Infantile Neuroaxonal Dystrophy Research Articles

14-3-3 Proteins, particularly of the epsilon isoform, are detectable in cerebrospinal fluids of cerebellar diseases in children

Background: Detection of 14-3-3 proteins in cerebrospinal fluid (CSF) is a powerful tool for elucidating the mechanisms of neurological disorders. There have been useful studies on 14-3-3 CSF protein detection in Creutzfeldt–Jakob disease and other neurological disorders, but none on cerebellar diseases. Objective: To elucidate whether 14-3-3 CSF proteins are a sensitive biomarker of cerebellar disruption in children. Materials and Methods: We examined 14-3-3 CSF proteins by immunoblotting in seven patients with cerebellar disorders: two with acute cerebellitis, two with acute cerebellar ataxia, and three with cerebellar atrophy. We also investigated 14-3-3 CSF proteins in four cases of febrile seizure and three of influenza-related encephalopathy. Isoforms of 14-3-3 proteins were also identified using isoform-specific antibodies. Results: 14-3-3 proteins were detected in CSF of six patients with cerebellar disorders, the exception being one with acute cerebellar ataxia caused by viral infection. Interestingly, only the 14-3-3 ε isoform was detected in two tested patients with cerebellar involvement. Moreover, longitudinal analysis of 14-3-3 CSF proteins in one patient with infantile neuroaxonal dystrophy showed that the 14-3-3 band density proportionally decreased when the cerebellar atrophy gradually progressed. Another CSF derived from a case of febrile seizure showed no 14-3-3 proteins, whereas all those derived from influenza-related encephalopathy demonstrated 14-3-3 CSF proteins with six isoforms. Conclusions: This is the first report on 14-3-3 CSF proteins as a significant biomarker of cerebellar disruption, as well as other brain diseases. Since 14-3-3 ε is localized in the molecular layer of cerebellum, the unique detection of 14-3-3 ε may indicate cerebellar involvement in the brain.

Genetic axonal neuropathies and neuronopathies of pre‐natal and infantile onset

The infantile-onset axonal neuropathies and neuronopathies are an uncommon and heterogeneous group of conditions causing weakness, wasting, and developmental delay in early childhood. Many are associated with central nervous system or other systemic manifestations and cause early mortality. We review the axonal Charcot-Marie-Tooth subtypes with onset in infancy, spinal muscular atrophy, and related syndromes of early infancy, giant axonal neuropathy, infantile neuroaxonal dystrophy, hereditary motor and sensory neuropathy with agenesis of the corpus callosum, early-onset neuropathies associated with mitochondrial disorders, and other less well-delineated clinical entities. Useful clinical and neuropathologic features in the diagnostic work-up of these conditions are also presented.

Follow‐up study of 25 Chinese children with PLA2G6‐associated neurodegeneration

To perform a follow-up of 25 Chinese children with gene-confirmed PLA2G6-associated neurodegeneration (PLAN). We recruited patients with infantile neuroaxonal dystrophy (INAD) according to the criteria proposed by Nardocci et al. Follow-up was conducted from 7 months to 8 years after the first visit. The PLA2G6 gene was sequenced, and copy number variation (CNV) was detected in patients with only one mutant allele and in mutation-negative patients. Patients with late-onset PLAN until 2012 were reviewed. All patients with INAD exhibited rapid decline in motor and mental function, consistent with previous reports from other populations. Epileptic seizures occurred in 16.7%. One teenager with late-onset PLAN was diagnosed and followed up. The age of disease onset in published late-onset PLAN ranged between 18 months and 37 years. Initial presentations included gait instability (79.0%), mood/behavior changes (10.5%), dysarthria (5.26%) and cognitive deterioration (5.3%). Compared with INAD, cerebellar atrophy (42.1%) was less frequent in the late-onset cases, with cerebral atrophy more common (71.4%). Brain iron accumulation was seen in 52.6%. PLA2G6 mutations were identified by DNA sequencing in 92.3% of clinically diagnosed INAD cases and in the late-onset case. Twenty-seven different mutations were found, of which 13 were novel. No CNVs were detected. Maternal uniparental disomy was confirmed in one INAD case. This is the largest report on PLAN in the Chinese population. We suggest that PLA2G6 should be screened in any patient exhibiting progressive gait disturbance, bradykinesia, dysarthria, tremors, mood/behavior changes or cognitive decline, especially when associated with cerebellar atrophy and/or iron accumulation and/or cerebral atrophy.

PLA2G6 Mutations and Other Rare Causes of Neurodegeneration with Brain Iron Accumulation

There is a wide variety of genetic and sporadic causes for neurodegenerative disorders with apparent brain iron accumulation on magnetic resonance imaging. Rare recessive causes include PLA2G6 mutations (infantile neuroaxonal dystrophy), and mutations of ATP13A2 (Kufor Rakeb syndrome) and FA2H. A variety of sporadic neurological disorders can present brain iron accumulation on imaging, including multiple sclerosis and neurological manifestations of HIV infection. The relevant clinical and imaging features will be discussed.

Rapid genetic diagnosis in single‐gene movement disorders

Rapid genetic diagnosis in single‐gene movement disorders

Severe disturbance in the Ca2+ signaling in astrocytes from mouse models of human infantile neuroaxonal dystrophy with mutated Pla2g6

Infantile neuroaxonal dystrophy (INAD; OMIM #no. 256600) is an inherited degenerative nervous system disorder characterized by nerve abnormalities in brain, spinal cord and peripheral nerves. About 85% of INAD patients carry mutations in the PLA2G6 gene that encodes for a Ca(2+)-independent phospholipase A(2) (VIA iPLA(2)), but how these mutations lead to disease is unknown. Besides regulating phospholipid homeostasis, VIA iPLA(2) is emerging with additional non-canonical functions, such as modulating store-regulated Ca(2+) entry into cells, and mitochondrial functions. In turn, defective Ca(2+) regulation could contribute to the development of INAD. Here, we studied possible changes in ATP-induced Ca(2+) signaling in astrocytes derived from two mutant strains of mice. The first strain carries a hypomorphic allele of the Pla2g6 that reduces transcript levels to 5-10% of that observed in wild-type mice. The second strain carries a point mutation in Pla2g6 that results in inactive VIA iPLA(2) protein with postulated gain in toxicity. Homozygous mice from both strains develop pathology analogous to that observed in INAD patients. The nucleotide ATP is the most important transmitter inducing Ca(2+) signals in astroglial networks. We demonstrate here a severe disturbance in Ca(2+) responses to ATP in astrocytes derived from both mutant mouse strains. The duration of the Ca(2+) responses in mutant astrocytes was significantly reduced when compared with values observed in control cells. We also show that the reduced Ca(2+) responses are probably due to a reduction in capacitative Ca(2+) entry (2.3-fold). Results suggest that altered Ca(2+) signaling could be a central mechanism in the development of INAD pathology.

Infantile Cerebellar-Retinal Degeneration Associated with a Mutation in Mitochondrial Aconitase, ACO2

Degeneration of the cerebrum, cerebellum, and retina in infancy is part of the clinical spectrum of lysosomal storage disorders, mitochondrial respiratory chain defects, carbohydrate glycosylation defects, and infantile neuroaxonal dystrophy. We studied eight individuals from two unrelated families who presented at 2-6 months of age with truncal hypotonia and athetosis, seizure disorder, and ophthalmologic abnormalities. Their course was characterized by failure to acquire developmental milestones and culminated in profound psychomotor retardation and progressive visual loss, including optic nerve and retinal atrophy. Despite their debilitating state, the disease was compatible with survival of up to 18 years. Laboratory investigations were normal, but the oxidation of glutamate by muscle mitochondria was slightly reduced. Serial brain MRI displayed progressive, prominent cerebellar atrophy accompanied by thinning of the corpus callosum, dysmyelination, and frontal and temporal cortical atrophy. Homozygosity mapping followed by whole-exome sequencing disclosed a Ser112Arg mutation in ACO2, encoding mitochondrial aconitase, a component of the Krebs cycle. Specific aconitase activity in the individuals' lymphoblasts was severely reduced. Under restrictive conditions, the mutant human ACO2 failed to complement a yeast ACO1 deletion strain, whereas the wild-type human ACO2 succeeded, indicating that this mutation is pathogenic. Thus, a defect in mitochondrial aconitase is associated with an infantile neurodegenerative disorder affecting mainly the cerebellum and retina. In the absence of noninvasive biomarkers, determination of the ACO2 sequence or of aconitase activity in lymphoblasts are warranted in similarly affected individuals, based on clinical and neuroradiologic grounds.

Disturbed brain phospholipid and docosahexaenoic acid metabolism in calcium-independent phospholipase A2-VIA (iPLA2β)-knockout mice

Calcium-independent phospholipase A2 group VIA (iPLA2β) releases docosahexaenoic acid (DHA) from phospholipids in vitro. Mutations in the iPLA2β gene, PLA2G6, are associated with dystonia-parkinsonism and infantile neuroaxonal dystrophy. To understand the role of iPLA2β in brain, we applied our in vivo kinetic method using radiolabeled DHA in 4 to 5-month-old wild type (iPLA2β+/+) and knockout (iPLA2β−/−) mice, and measured brain DHA kinetics, lipid concentrations, and expression of PLA2, cyclooxygenase (COX), and lipoxygenase (LOX) enzymes. Compared to iPLA2β+/+ mice, iPLA2β−/− mice showed decreased rates of incorporation of unesterified DHA from plasma into brain phospholipids, reduced concentrations of several fatty acids (including DHA) esterified in ethanolamine- and serine-glycerophospholipids, and increased lysophospholipid fatty acid concentrations. DHA turnover in brain phospholipids did not differ between genotypes. In iPLA2β−/− mice, brain levels of iPLA2β mRNA, protein, and activity were decreased, as was the iPLA2γ (Group VIB PLA2) mRNA level, while levels of secretory sPLA2-V mRNA, protein, and activity and cytosolic cPLA2-IVA mRNA were increased. Levels of COX-1 protein were decreased in brain, while COX-2 protein and mRNA were increased. Levels of 5-, 12-, and 15-LOX proteins did not differ significantly between genotypes. Thus, a genetic iPLA2β deficiency in mice is associated with reduced DHA metabolism, profound changes in lipid-metabolizing enzyme expression (demonstrating lack of redundancy) and of phospholipid fatty acid content of brain (particularly of DHA), which may be relevant to neurologic abnormalities in humans with PLA2G6 mutations.

Genetic ablation of PLA2G6 in mice leads to cerebellar atrophy characterized by Purkinje cell loss and glial cell activation.

Infantile neuroaxonal dystrophy (INAD) is a progressive, autosomal recessive neurodegenerative disease characterized by axonal dystrophy, abnormal iron deposition and cerebellar atrophy. This disease was recently mapped to PLA2G6, which encodes group VI Ca2+-independent phospholipase A2 (iPLA2 or iPLA2β). Here we show that genetic ablation of PLA2G6 in mice (iPLA2β-/-) leads to the development of cerebellar atrophy by the age of 13 months. Atrophied cerebella exhibited significant loss of Purkinje cells, as well as reactive astrogliosis, the activation of microglial cells, and the pronounced up-regulation of the pro-inflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β). Moreover, glial cell activation and the elevation in TNF-α and IL-1β expression occurred before apparent cerebellar atrophy. Our findings indicate that the absence of PLA2G6 causes neuroinflammation and Purkinje cell loss and ultimately leads to cerebellar atrophy. Our study suggests that iPLA2β-/- mice are a valuable model for cerebellar atrophy in INAD and that early anti-inflammatory therapy may help slow the progression of cerebellar atrophy in this deadly neurodegenerative disease.

発症初期より経過を追えたinfantile neuroaxonal dystrophyの兄弟例

発症初期より経過を追えたinfantile neuroaxonal dystrophyの兄弟例

Infantile neuroaxonal dystrophyの末梢神経にみられるジストロフィー線維の頻度

Infantile neuroaxonal dystrophyの末梢神経にみられるジストロフィー線維の頻度

Neuroaxonal Dystrophy in Calcium-Independent Phospholipase A2β Deficiency Results from Insufficient Remodeling and Degeneration of Mitochondrial and Presynaptic Membranes

Infantile neuroaxonal dystrophy (INAD) is a fatal neurodegenerative disease characterized by the widespread presence of axonal swellings (spheroids) in the CNS and PNS and is caused by gene abnormality in PLA2G6 [calcium-independent phospholipase A(2)β (iPLA(2)β)], which is essential for remodeling of membrane phospholipids. To clarify the pathomechanism of INAD, we pathologically analyzed the spinal cords and sciatic nerves of iPLA(2)β knock-out (KO) mice, a model of INAD. At 15 weeks (preclinical stage), periodic acid-Schiff (PAS)-positive granules were frequently observed in proximal axons and the perinuclear space of large neurons, and these were strongly positive for a marker of the mitochondrial outer membrane and negative for a marker of the inner membrane. By 100 weeks (late clinical stage), PAS-positive granules and spheroids had increased significantly in the distal parts of axons, and ultrastructural examination revealed that these granules were, in fact, mitochondria with degenerative inner membranes. Collapse of mitochondria in axons was accompanied by focal disappearance of the cytoskeleton. Partial membrane loss at axon terminals was also evident, accompanied by degenerative membranes in the same areas. Imaging mass spectrometry showed a prominent increase of docosahexaenoic acid-containing phosphatidylcholine in the gray matter, suggesting insufficient membrane remodeling in the presence of iPLA(2)β deficiency. Prominent axonal degeneration in neuroaxonal dystrophy might be explained by the collapse of abnormal mitochondria after axonal transportation. Insufficient remodeling and degeneration of mitochondrial inner membranes and presynaptic membranes appear to be the cause of the neuroaxonal dystrophy in iPLA(2)β-KO mice.

P18.9 Infantile neuroaxonal dystrophy: Are there clinical clues for early diagnosis?

P18.9 Infantile neuroaxonal dystrophy: Are there clinical clues for early diagnosis?

MRI Findings in Patients with Clinical Onset Consistent with Infantile Neuroaxonal Dystrophy (INAD), Literature Review, Clinical and MRI Follow-up

Infantile neuroaxonal dystrophy (INAD) is a rare autosomal recessive neurodegenerative disorder characterized by infantile onset and rapid progression of psychomotor regression and hypotonia evolving into spasticity. The neuroradiologic hallmark of the disease is represented by progressive cerebellar atrophy. Prior to the discovery of mutations in the PLA2G6 gene in family with INAD, the clinical diagnosis of the disease had been confirmed by the presence of spheroid bodies (SB) in a peripheral nerve biopsy. Various studies have found that some patients with mutations lacked SB and some without mutations had SB, indicating incomplete detection using either pathologic or molecular methods (7). This, together with the observation that the spectrum of clinical features associated with mutations in PLA2G6 is broader than previously described, has increased the usefulness of Magnetic Resonance (MR) in INAD diagnosis, particularly in the frequent occurrence of atypical cases, especially in the early stages of the disease. We retrospectively reviewed the MR studies of eight patients in whom clinical and imaging onset met the typical criteria for INAD. Their clinical and MR imaging (MRI) onset and follow-up were evaluated together with the neuroradiological findings reported in the literature in order to identify MRI features useful in differentiating INAD from other diseases with similar clinical onset and to discuss which of them are the most important, thus suggesting INAD diagnosis. Our contribution included the use of Proton Spectroscopy ((1)H-MR), diffusion weighted MR imaging (DWI) and diffusion tensor imaging (DTI) in the follow-up of seven of the eight patients. The literature reviewed included attempts to correlate clinical and MR data with the genotype in the group of patients carrying PLA2G6 mutations. From the limited and inhomogeneous cohort of patients included in our study, a correlation between the MR features, phenotype and genotype was not exhaustive.

Fetal Akinesia Deformation Sequence and Neuroaxonal Dystrophy without PLA2G6 Mutation

We present autopsy findings of a stillborn female infant at 20 to 21 weeks' gestation with neuroaxonal dystrophy. External examination showed features of fetal akinesia deformation sequence. Internal examination showed hypoplasia of the cerebellum, corpus callosum, and optic nerves, as well as nuclear cataracts. Light and electron microscopic examinations showed widespread axonal spheroids in the central and peripheral nervous systems. Gene sequencing failed to reveal PLA2G6 mutations, indicating that fetal neuroaxonal dystrophy presenting as fetal akinesia deformation sequence is genetically distinct from infantile neuroaxonal dystrophy and related disorders. In addition, placental examination showed α-fetoprotein-positive, eosinophilic, globular inclusions in the cytoplasm of a few villous macrophages. The significance of this novel histologic finding is unclear.

Imaging decreased brain docosahexaenoic acid metabolism and signaling in iPLA2β (VIA)-deficient mice

Ca(2+)-independent phospholipase A(2)β (iPLA(2)β) selectively hydrolyzes docosahexaenoic acid (DHA, 22:6n-3) in vitro from phospholipid. Mutations in the PLA2G6 gene encoding this enzyme occur in patients with idiopathic neurodegeneration plus brain iron accumulation and dystonia-parkinsonism without iron accumulation, whereas mice lacking PLA2G6 show neurological dysfunction and neuropathology after 13 months. We hypothesized that brain DHA metabolism and signaling would be reduced in 4-month-old iPLA(2)β-deficient mice without overt neuropathology. Saline or the cholinergic muscarinic M(1,3,5) receptor agonist arecoline (30 mg/kg) was administered to unanesthetized iPLA(2)β(-/-), iPLA(2)β(+/-), and iPLA(2)β(+/+) mice, and [1-(14)C]DHA was infused intravenously. DHA incorporation coefficients k* and rates J(in), representing DHA metabolism, were determined using quantitative autoradiography in 81 brain regions. iPLA(2)β(-/-) or iPLA(2)β(+/-) compared with iPLA(2)β(+/+) mice showed widespread and significant baseline reductions in k* and J(in) for DHA. Arecoline increased both parameters in brain regions of iPLA(2)β(+/+) mice but quantitatively less so in iPLA(2)β(-/-) and iPLA(2)β(+/-) mice. Consistent with iPLA(2)β's reported ability to selectively hydrolyze DHA from phospholipid in vitro, iPLA(2)β deficiency reduces brain DHA metabolism and signaling in vivo at baseline and following M(1,3,5) receptor activation. Positron emission tomography might be used to image disturbed brain DHA metabolism in patients with PLA2G6 mutations.

Phenotypic spectrum of patients with PLA2G6 mutation and PARK14 -linked parkinsonism

PLA2G6 is the causative gene for infantile neuroaxonal dystrophy, neurodegeneration associated with brain iron accumulation, and Karak syndrome. Based on previous reports, patients with PLA2G6 mutations could show axonal dystrophy, dystonia, dementia, and cerebellar signs. Recently, PLA2G6 was also reported as the causative gene for early-onset PARK14-linked dystonia-parkinsonism. To clarify the role of PLA2G6 mutation in parkinsonism, we conducted mutation analysis in 29 selected patients with very early-onset (≤ 30, mean 21.2 ± 8.4 years, ± SD) parkinsonism. These patients had other clinical features (e.g., mental retardation/dementia [14/29], psychosis [15/29], dystonia [11/29], and hyperreflexia [11/29]). Two novel compound heterozygous PLA2G6 mutations were detected (patient A: p.F72L/p.R635Q; patients B1 and B2: p.Q452X/p.R635Q). All 3 patients had early-onset l-dopa-responsive parkinsonism with dementia and frontotemporal lobar atrophy. Disease progression was relatively rapid. SPECT in patient B1 showed frontotemporal lobar hypoperfusion. MRI in patient A showed iron accumulation in the substantia nigra and striatum. Although the clinical presentation of PLA2G6-associated neurodegeneration was reported to be homogeneous, our findings suggest patients with PLA2G6 mutation could show heterogeneous phenotype such as dystonia-parkinsonism, dementia, frontotemporal atrophy/hypoperfusion, with or without brain iron accumulation. Based on the clinical heterogeneity, the functional roles of PLA2G6 and the roles of PLA2G6 variants including single heterozygous mutations should be further elucidated in patients with atypical parkinsonism, dementia, or Parkinson disease. PLA2G6 mutations should be considered in patients with early-onset l-dopa-responsive parkinsonism and dementia with frontotemporal lobar atrophy.

Catalytic Function of PLA2G6 Is Impaired by Mutations Associated with Infantile Neuroaxonal Dystrophy but Not Dystonia-Parkinsonism

BackgroundMutations in the PLA2G6 gene have been identified in autosomal recessive neurodegenerative diseases classified as infantile neuroaxonal dystrophy (INAD), neurodegeneration with brain iron accumulation (NBIA), and dystonia-parkinsonism. These clinical syndromes display two significantly different disease phenotypes. NBIA and INAD are very similar, involving widespread neurodegeneration that begins within the first 1–2 years of life. In contrast, patients with dystonia-parkinsonism present with a parkinsonian movement disorder beginning at 15 to 30 years of age. The PLA2G6 gene encodes the PLA2G6 enzyme, also known as group VIA calcium-independent phospholipase A2, which has previously been shown to hydrolyze the sn-2 acyl chain of phospholipids, generating free fatty acids and lysophospholipids.Methodology/Principal FindingsWe produced purified recombinant wildtype (WT) and mutant human PLA2G6 proteins and examined their catalytic function using in vitro assays with radiolabeled lipid substrates. We find that human PLA2G6 enzyme hydrolyzes both phospholipids and lysophospholipids, releasing free fatty acids. Mutations associated with different disease phenotypes have different effects on catalytic activity. Mutations associated with INAD/NBIA cause loss of enzyme activity, with mutant proteins exhibiting less than 20% of the specific activity of WT protein in both lysophospholipase and phospholipase assays. In contrast, mutations associated with dystonia-parkinsonism do not impair catalytic activity, and two mutations produce a significant increase in specific activity for phospholipid but not lysophospholipid substrates.Conclusions/SignificanceThese results indicate that different alterations in PLA2G6 function produce the different disease phenotypes of NBIA/INAD and dystonia-parkinsonism. INAD/NBIA is caused by loss of the ability of PLA2G6 to catalyze fatty acid release from phospholipids, which predicts accumulation of PLA2G6 phospholipid substrates and provides a mechanistic explanation for the accumulation of membranes in neuroaxonal spheroids previously observed in histopathological studies of INAD/NBIA. In contrast, dystonia-parkinsonism mutations do not appear to directly impair catalytic function, but may modify substrate preferences or regulatory mechanisms for PLA2G6.

Expression of PLA2G6 in human fetal development: Implications for infantile neuroaxonal dystrophy

Mutations in PLA2G6, which encodes calcium-independent phospholipase A 2 group VIA (iPLA2-VIA), underlie the autosomal recessive disorder infantile neuroaxonal dystrophy (INAD). INAD typically presents in the first year of life, and leads to optic atrophy and psychomotor regression. We have examined PLA2G6 expression in early human embryonic development by in situ hybridization. At Carnegie Stage (CS) 19 (approximately 7 post-conception weeks [PCW]), strong expression is evident in the ventricular zone (VZ) of midbrain and forebrain suggestive of expression in neural stem and progenitor cells. At CS23 (8 PCW) expression is also detectable in the VZ of the hindbrain and the subventricular zone (SVZ) of the developing neocortex, ganglionic eminences and diencephalon. By 9 PCW strong expression in the post-mitotic cells of the cortical plate can be seen in the developing neocortex. In the eye, expression is seen in the lens and retina at all stages examined. PLA2G6 expression is also evident in the alar plate of the spinal cord, dorsal root ganglia, the retina and lens in the eye and several non-neuronal tissues, including developing bones, lung, kidney and gut. These findings suggest a role for PLA2G6 in neuronal proliferation throughout the developing brain and in maturing neurons in the cortical plate and hindbrain. Although widespread PLA2G6 expression is detected in neuronal tissues, the pattern shows dynamic changes with time and indicates that INAD pathogenesis may begin prior to birth.

Inherited neuroaxonal dystrophy in dogs causing lethal, fetal‐onset motor system dysfunction and cerebellar hypoplasia

Neuroaxonal dystrophy in brainstem, spinal cord tracts, and spinal nerves accompanied by cerebellar hypoplasia was observed in a colony of laboratory dogs. Fetal akinesia was documented by ultrasonographic examination. At birth, affected puppies exhibited stereotypical positioning of limbs, scoliosis, arthrogryposis, pulmonary hypoplasia, and respiratory failure. Regional hypoplasia in the central nervous system was apparent grossly, most strikingly as underdeveloped cerebellum and spinal cord. Histopathologic abnormalities included swollen axons and spheroids in brainstem and spinal cord tracts; reduced cerebellar foliation, patchy loss of Purkinje cells, multifocal thinning of the external granular cell layer, and loss of neurons in the deep cerebellar nuclei; spheroids and loss of myelinated axons in spinal roots and peripheral nerves; increased myocyte apoptosis in skeletal muscle; and fibrofatty connective tissue proliferation around joints. Breeding studies demonstrated that the canine disorder is a fully penetrant, simple autosomal recessive trait. The disorder demonstrated a type and distribution of lesions homologous to that of human infantile neuroaxonal dystrophy (INAD), most commonly caused by mutations of phospholipase A2 group VI gene (PLA2G6), but alleles of informative markers flanking the canine PLA2G6 locus did not associate with the canine disorder. Thus, fetal-onset neuroaxonal dystrophy in dogs, a species with well-developed genome mapping resources, provides a unique opportunity for additional disease gene discovery and understanding of this pathology.