Episodic Falling Syndrome

The EFS (Episodic Falling Syndrome) is a genetic disease known from 1960 in Cavalier King Charles Spaniel. The disease is caused by 15.7 kbp deletion in BCAN-gene. So far, no other breed affected with this disease has been found.
The symptoms of EFS vary, but they all are caused by temporary inability to relax the affected limb and trunk muscles.  The sings are usually induced by physical or psychological stress (exercise, excitement, frustration), except in severe cases, when the signs become chronic and happen with no apparent cause.  The frequency, type and severity of the episodes may increase, decrease or change as the dog gets older.  
The EFS symptoms usually arise from three to seven months of age and affect both female and male dogs. The episodes are usually brief, but the clinical signs vary from case to case and the length of an episode can range from a few seconds to several minutes. During the attack, the dogs gait becomes stiff and so-called bunny-hopping gait occurs. The dog may lose coordination during walking, with the head held down leading to collapse, either to the side or forwards.  Uncontrolled movement of limbs, rolling from side to side in cramps, stiff jaws, wild look, slobber, etc. may occur during the collapse. During the episodes the dog remains fully conscious and mentally normal. The dog is exactly aware of what is happening and how he is loosing control of its body. After episodes, in most instances the dog recovers relatively quickly, stands up and continues as if nothing unusual has happened.
If the episode is severe or lengthy, the dogs may lapse into repeated lengthy episodes of the syndrome or may suffer permanent neurological damage or not be able to recover from the attacks. These seriously affected dogs have to be euthanized.

EFS 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). Because of high risk of producing affected offspring, mating of two N/P animals (carriers) can not be recommended.

References:

Forman OP, Penderis J, Hartley C, Hayward LJ, Ricketts SL, et al. (2012) Parallel Mapping and Simultaneous Sequencing Reveals Deletions in BCAN and FAM83H Associated with Discrete Inherited Disorders in a Domestic Dog Breed. PLoS Genet 8(1): e1002462. doi:10.1371/journal.pgen.1002462