Mouse models of NADK2 deficiency analyzed for metabolic and gene expression changes to elucidate pathophysiology

NADK2 encodes the mitochondrial isoform of NAD Kinase, which phosphorylates nicotinamide adenine dinucleotide (NAD). Rare recessive mutations in human NADK2 are associated with a syndromic neurological mitochondrial disease that includes metabolic changes such as hyperlysinemia and 2,4 dienoyl CoA reductase (DECR) deficiency. However, the full pathophysiology resulting from NADK2 deficiency is not known. Here we describe two chemically-induced mouse mutations in Nadk2, S326L and S330P, which cause a severe neuromuscular disease and shorten lifespan. The S330P allele was characterized in detail and shown to have marked denervation of neuromuscular junctions by 5 weeks of age and muscle atrophy by 11 weeks of age. Cerebellar Purkinje cells also showed progressive degeneration in this model. Transcriptome profiling on brain and muscle was performed at early and late disease stages. In addition, metabolomic profiling was performed on brain, muscle, liver, and spinal cord at the same ages. Combined transcriptomic and metabolomic analyses identified hyperlysinemia, DECR deficiency, and generalized metabolic dysfunction in Nadk2 mutant mice, indicating relevance to the human disease. We compared findings from the Nadk model to equivalent RNAseq and metabolomic datasets from a mouse model of infantile neuroaxonal dystrophy, caused by recessive mutations in Pla2g6. This enabled us to identify disrupted biological processes that are common between these mouse models of neurological disease, such as translation, and those processes that are gene-specific such as glycolysis and acetylcholine binding. These findings improve our understanding of the pathophysiology of both Nadk2 and Pla2g6 mutations, as well as pathways common to neuromuscular/neurodegenerative diseases.

Neuroimaging of Pediatric Cerebellum in Inherited Neurodegenerative Diseases

In the study of cerebellar degenerative diseases, morphologic imaging (computed tomography, CT and magnetic resonance imaging, MRI) is the most common examination. From the clinical and genetic point of view, cerebellar degenerative diseases include heterogeneous conditions in which MRI may show isolated cerebellar atrophy or cerebellar atrophy associated with other cerebellar or supratentorial abnormalities. Neuroradiological progression is often observed. In congenital disorders of glycosylation (CDG), for example, MRI may be normal, may demonstrate mild cerebellar atrophy or, in the advanced stages of the disease, marked atrophy of the cerebellar hemispheres and vermis associated with the abnormal signal intensity of the cerebellar cortex and white matter and brainstem hypotrophy. In spinal cerebellar ataxias (SCAs), very rare in the pediatric population, MRI may demonstrate isolated cerebellar atrophy or cerebellar and brainstem atrophy. MRI shows characteristic findings in other diseases, strongly suggesting a distinct disorder, such as neuroaxonal dystrophy, ARSACS, ataxia-telangiectasia, or precise mitochondrial diseases. An example of neurodegenerative disorder with prenatal onset is pontocerebellar hypoplasia (PCH). PCH represents a group of neurodegenerative disorders characterized by microcephaly, early cerebellar hypoplasia, and variable atrophy of the cerebellum and ventral pons, genetically divided into several subtypes. Cerebellar hypoplasia visible on MRI is often the first sign that suggests the clinical diagnosis. In most cases, the PCH subtype may demonstrate a characteristic pattern distinguishable at MRI. Selective involvement of the cerebellum, sometimes accompanied by brainstem or supratentorial abnormalities in different combinations, may help restrict the differential diagnosis and may address the specific molecular screening.

New Insights of Phospholipase A2 Associated Neurodegeneration Phenotype Based on the Long-Term Follow-Up of a Large Hungarian Family

IntroductionPhospholipase A2-associated Neurodegeneration (PLAN) is a group of neurodegenerative diseases associated with the alterations of PLA2G6. Some phenotype-genotype association are well known but there is no clear explanation why some cases can be classified into distinct subgroups, while others follow a continuous clinical spectrum.MethodsLong-term neurological, and psychiatric follow-up, neuropathological, radiological, and genetic examinations, were performed in three affected girls and their family.ResultsTwo 24-years old twins and their 22-years old sister harbored the p.P622S, and p.R600W mutation in PLA2G6. The age of onset and the most prominent presenting symptoms (gaze palsy, ataxia, dystonia, psychomotor regression indicated atypical neuroaxonal dystrophy (ANAD), however, optic atrophy, severe tetraparesis would fit into infantile neuroaxonal dystrophy (INAD). All siblings had hyperintensity in the globi pallidi and substantiae nigrae which is reported in ANAD, whereas it is considered a later neuroradiological marker in INAD. The slow progression, rigidity, bradykinesis, and the prominent psychiatric symptoms indicate PLA2G6-related dystonia-parkinsonism. Abnormal mitochondria, lipid accumulation and axonal spheroids were observed in the muscle and nerve tissue. Brain deposition appeared 6 years following the initial cerebellar atrophy. Mild MRI alterations were detected in the asymptomatic carrier parents.ConclusionThe colorful clinical symptoms, the slightly discordant phenotype, and the neuroimaging data in the family supports the view that despite the distinct definition of age-related phenotypes in PLAN, these are not strict disease categories, but rather a continuous phenotypic spectrum. The mild MRI alterations of the parents and the family history suggest that even heterozygous pathogenic variants might be associated with clinical symptoms, although systematic study is needed to prove this.

Insights into Lewy body disease from rare neurometabolic disorders

Professor Kurt Jellinger is well known for his seminal work on the neuropathology of age-associated neurodegenerative disorders, particularly Lewy body diseases. However, it is less well known that he also contributed important insights into the neuropathological features of several paediatric neurometabolic diseases, including Alpers–Huttenlocher syndrome, a syndrome of mitochondrial disease caused by POLG mutations, and infantile neuroaxonal dystrophy, a phenotype resulting from PLA2G6 mutations. Despite these rare diseases occurring in early life, they share many important pathological overlaps with age-associated Lewy body disease, particularly dysregulation of α-synuclein. In this review, we describe several neurometabolic diseases linked to Lewy body disease mechanisms, and discuss the wider context to pathological overlaps between neurometabolic and Lewy body diseases. In particular, we will focus on how understanding disease mechanisms in neurometabolic disorders with dysregulated α-synuclein may generate insights into predisposing factors for α-synuclein aggregation in idiopathic Lewy body diseases.

Fetal neuroaxonal dystrophy: a further etiology of fetal akinesia

Neuroaxonal Dystrophies (NAD) are neurodegenerative diseases characterized by axonal “spheroids” occurring in different age groups. The identification of mutations delineated new molecular entities in these disorders. We report neuropathological data of a new form of NAD, characterized by a precocious prenatal onset, different from classical and conatal Infantile Neuroaxonal Dystrophy (INAD).We studied 5 fetuses examined after pregnancy termination and 2 term neonates deceased just after birth, 4/7 born from consanguineous parents. All subjects presented severe fetal akinesia sequence with microcephaly. In 4/7 cases, a molecular study was performed. In all cases, “spheroids” with typical immunohistochemical features were identified, with variable spreading in the central and peripheral nervous system. Basal ganglia, brainstem, cerebellum, and spinal cord involvement was constant. Associated CNS malformations, unusual in INAD, were associated including hydrocephalus (2), callosal agenesis/hypoplasia (2), olfactory agenesis (1), cortical (3) and retinal (1) anomalies. None of the cases demonstrated mutations in PLA2G6, found in INAD. The clinical and neuropathological features of these fetal cases are different from those of “classical” INAD. The absence of mutations in PLA2G6, in addition, suggests that the fetal NAD is a new entity, distinct from INAD, with different molecular basis. Associated malformations suggest a wide phenotypic spectrum and probable genetic heterogeneity. Finally, fetal NAD is an additional etiology of fetal akinesia.LEARNING OBJECTIVESThis presentation will enable the learner to:Diagnose this rare form of neuroaxonal dystrophy (NAD) occurring precociously, in the fetal life, as soon as the second trimester, different from the infantile form of NAD. 1.Describe the phenotypic spectrum of this fetal NAD; fetal akinesia sequence, microcephaly and various brain malformations, different from the “classical” and conatal forms of infantile neuroaxonal dystrophy.2.Consider this etiology in the diagnosis of fetal akinesia sequence.

Emerging Disease-Modifying Therapies in Neurodegeneration With Brain Iron Accumulation (NBIA) Disorders

Neurodegeneration with Brain Iron Accumulation (NBIA) is a heterogeneous group of progressive neurodegenerative diseases characterized by iron deposition in the globus pallidus and the substantia nigra. As of today, 15 distinct monogenetic disease entities have been identified. The four most common forms are pantothenate kinase-associated neurodegeneration (PKAN), phospholipase A2 group VI (PLA2G6)-associated neurodegeneration (PLAN), beta-propeller protein-associated neurodegeneration (BPAN) and mitochondrial membrane protein-associated neurodegeneration (MPAN). Neurodegeneration with Brain Iron Accumulation disorders present with a wide spectrum of clinical symptoms such as movement disorder signs (dystonia, parkinsonism, chorea), pyramidal involvement (e.g., spasticity), speech disorders, cognitive decline, psychomotor retardation, and ocular abnormalities. Treatment remains largely symptomatic but new drugs are in the pipeline. In this review, we discuss the rationale of new compounds, summarize results from clinical trials, provide an overview of important results in cell lines and animal models and discuss the future development of disease-modifying therapies for NBIA disorders. A general mechanistic approach for treatment of NBIA disorders is with iron chelators which bind and remove iron. Few studies investigated the effect of deferiprone in PKAN, including a recent placebo-controlled double-blind multicenter trial, demonstrating radiological improvement with reduction of iron load in the basal ganglia and a trend to slowing of disease progression. Disease-modifying strategies address the specific metabolic pathways of the affected enzyme. Such tailor-made approaches include provision of an alternative substrate (e.g., fosmetpantotenate or 4′-phosphopantetheine for PKAN) in order to bypass the defective enzyme. A recent randomized controlled trial of fosmetpantotenate, however, did not show any significant benefit of the drug as compared to placebo, leading to early termination of the trials' extension phase. 4′-phosphopantetheine showed promising results in animal models and a clinical study in patients is currently underway. Another approach is the activation of other enzyme isoforms using small molecules (e.g., PZ-2891 in PKAN). There are also compounds which counteract downstream cellular effects. For example, deuterated polyunsaturated fatty acids (D-PUFA) may reduce mitochondrial lipid peroxidation in PLAN. In infantile neuroaxonal dystrophy (a subtype of PLAN), desipramine may be repurposed as it blocks ceramide accumulation. Gene replacement therapy is still in a preclinical stage.

Hereditary myelopathies in dogs

The purpose of the current review is to summarize data regarding hereditary myelopathies in dogs. Canine degenerative myelopathy (DM) is a progressive disease prevalent in senior (≥8 years old), large breed-dogs, predominating in German shepherd dog. Neurolocalization indicates a thoracolumbar, upper motor neuron, lesion; it can progress to the thoracic limbs and later to lower motor neurons of all limbs resembling human amyotrophic lateral sclerosis (ALS). Tentative diagnosis is based on ruling out other progressive myelopathies. Clinical similarities between ALS and DM made superoxide dismutase 1 gene (SOD1) a viable candidate gene as an etiopathogenic factor. Α E40K missense mutation of the SOD1 has been linked to DM. A genetic test for DM exists, which will aid breeding programs to eliminate the disease. Exercise and physiotherapy are important to slow the progression of DM. Long-term prognosis is poor as dogs become non-ambulatory within 4-6 months from the time of diagnosis. Dystrophic myelopathies include Afgan hound myelopathy/hereditary necrotizing myelopathy in Kooikerhondje dogs, leukoencephalomyelopathy and neuroaxonal dystrophy in Rottweilers and spongiform leukoencephalomyelopathy. A similar myelopathy is Jack Russell and Fox terrier hereditary ataxia. Their etiology is suspected to be hereditary and they appear at a young age. They are diagnosed solely postmortem with histopathological examination. There is no etiologic treatment and the prognosis is poor except for Rottweiler neuroaxonal dystrophy and Jack Russel ataxia due to the extremely slow progression of symptoms. Syringomyelia is characterized by the formation of fluid filled cavities within the spinal cord and outside the central canal that may communicate with the central canal and it is caused mainly due to Chari-like malformation (CLM). The most important clinical sign is neuropathic pain and is localized in the cervical region of the spinal cord. Progression of the disease varies, there are severe disabilities due to pain or it can be an incidental finding. CT and MRI are the preferable ways to detect the lesions. For CLM, therapy includes surgical and medical management. Drugs can be divided into analgesics (non-steroidal anti-inflammatory, gabapentin, pregabalin, tramadol), drugs reducing cerebrospinal fluid (CSF) production (omeprazole, acetazolamide, furosemide) and corticosteroids. Medical therapy diminishes the severity of clinical signs but never succeeds full resolution.

Rare health conditions 45: Holt-Oram syndrome, infantile neuroaxonal dystrophy, query (Q) fever

The purpose of this series is to highlight a range of rare health conditions. Rare health conditions are those that affect no more and usually fewer than 1 person in every 2000 and many healthcare assistants and nurses will encounter some of these conditions given the high number of them. This 45th article will explore three of these conditions: Holt-Oram syndrome, infantile neuroaxonal dystrophy and query (Q) fever.