Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
26 © Schattauer 2012 Original Article Hereditary polyneuropathy in the Alaskan Malamute* K. Rentmeister1; T. Bilzer3; S. Petri2; G. Schanen4; M. Fehr1; O. Distl2; A. Tipold1 1Department of Small Animal Medicine and Surgery, University of Veterinary Medicine Hannover (Foundation), Hannover, Germany; 2Institute for Animal Breeding and Genetics, University of Veterinary Medicine Hannover (Foundation), Hannover, Germany; 3Institute of Neuropathology, Heinrich Heine University, Düsseldorf, Germany; 4Small Animal Clinic Elmer-Kornberg – Schanen, Trier, Germany Key words Schlüsselwörter Dog, electrodiagnosis, muscle- and nerve biopsy, segregation analysis Hund, Elektrodiagnostik, Muskel- und Nervbiopsie, Segregationsanalyse Summary Zusammenfassung Objective: To prove the hypothesis that a polyneuropathy in Alaskan Malamutes has a genetic background. Material and methods: Pedigrees of 131 related Alaskan Malamutes were included in the current study. Neurological examination, electrodiagnosis as well as muscle and nerve biopsies could be performed in 10 dogs. Information about the disease status of the other 121 Alaskan Malamutes were supplied by referring veterinarians, breeders and owners. Segregation analysis using four different models (monogenic, polygenic, mixed monogenicpolygenic and the phenotypic model) was performed on 71 dogs to test the different mechanisms of genetic transmission. Results: In seven clinically affected dogs abnormal electromyographic findings and reduced nerve conduction velocity were detected. Suspected diagnosis of polyneuropathy was confirmed by nerve biopsy results, characterized by axonal degeneration and hypomyelination. Muscle specimens revealed signs of neurogenic myopathy. Three related clinically normal Alaskan Malamutes also displayed moderate neuromuscular changes in histopathology. In the segregation analysis the polygenic model proved as best suitable to explain the observed segregation pattern among all other models tested. Conclusion: The current study could demonstrate that polyneuropathy in Alaskan Malamutes is a hereditary disease with variable phenotypic expression ranging from severely affected to subclinical forms, which has to be considered in future gene analysis studies. Ziel der Untersuchung war die Überprüfung der Hypothese, dass die Polyneuropathie des Alaskan Malamute eine erbliche Komponente hat. Material und Methoden: Um diese Hypothese zu bestätigen, wurden Abstammungsnachweise von 131 verwandten Alaskan Malamutes herangezogen. Bei 10 Hunden waren eine neurologische Untersuchung, Elektrodiagnostik und Beurteilung von Nerven- und Muskelbioptaten möglich. Weitere Informationen über den Gesundheitsstatus von 121 Alaskan Malamutes konnten über Haustierärzte, Züchter und Besitzer eingeholt werden. Zur Testung der verschiedenen Mechanismen eines Erbgangs wurde bei 71 Hunden eine Segregationsanalyse durchgeführt, die vier Modelle (monogen, polygen, gemischt monogen-polygen und phänotypische Verteilung) beinhaltete. Ergebnisse: Bei sieben erkrankten Alaskan Malamutes ließen sich Spontanaktivität im Elektromyogramm und eine erniedrigte Nervenleitgeschwindigkeit nachweisen. Die histologische Untersuchung von Muskel- und Nervbioptaten bestätigte die Verdachtsdiagnose einer Polyneuropathie. Diagnostiziert wurden eine neurogene Muskelatrophie, Axondegeneration und Hypomyelinogenese. Drei verwandte, zum Zeitpunkt der Untersuchung klinisch unauffällige Hunde wiesen histopathologisch ebenfalls geringgradige neuromuskuläre Veränderungen auf. Das polygene Modell der Segregationsanalyse konnte das beobachtete Segregationsmuster am besten erklären. Schlussfolgerung: Es ließ sich zeigen, dass es sich bei der Polyneuropathie des Alaskan Malamute um eine genetische Erkrankung handelt. Der Phänotyp ist sehr variabel und reicht von Tetraparesen bis zu subklinischen Formen. Diese subklinischen Formen müssen bei zukünftigen Genanalysen berücksichtigt werden. Correspondence to Kai Rentmeister Tierärztliche Praxis für Neurologie Mainfrankenpark 16b 97337 Dettelbach E-Mail: [email protected] Hereditäre Polyneuropathie beim Alaskan Malamute Tierärztl Prax 2012; 40 (K): 26–34 Received: October 13, 2011 Accepted after revision: December 16, 2011 * Dedicated to the 60th birthday of Prof. Dr. Ingo Nolte. Tierärztliche Praxis Kleintiere 1/2012 Downloaded from www.tieraerztliche-praxis.de on 2017-06-17 | IP: 88.99.165.207 For personal or educational use only. No other uses without permission. All rights reserved. K. Rentmeister: Hereditary polyneuropathy in the Alaskan Malamute Introduction Clinical and neurological examination Since the late 1970s various case reports about hereditary polyneuropathies in different canine breeds have been described such as the giant axonal neuropathy in German shepherds (11, 12), the progressive axonopathy in Boxers (16), the hypomyelinating polyneuropathy in the Golden retriever (3), the laryngeal paralysispolyneuropathy complex in Bouviers de Flandre (24), young Dalmatians (6), young Rottweilers (17) and Siberian Huskies (21), the distal sensorimotor polyneuropathy in the Rottweiler (5), the hypertrophic neuropathy in the Tibetan terrier (8) and Mastiff (22), the sensory neuropathies in the English pointer (9, 10) and Dachshund (13), and the distal symmetric polyneuropathy in the Great Dane (2). A recent review was provided by Granger (15). Also in Alaskan Malamutes a hereditary polyneuropathy has been suspected. The first affected dogs were examined in Norway between the years 1977 to 1979 by Moe et al. (18), Moe and Bjerkas (19) and Moe (20). A total of 12 dogs could be traced back to one common ancestor. Braund et al. (7) presented 11 cases of Alaskan Malamutes with polyneuropathy from different litters. Although the authors strongly suggested a genetic disease, several clinical, electrodiagnostical and histopathological differences to the dogs examined by Moe et al. (18) could be found. Using the term “idiopathic polyneuropathy in Alaskan Malamutes”, Braund et al. (7) distinguished this condition from the hereditary form previously described in Norway. The objective of the present study was to elucidate whether a hereditary polyneuropathy exists in the Alaskan Malamute and to substantiate the clinical findings by electrodiagnostical, histopathological examinations and segregation analyses. General and neurological examination was performed on 10 Alaskan Malamutes (dogs 30, 31, 50, 51, 52, 53, 65, 66, 76 & the control dog). Concerning the remaining littermates (dogs 54, 55, 56 & 57), the information about the clinical status is based upon telephone calls with the referring veterinarians, the breeders or the owners. Material and methods Dogs A total of 131 Alaskan Malamutes were included in the present study (씰Fig. 1). Each dog received a number according to the information given by the breeders. Initially, two Alaskan Malamutes were presented at the Department of Small Animal Medicine and Surgery, Veterinary School of Hannover, Germany, with a history of abnormal vocalization characterized by hoarse barking since three months, progressively decreasing muscle tone, weakness and exercise intolerance (dogs 52 & 53). Their littermates (dogs 51, 54, 55, 56 & 57), their parents (sire = dog 31, dam = dog 50) and four related dogs (dogs 30, 65, 66 & 76) were investigated. Another non-related and clinically healthy Alaskan Malamute of the same breeder was added as control dog. In collaboration with the breeders, a pedigree of 131 related dogs could finally be established. The ancestors of the Alaskan Malamutes examined in Hannover, Germany, were directely related with the Norwegian dogs (dogs 101–131) described by Moe et al. (18) and Moe and Bjerkas (19). Further examinations Routine hematology and blood chemistry was performed on dogs 31, 50, 51, 52, 53 & 76. Additional examinations (T4, TSH, antiacetylcholine-receptor antibodies) and edrophonium chloride testing (Tensilon®, Roche, 0.2 mg/kg BW) were performed on dog 52. Radiographs of thorax and abdomen were taken from dogs 31, 50, 51, 52 & 53. For electrodiagnostic testing as well as muscle and nerve biopsies all dogs received general anaesthesia, which was induced by intravenous injection of diazepam (1.0 mg/kg BW) and levomethadone (0,6 mg/kg BW), and maintained by inhalation of isoflurane and oxygen. Electrodiagnostic testing was performed using a Nicolet Viking IV-D electrodiagnostic device (Würzburg-Höchberg, Germany). Electromyography (EMG) and motor nerve conduction velocity (NCV) on common peroneus and radialis nerve was tested on all 10 dogs previously undergoing neurological examination (dogs 30, 31, 50, 51, 52, 53, 65, 66, 76 & the control dog). Muscle and nerve biopsies of seven Alaskan Malamutes (dogs 30, 31, 50, 51, 52, 53 & 76) were taken at the proximal lateral stifle level from the common peroneus nerve and the lateral head of the gastrocnemius muscle according to established surgical techniques (4). The biopsies were immediately stored in small plastic tubes and cooled using gel freeze packs without adding any fixative. They were transported to the Institute of Neuropathology of Heinrich Heine University, Düsseldorf, by overnight express. Muscle specimens were orientated in transverse and longitudinal directions, embedded in tragant, frozen in isopentane at –135 °C, and stored in airtight plastic tubes at –80 °C. Cryostat sections of muscle and nerve specimens of 6–10 μm were stained with hematoxylin and eosin (H&E), and Gomori trichrome according to Engel; in addition, muscle specimens were treated with reduced nicotinamide adenine dinucleotide tetrazolium reductase (NADH-TR, pH 9.5), oil red O, myosine adenosine triphosphatase (ATPase, pH 10.0 and 4.3), and acidic phosphatase. In parallel, parts of the nerve specimens were fixed in a mixture of 2.5% formalin and 1% glutaraldehyde, buffered at pH 7.4, and processed for paraffin-histology or embedded in Epon, respectively. Semithin transverse sections were stained with toluidine-blue. Pedigrees The relationship between all 131 Alaskan Malamutes is shown in 씰Figure 1. Information about the disease status of 121 Alaskan © Schattauer 2012 Tierärztliche Praxis Kleintiere 1/2012 Downloaded from www.tieraerztliche-praxis.de on 2017-06-17 | IP: 88.99.165.207 For personal or educational use only. No other uses without permission. All rights reserved. 27 28 K. Rentmeister: Hereditary polyneuropathy in the Alaskan Malamute Fig. 1 Pedigrees of 131 Alaskan Malamutes. A) complete pedigree, B) subpedigree-1, C) subpedigree-2. ■ = male dog, ● = female dog, ◊ = dog of unknown sex, ■ = not examined, grey filling of the symbols: clinically normal dog with positive histopathology, black filling of the symbols: clinically affected dog with positive electrodiagnostical and/or histopathological examination. Malamutes was supplied by referring veterinarians, breeders and owners. This pedigree includes four nucleus families being paternal half sibs, which are connected to another affected pedigree member (dog 96) via their sire. A direct relationship between the four paternal half sib groups and the further affected members of the pedigree could not be found. The litter with the dogs 51–57 was inbred as well as the affected dogs 31, 50 and 76. Because information on the disease status of ancestors was often missing, the complex pedigree (씰Fig. 1A) was divided in two subpedigrees for segregation analysis: subpedigree-1 (씰Fig. 1B) including a total of 29 dogs and subpedigree-2 (씰Fig. 1C) with a total of 42 dogs. Dogs 93–95 and 97–100 of subpedigree-1 were reported to perform well Tierärztliche Praxis Kleintiere 1/2012 © Schattauer 2012 Downloaded from www.tieraerztliche-praxis.de on 2017-06-17 | IP: 88.99.165.207 For personal or educational use only. No other uses without permission. All rights reserved. K. Rentmeister: Hereditary polyneuropathy in the Alaskan Malamute on the sled team and although not examined were considered to be clinically healthy. In consequence, the segregation analysis included eight litters with a total of 71 Alaskan Malamutes. distributed. Degrees of freedom for the likelihood ratio test statistic are given by the difference of the number of independently estimated parameters for the models compared. Segregation analysis Results The mode of inheritance was tested by employing complex segregation analysis models developed by Bonney (1) and Elston (14). The analysis was performed by using S.A.G.E., Version 3.0. The joint likelihood function for each pedigree was maximized conditionally on the phenotypes of the probands (dog 52 in subpedigree-2 and dog 131 in subpedigree-1). Ascertainment correction was applied as the pedigrees were non-randomly ascertained. Clinically normal dogs with positive histopathology were coded with “1” (grey coloured in 씰Fig. 1), clinically affected dogs with positive histological or/and electromyographical findings were coded with “2” (black coloured in 씰Fig. 1). Four different groups of models were considered in the segregation analysis: ● Monogenic inheritance: This model assumes one gene locus with two alleles in Hardy-Weinberg equilibrium. The allele effects can be recessive, dominant or arbitrary. The transmission probabilities in this case are τAA = 1, τAB = 0.5 and τBB = 0. The transmission parameter is the probability that a parent of genotype AA transmits allele A to offspring with genotype AA, AB or BB. The transmission probabilities are used to construct the genotypic probability distributions of offspring in dependence on the parental genotypes. Therefore, genotypes can be defined as types that transmit to offspring in Mendelian fashion. ● Polygenic inheritance: The effects of parents on offspring were regarded as logistic regressions. Three different submodels were specified. Submodel 1 (type of familiar correlation = 2) included the effect of the affected parents and spouses, submodel 2 (type of familiar correlation = 4) the effect of unaffected parents and spouses as well as the effect of affected parents and spouses. Submodel 3 (type of familiar correlation = 6) distinguished between affected sires, dams, and spouses as well as between unaffected sires, dams, and spouses. ● Mixed monogenic-polygenic inheritance (mixed major gene): This model described the inheritance by using monogenic and polygenic components as described above. The major gene effect was modelled as recessive, dominant or arbitrary effect in each of the three submodels for polygenic inheritance. ● Only one phenotypic distribution (μ-model): In this model only one phenotypic distribution with an arbitrary mean was used. Results of neurological, electrodiagnostical and histological examinations are summarised in 씰Table 1. Clinical and neurological examination Clinical examination of all dogs was normal. At neurological examination, all Alaskan Malamutes had normal consciousness, behaviour and posture. All dogs were pacing except dog 76. In dog 52, gait analysis revealed tetraparesis with exercise intolerance. The postural reactions were generally decreased. Cranial nerve examination showed strong atrophy of the muscles innervated by the trigeminal nerve, and abnormal vocalization was characterized by a hoarse bark. Spinal reflexes were absent or markedly reduced. The muscle tone was reduced and a severe general muscle atrophy was noticed, especially on the hind limbs. Superficial and deep pain seemed to be normal or only slightly depressed. Affection of the phrenic nerve was suggested because of an abdominal type of respiration. Dog 53 had similar, but less apparent signs. Dog 31 only displayed mild proprioceptive deficits in both front legs, dog 66 and 76 had slightly decreased postural reactions and spinal reflexes in the rear (씰Table 1). The remaining Malamutes (dogs 30, 50, 51, 65 & the control dog) showed no neurological abnormalities. Two owners informed us, that dogs 55 & 56 also displayed deficits in form of abnormal vocalization, exercise intolerance and slight gait abnormalities, but refused any examinations. According to the results of neurological examination, a generalised polyneuropathy was suspected. Further examinations Results of routine hematology and blood chemistry were normal. Additional testing performed on dog 52 excluded hypothyroidism (T4 = 1.5 μg/dl, TSH = 0.2 ng/ml) and ruled out myasthenia gravis by negative edrophonium chloride testing and absent antiacetylcholine-receptor antibodies. Plain radiographs of thorax and abdomen (dogs 31, 50, 51, 52 & 53) were normal. Electrodiagnostic findings The different models were compared by using likelihood ratio tests. A saturated model (most general model) was fitted to the data and the likelihood of this model was used in the denominator of the likelihood ratio test. In the numerator of the likelihood ratio test the likelihood of the model being tested has to be nested in the model of the denominator. Then, the natural logarithm of the likelihood ratio multiplied by minus two is asymptotically chi-square Electromyographic examination (EMG) revealed positive sharp waves in dogs 53 and 66 in interosseous, cranial tibial and quadriceps muscles. In addition, dog 53 had reduced insertion potentials in the muscles of the front legs. In dog 52, EMG was characterized by reduced insertion potentials, fibrillation potentials and positive sharp waves. © Schattauer 2012 Tierärztliche Praxis Kleintiere 1/2012 Downloaded from www.tieraerztliche-praxis.de on 2017-06-17 | IP: 88.99.165.207 For personal or educational use only. No other uses without permission. All rights reserved. 29 30 K. Rentmeister: Hereditary polyneuropathy in the Alaskan Malamute Pedigree-Nr. Age Sex Neurologic signs Electrodiagnosis Histopathology 30 11y 10ms f clinically normal EMG: normal; NCV = 88 m/s moderate degenerative polyneuropathy 31 (sire) 6y 6ms m postural reactions reduced in both frontlegs EMG: normal; NCV = 62 m/s moderate degenerative polyneuropathy 50 (dam) 3y 2ms f clinically normal EMG: normal; NCV = 73 m/s marginal degenerative polyneuropathy 51 1y 2ms f clinically normal EMG: normal; NCV = 60 m/s marginal degenerative polyneuropathy 52 1y 2ms m marked tetraparesis, exercise intolerance, pacing, depressed proprioception and absent spinal reflexes, general muscle atrophy including muscles innervated by the trigeminal nerve, abnormal vocalization EMG: decreased insertion severe degenerative potentials, fibrillation po- polyneuropathy tentials and positive sharp waves; NCV: no evaluation due to flat evoked potentials 53 1y 2ms f tetraparesis, proprioception and spinal reflexes reduced, abnormal vocalization EMG: positive sharp waves, moderate degenerative reduced insertion potenpolyneuropathy tials, positive decremental response; NCV = 29 m/s 55 1y 2ms f abnormal vocalization, exer- not performed cise intolerance and slight gait abnormalities* not performed 56 1y 2ms f abnormal vocalization, exer- not performed cise intolerance and slight gait abnormalities* not performed 65 2y 9ms m clinically normal not performed 66 2y 10ms f proprioception and spinal re- EMG: positive sharp flexes reduced in the rear waves; NCV = 72 m/s not performed 76 7ms m proprioception and spinal re- EMG: normal; flexes reduced in the rear NCV = 65 m/s marginal degenerative polyneuropathy control 4y 11ms m clinically normal not performed EMG: normal; NCV = 83 m/s EMG: normal; NCV = 81 m/s Table 1 Neurological, electrodiagnostic and histopathological results in 12 related Alaskan Malamutes. EMG: electromyogram; NCV: nerve conduction velocity; f: female; m: male; ms: months; y: years. * information provided by local veterinarian Motor nerve conduction velocity (NCV) from the peroneal or radialis nerve (씰Table 1) ranged from 60 to 93 m/sec in dogs 30, 31, 50, 51, 65, 66, 76 & the control dog and was reduced in dog 53 (29 m/sec). In dog 52, NCV could not be determined because of flat evoked potential curves. Dog 53 showed a slight decremental response on repetitive stimulation of the peroneal nerve. Histopathological findings Dogs with neurological deficits and positive electrodiagnostic findings had moderately to severely affected muscles. Pathological bimodal fibre size variation was the most prominent finding in dogs 30 (moderate), 31 (moderate), 52 (severe) and 53 (moderate) characterised by scattered angular atrophic as well as hypertrophic fibres (씰Fig. 2A). Both fibre types were involved, whereby most of the hypertrophic ones belonged to type 1, and most of the atrophic fibres to type 2 (씰Fig. 2B). Occasionally there was evidence of fibre type grouping. Some of the hypertrophic fibres had a slightly dystrophic shape. Myofibrils seemed to be normal, and no vacuoles or storage material could be found. Internal nuclei were rare. Fibresplitting as well as clusters of myogenic nuclei as sign of regeneration occurred. Additionally, fibre degeneration and focal necrosis with phagocytosis (씰Fig. 2C) was observed. There was no evidence of inflammation in any of the specimens. Muscles of three clinically normal dogs (50, 51 & 76) were also affected: they had a slightly altered fibre calibre spectrum with individually disseminated – mostly angular – fibre atrophies. Tierärztliche Praxis Kleintiere 1/2012 © Schattauer 2012 Downloaded from www.tieraerztliche-praxis.de on 2017-06-17 | IP: 88.99.165.207 For personal or educational use only. No other uses without permission. All rights reserved. K. Rentmeister: Hereditary polyneuropathy in the Alaskan Malamute In endomysial nerve fascicles (씰Fig. 3A), as well as in peripheral nerve cross sections (씰Fig. 3B) of dogs 31, 52 & 53, alterations of the myelin-axon-relation were present. This was characterized either by axonal swelling, degeneration and/or demyelination, complete loss of myelinated fibres, Schwann cell proliferation, infiltrating macrophages and mild to moderate endoneural fibrosis. Signs of remyelination were reflected by very thin myelin sheaths, being inappropriate for the axonal diameter. In dogs 30 and 52, evidence of axonal necrosis was visible by myelin ovoids and balls (씰Fig. 3C). In the clinically normal dogs 50, 51 & 76, several degenerated and hypomyelinated axons in peripheral nerve fascicles were found. Pedigrees The prevalence of polyneuropathy among the analysed families was 29.6%. In total 21 affected animals could be either examined in our clinic or by the referring veterinarian. These puppies displayed weakness and reduced spinal reflexes. Among the affected puppies three were males, nine were females, and in nine affected animals the sex was unknown. The differences in prevalence of polyneuropathy among sexes were not significant (p = 0.153). All families with affected puppies were related to each other. Inbreeding coefficients among litters varied from 0% to 20.0%. However, no significant differences in prevalences for polyneuropathy due to the inbreeding coefficient could be observed (p = 0.11). Segregation analysis The model with only one phenotypic distribution was compared with the monogenic, polygenic and mixed major gene models. The Mendelian models and mixed major gene models were not significantly different from the environmental model (μ-model, 씰Table 2). The polygenic model with the logistic regression of offspring on affected parents and spouses explained the segregation significantly better than the environmental model. The further likelihood ratio tests compared the polygenic model with the Mendelian and mixed major gene models. The polygenic model fitted the data significantly better than the Mendelian models applied (씰Table 3). Also, the mixed major gene model could not improve the estimates of the polygenic model significantly, as was shown by the likelihood ratio test between these models. The likelihood ratio test of the polygenic model against the most general model was not significant indicating that the polygenic model fitted the data sufficiently well (씰Table 4). Summarising the results of the segregation analysis the polygenic model proved as best suitable to explain the observed segregation pattern in the available pedigree. Thus, the hypothesis of a strong genetic background for polyneuropathy in this pedigree of Alaskan Malamutes was supported by the segregation analyses performed. Allowing the transmission probability for τAB to vary in the mixed major gene model with arbitrary gene effects led to a Fig. 2 A) Cross-section of the quadriceps muscle of dog 53 showing bimodal fibre size variation with atrophic fibres – predominately angular (arrows) as well as large fibres (hematoxylin-eosin, cryostat-section, ×400). B) Fibre size variations with hypertrophic type 1 muscle fibres (blue) and atrophic type 2 muscle fibres (brown). Normal myofibrils, no vacuoles or storage materials (NADH-TR, pH 9.5; cryostat-section, ×400). C) Occasional fibre degeneration and focal necrosis with phagocytosis (arrows), no evidence of inflammation (Gomori-trichome/Engel, cryostat-section, ×400). © Schattauer 2012 Tierärztliche Praxis Kleintiere 1/2012 Downloaded from www.tieraerztliche-praxis.de on 2017-06-17 | IP: 88.99.165.207 For personal or educational use only. No other uses without permission. All rights reserved. 31 32 K. Rentmeister: Hereditary polyneuropathy in the Alaskan Malamute Fig. 3 A) Intramuscular nerve fascicle of the quadriceps muscle of dog 52 with varying axonal diameters, partial demyelination and beginning endoneural fibrosis (Gomori-trichome/Engel, cryostat section, ×800). B) Branch of the ischiadic nerve of dog 52, with severe axonal degeneration and demyelination (paraffin section, hematoxylin-eosin, ×600). C) Myelin ovoids and balls within the same nerve branch (paraffin-section, hematoxylin-eosin, ×300). value of 15.66 for the –2log-likelihood with an estimate for τAB = 0.91. This result also showed that mixed major gene models with transmission probabilities for Mendelian inheritance could not be fitted to this data set. A similar result was also found for monogenic models, when τAB was not fixed to a value of 0.5. The reason, why the monogenic and mixed monogenicpolygenic inheritance models could not sufficiently well explain the data was that the distributions of types in the pedigrees deviated significantly from genotypic distributions for Mendelian inheritance. Discussion The purpose of this prospective study was to evaluate, if the polyneuropathy found in the Alaskan Malamute breed has a genetic background. In dogs 52 and 53, a sensorimotor polyneuropathy with severe clinical expression was suspected after neurological examination. Some of their relatives also had neurological deficits corresponding to a peripheral nerve lesion. However, these dogs were only moderately or subclinically affected, implying a polyneuropathy characterized by a wide range of clinical expressions. The observed neurological deficits (i. e. tetraparesis progressing to tetraplegia, exercise intolerance, inability to jump and walk up stairs, proprioceptive deficits, general hyporeflexia and severe muscle atrophy) were almost identical to those reported by Braund et al. (7). In contrast to Moe et al. (18) and Moe and Bjerkas (19) the Malamutes participating in our study displayed no signs of visceral nerve impairment (coughing, dyspnoea, regurgitation and megaoesophagus) except abnormal vocalization. Electrodiagnostic testing had an excellent correlation to the clinical severeness of neurological deficits, however in contrast to histopathology electrodiagnostic work up was not sensitive enough to detect subclinical stages. This can be explained by the fact, that moderate demyelination and slight axonal degeneration does not necessarily influence NCV if a sufficient number of large and fast conducting nerve fibres are still present (23). The histopathological changes resemble those described both by Moe et al. (18) and Braund et al. (7). According to the findings of Braund et al. (7), the peripheral neuropathy observed in our dogs is a primary axonopathy, characterised by axon swelling and degeneration, loss of myelinated nerve fibres as well as demyelination and remyelination in parallel. Neurogenic muscular atrophy of varying degree was present in all dogs. A new finding, however, is that the muscle fibre calibre spectrum was slightly to moderately irregular in three clinically normal Alaskan Malamutes. These dogs with slight but distinctive neurogenic myopathy and axonal changes are considered to be subclinically affected, an aspect we were able to describe for the first time in hereditary poly- Tierärztliche Praxis Kleintiere 1/2012 © Schattauer 2012 Downloaded from www.tieraerztliche-praxis.de on 2017-06-17 | IP: 88.99.165.207 For personal or educational use only. No other uses without permission. All rights reserved. K. Rentmeister: Hereditary polyneuropathy in the Alaskan Malamute neuropathy in the Alaskan Malamute. In correlation with Braund et al. (7), histopathology revealed no signs of metabolic/toxic or immunopathological disease. Interestingly, at least two of our affected dogs were older than the previously reported (7) age of onset Table 2 Comparisons between the μ-model and the other models under hypothesis using regressive logistic models for complex segregation analysis of polyneuropathy in Alaskan Malamutes. for polyneuropathy in Alaskan Malamutes (10–18 months): their age was 6.5 years (dog 31) and almost 12 years (dog 30). Due to their minor neuromuscular changes these dogs probably were able to functionally compensate their subclinical disease. –2 log likelihood χ2 df-χ2 P 1 34.28 – – – 5 26.34 7.94 4 0.094 Mendelian recessive – 5 27.50 6.78 4 0.148 Mendelian arbitrary – 7 26.69 7.59 6 0.270 polygenic model 2 6 22.33 11.95 5 0.036 4 8 22.33 11.95 7 0.102 6 8 22.33 11.95 7 0.102 2 9 20.35 13.93 8 0.084 4 11 20.35 13.93 10 0.176 6 11 20.35 13.93 10 0.176 2 9 21.72 12.56 8 0.128 4 11 21.72 12.56 10 0.249 6 11 21.72 12.56 10 0.249 2 11 22.59 11.69 10 0.306 4 13 21.50 12.78 12 0.385 6 13 21.50 12.78 12 0.385 Tested hypothesis Familiar correlation μ-model – Mendelian dominant mixed model with dominant major gene mixed model with recessive major gene mixed model with arbitrary major gene df – χ : difference of –2log likelihood between the model under hypothesis and the μ-model. df-χ2: difference of the degrees of freedom between the model under hypothesis and the μ-model. 2 Table 3 Comparisons between the polygenic model and the other models under hypothesis using regressive logistic models for complex segregation analysis of polyneuropathy in Alaskan Malamutes. –2 log likelihood χ2 df-χ2 P 6 22.33 – – – – 5 26.34 4.01 1 0.045 Mendelian recessive – 5 27.50 5.17 1 0.023 Mendelian arbitrary – 7 26.69 4.36 1 0.042 mixed model with dominant major gene 2 9 20.35 1.98 3 0.576 4 11 20.35 1.98 5 0.852 6 11 20.35 1.98 5 0.852 2 9 21.72 0.61 3 0.894 4 11 21.72 0.61 5 0.988 6 11 21.72 0.61 5 0.988 2 11 22.59 0.26 5 0.995 4 13 21.50 0.83 7 0.997 6 13 21.50 0.83 7 0.997 Tested hypothesis Familiar correlation polygenic model 2 Mendelian dominant mixed model with recessive major gene mixed model with arbitrary major gene df χ : difference of –2log likelihood between the model under hypothesis and the polygenic model. df-χ2: difference of the degrees of freedom between the model under hypothesis and the polygenic model. 2 © Schattauer 2012 Tierärztliche Praxis Kleintiere 1/2012 Downloaded from www.tieraerztliche-praxis.de on 2017-06-17 | IP: 88.99.165.207 For personal or educational use only. No other uses without permission. All rights reserved. 33 34 K. Rentmeister: Hereditary polyneuropathy in the Alaskan Malamute Table 4 Comparisons between the most general model and the polygenic model using regressive logistic models for complex segregation analysis of polyneuropathy in Alaskan Malamutes. Tested Familiar df hypothesis correlation most general 6 model polygenic model –2 log like- χ2 lihood – df-χ2 P 17 8.77 – – 2 6 22.33 13.56 11 0.258 4 8 22.33 13.56 9 0.139 6 8 22.33 13.56 9 0.139 χ: difference of –2log likelihood between the model under hypothesis and the most general model. df-χ2: difference of the degrees of freedom between the model under hypothesis and the most general model. The present study could prove that the Alaskan Malamute polyneuropathy definitely has a hereditary nature. The hypothesis of a monogenic recessive inheritance for this polyneuropathy as suggested by Moe et al. (18) and Moe and Bjerkas (19) had to be rejected, since the distribution of affected dogs did not fit to the Mendelian ratios. This could be shown by two different tests in our genetic analysis. The most probable hypothesis that was accepted by the models used was a polygenic transmission from parents to offspring. This polygenic mode of inheritance may also explain the various phenotypic clinical expressions ranging from severe tetraplegia to subclinical stages. The number of genes responsible cannot be determined using complex segregation analyses as the number of possible models increases exponentially with the number of gene loci and alleles considered. A mixed model with a dominant major gene could not completely be ruled out, since some of the ancestors with unknown disease status could have been subclinically affected. Subclinical affected animals, which were not examined histopathologically, might be the cause that the mixed model could not be rejected and are a limitation to the study. Further investigations are warranted to clarify the genetic model and to identify possible mutations causing the Alaskan Malamute polyneuropathy. Conflict of interest The authors confirm that they do not have any conflict of interest. Conclusion for practice The current study could demonstrate that polyneuropathy in Alaskan Malamutes is a hereditary disease with variable phenotypic expression ranging from severely affected (weakness, tetraparesis, abnormal vocalization, abnormal performance as a sledge dog) to subclinical forms. Especially these subclinical forms have to be considered for breeding programs and future gene analysis studies trying to detect possible gene mutations. References 1. Bonney GE. Regressive logistic models for familial disease and other binary traits. Biometrics 1986; 42: 611–625. 2. Braund KG, Luttgen PJ, Redding RW, Rumph PF. Distal symmetrical polyneuropathy in a dog. Vet Pathol 1980; 17: 422–435. 3. Braund KG, Metha JR, Toivio-Kinnucan M, Amling KA Shell LG, Matz ME. Congenital hypomyelinating polyneuropathy in two Golden Retriever Littermates. Vet Pathol 1989; 26: 202–208. 4. Braund KG. Nerve and muscle biopsy techniques. Prog Vet Neurol 1991; 2: 35–56. 5. Braund KG, Toivio-Kinnucan M, Vallat JM, Metha JR, Levesque DC. Distal sensorimotor polyneuropathy in mature Rottweiler dogs. Vet Pathol 1994; 31: 316–326. 6. Braund KG, Shores A, Cochrane S, et al. Laryngeal paralysis-polyneuropathy complex in young Dalmatian dogs. Am J Vet Res 1994; 55: 534–542. 7. Braund KG, Shores A, Lowrie CT, Steinberg HS, Moore MP, Bagley RS, Steiss JE. Idiopathic polyneuropathy in Alaskan Malamutes. J Vet Intern Med 1997; 11 (4): 243–249. 8. Cummings JF, Cooper BJ, de Lahunta A, van Winkle TJ. Canine inherited hypertrophic neuropathy. Acta Neuropathol 1981; 53: 137–143. 9. Cummings JF, de Lahunta A, Winn SS. Acral mutilation and nociceptive loss in English pointer dogs. A canine sensory neuropathy. Acta Neuropathol 1981; 53 (2): 119–127. 10. Cummings JF, de Lahunta A, Braund KG, Mitchell WJ Jr. Hereditary sensory neuropathy. Nociceptive loss and acral mutilation in pointer dogs: canine hereditary sensory neuropathy. Am J Pathol 1983; 112 (1): 136–138. 11. Duncan ID, Griffiths IR. Canine giant axonal neuropathy. Vet Rec 1977; 101 (22): 438–441. 12. Duncan ID, Griffiths IR, Carmichael S, Henderson S. Inherited canine giant axonal neuropathy. Muscle Nerve 1981; 4: 223–227. 13. Duncan ID, Griffiths IR, Munz M. The pathology of a sensory neuropathy affecting long haired dachshund dogs. Acta Neuropathol 1982; 58: 141–151. 14. Elston RC. Models for discrimination between alternatives modes of inheritance. In: Advances in statistical methods for genetic improvement of livestock, 1st edn. Gianola D, Hammond K, eds. Berlin: Springer 1989; 41–55. 15. Granger N. Canine inherited motor and sensory neuropathies: an update classification in 22 breeds and comparison to Charcot-Marie-Tooth disease. Vet J 2011; 188: 274–285. 16. Griffiths IR. Progressive axonopathy: An inherited neuropathy of Boxer dogs: 1. Further studies of the clinical and electrophysical features. J Small Anim Pract 1985; 26: 381–392. 17. Mahoney OM, Knowles KE, Braund KG, Averill DR Jr, Frimberger AE. Laryngeal paralysis-polyneuropathy complex in young Rottweilers. J Vet Intern Med 1998; 12 (5): 330–337. 18. Moe L, Bjerkas I, Nöstvold SO, Oftedal SI. Hereditaer Polyneuropathi hos Alaskan Malamute. In: Proceedings of 14th Nordic Veterinary Congress 1982; 171–172. 19. Moe L, Bjerkas I. Hereditary polyneuropathy in the Alaskan Malamute. Proceedings of 3rd Annual Symposium of the European Society of Veterinary Neurology (ESVN), Berne, Switzerland, Sept. 1989; 28–29. 20. Moe L. Hereditary Polyneuropathy of Alaskan Malamutes. In: Current Veterinary Therapy XI. Small Animal Practice, 11th ed. Kirk RW et al., eds). Philadelphia: Saunders; 1992; 1038–1039. 21. O’Brien JA, Hendriks J. Inherited laryngeal paralysis: Analysis in the Husky cross. Vet Q 1986; 8: 301–302. 22. Sponenberg DP, de Lahunta A. Hereditary hypertrophic neuropathy in Tibetian Mastiff Dogs. J Heredity 1981; 72 (4): 287. 23. Steiss JE. Electrodiagnostic evaluation. In: Clinical Neurology in Small Animals – Localisation, Diagnosis and Treatment, 1st edn. Braund KG, ed. Ithaca, New York: International Veterinary Information Service 2001 (www.ivis. org). 24. Venker-van Haagen AJ, Hartmann W, Goedegebuure SA. Spontaneous laryngeal paralysis in young Bouviers. J Am Anim Hosp Assoc 1978; 14: 714–720. Tierärztliche Praxis Kleintiere 1/2012 © Schattauer 2012 Downloaded from www.tieraerztliche-praxis.de on 2017-06-17 | IP: 88.99.165.207 For personal or educational use only. No other uses without permission. All rights reserved.