Dental and Craniofacial Findings in Eight Miniature Schnauzer Dogs Affected by Myotonia Congenita: Preliminary Results

Abstract

Myotonia is a clinical sign characterized by the delay of skeletal muscle relaxation following the cessation of a voluntary activity or the termination of an electrical or mechanical stimulus. Recently, Miniature Schnauzers with myotonia congenita associated with defective chloride ion conductance across the skeletal muscle membrane were identified. Congenital myotonia in these dogs appears to follow an autosomal recessive mode of inheritance. Craniofacial and dental findings of eight Miniature Schnauzer dogs with myotonia congenita are described in the present paper. These findings include: delayed dental eruption of both deciduous and permanent dentition: persistent deciduous dentition; unerupted or partially erupted permanent teeth: crowding and rotation of premolar and or incisor teeth: missing teeth: increased interproximal space between the maxillary fourth premolar and first molar teeth: decreased interproximal space between the maxillary canine and lateral incisor teeth: inability to fully close the mouth due to malocclusion: distoclusion: and, decreased mandibular range of motion. A long narrow skull with a flattened zygomatic arch and greater mandibular body curvature were also consistent findings in the affected dogs. The small number of dogs studied prevents conclusive statements about the origin of these abnormalities, however it is interesting that only 1 of 45 unaffected Miniature Schnauzer dogs showed similar traits.

Dental Abnormalities in Immature Dogs with a History of Mandibular Fractures

“…1,2 Amelogenesis imperfecta, peg teeth, abnormal number of roots or crown cusps, dilacerations of the crown and root, and unerupted or partially erupted teeth have been associated with genetic diseases. [3][4][5][6][7] Enamel hypoplasia and hypomineralization, tooth resorption, and an abnormal shape of the crown or root may occur due to acquired local (eg, trauma, inflammation) or systemic (eg, fever, malnutrition, viral infection, fluoride intoxication) conditions. However, the etiology of many dental abnormalities often remains unknown.…”

Detection of a genetic mutation for myotonia congenita among Miniature Schnauzers and identification of a common carrier ancestor

“…[13][14][15] The DNA test results of the 7 dogs with clinical signs were confirmed by analysis of DNA sequencing, which revealed only the mutant allele in the 4 affected dogs, whereas the other 3 dogs had the normal sequence for the ClC-1 allele (data not shown). Of the 4 homozygous myotonic Miniature Schnauzers, 3 were from eastern Pennsylvania and 1 was from Ohio, and all of them had typical signs of myopathy and superior prognathism.…”

“…[13][14][15][16] Myotonia congenita has been characterized best in Miniature Schnauzers, a breed in which it is inherited as an autosomal recessive trait. 15 The biochemical defect relates to reduced chloride conductance across the skeletal muscle membrane resulting in increased sarcolemmal excitability. Myotonic Miniature Schnauzers have hypertrophic skeletal muscles, difficulty in rising after a period of rest, a stiff and stilted gait when walking, and a bunnyhop type movement when running.…”

Disorders of Involuntary Movement

“…20,27,28 Individual dogs of various other breeds also have been described. 27 Abnormalities include delayed eruptions of deciduous and permanent dentition, increased interdental spaces, malocclusions, difficulty opening and closing the mouth, mandibular brachygnathism, protrusion of the tongue, and flattening of the zygomatic arch. Although clinical signs are present at birth, muscle stiffness is more evident at the time pups begin to walk.…”