Америкалық миотониялық ешкі туралы мақала

American breed of meat goat

The myotonic goat or Tennessee fainting goat is an American breed of goat. It is characterised by myotonia congenita, a hereditary condition that may cause it to stiffen or fall over when excited or startled. It may also be known as the fainting goat, falling goat, stiff legged goat or nervous goat, or as the Tennessee wooden leg goat. Four goats of this type were brought to Tennessee in the 1880s. Myotonic goats tend to be less preferred for sustainable meat production.

The myotonic goat is important in history for researching and clarifying the role of chloride in muscle excitation. Fainting goats were first brought to Marshall County, Tennessee, in the 1880s. The fainting was first described in scientific literature in 1904, and described as a "congenital myotonia" in 1939. The mutation in the goat gene that causes this muscle stiffness was discovered in 1996, several years after the equivalent gene had been discovered in humans and mice. 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. In affected goats, the CLCN1 gene contains a missense mutation; the amino acid alanine is replaced with a proline residue. 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. It has been shown that the increased muscle excitability is largely accounted for by the lack of chloride permeability in these fibers. 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. Previous studies have also 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 neither antagonizes the condition, nor prevents it. Also, like the goats, it can range from mild to severe.

From the study above, it was found that a change in the nucleotide sequence caused a proline substitution for alanine residue in the carboxyl terminus of the goat's chloride channel. The mutation in the goat gene that causes this muscle stiffness was discovered in 1996, several years after the equivalent gene had been discovered in humans and mice. 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.