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A characterization of myotonia is an increase in the tendency of the skeletal muscles to respond with repetitive action potentials and after discharges when stimulated

The increased muscle excitability has been shown to be largely accounted for by the lack of chloride permeability in these fibers.

Myotonia is also characterized by a significant increase in the fast isomyosins in each muscle type in the affected animals

Isolated intercostal muscle from goats with the condition were significantly different than that of normal goats in terms of temperature dependence of the resting membrane resistance and potassium efflux

These differences help to explain increases in the severity of myotonia in the whole animal that occurs upon decreasing the temperature of the involved muscles

The muscle fibers of the myotonic goat were found to be highly resistant, this was shown to be due to the blocking of chloride conductance.

Normal goat fibers were able to be made myotonic by blocking the chloride conductance by using myotonia inducing drugs or by substituting an anion that is unable to pass through a semi-permeable membrane.

In a study testing the effect of hydration on myotonia in goats, it was found that upon depriving goats of water, the myotonic symptoms disappeared within 3 days and returned fully within 2-3 days of water being provided.

Terms previously used to classify these goats included “falling goats”, “stiff legged goats”, “falling down goat”, “nervous goat”, “epileptic goats”, and “fainting goats”.

The main reasons known for continuing to breed these goats has been for the observation of this behaviour and their ability to be kept in minimally fenced farms because of their lack of desire to jump over anything over 0.5m.

If startled by sudden movements or loud noises, they will attempt to escape from the disturbance, generally followed by a startle reaction. In more severe cases, this reaction results in strong tetanic contractions of the agonist and antagonist muscles, causing an uncontrolled stiffness that may cause the goat to remain “frozen” in the position that it was in previous to the attack, or cause it to fall to the ground.

During an attack, which may last from 5-20 seconds, the goat can often be picked up without any bending or movement occurring in its body.

In the case of goats that are less severely affected with the condition, there may be only some localized stiffness observed in the legs.

If repeated attacks are precipitated in a goat with severe myotonia within 5-10 minutes of each other, the attacks become less severe, or completely stop altogether. After a period of rest of about 20-30 minutes, a severe attack can be induced again.

The myotonic goat, similar to humans with congenital myotonia, exhibits no obvious muscle wasting, are rarely incapacitated by the condition, and lives a normal life span.

The experiments of Brown and Harvey in 1939 with the myotonic goat made a major contribution to the understanding of the physiological basis of this condition and influenced many other theories of myotonia and its causes.

Observations were made regarding the development of this condition in kids. It was observed that there were no abnormalities in percussion response or stiffness during the first 14 days of a newborn goat’s life. The first percussion responses were observed during days 18-143, and the stiffening and/or falling begins to occur during days 20-173.

Congenital myotonia can be inherited as an autosomal dominant trait (with incomplete penetrance) or a recessive trait, resulting in the varying severity of the condition.

A single nucleotide change resulting in a missense mutation that causes a disturbance in the functioning of the chloride channel explaining the underlying cause of myotonia congenita.

This missense mutation occurs in a sequence of seven amino acids that are included in a group of closely related channels including that of humans and rats.

Previous studies have reported that taurine, an amino sulphonic acid, when given to myotonic patients can reduce the symptoms of the condition. However, it has been shown that it does not antagonize the condition, nor prevent it.