Orlando Paciello » 6.Congenital and hereditary muscle disorders in farm animals

Congenital and hereditary muscle disorders in farm animals

Many hereditary, congenital or neonatal defects can affect muscles.
Hereditary muscle disorders can be seen at birth or soon afterwards, or can appear years later.
Molecular biology and genetic testing have combined to produce better knowledge of many myopathies in animals and have made it possible to identify affected animals or those who are carriers of genetic disease.

Innervation defect

• Congenital lower motor neurone disease leads to serious alterations in the development of muscle fibres.
• Innervation plays a fundamental role in the development and maturation of myofibres and the muscle lesions which result from a genetic defect affecting the nerves can be serious and complex.
• The most common example of this type of defect is congenital arthrogryposis

Congenital arthrogryposis

This refers to persistent flexion of a joint because of muscle spasm or retraction, or because of intra and extracapsular ankylosis.
CAR = Congenital articular rigidity which is seen in lambs, calves, foals and piglets falls into the category of malformation of the joints or muscular aplasia or hypoplasia.
It is characterised by stiffness of single or multiple joints (arthrogryposis multiplex congenita), is non-progressive, is caused by alterations to the nervous system and is often associated with skeletal malformation.

Congenital arthrogryposis  (cont.)

The muscle groups in the affected joints are hypoplastic, i.e. the muscles are not fully developed and muscle tissue is replaced by adipose and fibrous tissue. In bovines, the disease occurs in different breeds but especially in:

• Shorthorn;
• Charolais;
• Piemontese;
• Swedish dole;
• Merino and corriedale sheep;
• Norwegian fjord horses.

Congenital myofibrillar hypoplasia (splayleg)

The most significant congenital defect in intensively reared swine (pietrain, landrace and large White).
There is congenital myofibrillar hypoplasia which leads to muscle weakness in the hind quarters and less frequently in the front making it difficult for the animal to stand. The limbs are held in abduction, like a sitting down dog with limbs outstretched and splayed.

Congenital myofibrillar hypoplasia (splayleg)

The etiology of this disease is believed to be multi-factorial. Factors to do with food, toxins or environment probably combine with a hereditary predisposition.

It has been noted that incidence of the disease increases with episodes of PRRS (Porcine reproductive respiratory syndrome).

Diaphragmatic myopathy in Meuse-Rhine-Yssel cattle

• Seen in bovines of the Meuse-Rhine-Yssel breed. Affects mainly diaphragm and intercostal muscles. Age varies from 2-10 years with an average of 5.
• The muscles appear pale, swollen and rigid.

Progressive congenital myopathy in ovines

• With the Merino breed of sheep there is a well-known progressivecongenital myopathy which reveals itself in stunted growth and progressive difficulty with flexion of the posterior limbs from 3-4 weeks of age onwards. The animals die in first 6-18 months of life as the dystrophy gradually worsens.
• The muscles look hard and grey-coloured.

Spider Lamb Syndrome ( Hereditary Chondrodysplasia )

A genetic disease characterized by skeletal deformity in young lambs. It is a recessive hereditary disorder.

This means that any lambs with the disease received a recessive gene from both parents.

This disease is seen mainly in black-faced lambs.

• 75% Suffolk
• 25% Hampshire

Flexor deformity in foals

Flexor deformity is a pathologic condition affecting the joints, characterized by deviation in the sagittal plane and persistent hyperflexion in one articular region, resulting in altered biomechanics of the joint.
The most frequent sites for this kind of deformity are:
metacarpal / tarsal phalangeal and carpal joints, and more rarely the distal interphalangeal joints, tarsals or vertebral column.

Flexor deformity in foals (cont.)

In foals, as in children, symptoms like “flexor deformity” and “hypotonia and/or muscle weakness” may be the expression of congenital neuromuscular pathologies.

Causes of flexor deformity in children

In children, many congenital myopathies present with flexor deformity, muscle hypotonia, reduction of visus and difficulty feeding.

Congenital myopathies present typical morphological changes which show up on histochemical tests.
They are often associated with a predominance or hypotrophy of type I fibres.

Central Core Disease (CCD)

• The first Congenital Myopathy to be discovered (1956).
• Congenital hypotonia, muscle weakness and flexor deformity are the main symptoms
• Histologically it is characterised by well-defined rounded areas (cores) inside the type I fibres.
• Cores look like areas without mitochondrial activity and with oxidative insufficiency.

Nemalinic Myopathy

Congenital, non-progressive myopathy, characterised by small subsarcolemma rod structures between the myofibrils.
These structures correspond to the Z band and are continuous with actin filaments.
Congenital hypotonia, generalized muscle weakness, alterations to facial musculature and accompanying palatoschisis with relevant clinical symptoms.

Myotubular Myopathy

Myotubular myopathy is perhaps the most serious congenital muscle pathology.
Predominant clinical symptoms are serious hypotonia, insufficiency in spontaneous movement, contracture in neck muscles, multiple flexor deformity and cardiac and respiratory insufficiency.
Histologically the myofibres sometimes appear undifferentiated and similar to those of muscle fibres at the fetal stage.
A transparent halo can be seen around the nuclei, which demonstrates intense oxidative enzyme activity.

Desminic myopathy

A protein accumulation myopathy, which is indicative of a defect in protein catabolism.
Areas of desmina deposits show a lack of oxidative and ATPase activity. The amorphous material can form spheroid aggregates or widespread filaments within the sarcoplasm.
New-borns present with generalized muscle-weakness and cardiomyopathies as well as flexor deformity.

Fibre type diproportion

Pathology present at birth, characterized by a prevalence (> 12%) and congenital hypotrophy of type I muscle fibres.

Predominant symptoms are muscle weakness, delayed neuromuscular transmission, muscle contractures and respiratory difficulty.