Genetic basis - Caused by a missense mutation (c.85G>A) in the CHAT gene encoding choline acetyltransferase. The mutation leads to reduced presynaptic synthesis of acetylcholine at the neuromuscular junction. Inherited in an autosomal recessive manner, requiring two mutated copies for disease to manifest.
Pathophysiology - CHAT deficiency impairs acetylcholine production, necessary for muscle contraction signals. Results in a presynaptic neuromuscular transmission defect. Causes episodic muscle weakness and transient paralysis after exercise.
Clinical Signs - Onset usually by 2 weeks of age. Symptoms begin as short strides and worsen with exercise. Puppies eventually lie down with legs bent. Symptoms improve temporarily after rest but return when exercise continues. Generalized muscle weakness worsens with activity. Reduced mobility and spinal reflexes. Ability to bear weight declines over time.
Diagnosis - Clinical examination and neuromuscular evaluation. Confirmed by genetic testing for CHAT mutation.
Why This Matters to Breeders and Vets - Breeders: Early testing prevents breeding two carriers, limiting affected offspring. Vets: Awareness facilitates accurate diagnosis and appropriate management of symptoms.