Spinal Muscular Atrophy in Dogs

Spinal muscular atrophy is a rare disease that is most commonly seen as an inherited condition. Hereditary canine spinal muscular atrophy (HCSMA) closely resembles amyotrophic lateral sclerosis (ALS) and spinal muscular atrophies (SMAs) seen in humans. These diseases affect the motor neurons of the brain and spinal cord and are normally seen in puppies. This condition was initially identified and studied in Brittany Spaniels.

Clinical Signs

Three clinical syndromes were identified:

• Accelerated (early) disease where puppies start showing clinical signs before weaning (<8 weeks of age). Clinical signs are profound and progressive.
• Intermediate disease where puppies start to show clinical signs after weaning, which were initially mild, but progressive. Clinical signs usually present by 4 – 6 months.
• Chronic (delayed) disease where dogs show very mild clinical signs, but have a normal life span. Clinical signs are usually seen under 1 year of age.

Clinical signs can vary based on severity of disease and which clinical syndrome is present. The most severe clinical signs are marked weakness, inability to stand/ambulate, trouble eating or breathing due to muscle weakness, and incontinence. Less severe clinical signs include trouble walking (resulting in crawling or instability in the hindlimbs) and temperature regulation impairments (due to inability to pant). Hindlimbs are more affected than forelimbs, or clinical signs start in the hindlimbs and move forward.

Diagnosis and Predisposed Breeds

Diagnosis is based on clinical signs and classic affected breed predilection. Confirmatory diagnosis can be completed through nerve/muscle biopsies.

There are no documented treatment options for HCSMA in dogs. Most puppies are euthanized due to inability to walk or develop complications secondary to inability to eat and breath normally.

Breed predilections:

• Brittany Spaniels were the initial subjects for the study and identification of HCSMA.
• In the Rottweiler breed, early or accelerated syndrome has been noted in young puppies and is rapidly progressive.
• Swedish Lapland puppies are usually affected at <8 weeks of age.
• Stockard’s paralysis has been noted in St. Bernards bred with Great Danes or Bloodhounds. Clinical signs are normally seen between 11 – 14 weeks of age, ultimately resulting in severe degeneration of neurons in the lumbar spine.
• English Pointers may develop intermediate syndrome as they age.
• German Shepherds have been noted to develop a focal form of spinal muscular atrophy, mainly affecting one or both thoracic limbs.

Spinal Muscular Atrophy in Cats

A similar disease process has been noted in cats, mainly in the Maine Coon breed. Kittens usually develop signs by 3 – 4 months of age, predominantly noted in the hind limbs, but less progressive than in dogs. The Veterinary Genetic Laboratory at UC Davis has developed a genetic test to isolate individuals that should not be used for breeding or that may develop clinical signs.