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Tissue-resident macrophages of the brain, including microglia, are implicated in the pathogenesis of various CNS disorders and are possible therapeutic targets by their chemical depletion or replenishment by hematopoietic stem cell therapy. Nevertheless, a comprehensive understanding of microglial function and the consequences of microglial depletion in the human brain is lacking. In human disease, heterozygous variants in CSF1R, encoding the Colony-stimulating factor 1 receptor, can lead to adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) possibly caused by microglial depletion. Here, we investigate the effects of ALSP-causing CSF1R variants on microglia and explore the consequences of microglial depletion in the brain. In intermediate- and late-stage ALSP post-mortem brain, we establish that there is an overall loss of homeostatic microglia and that this is predominantly seen in the white matter. By introducing ALSP-causing missense variants into the zebrafish genomic csf1ra locus, we show that these variants act dominant negatively on the number of microglia in vertebrate brain development. Transcriptomics and proteomics on relatively spared ALSP brain tissue validated a downregulation of microglia-associated genes and revealed elevated astrocytic proteins, possibly suggesting involvement of astrocytes in early pathogenesis. Indeed, neuropathological analysis and in vivo imaging of csf1r zebrafish models showed an astrocytic phenotype associated with enhanced, possibly compensatory, endocytosis. Together, our findings indicate that microglial depletion in zebrafish and human disease, likely as a consequence of dominant-acting pathogenic CSF1R variants, correlates with altered astrocytes. These findings underscore the unique opportunity CSF1R variants provide to gain insight into the roles of microglia in the human brain, and the need to further investigate how microglia, astrocytes, and their interactions contribute to white matter homeostasis.

Astrocytes regulate central nervous system development, maintain its homeostasis and orchestrate repair upon injury. Emerging evidence support functional specialization of astroglia, both between and within brain regions. Different subtypes of gray matter astrocytes have been identified, yet molecular and functional diversity of white matter astrocytes remains largely unexplored. Nonetheless, their important and diverse roles in maintaining white matter integrity and function are well recognized. Compelling evidence indicate that impairment of normal astrocytic function and their response to injury contribute to a wide variety of diseases, including white matter disorders. In this review, we highlight our current understanding of astrocyte heterogeneity in the white matter of the mammalian brain and how an interplay between developmental origins and local environmental cues contribute to astroglial diversification. In addition, we discuss whether, and if so, how, heterogeneous astrocytes could contribute to white matter function in health and disease and focus on the sparse human research data available. We highlight four leukodystrophies primarily due to astrocytic dysfunction, the so-called astrocytopathies. Insight into the role of astroglial heterogeneity in both healthy and diseased white matter may provide new avenues for therapies aimed at promoting repair and restoring normal white matter function.

Astrocytes regulate central nervous system development, maintain its homeostasis and orchestrate repair upon injury. Emerging evidence support functional specialization of astroglia, both between and within brain regions. Different subtypes of gray matter astrocytes have been identified, yet molecular and functional diversity of white matter astrocytes remains largely unexplored. Nonetheless, their important and diverse roles in maintaining white matter integrity and function are well recognized. Compelling evidence indicate that impairment of normal astrocytic function and their response to injury contribute to a wide variety of diseases, including white matter disorders. In this review, we highlight our current understanding of astrocyte heterogeneity in the white matter of the mammalian brain and how an interplay between developmental origins and local environmental cues contribute to astroglial diversification. In addition, we discuss whether, and if so, how, heterogeneous astrocytes could contribute to white matter function in health and disease and focus on the sparse human research data available. We highlight four leukodystrophies primarily due to astrocytic dysfunction, the so-called astrocytopathies. Insight into the role of astroglial heterogeneity in both healthy and diseased white matter may provide new avenues for therapies aimed at promoting repair and restoring normal white matter function.

Leukodystrophies are genetically determined disorders characterized by the selective involvement of the central nervous system white matter. Onset may be at any age, from prenatal life to senescence. Many leukodystrophies are degenerative in nature, but some only impair white matter function. The clinical course is mostly progressive, but may also be static or even improving with time. Progressive leukodystrophies are often fatal, and no curative treatment is known. The last decade has witnessed a tremendous increase in the number of defined leukodystrophies also owing to a diagnostic approach combining magnetic resonance imaging pattern recognition and next generation sequencing. Knowledge on white matter physiology and pathology has also dramatically built up. This led to the recognition that only few leukodystrophies are due to mutations in myelin- or oligodendrocyte-specific genes, and many are rather caused by defects in other white matter structural components, including astrocytes, microglia, axons and blood vessels. We here propose a novel classification of leukodystrophies that takes into account the primary involvement of any white matter component. Categories in this classification are the myelin disorders due to a primary defect in oligodendrocytes or myelin (hypomyelinating and demyelinating leukodystrophies, leukodystrophies with myelin vacuolization); astrocytopathies; leuko-axonopathies; microgliopathies; and leuko-vasculopathies. Following this classification, we illustrate the neuropathology and disease mechanisms of some leukodystrophies taken as example for each category. Some leukodystrophies fall into more than one category. Given the complex molecular and cellular interplay underlying white matter pathology, recognition of the cellular pathology behind a disease becomes crucial in addressing possible treatment strategies.

Globoid cell leukodystrophy (GLD; Krabbe's disease), caused by a genetic galactosylceramidase deficiency, affects both the central and peripheral nervous systems (CNS and PNS). Allogenic hematopoietic stem-cell transplantation (HSCT) has been beneficial for clinical improvement of this disease. However, recent reports by Siddiqi et al. suggested that none of their transplanted patients achieved complete normalization of their peripheral nerve function, despite the well-documented remyelination of the CNS and PNS in the treated patients. We hypothesized that the PNS dysfunction in GLD is due to altered Schwann cell-axon interactions, resulting in structural abnormalities of the node of Ranvier and aberrant expression of ion channels caused by demyelination and that the persistence of this altered interaction is responsible for the dysfunction of the PNS after HSCT. Since there has not been any investigation of the Schwann cell-axonal relationship in twitcher mice, an authentic model of GLD, we first investigated structural abnormalities, focusing on the node of Ranvier in untreated twitcher mice, and compared the results with those obtained after receiving bone marrow transplantation (BMT). As expected, we found numerous supernumerary Schwann cells that formed structurally abnormal nodes of Ranvier. Similar findings, though at somewhat variable extent, were detected in mice treated with BMT. Activated supernumerary Schwann cells expressed GFAP immunoreactivity and generated Alcian blue-positive extracellular matrix (ECM) in the endoneurial space. The processes of these supernumerary Schwann cells often covered and obliterated the nodal regions. Furthermore, the distribution of Na(+) channel immunoreactivity was diffuse without the concentration at the nodes of Ranvier as seen in wild-type mice. Neither K(+) channels nor Neurexin IV/ Caspr/ Paranoidin (NCP-1) were detected in the twi/twi sciatic nerve. The results of our study suggest the importance of normalization of the Schwann cell-axon relationship for the functional recovery of peripheral nerves, when one considers therapeutic strategies for PNS pathology in GLD.

Lysosomal storage disorders (LSDs) are genetically inherited diseases characterized by the accumulation of disease-specific biological materials such as proteolipids or metabolic intermediates within the lysosome. The lysosomal compartment's central importance to normal cellular function can be appreciated by examining the various pathologies that arise in LSDs. These disorders are invariably fatal, and many display profound neurological impairment that begins in childhood. However, recent studies have revealed that several LSDs also have irregularities in the function of the immune system. Gaucher disease, mucopolysaccharidosis VII, and alpha-mannosidosis are examples of a subset of LSD patients that are predisposed towards immune suppression. In contrast, GM2 gangliosidosis, globoid cell leukodystrophy, Niemann-Pick disease type C1 and juvenile neuronal ceroid lipofuscinosis are LSDs that are predisposed towards immune system hyperactivity. Antigen presentation and processing by dedicated antigen presenting cells (APCs), secretion of pore-forming perforins by cytotoxic-T lymphocytes, and release of pro-inflammatory mediators by mast cells are among the many crucial immune system functions in which the lysosome plays a central role. Although the relationship between the modification of the lysosomal compartment in LSDs and modulation of the immune system remains unknown, there is emerging evidence for early neuroimmune responses in a variety of LSDs. In this review we bridge biochemical studies on the lysosomal compartment's role in the immune system with clinical data on immune system irregularities in a subset of LSDs.

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is a progressive cerebral white matter disease with onset in childhood, caused by mutations in the MLC1 gene. MLC1 is a protein with unknown function that is mainly expressed in the brain in astrocytic endfeet at the blood-brain and cerebrospinal fluid-brain barriers. It shares its localization at astrocytic endfeet with the dystrophin-associated glycoprotein complex (DGC). The objective of the present study was to investigate the possible association of MLC1 with the DGC. To test this hypothesis, (co)-localization of DGC-proteins and MLC1 was analyzed by immunohistochemical stainings in gliotic brain tissue from a patient with multiple sclerosis, in glioblastoma tissue and in brain tissue from an MLC patient. In control tissue, a direct protein interaction was tested by immunoprecipitation. Results revealed that MLC1 is co-localized with DGC-proteins in gliotic brain tissue. We demonstrated that both MLC1 and aquaporin-4, a member of the DGC, were redistributed in glioblastoma cells. In MLC brain tissue, we showed absence of MLC1 and altered expression of several DGC-proteins. We demonstrated a direct protein interaction between MLC1 and Kir4.1. From these results we conclude that MLC1 is associated with the DGC at astrocytic endfeet.

We report here a case of orthochromatic leukodystrophy with spheroids. A 40-year-old woman developed forgetfulness. About 1 year after the onset, clinical examination confirmed global intellectual deterioration with amnesia, spatiotemporal disorientation, and impairment of judgment. At age 43, she experienced tonic-clonic convulsions several times, and died of pneumonia at the age of 44. Alzheimer's disease was suspected clinically. Pathologically, there was severe diffuse demyelination of the deep white matter of the frontal, parietal and occipital lobes with relative preservation of the subcortical U fibers. In the central demyelinated areas, myelin loss was severe with diffuse gliosis, moderate loss of axons, and many axonal spheroids. At the periphery of the severely degenerated regions, there were a lot of macrophages and most had non-metachromatic lipid granules. The cerebral cortex was intact. The neuropathological findings of this case are consistent with hereditary diffuse leukoencephalopathy with spheroids (HDLS). Ten cases of HDLS were reviewed and presented many findings in common. The gray matter was intact and U fibers were well preserved in most cases. In white matter lesions, severe loss of myelin, moderate to severe axonal loss, much axonal swelling, and the presence of macrophages and hypertrophic astrocytes were common findings. In some cases with HDLS, dementia appeared without obvious neurological manifestations in the early stage. We should remember that some cases with HDLS show clinical symptoms similar to Alzheimer's disease, especially in the early stage.

We present a two-generation family consisting of a father and two daughters, who had an adult-onset leukodystrophy characterized by widespread destruction of cerebral white matter with neuroaxonal spheroids. The mode of inheritance appears to be autosomal dominant. All three patients presented with a variety of motor and cognitive symptoms, including frontal lobe signs, 4-7 years before death. Each followed a chronic course until death at ages 39, 46, and 51. At autopsy, the white matter loss was widespread but most prominent in the cerebrum with descending corticospinal tract degeneration and relative sparing of subcortical U-fibers. Pigmented glial cells were present, most of which appear to be macrophages, but inconstantly Prussian blue-positive. This disease is consistent with published reports of hereditary diffuse leukoencephalopathy with spheroids (HDLS). However, a review of the literature and a personal review of the neuropathology of the original case of the pigmentary type of orthochromatic leukodystrophy (POLD) reveal overlapping clinical and neuropathologic features between these two previously distinct entities, suggesting a common pathogenetic and perhaps etiological relationship between the two.

Childhood ataxia with diffuse central nervous system hypomyelination syndrome (CACH) is a recently described leukodystrophy of unknown etiology. To characterize the neuropathological features and gain insight as to the pathogenesis of this disorder, we studied cerebral tissue from six patients with the CACH syndrome. Evaluation of toluidine blue-stained, semithin sections of white matter from CACH patients disclosed unusual cells with "foamy" cytoplasm, small round nuclei and fine chromatin. Electron microscopy (EM) revealed cells in the white matter with abundant cytoplasm containing many mitochondria and loosely clustered, membranous structures, but lacking the lysosomal structures seen in macrophages. Further analysis of tissue sections with antibodies and special stains demonstrated that the abnormal cells with abundant cytoplasm labeled with oligodendroglial markers, but did not react with macrophage or astrocytic markers. Double immunolabeling with macrophage and oligodendroglial markers clearly distinguished macrophages from the "foamy" oligodendroglial cells (FODCs). Proteolipid protein (PLP) mRNA in situ hybridization demonstrated PLP mRNA transcripts in a high proportion of oligodendrocytes in CACH patients compared to control patients, and PLP mRNA transcript signal in cells, morphologically consistent with FODCs. Normal and pathological brain control tissues did not contain FODCs. These neuropathological findings will be useful pathological identifiers of CACH, and may provide clues to the pathogenesis of this disorder.

We report neuropathological, biochemical and molecular studies on two patients with childhood ataxia with diffuse central nervous system hypomyelination (CACH) syndrome, a leukodystrophy recently defined according to clinical and radiological criteria. Both had severe cavitating orthochromatic leukodystrophy without atrophy, predominating in hemispheric white matter, whereas U-fibers, internal capsule, corpus callosum, anterior commissure and cerebellar white matter were relatively spared. The severity of white matter lesions contrasted with the rarity of myelin breakdown products and astroglial and microglial reactions. In the white matter, there was an increase in a homogeneous cell population with the morphological features of oligodendrocytes, in many instances presenting an abundant cytoplasm like myelination glia. These cells were negative for glial fibrillary acidic protein and antibodies PGM1 and MIB1. Some were positive for myelin basic protein, proteolipid protein (PLP), and myelin oligodendrocyte glycoprotein, but the majority were positive for human 2'-3' cyclic nucleotide 3' phosphodiesterase and all were positive for carbonic anhydrase II, confirming that they are oligodendrocytes. Myelin protein and lipid content were reduced. The PLP gene, analyzed in one case, was not mutated or duplicated. The increased number of oligodendrocytes without mitotic activity suggests an intrinsic oligodendroglial defect or an abnormal interaction with axons or other glial cells. This neuropathological study supports the notion that CACH syndrome constitutes a specific entity.

The twitcher (twi/twi) is an authentic murine model of human globoid cell leukodystrophy (GLD), caused by a deficiency of galactosylceramidase. Similar to human GLD, the twitcher shows progressive deterioration of neurological function and its neuropathology is characterized by a collection of periodic acid-Schift stain (PAS)-positive macrophages in the areas of demyelination. However, there are some differences in the clinico-pathological aspects between human and murine GLD. We investigated the spacio-temporal progression of neuropathology in twitcher from postnatal day (PND) 10 to 45. No clinical symptoms or neuropathological changes were apparent in twi/twi until PND 15. Generally, infiltration of macrophages, concomitant with myelin degeneration, was recognized in the cerebellar white matter and the brain stem after PND 20, then in cerebral white matter after PND 25, and in cerebral and cerebellar gray matter after PND 30. The demyelination was very severe in the radix of the 8th and the 5th cranial nerves. The neurological symptoms such as tremor, spasticity and cranial nerve dysfunction were well correlated with the progression of pathological changes. Demyelination progressed in an orderly fashion such that myelin degeneration began 10 to 20 days after the commencement of myelination in any of the given nerve fiber tracts. This suggests that there are no significant differences in the metabolism of galactocerebroside in the myelin and myelin-forming cells in individual nerve fiber tracts throughout the murine brain. Over-expression of glial fibrillary acidic protein was already present before the initiation of obvious demyelination. In addition to the areas of demyelination, focal clustering of PAS-positive cells were seen in close association with neurons in the basal ganglia and hippocampus in this murine GLD twitcher, whereas in human GLD, PAS-positive cells tended to be limited within the white matter. Understanding of these orderly patterns of neuropathological features is of essential importance for evaluating the results of the forthcoming gene therapy.

Previous imaging studies in infants with globoid cell leukodystrophy (GLD) using computed tomography have demonstrated a reduction in cerebral white matter and increased density symmetrically in the regions of the thalami, periventricular white matter, and the internal capsules. Correlation of these findings with morphologic studies at necropsy has not been made. In particular, deposition of calcium has not been described. We have evaluated two children with GLD confirmed by the absence of leukocyte galactosylceramide beta-galactosidase activity using repeated magnetic resonance (MR) scans in each and correlated the imaging results with post-mortem analyses in one. Neuropathologic examination revealed abnormalities typical for GLD. In addition to the absence of normal myelination throughout cerebral and cerebellar white matter, MR images demonstrated the presence of a paramagnetic effect in the regions of the thalami, corona radiata, and centra semiovale. We have observed in histologic preparations from these areas a dense accumulation of globoid cells and some calcium, which we suggest may be responsible for producing the paramagnetic effect.

The present report documents a family with three cases in two successive generations of pigmentary orthochromatic leukodystrophy (POLD). The clinical features of these cases and histochemical and ultrastructural investigations of two of the brains from successive generations are discussed. A review of the familial cases of POLD reported in the literature is also presented. Transmission of these cases was by a dominant inheritance. Onset of the clinical symptoms occurred at 42 to 54 years of age; duration of the disease was from 2-11 years, and death occurred at 45 to 57 years of age. Clinical manifestations of all three cases were severe headaches; bilateral pyramidal, pseudobulbar, cerebellar, and frontal release signs; gait disturbances; euphoria, or apathy; epileptic seizures; and dementia. The neuropathological pattern consists of slight cerebral atrophy, brownish discoloration of the cerebral white matter with demyelination and severe gliosis, sparing the sub-cortical U fibers; presence in the macrophages of lipid pigment granules that are sudanophilic, non metachromatic, and PAS and iron positive. The electron microscopic pattern of the lipid pigment in the macrophages is that of ceroid: electron-dense, membrane-bound intracytoplasmic lysosomes with curvilinear and/or fingerprint profiles.

Inherited deficiency for the lysosomal enzyme arylsulfatase A (ASA) leads to lysosomal storage of sulfatides and to dramatic demyelination in the CNS of humans (metachromatic leukodystrophy, MLD). As an animal model, ASA(-/-) mice have previously been generated by disruption of the ASA gene and are known to develop lysosomal sulfatide storage similar to that in human MLD, and, moreover, to become deaf because of degeneration of the primary neurons of the auditory pathway. The present study deals with the cellular and topographic distribution of sulfatide storage throughout the CNS of ASA(-/-) mice between a few days and 24 months of age. Sulfatide accumulation was detected on the ultrastructural level and by histochemical staining with alcian blue. Sulfatide storage was found in oligodendroglia and neurons in young mice, and in activated microglia (phagocytes) in adult mice. Neuronal sulfatide storage was most prominent in many nuclei of the medulla oblongata and pons, and in several nuclei of midbrain and forebrain. Sulfatide-storing phagocytes were most frequent in the white matter tracts of aged ASA(-/-) mice, whereas no widespread demyelination was obvious. Loss of neurons was found in two nuclei of the auditory pathway of aged ASA(-/-) mice (ventral cochlear nucleus and nucleus of trapezoid body). The distributional pattern of sulfatide storage throughout the CNS of ASA(-/-) mice largely corresponds to data reported for human MLD. An important difference, however, which remains unexplained at present, is the absence of obvious demyelination from the CNS of ASA(-/-) mice up to the age of 2 years.

Very long chain fatty acids (VLCFA) were found to be markedly increased and phytanic acid was borderline above normal in formalin-fixed brain white matter of case with an unusual type of familial leukodystrophy with epitheloid cells as described previously by Gullotta et al. [Neuropädiatrie (1970) 2: 173-186]. Increased VLCFA in brain clearly demonstrate that the patient had suffered from a peroxisomal disease. This diagnosis is corroborated by ultrastructural findings in brain showing typical lamellar inclusions. The particular type of peroxisomal disorder present in case (heterozygote of X-linked adrenoleukodystrophy?) remains speculative.

We report herein a sporadic case of the pigmentary type of orthochromatic leukodystrophy with early onset and very rapid clinical course. The patient's development was normal until 2 years old, when he experienced visual disturbance. Rapid deterioration resulted in death 1.5 years after the onset. Metachromatic leukodystrophy, globoid cell leukodystrophy and adrenoleukodystrophy were excluded by biochemical assays. Autopsy findings were compatible with the diagnosis of the pigmentary type of orthochromatic leukodystrophy. However, there were unique findings of severe neuronal loss and the collection of globoid-like cells in the interface of the gray matter and the white matter. Immunohistochemical staining of myelin basic protein, proteolipid protein and galactocerebroside demonstrated that these myelin constituents were equally preserved in the posterior column, while absent in the lateral and anterior columns of the spinal cord.

A brother and sister developed a slowly progressive neurological disorder with cerebellar and pyramidal signs and mild dementia. The brother developed symptoms at 6 months and died aged 11 years; the sister developed symptoms at 3 years and died aged 18 years. At post-mortem both had severe widespread central nervous system demyelination with islands of preserved myelin, and small amounts of sudanophilic lipid products. Metachromatic material, globoid cells, and adrenal abnormalities were not seen. The features were those of Pelizaeus-Merzbacher disease (PMD). It has been proposed, on the basis of only a few family studies, that PMD is an X-linked recessive disorder. These cases suggest that autosomal recessive inheritance may occur.

This is the first pathologic report of an infant at 37 weeks' gestation with Alexander's disease. The findings demonstrate that the disease can arise in utero and be extensive at birth before myelination begins.

One case of each of the following human leukodystrophies was examined immunocytochemically with antisera against myelin basic protein (MBP), myelin associated glycoprotein (MAG) and gliofibrillary acidic protein (GFA): Metachromatic leukodystrophy (MLD), connatal adrenoleukodystrophy (ALD), sudanophilic leukodystrophy of the adult (SLD) and connatal Pelizaeus-Merzbacher disease (PMD). A case of canine globoid cell leukodystrophy (GLD) was also included under the assumption that this disease was the same in the dog as in man. It was shown that the storage process in MLD and GLD did not involve MBP or MAG and that the breakdown of myelin with the formation of fat granule cells containing droplets of neutral fat in ALD and SLS proceeds in a similar way as in experimental Wallerian degeneration. In PMD, MBP is present in the vicinity of axons not surrounded by a myelin sheath demonstrable with conventional means. The globoid cells of GLD could be demonstrated to be of non-astrocytic origin.

Chronologic events of demyelination were investigated in the spinal cord of the twitcher mouse, an authentic murine model of human globoid cell leukodystrophy (GLD) from 5 to 45 days postnatal. There was very little evidence of myelin degeneration before day 25 although clustered or scattered globoid cells were already noted in the dorsal columns and intramedullary portion of the ventral roots. Globoid cells contained typical cytoplasmic inclusions and in those which were found adjacent to degenerating myelin and naked axons, myelin debris were conspicuous in their cytoplasm. Vesiculation of myelin and a feature of globoid cells stripping myelin lamellae were noted in the area of demyelination. Myelin and oligodendroglial degeneration became pronounced throughout the spinal white matter after day 40 but globoid cells tended to be more concentrated in the dorsal columns. Our observations suggest that the emergence of globoid cells in GLD is in response to the changes in biochemical environment (i.e., excessive presence of galactosylceramide in the tissue?), and these cells appear to have a role as phagocytic cells in removing myelin lamellae.

Clinical and morphological findings in an 8-year-old Jewish girl with spongy leukodystrophy are presented. Ultrastructural changes indicated that this may be a form of Canavan's disease with some atypical features. Biochemical measurements indicated that synaptosomal membranes prepared from the striatum but not from the cerebral cortex were deficient in protein kinase activity based on incorporation of 32P into proteins. Both areas contained the same spectrum of proteins. Cyclic AMP (cAMP) measurements indicated no significant differences between brain areas, or when compared to tissue obtained from a stillborn and a 5-year-old child.

Twins with high-risk globoid cell leukodystrophy (GLD) at the 6th gestational month were studied morphologically and enzymatically. One of them was affected and the other was probably the carrier of this disease. Central nervous system and other viscera developed normally for the gestational age in both fetuses. The lesions of GLD were found in the fetus with marked deficiency of galactocerebrosidase, but not in the probable carrier. The lesions were located only in the considerably myelinated areas viz., the brain stem and the spinal cord. Ultrastructurally, the globoid cells in the fetal GLD seemed to originate from glial cells, probably oligodendroglia.

Two new cases of Krabbe disease were diagnosed prenatally in a family with two previous affected children. The activity of galactosylceramide-beta-galactosidase was virtually absent in cultured amniotic cells. The prenatal diagnosis was confirmed enzymatically in cultured fibroblasts, brain, and visceral organs. Light and electron microscopy studies in both fetuses, 20 and 23 weeks of gestational age respectively, revealed the presence of typical globoid cells in the white matter of the spinal cord. Specific inclusions were also found in the brain stem and in peripheral nerves of the second fetus. A comparison with other Krabbe disease fetuses described in the literature contributes to the consensus that abnormal morphological findings can be expected in particular in the most actively myelinating areas of the nervous system. Although most of the cells containing the specific inclusions are probably non-glial in nature, some of them could represent myelination glia.

A light and electron microscopic study was performed on the cerebral white matter in a case of adrenoleukodystrophy (ALD) with peculiar symptoms of olivopontocerebellar atrophy. The affected white matter on the light microscope had many macrophages containing characteristic membrane-bound linear inclusions. The unaffected white matter on the light microscope demonstrated the following ultrastructural changes: (1) slight but definite degeneration of myelin sheaths scattered among apparently normal myelinated axons; (2) oligodendroglia-like cells containing membrane-free intracytoplasmic inclusions; and (3) many swollen astrocytes containing the same membrane-bound linear inclusions as those in the macrophages within the affected white matter. The mechanism of demyelination in ALD is also discussed.

A new neurological mutant mouse shows a gracile axonal dystrophy (GAD). The degenerative lesion develops by postnatal day 80, first appearing in the most rostral portion of the gracile fascicles. This lesion then extends caudally to involve the entire gracile fascicles. Many axonal swellings (dystrophies) also appear in the degenerative lesions in proportion to their severity. The clinical findings develop in keeping with these pathological changes, and are characterized by tremor, ataxia and difficulty in moving the hind limbs. These start around day 80, and progress gradually to death about day 150. The lumbar dorsal roots, their spinal root ganglia and peripheral nerves are normal. Electron microscopic study shows dystrophic axons packed with neurofilaments, mitochondria and tubulovesicular structures. These may reflect some stagnation of axonal transport. The distribution of the lesions suggest that the GAD mouse has a central distal axonopathy involving primary sensory neurons of the lumbar dorsal root ganglia.

Sub-plasmalemmal linear densities of variable length (0.1 approximately 1.0 mu) were found to be a constant feature of globoid cells in human as well as in canine globoid cell leukodystrophy (GLD). Similar densities were also observed in experimental globoid cells and epithelioid cells in chronic granuloma but not in glial cells. The linear densities always appeared without any relation to basal laminae. These observations together with the other reports of similar structures in lymphoma, fibroma and sarcoidosis suggest that the sub-plasmalemmal density is a structure frequently observed in mesenchymal cells, and may be another supporting feature for possible mesenchymal origin of globoid cells.

Two cases of a peculiar progressive encephalopathy clinically resembling a leukodystrophy, occurring in siblings, are reported. In both cases there was diffuse involvement of the white matter, with necrosis and vascular proliferation, the histological picture being similar to that observed in subacute necrotizing encephalomyelopathy. All grey structures were normal, except for a slight spongiosis of the locus niger in both cases.

The presence and significance of intranuclear bodies in astrocytes and vacuoles delimited by a single membrane in neurones and nucleolar changes are described in two cases of leukodystrophy.

A variety of peripheral nerves were studied by light microscopy from 7 young Cairn Terrier dogs which were necropsied and histologically diagnosed as having canine globoid-cell leukodystrophy (Krabbe's type). All nerves examined had severe degenerative changes in axons and myelin sheaths, similar to lesions in human cases of Krabbe's disease. Endoneurial fibrosis was not prominent but many PAS positive macrophages and a mode-rate number of mast cells were in the endoneurium. However, the dorsal root ganglia had no detectable changes in neurons nor proliferation of capsule cells or interstitial cells. Myopathy in the form of muscle atrophy and degeneration of muscle nuclei was seen in two dogs. Thus, in canine globoid-cell leukodystrophy, lesions occur widespread in the peripheral as well as in the central nervous system.