NCL5 (Neuronal ceroid lipofuscinosis type 5) in Golden Retrievers

Neuronal ceroid lipofuscinosis (NCL) is a neurodegenerative disorder which affects people, dogs and other animals (e.g. cattle, sheep, horses). In some animals the causal mutation leading to NCL has not been described yet. In connection with NCL in animals and people mutations in six different genes CLN 1,2,3,4,5,6,8 (Daly et al. 1998, Gupta et al. 2001) have been described for now. Each mutation in the given gene causes a unique form of NCL.

The NCL occurs in many canine breeds, such as Border collie, English setter, American Bulldog, and Dachshund, Polish Lowland Sheepdog or Tibetan terrier.  In Golden Retriever breed, specific causal mutation has been found in connection with NCL.  It is a mutation in the gene for lysosomal glycoprotein CLN5 (CLN5: c.934_935delAG) that plays an important role in degradation and recycling of damaged or unnecessary proteins in lysosomes.  This mutation causes shifting of the reading frame and results in an early stop codon. This mutant protein lacks 39 C-terminal amino acids and so its properties and functions are changed. Due to this, the autofluorescent storage material is accumulated in neurons in the central nervous system including in the retina. The neuronal ceroid lipofuscinosis is characterized by accumulation of lipopigments (ceroid a lipofuscin) in lysosomes.

The clinical symptoms of this disease are progressive neurological signs including disorientation, worsening of motor functions, anxiety, aggression, seizures and problems with food intake. Usually visual impairment and loss of vision occur as well. The onset of the disease and its clinical course vary substantially between breeds. In Golden retrievers, the first signs occur most often after 15 month of age. The degree of neurodegeneration increases with the age and all affected dogs develop psychological abnormalities and spasms. Changes in gait and posture – stumbling, leg stiffness, tremor - can be observed as well.

NCL is inherited autosomally recessively which means that the disease develops only in those dogs who inherit mutated allele from both parents. Carriers of mutated allele (heterozygotes) are clinically healthy but transmit the mutation on their offsprings. In case of mating two heterozygous dogs there is a theoretical chance that 25% of offsprings will be absolutely healthy, 50% will be carriers a 25% will inherit from both parents mutated allele and therefore will be NCL affected.

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Reference:

Gilliam, D., Kolicheski, A., Johnson, G.S., Mhlanga-Mutangadura, T., Taylor, J.F., Schnabel, R.D., Katz, M.L. : Golden Retriever dogs with neuronal ceroid lipofuscinosis have a two-base-pair deletion and frameshift in CLN5. Mol Genet Metab 115:101-9, 2015