9-year-old, spayed female, Basset hound, dog, (Canis lupus familiars).The dog had generalized seizures, intermittent tremor, high amplitude myoclonia and altered behavior since a few weeks. The seizures were controlled with antiepileptic drugs over a period of 4 weeks prior to euthanasia.
Only the formalin fixed brain of the animal was obtained and no gross lesions were noted.
Brain, cerebral cortex: Multifocally and haphazardly distributed within the white and gray matter, nerve cell bodies, axons, dendrites and occasional the neuropil contain large, up to 20 Î¼m in diameter, round, basophilic to amphophilic inclusions.Â Nerve cell bodies are enlarged up to 40 Î¼m in diameter by the inclusions and most nuclei are compressed or displaced to the periphery.Â Inclusions have a homogeneous core with a more faintly staining radiating periphery and are PAS-positive, also accentuating their structure.Â Multifocally neurons contain fine granular golden-brown pigment in their cytosol (lipofuscin).Â Additionally, there is mild, multifocal satellitosis and mild diffuse increase in microglia.
Brain, cerebral cortex: Polyglucosan (Lafora) bodies, diffuse, numerous with mild multifocal satellitosis and microgliosis.
Lafora disease (LD) is a rare autosomal recessive disorder that was first described in humans in 1911 by a Spanish neurologist named Gonzalo Rodr+ï¿½-ï¿½guez Lafora.Â Clinically, this neurologic disorder is characterized by early onset during adolescence of symptoms including stimulus-sensitive grand mal tonic-clonic, absence, visual and myoclonic seizures.Â The disease then rapidly progresses to dementia, psychosis, cerebellar ataxia, dysarthria, amaurosis, mutism, muscle wasting and respiratory failure leading to death within 10 years after onset.(2,12,17) It is most commonly seen in populations and parts of the world where there is a high rate of consanguinity.(4)
Histopathologically, LD is characterized by the presence of pathognomonic inclusions named Lafora bodies (LB) especially in the brain, spinal cord and other tissues such as skin, liver, cardiac and skeletal muscle.(2) In the central nervous system LB are localized mostly in the perikarya.Â These inclusions can become very large, leading to cell death.(1)
LB are carbohydrate storage products that are composed of polyglucosans, which are abnormally formed glycogen molecules that resemble starch.Â This polyglucosans are poorly branched which makes them insoluble leading to the formation of the characteristic intracellular inclusions.(14)
In most cases this disorder is caused by mutations in one of two different genes, EPM2A and EPM2B (also known as NHLRC1) which encode the proteins laforin and malin, respectively.(3,11) Laforin is a glycogen phosphatase which plays an important role in glycogen metabolism and is involved in dephosphorylation of complex carbohydrates such as amylopectin and glycogen and thus preventing the soluble glycogen molecules from becoming insoluble polyglucosans.(9) Malin on the other hand is an E3 ubiquitin ligase that is believed to target laforin catalyzing its polyubiquitination and thus its degradation.Â However, the specific role of malin in this process is yet to be determined.(9)
In the dog LD has been reported in the Basset Hound, Miniature Wirehaired Dachshund, Poodle and Beagle also.(8,18) In these animals progressive myoclonus is associated with the presence of intraneuronal storage of complex polyglucosans forming the so-called LB.(8)
LB in the dog appear as spherical basophilic to amphophilic, mostly intracytoplasmatic inclusions with peripheral radiating filaments; their size may vary from 5 to 20 Î¼m and can be localized in the dendrites, axons or perikarya (unlike in humans).(2) LB may be found anywhere along the neuroaxis and retinal ganglion cells but in dogs with neuronal disease they are most common in the Purkinje cells and neurons of the caudate, thalamic and periventricular nuclei.(18) LB are PAS positive, diastase resistant, stain positively with Bests carmine, methenamine silver, and Weils.(7) In electron microscopy, they are not membrane bound and are composed of fibrillary and electron-dense, sometimes granular components in varying proportions.Â They are often associated with rough endoplasmic reticulum and Golgi.Â LB present as accumulations of insoluble complex glycoprotein polymers that need to be distinguished from other types of polyglucosan bodies such as Lafora-like bodies, corpora amylacea, and amylopectin bodies.(14) The distinction between LB and other inclusions is performed based on clinical features and tissue distribution of the inclusions.(15)
Corpora amylacea are inclusions that are formed in normal aging cells and are chemically and histochemically indistinguishable from LB.Â Corpora amylacea can be found in axons and astrocytic processes but not in the perikarya, unlike LB.(15)
Amylopectin bodies are formed in patients with glycogen storage disease type IV or glycogen branching enzyme deficiency.(19,20) They result from accumulation of abnormal polysaccharides and are mostly indistinguishable from LB in terms of morphology and distribution and thus the clinical presentation of the disease should be used in their distinction.(19,20)
Lafora-like bodies are also very similar in their morphology and distribution but are observed in normal aged animals without neurologic symptoms.(19)
In cases of LD, typically LB are also found in skeletal muscle samples where they lie between myofibrils or beneath the sarcolemma and therefore muscle biopsies can be used for the diagnosis of the disease.(15) In the case presented here, a biopsy of the cranial tibial muscle was submitted for histopathological analysis and accumulations of PAS positive, diastase resistant, brightly staining material forming focal intraparenchymal subsarcolemmal accumulations consistent with LB were found in the skeletal muscle fibers.
The canine counterpart of LD seems to be associated with a mutation in the EPM2B gene, more precisely a dodecamer expansion in the gene.(10) This mutation was observed in 5% of Miniature Wirehaired Dachshunds in England.(10)
The presence of LB associated with neurologic disease has also been documented in cats and cows.(5,16) A recent report described a Lafora-ï¿½s-like disease in a fennec fox (Vulpes zerda)(7) and another report demonstrated LB in the brain of an aged captive raccoon (Procyon lotor).(6)
Brain, cerebrum, frontal lobes: Polyglucosan bodies, intraneuronal, numerous.
As the contributor states in this informative summary of Laforas disease, the genetic mutation in dogs involves the EPM2B gene.Â Recently a DNA test for the autosomal recessive mutation that identifies clear, carrier, and affected dogs has been developed and is currently available in the United Kingdom.(13)
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