Myotonia congenita 2 / congenital myotonia (CLCN1-related) - Australian Cattle Dog and Border Collie

What does this test analyse?

This genetic test analyses the CLCN1 c.2665insA variant for myotonia congenita, also known as congenital myotonia or hereditary myotonia, in Australian Cattle Dogs and Border Collies.

CLCN1 encodes a chloride channel in skeletal muscle. When this channel does not function properly, muscles relax more slowly after contraction.

What does this condition mean?

Myotonia congenita causes clear muscle stiffness, especially when starting movement or making rapid postural changes. Dogs may show a stiff or robotic gait, muscle hypertrophy, swallowing difficulty, excessive salivation or noisy breathing.

This variant is described in the Australian Cattle Dog and is also offered as a relevant test for Border Collies. In some dogs stiffness can improve with continued movement, while excitement or active play can make signs more visible.

Inheritance and result

The trait is inherited as an autosomal recessive condition. Clear dogs have two normal copies, carriers have one copy of the tested variant and genetically affected dogs have two copies.

Practical value of this test

• The test shows whether a dog is clear, carrier or genetically affected for this CLCN1 variant.
• Breeders can identify carriers and avoid carrier x carrier matings.
• The result helps genetically explain stiffness or muscle hypertrophy in young dogs.
• Variant status can be documented within lines, families and breeding advice.
• The test supports targeted selection against congenital myotonia without automatically removing valuable carriers from breeding.