Lysosomal Storage Diseases (LSDs) – Lagotto romagnolo dogs

Hereditary degenerative diseases occur frequently in dogs as well as in humans. Many of them are caused by mutation in an identical gene. The occurrence of a neurodegenerative disease is associated with malfunction of degradation processes and subsequent accumulation of various types of cellular materials in the body´s cells. This disorder results in balance problems inside the nerve cells. These diseases are collectively called Lysosomal Storage Diseases (LSDs; lysosomal storage disorders).

The main systems responsible for the cellular degradation are specialized in degradation of organelles and proteins. In particular, lysosomes play an important role in degradation of proteins and represent the most important cellular degradation centre.  Their dysfunction and subsequent accumulation of waste material in their sacs causes a progressive cerebellar ataxia, altered function of degradation systems and neurodegeneration in affected individuals.  The histological examination revealed extensive swelling and cytoplasmic vacuolisation of Purkinje cells affecting the central and peripheral nervous systems. Further, slight atrophy of cerebellum and forebrain was visible. A frequent symptom accompanying the early stages of this disease is abnormal involuntary eye movement (nystagmus). In later stages of the disease substantial behavioural changes occur.  Typical symptoms are in particular depression, restlessness and aggression towards people and other dogs. The age of onset of clinical signs differ from dog to dog and can range from 4 months to 4 years. The rate of progression is also variable and the period from the occurrence of first signs to the euthanasia can last several months or years.

This autosomal recessive disease is caused by mutation c.1288G>A in ATG4D gene that has been identified only in Lagotto romagnolo dogs.  In related breeds no such mutation has been found.

LSDs in Lagotto romagnolo is a recessively inherited disease. The disease develops in dogs which inherit the mutated gene from each parent.  These dogs are designated as P/P (positive/positive). The carriers of the mutated gene are designated as N/P (negative/positive). The carriers inherited the mutated gene from one parent only and are without clinical signs. However, they pass the disease on to their offspring.  When mating two heterozygotes (N/P), there will be theoretically 25% of the offspring healthy, 50% of the offspring will be carriers and 25% of the offspring will inherit the mutated gene from both parents and will be affected by LSDs.  Mating one healthy dog (N/N) with a carrier of this mutation (N/P) will theoretically produce 50% carriers and 50% healthy offspring.  If a carrier (N/P) is mated with an affected dog (P/P), there will be theoretically 50% affected dogs and 50% carriers.

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Reference:

Kyöstilä, K., Syrjä, P., Jagannathan, V., Chandrasekar, G., Jokinen, T. S., Seppälä, E. H., Becker, D.,  Drögemüller, M., Dietschi, E., Drögemüller, C., Lang, J., Steffen, F., Rohdin, C., Jäderlund., K. H., Lappainen, A. K., Hahn, K., Wohlsein, P., Baumgärtner, W., Henke, D., Oevermann, A., Kere, J.,Lohi, H. & Leeb, T. (2015). A missense change in the ATG4D gene links aberrant autophagy to a neurodegenerative vacuolar storage disease. PLoS Genet, 11(4), e1005169.