Testing of dogs: Narcolepsy in Dachshunds

Narcolepsy in Dachshunds

Narcolepsy is a sleeping disorder characterised by shortened sleep latency and cataplexy (sudden temporary loss of muscle tone without loss of consciousness). Affected dogs are sleepy, unable to stay awake for extended periods of time and fall asleep faster than normal dogs. Cataplectic episodes occur usually in response to a positive emotional stimulus (food, play). The first signs of cataplexy are a buckling of both hind legs and a drooping of neck. The muscle weakness lasts for a few seconds to minutes. During the episodes of collapse the dog remains conscious, has its eyes open and is able to track objects with its eyes. If the collapse lasts more than a few minutes, the dog may fall asleep during the episode.

In Dachshunds, the disease is caused by a missense mutation c.160G>A in the HCRTR2 gene, which encodes a receptor for hypocretin-2. In normal dogs, hypocretin activity is enhanced by a positive feedback mechanism mediated by hypocretin-2 receptors. These receptors are thus a key element in the regulation of sleep and wakefulness.

The mode of inheritance of the mutation is autosomal recessive. This means that only individuals who inherit the mutated gene from both parents will develop the disease. Carriers of the mutated gene are clinically healthy but pass the mutation on to their offspring. In the case of a mating between two heterozygous individuals, theoretically 25% of the offspring will be completely healthy, 50% of the offspring will be carriers and 25% of the offspring will inherit the mutated gene from both parents and will therefore be affected by the disease.

The genetic test can clearly reveal the genotype of the animal and is a useful tool for breeders to prevent unintentional breeding of affected puppies.

.

References:

Hungs, M., Fan, J., Lin, L., Lin, X.Y., Grigoriadis, D., Maki, R.A., Mignot, E.: Identification and functional analysis of mutations in the hypocretin (Orexin) genes of narcoleptic canines (vol 11, pg 531, 2001) Genome Research 11:919, 2001.

Hungs, M., Fan, J., Lin, L., Lin, X.Y., Maki, R.A., Mignot, E.: Identification and functional analysis of mutations in the Hypocretin (Orexin) genes of narcoleptic canines Genome Research 11:531-539, 2001. Pubmed reference: 11282968.