L-2-Hydroxyglutaric aciduria in Staffordshire Bull Terriers

L2HGDH Missense Variant in a Cat with L-2-Hydroxyglutaric Aciduria

A 7-month-old, spayed female, domestic longhair cat with L-2-hydroxyglutaric aciduria (L-2-HGA) was investigated. The aim of this study was to investigate the clinical signs, metabolic changes and underlying genetic defect. The owner of the cat reported a 4-month history of multiple paroxysmal seizure-like episodes, characterized by running around the house, often in circles, with abnormal behavior, bumping into obstacles, salivating and often urinating. The episodes were followed by a period of disorientation and inappetence. Neurological examination revealed an absent bilateral menace response. Routine blood work revealed mild microcytic anemia but biochemistry, ammonia, lactate and pre- and post-prandial bile acids were unremarkable. MRI of the brain identified multifocal, bilaterally symmetrical and T2-weighted hyperintensities within the prosencephalon, mesencephalon and metencephalon, primarily affecting the grey matter. Urinary organic acids identified highly increased levels of L-2-hydroxyglutaric acid. The cat was treated with the anticonvulsants levetiracetam and phenobarbitone and has been seizure-free for 16 months. We sequenced the genome of the affected cat and compared the data to 48 control genomes. L2HGDH, coding for L-2-hydroxyglutarate dehydrogenase, was investigated as the top functional candidate gene. This search revealed a single private protein-changing variant in the affected cat. The identified homozygous variant, XM_023255678.1:c.1301A>G, is predicted to result in an amino acid change in the L2HGDH protein, XP_023111446.1:p.His434Arg. The available clinical and biochemical data together with current knowledge about L2HGDH variants and their functional impact in humans and dogs allow us to classify the p.His434Arg variant as a causative variant for the observed neurological signs in this cat.

Staffordshire Bull Terriers in the UK: their disorder predispositions and protections

Background

The Staffordshire Bull Terrier is a popular dog breed in the UK but there is limited reliable evidence on disorder predispositions and protections within the breed. Using anonymised veterinary clinical data from the VetCompass™ Programme, this study aimed to identify common disorders with predisposition and protection in the Staffordshire Bull Terrier. The study hypothesised that Staffordshire Bull Terriers would have higher odds of aggression compared with non-Staffordshire Bull Terriers.

Results

The clinical records of a random sample of dogs of all types were reviewed to extract the most definitive diagnoses for all disorders existing during 2016. A combined list from the 30 most common disorders in Staffordshire Bull Terriers and the 30 most common disorders in non-Staffordshire Bull Terriers was generated. Multivariable logistic regression was used to report the odds of each of these disorders in 1304 (5.8%) Staffordshire Bull Terriers compared with 21,029 (94.2%) non-Staffordshire Bull Terriers. After accounting for confounding, Staffordshire Bull Terriers had significantly increased odds of 4/36 (11.1%) disorders compared to non-Staffordshire Bull Terriers with highest odds for seizure disorder (OR 2.06; 95% CI 1.24 to 3.40; p = 0.005). Conversely, Staffordshire Bull Terriers had reduced odds of 5/36 (13.9%) disorders, with lowest odds for patellar luxation (OR 0.15; 95% CI 0.04 to 0.61; p = 0.008). There was no significant difference in the odds of aggression between Staffordshire Bull Terriers compared with non-Staffordshire Bull Terriers (OR 1.09; 95% CI 0.75 to 1.58; p = 0.644).

Conclusions

This study provides a reliable evidence base of breed-specific disorder predispositions and protections that can be used by breeders to optimise breeding decisions. The findings can assist prospective owners of Staffordshire Bull Terriers to make informed decisions when acquiring a dog. From the relative number of predispositions to protections identified, there is no evidence that Staffordshire Bull Terriers have higher overall health problems than non-Staffordshire Bull Terriers.

2-Hydroxyglutaric aciduria as a cause for seizure-like episodes in a domestic shorthair cat

Case summary

A 14-month-old male castrated domestic shorthair cat, which 2 months prior to presentation underwent hindlimb amputation following a road traffic accident, presented for investigation of four suspected generalised tonic–clonic seizures. Neurological examination was unremarkable. Routine blood work (haematology, biochemistry, ammonia, preprandial bile acids) was unremarkable. MRI of the brain identified marked symmetrical T2-weighted hyperintensities of the cerebellum and brainstem, mainly affecting the grey matter. Urine amino acid and mucopolysaccharide levels were unremarkable. Urine organic acids on two separate samples, 35 days apart, identified highly increased excretion of 2-hydroxyglutaric acid, indicative of 2-hydroxyglutaric aciduria. The cat was started on anticonvulsant therapy with phenobarbitone, which, at the point of writing, has improved seizure control, although the cat has not achieved seizure freedom.

Relevance and novel information

This case report describes the first reported case of a 2-hydroxyglutaric aciduria, an inherited neurometabolic disorder, as a cause for seizure-like episodes in a cat.

Clinical features and disease progression of L-2-hydroxyglutaric aciduria in 27 Staffordshire bull terriers

To describe the development of clinical signs (CS) and outcome of L-2-hydroxyglutaric aciduria (L-2-HGA), owners of 119 Staffordshire bull terriers positive for the known L-2-hydroxyglutarate dehydrogenase autosomal-recessive mutations were requested to complete a questionnaire regarding their pet's CS. Questionnaires were returned for 27 dogs, all with neurological abnormalities-not all questions were answered in all cases. The mean age of CS onset was 12 months (range 2.5-60). Gait dysfunction was reported in 26/26 dogs, with stiffness of all four limbs the most common (24/26) and earliest recognised abnormality. Kyphosis (19/26), body and/or head tremors (19/26) and hypermetria (15/26) were frequent. Behavioural changes were present in 24/27 dogs; most commonly staring into space (21/24), signs of dementia (17/24) and loss of training (15/24). Eighteen dogs demonstrated paroxysmal seizure-like/dyskinetic episodes. Nineteen (70 per cent) dogs were alive at a mean survival time of 76.6 months (12-170) after onset of CS. L-2-HGA was the cause of euthanasia in six dogs. Euthanasia occurred at a mean survival time of 44 months (8.5-93) after onset of CS, with 2/8 dogs euthanased within 12 months. L-2-HGA is considered a progressive neurological disease; however, CS can be successfully managed with affected dogs potentially living a normal lifespan.

International Veterinary Epilepsy Task Force recommendations for a veterinary epilepsy-specific MRI protocol

Epilepsy is one of the most common chronic neurological diseases in veterinary practice. Magnetic resonance imaging (MRI) is regarded as an important diagnostic test to reach the diagnosis of idiopathic epilepsy. However, given that the diagnosis requires the exclusion of other differentials for seizures, the parameters for MRI examination should allow the detection of subtle lesions which may not be obvious with existing techniques. In addition, there are several differentials for idiopathic epilepsy in humans, for example some focal cortical dysplasias, which may only apparent with special sequences, imaging planes and/or particular techniques used in performing the MRI scan. As a result, there is a need to standardize MRI examination in veterinary patients with techniques that reliably diagnose subtle lesions, identify post-seizure changes, and which will allow for future identification of underlying causes of seizures not yet apparent in the veterinary literature.

There is a need for a standardized veterinary epilepsy-specific MRI protocol which will facilitate more detailed examination of areas susceptible to generating and perpetuating seizures, is cost efficient, simple to perform and can be adapted for both low and high field scanners. Standardisation of imaging will improve clinical communication and uniformity of case definition between research studies. A 6–7 sequence epilepsy-specific MRI protocol for veterinary patients is proposed and further advanced MR and functional imaging is reviewed.

L-2 hydroxyglutaric aciduria in a South African Staffordshire Bull Terrier

L-2 hydroxyglutaric aciduria is an autosomal recessive error of metabolism that manifests as an encephalopathy. The most common presenting signs are seizures, tremors, ataxia and/ or dementia. Some affected dogs show only subtle behavioural changes. Amongst canines, the condition has been best described in Staffordshire Bull Terriers. Although this is the first reported case in South Africa, at least three other affected dogs have been indentified by polmerase chain reaction (PCR) in this country. Affected dogs have normal haematology, serum biochemistry and routine urine analysis. This report discusses the advantages and limitations of the three main diagnostic modalities, namely: magnetic resonance imaging, urine gas chromatography-mass spectrometry and genetic testing. The aim of this report is to increase awareness of the condition, assist diagnosis in encephalopathic dogs and improve detection of carriers amongst breeding stock.

Genome-wide association analysis identifies a mutation in the thiamine transporter 2 (SLC19A3) gene associated with Alaskan Husky encephalopathy

Alaskan Husky Encephalopathy (AHE) has been previously proposed as a mitochondrial encephalopathy based on neuropathological similarities with human Leigh Syndrome (LS). We studied 11 Alaskan Husky dogs with AHE, but found no abnormalities in respiratory chain enzyme activities in muscle and liver, or mutations in mitochondrial or nuclear genes that cause LS in people. A genome wide association study was performed using eight of the affected dogs and 20 related but unaffected control AHs using the Illumina canine HD array. SLC19A3 was identified as a positional candidate gene. This gene controls the uptake of thiamine in the CNS via expression of the thiamine transporter protein THTR2. Dogs have two copies of this gene located within the candidate interval (SLC19A3.2 – 43.36–43.38 Mb and SLC19A3.1 – 43.411–43.419 Mb) on chromosome 25. Expression analysis in a normal dog revealed that one of the paralogs, SLC19A3.1, was expressed in the brain and spinal cord while the other was not. Subsequent exon sequencing of SLC19A3.1 revealed a 4bp insertion and SNP in the second exon that is predicted to result in a functional protein truncation of 279 amino acids (c.624 insTTGC, c.625 C>A). All dogs with AHE were homozygous for this mutation, 15/41 healthy AH control dogs were heterozygous carriers while 26/41 normal healthy AH dogs were wild type. Furthermore, this mutation was not detected in another 187 dogs of different breeds. These results suggest that this mutation in SLC19A3.1, encoding a thiamine transporter protein, plays a critical role in the pathogenesis of AHE.

Severe subacute necrotizing encephalopathy (Leigh-like syndrome) in American Staffordshire bull terrier dogs

Seventeen American Staffordshire bull terrier puppies, 6-8 weeks of age, from seven closely related litters, presented with rapidly progressive central vestibular neurological signs. Previously reported hereditary ataxias in the breed, including l-2 hydroxyglutaric aciduria and cerebellar cortical degeneration, as well as thiamine deficiency, were excluded. Elevated lactate levels and lactate:pyruvate ratios gave supporting evidence of a defect of the respiratory chain or Leigh-like syndrome. Histopathology in all cases showed a bilaterally symmetrical necrotizing encephalopathy, with malacia of the neuropil centred on the vestibular and olivary nuclei of the brainstem. This is the first documentation of a heritable rapidly progressive lethal necrotizing encephalopathy consistent with Leigh-like syndrome, in American Staffordshire bull terrier dogs.

L-2-hydroxyglutaric aciduria in two female Yorkshire terriers

Two female Yorkshire terrier puppies were presented with generalized tonic-clonic seizures and ataxia. MRI revealed bilaterally symmetrical, diffuse regions of gray matter hyperintensity on T2-weighted and fluid-attenuated inversion recovery sequences. Urinary organic acids were quantified by gas chromatography-mass spectroscopy and were consistent with a diagnosis of L-2-hydroxyglutaric aciduria (L2HGA). The L2HGDH gene encodes for the enzyme L-2-hydroxyglutarate dehydrogenase, which helps break down L-2-hydroxyglutaric acid. In both puppies described in this report, a homozygous mutation at the translation initiation codon of the homolog canine L2HGDH gene was detected (c.1A>G; p.Met1?), confirming the diagnosis of L2HGA at the DNA level. Canine L2HGA is caused by more than one mutation of L2HGDH, as reported in humans.

A L2HGDH initiator methionine codon mutation in a Yorkshire terrier with L-2-hydroxyglutaric aciduria

Background

L-2-hydroxyglutaric aciduria is a metabolic repair deficiency characterized by elevated levels of L-2-hydroxyglutaric acid in urine, blood and cerebrospinal fluid. Neurological signs associated with the disease in humans and dogs include seizures, ataxia and dementia.

Case presentation

Here we describe an 8 month old Yorkshire terrier that presented with episodes of hyperactivity and aggressive behavior. Between episodes, the dog’s behavior and neurologic examinations were normal. A T2 weighted MRI of the brain showed diffuse grey matter hyperintensity and a urine metabolite screen showed elevated 2-hydroxyglutaric acid. We sequenced all 10 exons and intron-exon borders of L2HGDH from the affected dog and identified a homozygous A to G transition in the initiator methionine codon. The first inframe methionine is at p.M183 which is past the mitochondrial targeting domain of the protein. Initiation of translation at p.M183 would encode an N-terminal truncated protein unlikely to be functional.

Conclusions

We have identified a mutation in the initiation codon of L2HGDH that is likely to result in a non-functional gene. The Yorkshire terrier could serve as an animal model to understand the pathogenesis of L-2-hydroxyglutaric aciduria and to evaluate potential therapies.

An overview of L-2-hydroxyglutarate dehydrogenase gene (L2HGDH) variants: a genotype-phenotype study

L-2-Hydroxyglutaric aciduria (L2HGA) is a rare, neurometabolic disorder with an autosomal recessive mode of inheritance. Affected individuals only have neurological manifestations, including psychomotor retardation, cerebellar ataxia, and more variably macrocephaly, or epilepsy. The diagnosis of L2HGA can be made based on magnetic resonance imaging (MRI), biochemical analysis, and mutational analysis of L2HGDH. About 200 patients with elevated concentrations of 2-hydroxyglutarate (2HG) in the urine were referred for chiral determination of 2HG and L2HGDH mutational analysis. All patients with increased L2HG (n=106; 83 families) were included. Clinical information on 61 patients was obtained via questionnaires. In 82 families the mutations were detected by direct sequence analysis and/or multiplex ligation dependent probe amplification (MLPA), including one case where MLPA was essential to detect the second allele. In another case RT-PCR followed by deep intronic sequencing was needed to detect the mutation. Thirty-five novel mutations as well as 35 reported mutations and 14 nondisease-related variants are reviewed and included in a novel Leiden Open source Variation Database (LOVD) for L2HGDH variants (http://www.LOVD.nl/L2HGDH). Every user can access the database and submit variants/patients. Furthermore, we report on the phenotype, including neurological manifestations and urinary levels of L2HG, and we evaluate the phenotype-genotype relationship.

Neuropathological findings in a Staffordshire bull terrier with l-2-hydroxyglutaric aciduria

l-2-Hydroxyglutaric aciduria (l-2-HGA) is a hereditary neurometabolic disorder reported in human beings and dogs. An 11-month-old Staffordshire bull terrier was suspected to have the disease, on the basis of clinical signs and magnetic resonance imaging findings. l-2-HGA was confirmed by urinary organic analysis and DNA testing and the dog was humanely destroyed. Post-mortem findings consisted only of microscopical lesions in the brain, characterized by marked spongiform changes and predominantly affecting the grey matter of the cerebral cortex, thalamus, cerebellum and brainstem. The spongiform changes were characterized by well-demarcated, clear vacuoles located at perineuronal and perivascular sites. Immunohistochemical and ultrastructural examination confirmed that the affected cells were astrocytes.

Inherited metabolic disease in companion animals: searching for nature's mistakes

Inborn errors of metabolism are caused by genetic defects in intermediary metabolic pathways. Although long considered to be the domain of human paediatric medicine, they are also recognised with increasing frequency in companion animals. The diagnosis of diseased animals can be achieved by searching for abnormal metabolites in body fluids, although such screening programmes have, until now, not been widely available to the small animal clinician. A comprehensive battery of analytical tools exists for screening for inborn metabolic diseases in humans which can be applied to animals and serve not only for the diagnosis of affected patients but also to detect asymptomatic carriers and further our understanding of metabolic pathways in dogs and cats. Moreover, naturally occurring animal models of inherited metabolic diseases provide a unique opportunity to study the biochemical and molecular pathogenesis of these disorders and to investigate possible therapeutic options.

L-2-hydroxyglutaric aciduria: characterisation of the molecular defect in a spontaneous canine model

l-2-hydroxyglutaric aciduria (l-2-HGA) is a neurometabolic disorder that produces a variety of clinical neurological deficits, including psychomotor retardation, seizures and ataxia. The biochemical hallmark of l-2-HGA is the accumulation of l-2-hydroxyglutaric acid (l-2-HG) in cerebrospinal fluid, plasma and urine. Mutations within the gene L2HGDH (Entrez Gene ID 79944) on chromosome 14q22 encoding L-2-hydroxyglutaric acid dehydrogenase have recently been shown to cause l-2-HGA in humans. Using a candidate gene approach in an outbred pet dog population segregating l-2-HGA, the causal molecular defect was identified in the canine homologue of L2HGDH and characterised. DNA sequencing and pedigree analysis indicate a common founder effect in the canine model. The canine model shares many of the clinical and MRI features of the disease in humans and represents a valuable resource as a spontaneous model of l-2-HGA.

Refractory seizures associated with an organic aciduria in a dog

A 6-month-old, female Cavalier King Charles spaniel exhibited seizures that were difficult to control with standard anticonvulsants over a 12-month period. The diagnosis of an organic aciduria with excessive excretion of hexanoylglycine was determined when the dog was 20 months old. Recurrent and cluster seizures were eventually controlled with the addition of levetiracetam to potassium bromide and phenobarbital.

Microarrays in veterinary diagnostics

Microarrays have numerous applications in the clinical setting, and these uses are not confined to the study of common human diseases. Indeed, the high-throughput technology affects clinical diagnostics in a variety of contexts, and this is reflected in the increasing use of microarray-based tools in the development of diagnostic and prognostic tests and in the identification of novel therapeutic targets. While much of the value of microarray-based experimentation has been derived from the study of human disease, there is equivalent potential for its role in veterinary medicine. Even though the resources devoted to the study of animal molecular diagnostics may be less than those available for human research, there is nonetheless a growing appreciation of the value of genome-wide information as it applies to animal disease. Therefore, this review focuses on the basics of microarray experimentation, and how this technology lends itself to a variety of diagnostic approaches in veterinary medicine.