 of the ABCA4 gene. The causative variant was identified by Mäkeläinen et al., (2019) through whole-genome sequencing.
Affected dogs develop a slowly progressive retinal degeneration leading to visual impairment under both daylight and low-light conditions. Clinical signs include dilated pupils, reduced pupillary light responses, retinal changes visible on ophthalmic examination, and gradual deterioration of vision, although some vision is often retained throughout life (Mäkeläinen et al., 2019; Ekesten et al., 2022).
Genetic testing can identify clear, carrier, and affected dogs, enabling informed breeding decisions to prevent affected puppies.

Molecular mechanism

Macular corneal dystrophy is an inherited eye disorder caused by a mutation in the CHST6 gene (called LOC489707). In Labrador Retrievers, the causative variant was identified as a missense mutation c.814C\u0026gt;A (p.R272S), with affected dogs being homozygous for the variant, consistent with an autosomal recessive mode of inheritance (Tetas Pont et al., 2016).
The variant affects the normal structure of the cornea, leading to the accumulation of abnormal material within the corneal stroma. Affected Labrador Retrievers typically develop progressive corneal cloudiness and visual impairment between approximately 4.5 and 6 years of age. Clinical signs include diffuse corneal haze and multiple opaque deposits within the cornea, which may increase over time and result in reduced vision (Busse et al., 2019; 2013).
In a study of Labrador Retrievers, the mutant allele frequency was estimated at 0.017, corresponding to an estimated carrier frequency of approximately 3.3% (Tetas Pont et al., 2016).