Myotonia Congenita

Myotonia Congenita DNA Test Submission Form

Description:
Myotonia is a clinical sign characterized by the delay of skeletal muscle relaxation following the cessation of a voluntary activity or following the cessation of an electrical or mechanical stimulus. In humans, this is most readily noticed by a delayed ability to relax the hand following a handshake. We have been studying an inherited form of myotonic myopathy in miniature Schnauzers.

Various biochemical defects may result in myotonia including: reduced membrane chloride conductance, alterations in the kinetics of sodium channel inactivation, and, as of yet, undetermined membrane abnormalities. Electrophysiological studies and molecular studies have revealed myotonia congenita in the miniature Schnauzer results from a mutation in the skeletal muscle chloride channel (ClC-1). The mutation in the chloride channel results in replacement of a threonine residue in the D5 transmembrane segment with methionine.

A series of related miniature Schnauzer dogs with myotonia congenita have been studied at the Veterinary Hospital of the University of Pennsylvania. These studies have revealed that myotonic myopathy has an autosomal recessive mode of inheritance.

Myotonia congenita in the miniature Schnauzer may be effectively treated with 40 mg/kg procainamide given orally three times daily. At this concentration, signs of myotonia are markedly reduced. Dogs walk with less stiffness, their upper respiratory sounds decrease, and regurgitation resolves.

Clinical Signs:
Muscle stiffness that partially resolves with exercise.
Increase in muscle stiffness in response to any rapid change in posture.
Abnormal upper respiratory sounds especially when beginning to move.
Regurgitation that may occur when eating.
Protrusion of the tongue from the mouth at rest.
Compression of the tongue resulting in dimpling that persists for up to 30 seconds.
Diffuse skeletal muscle hypertrophy.
Shortening of the lower jaw (mandible).
Electromyographic (EMG) evidence of myotonic discharges of approximately 40 seconds duration.

Affected Breeds:
Miniature Schnauzer

Required Samples:
EDTA Blood, 1-2 mL or
2 Buccal Swabs

Price: $75 each