Congenital myopathy characterized by the presence of rod-shaped structures (nemaline rods) inside the muscle fibres, derived from sarcomere proteins. It affects the American Bulldog with weakness, arched posture and progressive muscle atrophy from an early age, with involvement of the respiratory and oesophageal musculature that conditions the prognosis. It is a natural model of human nemaline myopathies.

American Bulldog is the best-characterized breed. The carrier frequency in the breeding population is not systematically published (limited data).

- Generalized muscle weakness from puppyhood\n- Progressive muscle atrophy\n- Arched posture with cervical dorsiflexion\n- Dysphagia and drooling\n- Regurgitation due to megaesophagus\n- Progression with respiratory failure

Canine nemaline myopathy was described in a family of related American Bulldogs. Evans et al. (2016), using whole-exome sequencing of the dam, two affected and one unaffected dog, identified a nonsense mutation in NEB (loss of full-length NEB protein, with nonsense-mediated degradation). The variant was absent in 120 dogs from 24 breeds and in 100 unrelated American Bulldogs, so it may be private to the family. It is the first large animal model of NM characterized molecularly.

- Genotype breeding dogs before mating\n- Do not mate two carriers: 25% risk of affected homozygotes\n- A carrier can be mated to a clear dog; offspring intended for breeding must be tested\n- Exclude affected homozygous animals from breeding\n- After a confirmed clinical case, do not repeat the parental mating and communicate the status to the buyer

Differential diagnosis with myotubular myopathy (XL-MTM) and other congenital myopathies of the puppy. Muscle biopsy shows nemaline structures (rods) in the fibre; immunohistochemistry with α-actinin highlights them. Involvement of the oesophagus and respiratory muscles conditions the prognosis.

1. Evans JM et al. 2016. Exome sequencing reveals a nebulin nonsense mutation in a dog model of nemaline myopathy. Mamm Genome 27:495-502. PMID: 27215641
2. OMIA:002137-9615 - Nemaline myopathy, NEB-related. https://omia.org/OMIA002137/9615/