Congenital myasthenic syndrome (CMS)

General description

Symptoms of the disease are most of all a generalized skeletal muscle weakness, which worsens especially after exercise, stress or excitement. Signs can already be seen at just two weeks of age. Mobility and spinal reflexes of all limbs are reduced.

Breeds

Australian-Labradoodle (Cobberdog), Golden Retriever, Goldendoodle, Heideterrier, Jack Russell Terrier, Labradoodle, Labrador Retriever, Old Danish Pointing Dog, Parson Russell Terrier

Congenital myasthenic syndrome (CMS) - Golden Retriever

The COLQ gene is responsible for anchoring the enzyme acetylcholinesterase at the neuromuscular junction. This enzyme breaks down the neurotransmitter acetylcholine after signal transmission. Due to the COLQ gene variant, acetylcholine remains active for too long, which disrupts signal transmission and overstimulates the muscles. First signs usually appear in Golden Retrievers around the age of 4 weeks.

Congenital myasthenic syndrome (CMS) - Labrador Retriever

The COLQ gene is responsible for anchoring the enzyme acetylcholinesterase at the neuromuscular junction. This enzyme breaks down the neurotransmitter acetylcholine after signal transmission. Due to the COLQ gene variant, acetylcholine remains active for too long, which disrupts signal transmission and overstimulates the muscles. First signs usually appear in Labrador Retriever puppies around the age of 6 weeks.

Congenital myasthenic syndrome (CMS) - Old Danish Pointing Dog

The CHAT gene controls the production of the enzyme choline acetyltransferase, which synthesizes the neurotransmitter acetylcholine in nerve cells. Due to the gene variant, insufficient acetylcholine is produced, leading to a disturbed transmission of signals from nerve to muscle and thus to rapid muscle fatigue.

A typical feature is that the weakness temporarily improves after a short rest, but quickly returns with renewed activity. Thus, affected dogs can initially walk normally for a few minutes, then take shorter and shorter steps and eventually collapse from exhaustion; after a few minutes of rest, they can get up and walk again, before symptoms recur with continued exertion.

First symptoms may appear as early as 2 weeks of age.

Congenital myasthenic syndrome (CMS) - Russell Terrier

The CHRNE gene encodes part of the acetylcholine receptor in the muscle cell membrane. If this receptor is defective, the muscle cells can no longer effectively receive and respond to nerve signals. Accordingly, affected puppies often develop marked signs of weakness under exertion at around 4–5 weeks of age.

Congenital myasthenic syndrome (CMS) - Heideterrier

In Heideterriers, the first signs often appear just a few days after birth. As early as a few days old, it may be noticeable that the puppies cannot properly coordinate their forelegs and that reflexes are diminished or absent.

As the condition progresses, the affected animals develop a generalized muscle weakness that worsens throughout the day. Especially at night, the symptoms are usually most pronounced.

In more severe cases, it may occur that the puppies fall over sideways or are not able to stand up. Despite these pronounced physical limitations, their awareness and playfulness remain intact – the animals appear alert and interested but cannot adequately control their muscles.