Genetic basis of CJM in Belgian Shepherds - is caused by a missense mutation c.1054G>A in the YARS2 gene, which encodes mitochondrial tyrosyl-tRNA synthetase 2. The mutation leads to a dysfunctional YARS2 protein, impairing mitochondrial tRNA recognition and translation, affecting energy metabolism. YARS2 mutation causes an autosomal recessive inherited disorder; affected dogs have two copies of the mutation, while carriers have one copy and are asymptomatic. The mutation is particularly documented in Belgian Shepherd varieties such as Malinois, Groenendael, and Tervueren.
Pathophysiology - The YARS2 mutation disrupts mitochondrial protein synthesis, causing defects in energy metabolism. This leads to juvenile mortality characterized by cardiomyopathy (heart muscle disease) and multi-organ dysfunction. The disease is analogous to similar mitochondrial disorders in humans causing myopathy, lactic acidosis, and anemia.
Complications - Puppies appear normal at birth but typically develop symptoms by around 6 to 8 weeks of age. Signs include vomiting, uncoordinated movements, trembling, respiratory difficulties, and heart failure symptoms. The condition progresses rapidly, often resulting in death within days of symptom onset.
Why This Matters to Breeders and Vets - Genetic testing allows identification of carriers and affected dogs to inform breeding decisions. Since CJM is autosomal recessive, carrier dogs show no symptoms but can pass the mutation on. Avoiding carrier-to-carrier matings prevents affected puppies. Understanding CJM helps veterinarians with early diagnosis and management, although the condition is fatal.
Summary - Cardiomyopathy and Juvenile Mortality (CJM) in Belgian Shepherd dogs is a fatal autosomal recessive disease caused by a missense mutation in the YARS2 gene. It causes mitochondrial dysfunction leading to early-onset heart disease and multi-organ failure, typically resulting in death by 6-8 weeks of age. Genetic testing enables carrier detection, guiding responsible breeding to prevent affected litters while maintaining breed genetic health.
