Devon Rex Congenital Myasthenic Syndrome (CMS) or "spasticity"

Definition :

The name of Spasticity is not correct because this is a genetic myastenia. The neuromuscular junction of the proximal muscles of the forelimbs are preferentially affected.

Origin:

The disease was first described in 1974. In this time, breeders didn't know the origin. But as they saw recurred cases in several countries (Australia, New-Zealand, United-States, Great Britain and Netherlands), they supposed it had a genetic origin. Indeed, when the breed was created in the 60's, inbreeding was necessarily made in order to determine and to fix the breed standard. Because of this important inbreeding, the CMS of Devon Rex appeared.
Since this discover, pedigree of affected kittens were studied and breeders concluded to a recessive autosomal (as well males than females), monogenic (spt gene) hereditary transmission, because affected kittens were born from normal parents (healthy carriers: SPT/spt).

Clinical features:

The signs commonly develop on kittens of mean age of 4 to 7 weeks, but may occure until 12 or 14 weeks.

The kitten is active and mentally normal, but he displays abnormal bearing:

- A jerky, stiff and hypermetric gait of the forelimbs (high-stepping: like a "military walk"). The kitten runs with rabbit's jumps because of a lack of limbs' suppleness.
- The shoulders blades are held high (scapula protrusion).
- The neck arches downwards with the head held low (ventroflexion). The chin sometimes touches the chest. The flexion is more marked when the kitten walks, urinates or defecates.

 - He frequently stops playing for resting.

 - At rest, the kitten lies flat with his head held to one side, or he sits on his back croup, or he is leaning against an upright object so as to stretch out the chest.

- Feeding is difficult because the arched neck interferes with the normal feeding action of extending the neck. Drinking is particularly messy because the nose often dips below the surface of the liquid. As a result, aspiration pneumonia is the main cause of death of affected kittens.

Severity of symptoms varies from one cat to another and from one day to another on the same cat. Periods of few days of apparent normality alternate with a general deterioration (important musculoskeletal and respiratory difficulties, intense fatigue). Life expectancy is time-varying: from few months to several years if attentive cares are made.

Histopathologic lesions:

The affected muscular fibers are heterogeneous and degenerate. The more the animal grows old, the more the disorder becomes marked. There is no lesion of the nerves. The pathology is exclusively a muscular dystrophy secondary to a neuromuscular junction dysfunction.

Treatment:

No possible recovery, the disease lead to death at short, medium or long-term.

Prevention:

The investigation originated from the concern felt by breeders for the apparent prevalence of the condition and the likelihood of it being inherited. Quickly, transmission mode (recessive and autosomal) and inherence were evaluated. In the 80's, French and Dutch breeders led a rigorous selective reproduction program. The policy was not to breed from affected cats, but also from healthy carriers (which are difficult to detect). So, the frequency of the disease fell considerably. And since that time, only one case of CMS was reported in the scientific literature. Until recently, no new case of CMS was reported. But in 2012 and 2014, some new cases of CMS on Devon Rex re-appeared in Europe. So the scientific investigations restarted again.
 
The National Veterinary School of Alfort (France) with the support of "Antagène laboratory" (French veterinary laboratory) and LOOF (French feline pedigree organism) found the mutated gene in this disease in the Devon Rex and the Sphynx cats on June 2015. This is a great new for the breeds! Now, a screening genetic test exists in order to eradicate this affection. Note that the Veterinary Genetics Laboratory of UC Davis also provides the genetic test in these breeds. The article of the research and study is freely available here:

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0137019

In 2007, a young Sphynx female showed the same signs of the disease. As the two breeds are narrowed (Devon Rex have been used to develop Sphynx), a common genetic origin were supposed for these 2 diseases. This hypothesis was reinforced by another study (in 2008) showing a deficiency in a protein expression in one Devon Rex and two Sphynx with muscular dystrophy (myopathy). That suggests that myopathy is not only a Devon Rex breed disease.

Source: Les myopathies des chats devon rex et sphynx, une même maladie héréditaire ? Abitbol M, PVE (2009), 16-17
« Spasticity » in the Devon rex cat, Robinson R., Vet Record (1992) 130, 302