Homozygous CNP Mutation and Neurodegeneration in Weimaraners: Myelin Abnormalities and Accumulation of Lipofuscin-like Inclusions.

A progressive neurological disorder was observed in a male neutered Weimaraner. Clinical signs included fecal incontinence, lethargy, moderate paraparesis, proprioceptive pelvic limb ataxia, falling, cognitive decline, incoordination, decreased interest in food, changes in posture, and episodes of trance-like behavior. Neurologic signs were first observed at approximately 4 years, 10 months of age and progressed slowly. Magnetic resonance imaging showed generalized brain atrophy with areas of white matter pathology. Humane euthanasia was elected at 6 years, 7 months of age due to increasing severity of the neurological signs. Autofluorescent intracellular granules were observed in the cerebral and cerebellar cortexes, optic nerve, and cardiac muscle of the affected dog. These abnormal inclusions in the cerebral cortex and cardiac muscle immunolabeled with antibodies to mitochondrial ATP synthase subunit c protein, like that observed in the neuronal ceroid lipofuscinosis group of lysosomal storage diseases. Immunolabeling also demonstrated pronounced neuroinflammation in brain tissues. The ultrastructural appearances of the disease-related inclusion bodies in the brain and optic nerve were quite variable. The ultrastructure and locations of many of the inclusions in the nervous tissues suggested that they were derived, at least in part, from the myelin surrounding axons. The storage bodies in the cardiac muscle were located in mitochondria-rich regions and consisted of parallel arrays of membrane-like components interspersed with electron-dense flocculent material. The disease was characterized by pronounced abnormalities in the myelin of the brain and optic nerve consisting of distinctive areas of ballooning between the layers of myelin. The whole genome sequence generated from the affected dog contained a homozygous G-to-A missense mutation in CNP, which encodes proteins with CNPase enzyme activity and a structural role in myelin. The mutation predicts a Thr42Met amino acid sequence substitution. Genotyping of archived Weimaraner DNA samples identified an additional G > A variant homozygote with a clinical history and brain lesions similar to those of the proband. Of 304 Weimaraners and over 4000 other dogs of various breeds, the proband and the other Weimaraner that exhibited similar signs were the only two that were homozygous for the CNP missense variant. CNPase immunolabeling was widespread in brain tissues from normal dogs but was undetectable in the same tissues from the proband. Based on the clinical history, fluorescence and electron-microscopy, immunohistochemistry, and molecular genetic findings, the late-onset Weimaraner disorder likely results from the missense mutation that results in CNPase deficiency, leading to myelin abnormalities, accumulation of lysosomal storage bodies, and brain atrophy. Similar disorders have been associated with different CNP variants in Dalmatians and in human subjects.

Assessment of the prevalence and clinical features of cryptogenic epilepsy in dogs: 45 cases (2003-2011).

OBJECTIVE: To determine the prevalence and clinical features of cryptogenic epilepsy among dogs. DESIGN: Retrospective case series. ANIMALS: 214 client-owned dogs with onset of epileptic seizures at ≥ 7 years of age. PROCEDURES: A diagnostic imaging database was searched for dogs with symptomatic or cryptogenic epilepsy. Signalment, seizure history, and diagnostic information were recorded. Information regarding seizure frequency, administration of antiepileptic drugs (AEDs), owners' perceptions regarding quality of life, survival times, and causes of death for dogs with cryptogenic epilepsy was obtained via questionnaire. Variables were compared among dogs grouped according to diagnosis and age. RESULTS: 45 (21%) dogs had a diagnosis of cryptogenic epilepsy, and 169 (79%) had symptomatic epilepsy. In dogs 7 to 9 years and ≥ 10 years of age at the time of seizure onset, 31 of 106 (29%) and 14 of 108 (13%), respectively, had a diagnosis of cryptogenic epilepsy. At last follow-up, most (40 [89%]) dogs with cryptogenic epilepsy were receiving ≥ 1 AED. Thirty-one of 37 (84%) dogs typically had ≤ 1 seizure/mo following hospital discharge. Death was confirmed in 20 (44%) dogs with cryptogenic epilepsy and was related to seizures or AEDs in 7 Median survival time from onset of seizures was 52 months for all dogs with cryptogenic epilepsy. Median quality-of-life score (scale, 1 [poor] to 10 [excellent]) indicated by 34 owners of dogs with cryptogenic epilepsy was 10 before diagnosis and initiation of AED treatment and 8 afterward. CONCLUSIONS AND CLINICAL RELEVANCE: Cryptogenic epilepsy was diagnosed in a substantial proportion of dogs with an onset of epileptic seizures at ≥ 7 years of age. Seizure control was considered acceptable in most dogs.

Determination of immunoglobulin A concentrations in the serum and cerebrospinal fluid of dogs: an estimation of its diagnostic value in canine steroid-responsive meningitis-arteritis.

Previous studies on canine steroid-responsive meningitis-arteritis (SRMA) suggested that elevation of immunoglobulin A (IgA) concentrations in both serum and cerebrospinal fluid (CSF) is specific for SRMA throughout the different disease stages. Recent studies however have raised concerns about the value of this test. The purpose of this study was to investigate the diagnostic value of IgA concentration testing in paired CSF and serum samples. IgA concentrations of 525 paired canine CSF and serum samples were evaluated. Samples were obtained from dogs with SRMA (n=311) and dogs with miscellaneous conditions (n=214) such as other central nervous system (CNS) inflammatory diseases (n=34), CNS tumours (n=46), idiopathic epilepsy (n=42), intervertebral disc disease (n=46) and non-CNS diseases (n=46). Serum IgA concentrations were significantly higher in dogs with untreated SRMA compared to those with other diseases. IgA CSF concentrations were significantly higher in dogs with SRMA compared to other disease categories, with the exception of inflammatory CNS disease. The sensitivity for IgA concentrations in serum and CSF was 91% with a specificity of 78%. Analysis of 525 paired samples confirmed that IgA concentrations were higher in dogs with SRMA. Calculation of the diagnostic value of IgA concentration confirmed that the test is highly sensitive for SRMA. Testing paired CSF and serum samples for IgA is still recommended for the diagnosis of suspected cases of SRMA.

Possible drug-induced hepatopathy in a dog receiving zonisamide monotherapy for treatment of cryptogenic epilepsy.

A 9-year old female spayed Rottweiler was diagnosed with cryptogenic epilepsy and started on zonisamide monotherapy (8.3 mg/kg, PO, q 12 hr). Three weeks after the 1st dose of zonisamide the dog presented for vomiting, inappetence and icterus. Serum biochemistry showed marked elevation of liver enzymes, consistent with hepatocellular damage and cholestasis. No underlying cause for liver disease was identified and a drug-induced hepatopathy was suspected. Zonisamide was discontinued and replaced by potassium bromide. Supportive therapy consisted of intravenous fluids, antiemetics, antibiotics and hepatoprotectants. The dog made a complete recovery and serial serum biochemical examinations showed complete normalisation of liver parameters 8 weeks after discontinuation of zonisamide. Based on a human Drug-induced Liver Injury Diagnostic Scale, the likelihood for zonisamide-induced hepatopathy was classified as "possible". Veterinary practitioners and owners should be educated about the potential for an idiosyncratic drug reaction to zonisamide. If signs of hepatotoxicity are recognised early and zonisamide is discontinued, complete recovery is possible.