Charcot-Marie-Tooth disease (CMT)

Charcot-Marie-Tooth disease (CMT) is a group of degenerative motor and sensory neuropathies. This disease is the most common hereditary neuromuscular disorder in humans. In 2008, clinical, electrophysiological, and pathological findings of sensory and motor neuropathy have been described in Miniature Schnauzers. Despite of some scientific advances, the Charcot-Marie-Tooth disease still is a slowly progressive and non-curable disease.

At the onset of the disease, the puppies are 2-3 months old and the clinical symptoms develop gradually. In dogs above 3 years with CMT diagnosis, a long survival rate has been observed. Young Miniature Schnauzers below 2 years of age show regurgitations (happens when a mixture of gastric juices and sometime undigested food rises back up the esophagus and into the mouth without vomiting), caused by mega-esophagus and inspiratory dyspnea caused by laryngeal paralysis. Electrophysiological studies discovered reduced motor and sensory nerve conduction velocity. Incontinences might occur and pneumonia or progressive anorexia can develop occasionally. Other symptoms can be gait abnormalities caused by loss of muscles and flexor reflexes in hind legs.

Neuropathy in Miniature Schnauzers is characterized by the presence of focally folded myelin sheaths (also known as tomacula) and segmental demyelination. The disease is most probably connected with the mutation of SBF2 gene (also known as MTMR13) located on the canine chromosome 21. It is a deletion of 40 base pairs at the 3´site of exon 19 due to induction of a cryptic splice site in this exon. This genetic variant leads to insertion of a premature stop codon into a sequence of amino acids, and thus to truncation of the resulting protein by 1070 amino acids.

Mutation that causes CMT in Miniature Schnauzers is inherited as an autosomal recessive trait. That means the disease affects dogs with P/P (positive / positive) genotype only. The dogs with P/N (positive /negative) genotype are clinically without any symptom. They are genetically considered carriers of the disease (heterozygotes). In offspring of two heterozygous animals following genotype distribution can be expected: 25 % N/N (healthy non-carriers), 25 % P/P (affected), and 50 % N/P (healthy carriers).

As follows from the current statistic data, 68 % of the population of Miniature Schnauzer are not carriers of the mutation, approximately 28 % are carriers of the mutation and 4 % of the population suffer from this disease. Genetic tests enable us to determine the genotype of a dog and avoid mating two carriers. By testing, birth of dogs affected with CMT can be prevented.

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Reference:

Granger, N., Luján Feliu-Pascual, A., Spicer, C., Ricketts, S., Hitti, R., Forman, O., Hersheson, J., Houlden, H.: Charcot-Marie-Tooth type 4B2 demyelinating neuropathy in miniature Schnauzer dogs caused by a novel splicing SBF2 (MTMR13) genetic variant: a new spontaneous clinical model. PeerJ 7:e7983, 2019. Pubmed reference: 31772832