Congenital Myasthenic Syndrome in Doberman Pinscher Dogs Is Associated with a Homozygous Missense Variant in AGRN

Hereditary neuromuscular disorders in dogs can be difficult to classify since variants in different genes can result in similar clinical signs or variable phenotypes can be associated with the same DNA sequence variant. A disorder known for many years as Dancing Doberman Disease, suspected to be neuropathy or neuromyopathy, is characterized by repeated lifting and shifting of the pelvic limbs while standing and frequent sitting. More recently, Doberman Pinschers have been identified with a different and more severe phenotype characterized by a crouched stance and bunny hopping gait in the pelvic limbs that is termed duck walking. Dogs with both phenotypes show pelvic limb weakness, muscle atrophy, and fatigue, and clinical signs can progress to involve the thoracic limbs. These distinct phenotypes were evaluated clinically, histologically, and by whole-genome sequencing and genotyping a large cohort of affected and unaffected Doberman Pinschers. The same homozygous missense variant in AGRN (Dog 10K Boxer Tasha chr5:56,346,611,G>A; p.R1710H, XP 038377340.1) was associated with both disorders. AGRN encodes Agrin, an essential synaptic protein, that mediates clustering of acetylcholine receptors on the post-synaptic membrane at the neuromuscular junction. Variants in AGRN are associated with a congenital myasthenic syndrome (CMS) in humans. This is the first report of a CMS in dogs associated with an AGRN variant and expands the spectrum of known CMS genetic risk factors in this species. This study also highlights the importance of whole-genome sequencing (WGS) to accurately classify neuromuscular diseases as forms of CMS, which is not possible based on clinical presentation alone.