Tare Genetiche del Bovino
Congenital Pseudo-myotonia
Italian version
The clinical picture is mainly characterized by an exercise-induced
muscle contracture which prevents animals from performing muscular activities more intense than a simple walk at a slow pace.
In fact, when stimulated to move faster, the muscles immediately become stiff and "freeze up" temporarily, inducing a rigid and uncoordinated gait.
The hind legs appear to be more affected but the front legs are involved as well.
Scuffing the toe and bunny hopping are progressive exercise-induced findings in the hind legs whereas goose-stepping and circumduction (swinging outwards)
are the alterations at the level of the front legs.
The stiffness disappears as soon as the exercise ceases.
If the exercise is prolonged, the stiffness freezes the locomotion and the animals fall on the ground like a log.
The fall is simply due to the block of the leg musculature; in fact animals do
not pass out or lose consciousness as in fainting. After a few seconds, the
muscles relax and the animals regain their ability to get up and move as if
nothing had happened.
At a slow pace, the animals do not show any contractural crisis, even if they walk for long time.
No sign of weakness is noticed as well.
But if the ground is uneven (such as in the case of deep permanent straw-manure bedding) or if there are obstacles to be climbed over
(e.g. steps), their limbs may stiffen up again with consequent loss of coordination and falling is possible.
Animals also experience general muscular stiffening when startled; retraction of the bulbi and prominence of the third eyelid are other
common findings during these startle-elicited crises.
Clinical examination of the muscles "at rest" does not disclose any remarkable findings; muscle tone, tropism and growth are within
the physiologic range. Percussion myotonia is absent.
The symptoms are present at birth and remain practically unchanged for life.
Although growth performance is below expectations, the slaughtered animals reached a satisfactory weight.
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Routine hematology reveals no abnormalities. Biochemistry usually shows slightly increased levels of creatine kinase,
lactate dehydrogenase and aspartate aminotransferase. L-Lactate is normal at rest and after a crisis-free slow paced walk, but increases
immediately after stronger exercise accompanied by the occurrence of a crisis of stiffness (to approximately 8,0 mmol/l). Routine
hematology reveals no abnormalities.
Standard needle electromyography (information based on two subjects examined at the level of the muscles of the rump and the haunch)
shows normal spontaneous insertion activity and voluntary electrical activity. No myotonic discharges in the muscles are noticed after
exercise.
Routine histological preparations (HE, Trichrome) as well as more specific histochemical and histoenzymatic stains (ATPase, SDH, COX,
NADH, PAS, Oil-red-O) carried out on bioptic samples of the semimembranosus muscle of three live patients failed to show any remarkable
and helpful findings. The same negative result was obtained by the same histological examinations of the muscles of the rump, shoulder
and haunch of one slaughtered animal. In this subject, the histological examination of the nervous system (peripheral nerves, spinal cord,
brain and cerebellum) was also normal.
On the basis of the clinical findings and of the scanty results obtained by
collateral exams, we have adopted the term "Congenital Pseudo-myotonia":
- congenital, due to the fact that the symptoms are present since birth
- myotonia, because the main clinical characteristic is the exercise-induced
tonic contraction of the musculature
- pseudo-myotonia, because contrary to the true myotonia, the elctromyographic
examination doesn't show any alteration, not even during the phase of the muscle
contraction.
Similarly to the human "Brody’s disease", the Congenital Pseudomyotonia of Chianina breed is caused by a disorder of muscle function
based on an exercise-induced impairment of muscle relaxation due to a defect of calcium reuptake.
The disease is due to a defect of SERCA1 (Sarco-Endoplasmic Reticulum Ca2+ATPase 1); in fact, by pumping the calcium ions from the
sarcoplasma of the muscular fibre back into the sarco-endoplasmic reticulum, this enzymatic pump decreases the calcium concentration
within the sarcoplasma thus enabling the relaxation of the myofilaments .
A dysfunction of this pump provokes a delay of the reuptake of the calcium and, therefore, a delay of the relaxation of the muscle.
Congenital Pseudomyotonia in Chianina occurs in a familial pattern consistent with monogenic autosomal recessive inheritance. Until now,
all identified affected animals can be traced back to a single common male ancestor.
Recent molecular studies, including linkage analysis and mutation analysis, carried out in Bern by Cord Droegemueller, indicated that the
cause of the Pseudomyotonia is a missense mutation located in the ATP2A1 gene, the gene which codes for the SERCA1 pump.
The Institute of Genetics of the University of Berne developed a test for the detection of the carriers.
All young bulls admitted to the genetic center of Perugia should be tested before beginning the performance test.
Bibliography
Brody I.A. (1969)
"Muscle contracture induced by exercise: A syndrome attributable to
decreased Relaxing Factor"
New Engl. J Med., 281:187-192.
Testoni S., Boni P., Gentile A. (2007)
"Congenital Pseudomyotonia in Chianina Cattle"
Abstract book of the 15th International Congress of Mediterranian Federation for
Helath and Production of Ruminants, 15-19/05/2007, Kusadasi, Turchia, pag. 43.
Testoni S., Boni P., Gentile A. (2007)
"Congenital Pseudomyotonia in Chianina Cattle"
Proceedings VIII Middle European Buiatric Congress, 5-8/06/2007, Gura Humorului,
Romania, pag. 59.
Testoni S., Boni P., Sacchetto R., Maccatrozzo L., Pietra M., Liguori R.,
Mascarello F., Gentile A. (2008)
"Pseudomiotonia in bovini Chianini"
Ob. Doc. Vet., 29(3):11-15.
Testoni S., Boni P., Gentile A. (2008)
"Congenital Pseudomyotonia in Chianina Cattle"
Veterinary Record, in press
Drogemuller C., Drögemüller M., Leeb T., Mascarello F., Testoni S., Rossi M.,
Gentile A., Damiani E., Sacchetto R. (2008)
"Identification of a missense mutation in the bovine ATP2A1 gene in
congenital pseudomyotonia of Chianina cattle: An animal model of human Brody
disease"
Genomics, accepted for publication.