Severe retinal degeneration in a patient with Canavan disease.

Background: Canavan disease is an autosomal recessive, neurodegenerative disorder caused by mutations in ASPA, a gene encoding the enzyme aspartoacylase. Patients present with macrocephaly, developmental delay, hypotonia, vision impairment and accumulation of N-acetylaspartic acid. Progressive white matter changes occur in the central nervous system. The disorder is often fatal in early childhood, but milder forms exist. Materials and methods: Case report. Results: We present the case of a 31-year-old male with mild/juvenile Canavan disease who had severe vision loss due to a retinal degeneration resembling retinitis pigmentosa. Prior to this case, vision loss in Canavan disease had been attributed to optic atrophy based on fundoscopic evidence of optic nerve pallor. Investigations for an alternative cause for our patient's retinal degeneration were non-revealing. Conclusion: We wonder if retinal degeneration may not have been previously recognized as a feature of Canavan disease. We highlight findings from animal models of Canavan disease to further support the association between Canavan disease and retinal degeneration.

Antisense Oligonucleotide Reverses Leukodystrophy in Canavan Disease Mice.

Marked elevation in the brain concentration of N-acetyl-L-aspartate (NAA) is a characteristic feature of Canavan disease, a vacuolar leukodystrophy resulting from deficiency of the oligodendroglial NAA-cleaving enzyme aspartoacylase. We now demonstrate that inhibiting NAA synthesis by intracisternal administration of a locked nucleic acid antisense oligonucleotide to young-adult aspartoacylase-deficient mice reverses their pre-existing ataxia and diminishes cerebellar and thalamic vacuolation and Purkinje cell dendritic atrophy. Ann Neurol 2020;87:480-485.

N-acetylaspartate supports the energetic demands of developmental myelination via oligodendroglial aspartoacylase.

Breakdown of neuro-glial N-acetyl-aspartate (NAA) metabolism results in the failure of developmental myelination, manifest in the congenital pediatric leukodystrophy Canavan disease caused by mutations to the sole NAA catabolizing enzyme aspartoacylase. Canavan disease is a major point of focus for efforts to define NAA function, with available evidence suggesting NAA serves as an acetyl donor for fatty acid synthesis during myelination. Elevated NAA is a diagnostic hallmark of Canavan disease, which contrasts with a broad spectrum of alternative neurodegenerative contexts in which levels of NAA are inversely proportional to pathological progression. Recently generated data in the nur7 mouse model of Canavan disease suggests loss of aspartoacylase function results in compromised energetic integrity prior to oligodendrocyte death, abnormalities in myelin content, spongiform degeneration, and motor deficit. The present study utilized a next-generation "oligotropic" adeno-associated virus vector (AAV-Olig001) to quantitatively assess the impact of aspartoacylase reconstitution on developmental myelination. AAV-Olig001-aspartoacylase promoted normalization of NAA, increased bioavailable acetyl-CoA, and restored energetic balance within a window of postnatal development preceding gross histopathology and deteriorating motor function. Long-term effects included increased oligodendrocyte numbers, a global increase in myelination, reversal of vacuolation, and rescue of motor function. Effects on brain energy observed following AAV-Olig001-aspartoacylase gene therapy are shown to be consistent with a metabolic profile observed in mild cases of Canavan disease, implicating NAA in the maintenance of energetic integrity during myelination via oligodendroglial aspartoacylase.

Leukodystrophy with multiple beaded periventricular cysts: unusual cranial MRI results in Canavan disease.

A 3-year-old boy was admitted with psychomotor delay, spasticity, progressive visual loss, nystagmus, macrocephaly, and epileptic seizures for diagnostics. Cranial magnetic resonance imaging (MRI) revealed leukodystrophy and multicystic changes. Urine excretion of N-acetylaspartic acid was grossly increased, suggesting Canavan disease. Mutation screening of the ASPA gene confirmed this diagnosis. The underlying enzymatic defect causes accumulation of N-acetylaspartic acid and subsequent progressive myelin degeneration with characteristic spongy degeneration of the subcortical white matter, normally only seen histologically. We describe this case to show that spongy degeneration in Canavan disease may also be present macroscopically in the form of multiple beaded periventricular cysts on cranial MRI.

Intracerebroventricular administration of N-acetylaspartic acid impairs antioxidant defenses and promotes protein oxidation in cerebral cortex of rats.

N-acetylaspartic acid (NAA) is the biochemical hallmark of Canavan Disease, an inherited metabolic disease caused by deficiency of aspartoacylase activity. NAA is an immediate precursor for the enzyme-mediated biosynthesis of N-acetylaspartylglutamic acid (NAAG), whose concentration is also increased in urine and cerebrospinal fluid of patients affected by CD. This neurodegenerative disorder is clinically characterized by severe mental retardation, hypotonia and macrocephaly, and generalized tonic and clonic type seizures. Considering that the mechanisms of brain damage in this disease remain not fully understood, in the present study we investigated whether intracerebroventricular administration of NAA or NAAG elicits oxidative stress in cerebral cortex of 30-day-old rats. NAA significantly reduced total radical-trapping antioxidant potential, catalase and glucose 6-phosphate dehydrogenase activities, whereas protein carbonyl content and superoxide dismutase activity were significantly enhanced. Lipid peroxidation indices and glutathione peroxidase activity were not affected by NAA. In contrast, NAAG did not alter any of the oxidative stress parameters tested. Our results indicate that intracerebroventricular administration of NAA impairs antioxidant defenses and induces oxidative damage to proteins, which could be involved in the neurotoxicity of NAA accumulation in CD patients.

Effects of AAV-2-mediated aspartoacylase gene transfer in the tremor rat model of Canavan disease.

The tremor rat is a spontaneous epilepsy model with a seizure phenotype caused by a deletion in the aspartoacylase (ASPA) gene. The absence of ASPA expression in these animals results in undetectable levels of enzyme activity and the accumulation of the substrate N-acetyl-aspartate (NAA) in brain, leading to generalized myelin vacuolation and severe motor and cognitive impairment. In support of human gene therapy for CD, recombinant adeno-associated viral vector (AAV-2) expressing ASPA was stereotactically delivered to the tremor rat brain and effects on the mutant phenotype were measured. AAV-ASPA gene transfer resulted in elevated aspartoacylase bioactivity compared to untreated mutant animals and elicited a significant decrease in the pathologically elevated whole-brain NAA levels. Assessment of motor function via quantitative rotorod testing demonstrated that rats injected with AAV-ASPA significantly improved on tests of balance and coordinated locomotion compared to animals receiving control vectors. This study provides evidence that AAV-2-mediated aspartoacylase gene transfer to the brain improves biochemical and behavioral deficits in tremor rat mutants (tm/tm) and supports the rationale of human gene transfer for Canavan disease.

Canavan's leukodystrophy is associated with defects in cochlear neurodevelopment and deafness.

The authors present the temporal bone histopathology of two siblings (4 months old and 6 months old at autopsy) with Canavan's disease, an autosomal recessive leukodystrophy that is variably associated with sensorineural hearing loss. The histopathology demonstrated bilateral absence of the organ of Corti throughout the apical and basal cochlea and mild secondary atrophy of the spiral ganglia neurons. The vestibular end organs and ganglia were normal. These findings implicate a role of aminoacylase II in the neurodevelopment of the organ of Corti.

Upper airway abnormalities in Canavan disease.

OBJECTIVE: To describe upper airway anatomical abnormalities associated with Canavan disease. METHODS: Retrospective case report. RESULTS: Physical examination and laryngoscopy demonstrated oropharyngeal narrowing, macroglossia, and bronchial asymmetry in a child with Canavan disease. Tracheostomy decreased problems with chronic aspiration and obstructive sleep apnea. CONCLUSIONS: Oropharyngeal obstruction and bronchial asymmetry are previously undescribed upper airway abnormalities found in an individual with Canavan disease. Tracheostomy is an effective method of managing chronic aspiration and obstruction in these patients.

Oculodentodigital dysplasia with cerebral white matter abnormalities in a two-generation family.

Oculodentodigital dysplasia (ODDD) is an autosomal dominant disorder involving eye and face abnormalities, syndactyly, and enamel hypoplasia. Some individuals with ODDD also have spastic paraparesis. Previously, we reported on a woman with sporadic ODDD and progressive neurologic dysfunction who had cerebral white matter abnormalities demonstrated by magnetic resonance imaging (MRI). We now describe a 2-generation family with ODDD and progressive paraparesis associated with leukodystrophic changes documented by MRI. This family represents one of the largest pedigrees with ODDD described so far. The presence of abnormal white matter changes in both sporadic and inherited forms of ODDD suggests that the phenotype of ODDD should be expanded to include spastic paraparesis.

Deletion of mitochondrial DNA in patient with chronic tubulointerstitial nephritis.

We report a mitochondrial DNA deletion (2.6 kb) in a boy with tubulointerstitial nephritis in whom chronic renal failure and leukodystrophy subsequently developed. Elevated lactate values in plasma and cerebrospinal fluid were suggestive of a defect in the mitochondrial respiratory chain. High amounts of deleted mitochondrial DNA were present in muscle and cerebral white matter. On the basis of this observation, we suggest giving consideration to genetic defects of oxidative phosphorylation in any attempt to determine the origin of unexplained chronic tubulointerstitial nephritis, especially when seemingly unrelated organs are involved.