Congenital canine myasthenia gravis: I. Deficient junctional acetylcholine receptors

Congenital and inherited neurologic diseases in dogs and cats: Legislation and its effect on purchase in Italy

Many of the congenital neurologic diseases can result in incapacity or death of the animal. Some of them, such as idiopathic epilepsy and hydrocephalus, exhibit breed or familial predisposition and a genetic basis was proved or suggested. Some diseases can be presumptively diagnosed after a detailed signalment (breed predisposition), history (e.g. family history because many of these defects have familial tendencies), and through physical exam; other diagnostic methods (radiography, computed tomography, magnetic resonance, electrophysiologic tests, etc.) can provide supportive evidence for the congenital defect and help to confirm the diagnosis. Some cases can lead to civil law-suits when the lesions are congenital, but not easily recognizable, or when the lesions are hereditary but tend to became manifest only after some time (more than 12 months after the date of purchase, e.g., after the vice-free guarantee period has expired). Moreover, quite frequently an early diagnosis is not made because there are delays in consulting the veterinarian or the general practitioner veterinarian does not perceive subtle signs. This study was designed to focus on the medico-legal aspects concerning the buying and selling in Italy of dogs and cats affected by congenital and hereditary neurologic diseases that could constitute vice in these animals. While adequate provisions to regulate in detail the various aspects of pet sale have still to be drawn up by legislators, it may be helpful to involve breeders, by obliging them by contract to extend guarantees in the case of hereditary lesions, including neurologic diseases.

A CHRNE frameshift mutation causes congenital myasthenic syndrome in young Jack Russell Terriers

Congenital myasthenic syndromes (CMSs) are a group of rare genetic disorders of the neuromuscular junction resulting in structural or functional causes of fatigable weakness that usually begins early in life. Mutations in pre-synaptic, synaptic and post-synaptic proteins have been demonstrated in human cases, with more than half involving aberrations in nicotinic acetylcholine receptor (AChR) subunits. CMS was first recognized in dogs in 1974 as an autosomal recessive trait in Jack Russell Terriers (JRTs). A deficiency of junctional AChRs was demonstrated. Here we characterize a CMS in 2 contemporary cases of JRT littermates with classic clinical and electromyographic findings, and immunochemical confirmation of an approximately 90% reduction in AChR protein content. Loci encoding the 5 AChR subunits were evaluated using microsatellite markers, and CHRNB1 and CHRNE were identified as candidate genes. Sequences of the splice sites and exons of both genes revealed a single base insertion in exon 7 of CHRNE that predicts a frameshift mutation and a premature stop codon. We further demonstrated this pathogenic mutation in CHRNE in archival tissues from unrelated JRTs studied 34 years ago.

A COLQ Missense Mutation in Sphynx and Devon Rex Cats with Congenital Myasthenic Syndrome

An autosomal recessive neuromuscular disorder characterized by skeletal muscle weakness, fatigability and variable electromyographic or muscular histopathological features has been described in the two related Sphynx and Devon Rex cat breeds (Felis catus). Collection of data from two affected Sphynx cats and their relatives pointed out a single disease candidate region on feline chromosome C2, identified following a genome-wide SNP-based homozygosity mapping strategy. In that region, we further identified COLQ (collagen-like tail subunit of asymmetric acetylcholinesterase) as a good candidate gene, since COLQ mutations were identified in affected humans and dogs with endplate acetylcholinesterase deficiency leading to a synaptic form of congenital myasthenic syndrome (CMS). A homozygous c.1190G>A missense variant located in exon 15 of COLQ, leading to a C397Y substitution, was identified in the two affected cats. C397 is a highly-conserved residue from the C-terminal domain of the protein; its mutation was previously shown to produce CMS in humans, and here we confirmed in an affected Sphynx cat that it induces a loss of acetylcholinesterase clustering at the neuromuscular junction. Segregation of the c.1190G>A variant was 100% consistent with the autosomal recessive mode of inheritance of the disorder in our cat pedigree; in addition, an affected, unrelated Devon Rex cat recruited thereafter was also homozygous for the variant. Genotyping of a panel of 333 cats from 14 breeds failed to identify a single carrier in non-Sphynx and non-Devon Rex cats. Finally, the percentage of healthy carriers in a European subpanel of 81 genotyped Sphynx cats was estimated to be low (3.7%) and 14 control Devon Rex cats were genotyped as wild-type individuals. Altogether, these results strongly support that the neuromuscular disorder reported in Sphynx and Devon Rex breeds is a CMS caused by a unique c.1190G>A missense mutation, presumably transmitted through a founder effect, which strictly and slightly disseminated in these two breeds. The presently available DNA test will help owners avoid matings at risk.

A COLQ missense mutation in Labrador Retrievers having congenital myasthenic syndrome

Congenital myasthenic syndromes (CMSs) are heterogeneous neuromuscular disorders characterized by skeletal muscle weakness caused by disruption of signal transmission across the neuromuscular junction (NMJ). CMSs are rarely encountered in veterinary medicine, and causative mutations have only been identified in Old Danish Pointing Dogs and Brahman cattle to date. Herein, we characterize a novel CMS in 2 Labrador Retriever littermates with an early onset of marked generalized muscle weakness. Because the sire and dam share 2 recent common ancestors, CMS is likely the result of recessive alleles inherited identical by descent (IBD). Genome-wide SNP profiles generated from the Illumina HD array for 9 nuclear family members were used to determine genomic inheritance patterns in chromosomal regions encompassing 18 functional candidate genes. SNP haplotypes spanning 3 genes were consistent with autosomal recessive transmission, and microsatellite data showed that only the segment encompassing COLQ was inherited IBD. COLQ encodes the collagenous tail of acetylcholinesterase, the enzyme responsible for termination of signal transduction in the NMJ. Sequences from COLQ revealed a variant in exon 14 (c.1010T>C) that results in the substitution of a conserved amino acid (I337T) within the C-terminal domain. Both affected puppies were homozygous for this variant, and 16 relatives were heterozygous, while 288 unrelated Labrador Retrievers and 112 dogs of other breeds were wild-type. A recent study in which 2 human CMS patients were found to be homozygous for an identical COLQ mutation (c.1010T>C; I337T) provides further evidence that this mutation is pathogenic. This report describes the first COLQ mutation in canine CMS and demonstrates the utility of SNP profiles from nuclear family members for the identification of private mutations.

Acquired myasthenia gravis associated with oral sarcoma in a dog

Acquired myasthenia gravis is a common neuromuscular disorder resulting from autoantibody directed against the post-synaptic acetylcholine nicotinic receptors in skeletal muscle. Myasthenia gravis has been reported previously as a paraneoplastic syndrome. This case report presents myasthenia gravis secondary to an oral sarcoma in a juvenile Mastiffdog.

Myasthenia gravis and disorders of neuromuscular transmission

Myasthenia gravis is a disorder of neuromuscular transmission that occurs in congenital and acquired autoimmune forms. Acquired myasthenia gravis is probably the most common neuromuscular disorder in dogs that can be diagnosed and treated. An early, accurate diagnosis and appropriate therapy is of utmost importance to a good clinical outcome in this disorder. This article focuses on the diagnosis and treatment of acquired myasthenia gravis in dogs and cats with brief discussions of other disorders of neuromuscular transmission, including congenital myasthenia gravis, tick paralysis, botulism, and organophosphate intoxication.

Megaoesophagus secondary to acquired myasthenia gravis

Fifteen dogs with confirmed adult onset idiopathic megaoesophagus, in which no generalised muscle weakness was observed, were tested for the presence of acetylcholine receptor antibodies. Of these, six were found to have values greater than 0.6 nmol/litre, previously determined to be diagnostic of acquired myasthenia gravis. The mean serum titre value for these dogs was 5.59 nmol/litre (range 0.78 to 8.72 nmol/litre). It appears that a significant proportion of dogs presenting with megaoesophagus have myasthenia gravis and, if a prompt diagnosis and appropriate treatment can be instituted, clinical signs may improve.

Myasthenia gravis in the cat

Myasthenia gravis (MG) was diagnosed in four cats--one had an apparently congenital form and three had the acquired autoimmune form. All four cats were examined because of episodes of weakness including gait abnormalities, voice change, neck ventroflexion, and regurgitation. Palpebral reflexes were absent in all cats. Administration of edrophonium chloride resulted in transient resolution of clinical signs in all four cats. Three cats were tested for the presence of serum autoantibodies against acetylcholine receptor (AChR) by radioimmunoassay. Two cats with acquired MG had anti-AChR antibody titers of 10.5 and 96.8 nmol/l (normal, less than or equal to 0.03 nmol/l). Antibodies were not detected in the cat with presumptive congenital MG. All four cats were treated with pyridostigmine bromide. Two cats with acquired MG were euthanatized because of clinical deterioration. The third cat with acquired MG has been asymptomatic since 2 months after diagnosis. The cat with presumed congenital MG is alive 3 years after diagnosis.

Ultrastructure of motor endplates in canine congenital myasthenia gravis

Morphometric analysis was carried out on electron micrographs of motor endplates from three Jack Russell terriers affected with congenital myasthenia gravis (CMG) aged 10 weeks, 12 weeks and 22 weeks, respectively. Control endplates from age-matched pups and an adult Jack Russell were also examined. The results showed that postsynaptic membrane density was significantly increased in affected animals and secondary fold length was decreased. The ratio of postsynaptic to presynaptic membrane length was normal in the 10 and 12-week-old pups, but reduced in the 22-week-old CMG animal. These changes were unrelated to muscle fibre diameter and there was no evidence of a destructive process. It is suggested that the alteration in membrane folding pattern in this condition may be related to abnormal trophic influences during synaptogenesis.

Congenital canine myasthenia gravis: II. Acetylcholine receptor metabolism

Acetylcholine receptor (AChR) metabolism was studied in muscle from juvenile and adult dogs with congenital myasthenia gravis (CMG) and their unaffected littermates. Although the amount of AChR in the junctional region of innervated CMG muscle fibers was 25% of normal, or less, denervation of CMG fibers resulted in the appearance of AChR in extrajunctional membranes at as high a concentration as in denervated normal fibers. The rate of degradation of junctional AChR in CMG fibers explanted to organ culture did not differ significantly from normal. In monolayer cultures derived from enzyme-dissociated CMG muscle, myotubes of normal morphology developed, and the synthesis and degradation of AChR did not differ from normal. Addition of sera from dogs with the acquired autoimmune form of MG accelerated the degradation of AChR on cultured myotubes, but CMG dog sera were without effect. These data suggest that the low junctional membrane density of AChR in CMG does not reflect a primary inability of muscle to synthesize AChR, nor an accelerated degradation of AChR in the postsynaptic membrane, but rather a low insertion rate of AChR in the postsynaptic membrane.