Long-term stabilization after bone marrow transplantation in juvenile metachromatic leukodystrophy

Metachromatic Leukodystrophy: Diagnosis, Modeling, and Treatment Approaches

Metachromatic leukodystrophy is a lysosomal storage disease, which is characterized by damage of the myelin sheath that covers most of nerve fibers of the central and peripheral nervous systems. The disease occurs due to a deficiency of the lysosomal enzyme arylsulfatase A (ARSA) or its sphingolipid activator protein B (SapB) and it clinically manifests as progressive motor and cognitive deficiency. ARSA and SapB protein deficiency are caused by mutations in the ARSA and PSAP genes, respectively. The severity of clinical course in metachromatic leukodystrophy is determined by the residual ARSA activity, depending on the type of mutation. Currently, there is no effective treatment for this disease. Clinical cases of bone marrow or cord blood transplantation have been reported, however the therapeutic effectiveness of these methods remains insufficient to prevent aggravation of neurological disorders. Encouraging results have been obtained using gene therapy for delivering the wild-type ARSA gene using vectors based on various serotypes of adeno-associated viruses, as well as using mesenchymal stem cells and combined gene-cell therapy. This review discusses therapeutic strategies for the treatment of metachromatic leukodystrophy, as well as diagnostic methods and modeling of this pathology in animals to evaluate the effectiveness of new therapies.

Early clinical course after hematopoietic stem cell transplantation in children with juvenile metachromatic leukodystrophy

Background

Long-term outcomes of hematopoietic stem cell transplantation (HSCT) in children with juvenile metachromatic leukodystrophy (MLD) have been investigated systematically, while short-term effects of HSCT on the course of the disease remain to be elucidated.

Results

In this study, the clinical course was evaluated over the first 24 months following HSCT, conducted at our center in 12 children with juvenile MLD (mean follow-up 6.75 years, range 3–13.5) and compared with 35 non-transplanted children with juvenile MLD. Motor function (GMFM-88 and GMFC-MLD), cognitive function (FSIQ), peripheral neuropathy (tibial nerve conduction velocity), and cerebral changes (MLD-MR severity score) were tested prospectively.

Seven children remained neurologically stable over a long period, five exhibited rapid disease progression over the first 12 to 18 months after transplantation. In the latter, time from first gross motor symptoms to loss of independent walking was significantly shorter compared with non-transplanted patients at the same stage of disease (p < 0.02). Positive prognostic factors were good motor function (GMFM = 100%, GMFC-MLD = 0) and a low MR severity score (≤ 17) at the time of HSCT.

Conclusions

Our results show that if disease progression occurs, this happens early on after HSCT and proceeds faster than in non-transplanted children with juvenile MLD, indicating that HSCT may trigger disease progression.

Microglia damage precedes major myelin breakdown in X-linked adrenoleukodystrophy and metachromatic leukodystrophy

X-linked adrenoleukodystrophy (X-ALD) and metachromatic leukodystrophy (MLD) are two relatively common examples of hereditary demyelinating diseases caused by a dysfunction of peroxisomal or lysosomal lipid degradation. In both conditions, accumulation of nondegraded lipids leads to the destruction of cerebral white matter. Because of their high lipid content, oligodendrocytes are considered key to the pathophysiology of these leukodystrophies. However, the response to allogeneic stem cell transplantation points to the relevance of cells related to the hematopoietic lineage. In the present study, we aimed to better characterize the pathogenetic role of microglia in the above-mentioned diseases. Applying recently established microglia markers to human autopsy cases of X-ALD and MLD we were able to delineate distinct lesion stages in evolving demyelinating lesions. The immune-phenotype of microglia was altered already early in lesion evolution, and microglia loss preceded full-blown myelin degeneration both in X-ALD and MLD. DNA fragmentation indicating phagocyte death was observed in areas showing microglia loss. The morphology and dynamics of phagocyte decay differed between the diseases and between lesion stages, hinting at distinct pathways of programmed cell death. In summary, the present study shows an early and severe damage to microglia in the pathogenesis of X-ALD and MLD. This hints at a central pathophysiologic role of these cells in the diseases and provides evidence for an ongoing transfer of toxic substrates primarily enriched in myelinating cells to microglia.

Long-term outcomes after allogeneic hematopoietic stem cell transplantation for metachromatic leukodystrophy: the largest single-institution cohort report

BACKGROUND

Metachromatic Leukodystrophy (MLD) is a rare, fatal demyelinating disorder with limited treatment options. Published outcomes after hematopoietic stem cell transplantation (HSCT) are scant and mixed. We report survival and function following HSCT for a large, single-center MLD cohort.

METHODS

Transplant-related data, survival and serial measures (brain MRI, nerve conduction velocity (NCV), neurologic and neuropsychology evaluations) were reviewed. When possible, parental interviews informed current neurologic status, quality-of-life, and adaptive functioning. Gross motor and expressive functions for late-infantile (LI-MLD) and juvenile (J-MLD) patients were described using previously reported, MLD-specific scales.

RESULTS

Forty patients with confirmed MLD have undergone HSCT at our center. Twenty-one (53 %) survive at a median 12 years post-HSCT. Most deaths (n = 17) were treatment-related; two died from disease progression. Survival did not depend upon MLD subtype or symptom status at transplant. LI-MLD patients survive beyond reported life expectancy in untreated disease. Abnormal brain MRI and peripheral nerve conduction velocities (NCV) were common before HSCT. Following transplant, fewer patients experienced MRI progression compared to NCV deterioration. Sixteen LI-MLD and J-MLD survivors were evaluable for long-term gross motor and/or expressive language functioning using existing MLD clinical scoring systems. While most J-MLD patients regressed, the aggregate cohort demonstrated superior retention of function compared to published natural history. Seventeen LI-MLD, J-MLD and adult subtype (A-MLD) survivors were evaluable for long-term adaptive functioning, activities of daily living, and/or cognition. Relative cognitive sparing was observed despite overall global decline. Five sibling pairs (one LI-MLD and four J-MLD), in which at least one underwent transplant in our cohort, were evaluable. Within each familial dyad, survival or function was superior for the treated sibling, or if both siblings were transplanted, for the pre-symptomatic sibling.

CONCLUSIONS

HSCT is a viable treatment option for MLD, but has significant limitations. Later-onset phenotypes may benefit most from early, pre-symptomatic transplant. Until superior, novel treatment strategies are demonstrated, MLD patients should be carefully considered for HSCT.

Mesenchymal stem cells as cellular vectors for pediatric neurological disorders

Lysosomal storage diseases are a heterogeneous group of hereditary disorders characterized by a deficiency in lysosomal function. Although these disorders differ in their etiology and phenotype those that affect the nervous system generally manifest as a profound deterioration in neurologic function with age. Over the past several decades implementation of various treatment regimens including bone marrow and cord blood cell transplantation, enzyme replacement, and substrate reduction therapy have proved effective for managing some clinical manifestations of these diseases but their ability to ameliorate neurologic complications remains unclear. Consequently, there exists a need to develop alternative therapies that more effectively target the central nervous system. Recently, direct intracranial transplantation of tissue-specific stem and progenitor cells has been explored as a means to reconstitute metabolic deficiencies in the CNS. In this chapter we discuss the merits of bone marrow-derived mesenchymal stem cells (MSCs) for this purpose. Originally identified as progenitors of connective tissue cell lineages, recent findings have revealed several novel aspects of MSC biology that make them attractive as therapeutic agents in the CNS. We relate these advances in MSC biology to their utility as cellular vectors for treating neurologic sequelae associated with pediatric neurologic disorders.

Outcomes of haematopoietic stem cell transplantation for inherited metabolic disorders: a report from the Australian and New Zealand Children's Haematology Oncology Group and the Australasian Bone Marrow Transplant Recipient Registry

We report a retrospective analysis of 53 haematopoietic stem cell transplants for inherited metabolic disorders performed at ANZCHOG transplant centres between 1992 and 2008. Indications for transplant included Hurler syndrome, ALD, and MLD. The majority of transplants utilized unrelated donor stem cells (66%) with 65% of those being unrelated cord blood. Conditioning therapy was largely myeloablative, with Bu plus another cytotoxic agent used in 89% of recipients. Primary graft failure was rare, occurring in three patients, all of whom remain long-term survivors following the second transplant. The CI of grade II-IV and grade III-IV acute GVHD at day +100 was 39% and 14%, respectively. Chronic GVHD occurred in 17% of recipients. TRM was 12% at day +100 and 19% at one yr post-transplant. OS at five yr was 78% for the cohort, 73% for patients with ALD and 83% for patients with Hurler syndrome. There was no statistically significant difference in overall survival between unrelated marrow and unrelated cord blood donor groups. The development of interstitial pneumonitis was an independent variable shown to significantly impact on TRM and OS. In summary, we report a large cohort of patients with inherited metabolic disorders with excellent survival post-allogeneic transplant.

Juvenile metachromatic leukodystrophy 10 years post transplant compared with a non-transplanted cohort

Metachromatic leukodystrophy (MLD) is a rare inborn error of metabolism leading to severe neurological symptoms and early death. Hematopoietic SCT (HSCT) is considered a treatment option, but results are inconsistent and comparison with natural history is practically missing. We compare a girl with juvenile MLD 10 years after allogeneic HSCT not only with her untreated sister, but also with a large cohort of untreated patients. The girl received HSCT at the age of 5 years when first motor signs appeared. Over 10 years she was stable with respect to her clinical course and gained cognitive abilities. Magnetic resonance imaging (MRI) showed clear regression of white matter changes and magnetic resonance spectroscopy (MRS) demonstrated a reversal of the initial choline increase and N-acetyl-aspartate (NAA) decrease. Only axonal demyelinating neuropathy showed some progression. Her gross motor function and MRI-scores were clearly better compared with her sister and the cohort of untreated patients. Difference to her sister became apparent only 4 years after HSCT. We conclude that HSCT, early in the course of disease, can lead to stabilization of juvenile MLD with a course clearly different from the natural history. HSCT may prevent disease progression, if performed sufficient time before loss of walking, which typically initiates rapid deterioration.

Neurodevelopmental outcomes of umbilical cord blood transplantation in metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is an inherited demyelinating disease that causes progressive neurologic deterioration, leading to severe motor disability, developmental regression, seizures, blindness, deafness, and death. The disease presents as a late-infantile, juvenile, or adult form. Hematopoietic stem cell transplantation has been shown to slow disease progression. The purpose of this longitudinal study was to evaluate long-term treatment outcomes after unrelated donor umbilical cord blood (UCB) transplantation in pediatric patients according to disease burden and age at onset (ie, late-infantile versus juvenile). Engraftment, survival, treatment-related toxicity, graft-versus-host disease, neurophysiologic measures, and neurodevelopmental function were assessed. To evaluate whether signal intensity abnormalities on magnetic resonance imaging (ie, modified Loes scores) predict post-transplant cognitive and gross motor development, a general linear mixed model was fit to the data. Twenty-seven patients underwent transplantation after myeloablative chemotherapy; 24 patients engrafted after the initial transplantation. Seven patients died of infection, regimen-related toxicity, or disease progression. Twenty patients (6 with late-infantile onset and 14 with juvenile onset) were followed for a median of 5.1 years (range, 2.4 to 14.7). We found that patients with motor function symptoms at the time of transplant did not improve after transplantation. Brainstem auditory evoked responses, visual evoked potentials, electroencephalogram, and/or peripheral nerve conduction velocities stabilized or improved in juvenile patients but continued to worsen in most patients with the late-infantile presentation. Pretransplant modified Loes scores were highly correlated with developmental outcomes and predictive of cognitive and motor function. Children who were asymptomatic at the time of transplantation benefited most from the procedure. Children with juvenile onset and minimal symptoms showed stabilization or deterioration of motor skills but maintained cognitive skills. Overall, children with juvenile onset had better outcomes than those with late-infantile onset. As in other leukodystrophies, early intervention correlated with optimal outcomes. We conclude that UCB transplantation benefits children with presymptomatic late-infantile MLD or minimally symptomatic juvenile MLD.

Developing treatment options for metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) represents a devastating lysosomal storage disease characterized by intralysosomal accumulation of the sphingolipid sulfatide in various tissues. Three types of the disease are currently distinguished: the late-infantile, which is the most commonly observed, the juvenile and the adult type. Demyelination represents the main histopathological feature of the disorder, leading to neurological impairment with no curative treatment currently available. Nevertheless, the increased scientific interest on the disease has led to the experimental use of innovative therapeutic approaches in animal models, aiming to provide an effective therapeutic regimen for human patients, as well. This paper provides an overview of developing treatment options among patients with MLD. Apart from hematopoietic stem cell transplantation, already in use for decades, other recent data discussed includes umbilical cord blood and stem cell transplantation, enzyme replacement therapy, gene therapy and autologous hematopoietic transplantation of genetically modified stem cells. Gene therapy with oligodedroglial, neural progenitor, embryonic and microencapsulated recombinant cells represents add-on treatment options still on experimental level.

Unrelated umbilical cord blood transplant for juvenile metachromatic leukodystrophy: a 5-year follow-up in three affected siblings

Unrelated umbilical cord blood transplantation (UCBT) was used to treat three siblings with juvenile metachromatic leukodystrophy (jMLD). The efficacy of this therapy was measured over a 5-year period with serial neurological examinations, neuroimaging, nerve conduction studies (NCS), and neuropsychological evaluations (NPE). Outcomes were a function of disease stage at time of UCBT with alteration of disease course occurring in the first 2 years after UCBT and then subsequent halting of progression and stabilization of symptoms and disease.

Haematopoietic stem cell transplantation does not retard disease progression in the psycho-cognitive variant of late-onset metachromatic leukodystrophy

Haematopoietic stem cell transplantation has an unproven role in the management of late-onset metachromatic leukodystrophy: theoretically justified through the engraftment of enzyme-replete haematopoietic progenitors and restoration of capacity for sulphatide catabolism in neural tissue through enzyme recapture, the long-term outcome is unknown. The rarity of the psycho-cognitive variant and slow progression of late-onset disease impairs evaluation of treatment. We report detailed clinical and neuropsychological assessments after haematopoietic stem-cell transplantation in a patient with a late-onset psycho-cognitive form of metachromatic leukodystrophy. Cognitive decline, indistinguishable from the natural course of the disease, was serially documented over 11 years despite complete donor chimaerism and correction of leukocyte arylsulphatase A to wild type values; subtle motor deterioration was similarly noted and progressive cerebral volume loss was evident upon magnetic resonance imaging. Sensory nerve conduction deteriorated 17 months post-transplantation with apparent stabilisation at 11-year review. Haematopoietic stem-cell transplantation was ineffective for this rare attenuated variant of metachromatic leukodystrophy. In the few patients identified pre-symptomatically or with early-phase disease, clear recommendations are lacking; when transplantation is considered, umbilical cord blood grafts from enzyme-replete donors with adjunctive mesenchymal stem cell infusions from the same source may be preferable. Improved outcomes will depend on enhanced awareness and early diagnosis of the disease, so that promising interventions such as genetically modified, autologous stem cell transplantation have the best opportunity of success.

Metachromatic leukodystrophy: a case of triplets with the late infantile variant and a systematic review of the literature

Metachromatic leukodystrophy is a rare disorder with great clinical variability. We report the first case of triplets with the late infantile form of the disease and their systematic progression of symptoms. We reviewed the literature and identified all human studies that reported new cases since 1921. We analyzed survival by decade to assess the impact of historical changes in the management of care. Mean age at death and the 5-year survival from onset of symptoms for late infantile, juvenile, and adult phenotypes were 4.2 years and 24.9%, 17.4 years and 70.3%, and 43.1 years and 88.6%, respectively. The 5-year survival of cases reported after 1990 was significantly better than cases reported before 1970 in all subtypes of metachromatic leukodystrophy (late infantile: 52% vs 14%, juvenile: 100% vs 46%, adult: 95% vs 67%). Survival in the late infantile subtype was worse than that in other subtypes. Survival significantly improved over time in all subtypes.

Cord blood and bone marrow transplantation in inherited metabolic diseases: scientific basis, current status and future directions

Progressive degeneration of the central nervous system leading to the loss of neuromotor, neurophysiological and cognitive abilities is the fundamental clinical problem in patients with many inherited metabolic diseases (IMD). Worldwide experience shows that morbidity, quality of life, and survival in these patients can be improved by allogeneic haematopoietic stem cell transplantation (HSCT), particularly when performed early in the course of the disease. At present, while available for some conditions, exogenous enzyme replacement therapy is unable to correct cognitive and central nervous system disease because of its inability to cross the blood-brain barrier. In contrast, HSCT allows donor-derived, enzyme-producing cells to migrate to the brain and other organs providing a permanent enzyme replacement therapy. HSCT may also mediate non-hematopoietic cell regeneration or repair. Traditionally, bone marrow has been the graft source for IMD patients. However, in the last 5 years many studies utilizing unrelated donor umbilical cord blood (UCB) as a graft source have demonstrated that UCB provides rapid and increased access to transplantation with favourable outcomes. This review describes preclinical studies and past and present clinical treatment approaches and discusses current controversies and future directions of this promising field.

Umbilical cord blood transplantation for juvenile metachromatic leukodystrophy

Three siblings with metachromatic leukodystrophy underwent umbilical cord blood transplantation at different stages of disease. Neuroimaging, nerve conduction studies, neurological examinations, and neuropsychological examinations were used to measure outcome over 2 years. After transplant, the oldest sibling experienced disease progression. His two siblings had near or total resolution of signal abnormalities on neuroimaging. Their neuropsychological testing remained stable, and nerve conduction studies have shown improvement. These results indicate pretransplantation neurological examinations may be the most significant predictor of outcome after transplant. To our knowledge, this report is the first to document neurological outcome of metachromatic leukodystrophy treated by umbilical cord blood transplantation.

Leukoencephalopathies associated with inborn errors of metabolism in adults

The discovery of a leukoencephalopathy is a frequent situation in neurological practice and the diagnostic approach is often difficult given the numerous possible aetiologies, which include multiple acquired causes and genetic diseases including inborn errors of metabolism (IEMs). It is now clear that IEMs can have their clinical onset from early infancy until late adulthood. These diseases are particularly important to recognize because specific treatments often exist. In this review, illustrated by personal observations, we give an overview of late-onset leukoencephalopathies caused by IEMs.

[Neurological presentations of lysosomal diseases in adult patients]

Lysosomal diseases represent a large group of genetic storage disorders characterized by a defect in the catabolism of complex molecules within the lysosome. Effective treatments are now possible for some of them given progresses in bone-marrow transplantation, enzyme replacement therapy and substrate reduction therapy. Neurologists and psychiatrists are concerned by these diseases because they can present in adolescence or adulthood with progressive neuropsychiatric signs. Here we focus on late-onset clinical forms which can be met in an adult neurology or psychiatric department. Lysosomal diseases were classified into 3 groups: (1) leukodystrophies (metachromatic leukodystrophy, Krabbe's disease and Salla's disease); (2) Neurodegenerative or psychiatric-like diseases (GM1 and GM2 gangliosidoses, Niemann Pick type C disease, sialidosis type I, ceroid-lipofuscinosis, mucopolysaccharidosis type III); (3) multisystemic diseases (Gaucher's disease, Fabry's disease, alpha and B mannosidosis, Niemann Pick disease type B, fucosidosis, Schindler/Kanzaki disease, and mucopolysaccharidosis type I and II. We propose a diagnostic approach guided by clinical examination, brain MRI, electrodiagnostic studies and abdominal echography.

Bone marrow transplantation for lysosomal storage disorders

Bone marrow transplantation for lysosomal storage disorders has been used for the past 25 years. The early allure of a promising new therapy has given way to more realistic expectations, as it has become clear that bone marrow transplantation is not a cure, but merely ameliorates the clinical phenotype. The results in some disorders are more acceptable than in others. Significant challenges have emerged, particularly the poor mesenchymal and neurological responses. Important recent advances in lysosomal biology, both in health and disease, have helped us to better understand the results of bone marrow transplantation, and to rationalize its role in the treatment of lysosomal storage disorders alongside newer therapies. At the same time, they have helped researchers to explore new therapeutic applications of bone marrow cells, such as gene and stem cell therapy.

[Adult onset hereditary leukoencephalopathies]

In clinical practice, the term "genetic leukoencephalopathy" refers to a group of genetic diseases whose common point is to give an aspect of diffuse leukoencephalopathy on MRI. With progress in diagnostic techniques including radiology, biochemistry or genetics, a large number of hereditary diseases causing leukoencephalopathy have been identified. Although generally beginning in childhood, these diseases often have more insidious clinical forms which can begin in adulthood. These forms remain poorly known. Some are accessible to treatment so their diagnosis appears essential. The diagnostic steps must be guided by clinical examination (neurological, ophthalmological and systemic), electromyography and MRI. The purpose of this review is to propose a classification of the genetic leukoencephalopathies and to give a progress report applicable in neurological practice.

Results of the Cord Blood Transplantation Study (COBLT): Outcomes of Unrelated Donor Umbilical Cord Blood Transplantation in Pediatric Patients with Lysosomal and Peroxisomal Storage Diseases

The Cord Blood Transplantation Study (COBLT), sponsored by the National Heart, Lung, and Blood Institute, is a phase II multicenter study designed to evaluate the use of cord blood in allogeneic transplantation. In this report, we evaluated the outcomes of cord blood transplantation in 69 patients with lysosomal and peroxisomal storage diseases. Patients with mucopolysaccharidoses I to III, mucolipidoses (ML) II (n = 36), adrenoleukodystrophy (n = 8), metachromatic leukodystrophy (n = 6), Krabbe disease (n = 16), and Tay-Sachs disease (n = 3) were enrolled between August 1999 and June 2004. All patients received the same preparative regimen, graft-versus-host disease (GVHD) prophylaxis, and supportive care. End points included survival, engraftment, GVHD, and toxicity. Sixty-nine patients (64% men; 81% white) with a median age of 1.8 years underwent transplantation with a median cell dose of 8.7 x 10(7)/kg. One-year survival was 72% (95% confidence interval, 61%-83%). The cumulative incidence of neutrophil engraftment by day 42 was 78% (95% confidence interval, 67%-87%) at a median of 25 days. Grade II to IV acute GVHD occurred in 36% of patients. Cord blood donors are readily available for rapid transplantation. Cord blood transplantation should be considered as frontline therapy for young patients with lysosomal and peroxisomal storage diseases.

Variable onset of metachromatic leukodystrophy in a Vietnamese family

We report two siblings with metachromatic leukodystrophy, one who presented at 7 years of age (juvenile onset) and his sister who presented at 22 years of age (adult onset). They are compound heterozygotes for two novel mutations in the arylsufatase A gene (ARSA). The responsible mutations in this Vietnamese family consist of a missense mutation with 5% enzyme activity (R143G) and a nonsense mutation (W318ter), from which no enzyme activity would be expected. These mutations in the ARSA gene have not been previously reported and may be useful when diagnosing metachromatic leukodystrophy in other affected Vietnamese individuals. The variability in presentation suggests that the genotype alone is not sufficient to determine the onset and course of the disease and modifying genetic and perhaps nongenetic factors likely contribute.

Bone marrow transplantation for globoid cell leukodystrophy, adrenoleukodystrophy, metachromatic leukodystrophy, and Hurler syndrome

Bone marrow transplantation protocols for inherited metabolic storage diseases are unique for each disorder treated. Differences depend also upon how old the patient was when onset occurred and rate of progression of disease. Treatment is directed to prevent or ameliorate the inexorable neurological deterioration that is the major pathophysiological event in all of these inherited metabolic storage diseases.

Bone marrow transplantation as effective treatment of central nervous system disease in globoid cell leukodystrophy, metachromatic leukodystrophy, adrenoleukodystrophy, mannosidosis, fucosidosis, aspartylglucosaminuria, Hurler, Maroteaux-Lamy, and Sly syndromes, and Gaucher disease type III

Over 400 patients with lysosomal and peroxisomal storage diseases have received hematopoietic stem cell transplantation from normal donors. Without treatment, all of these diseases have an inexorable fate leading to central nervous system deterioration and early death. On the other hand, all of the engrafted hosts have had a remarkable positive clinical improvement in response to normalization of previously deficient enzymatic activity. Survival data for those engrafted indicates continued life-span as long as two decades beyond transplantation. The particular diseases treated in this way are included in this article. The specific indications and methods for transplantation are also included in this article.

Leukodystrophy and bone marrow transplantation: role of mixed hematopoietic chimerism

Bone Marrow Transplantation (BMT) is currently the most physiologic treatment for some types of leukodystrophies. In enzyme deficiency states, replacement of defective genes with cells carrying "normal" copies of these genes offers a natural form of gene therapy. This review will cover the various disease states which may be treated using bone marrow transplantation as well as the obstacles and advantages offered by this treatment modality. The potential for mixed hematopoietic chimerism, with reference to the advantages and disadvantages of treating various leukodystrophies, is reviewed. Finally, certain approaches which would reduce the morbidity and mortality associated with conventional BMT are discussed. If these obstacles can be overcome, BMT may offer the hope of cure to a number, but certainly not all, leukodystrophies.

Slow progression of juvenile metachromatic leukodystrophy 6 years after bone marrow transplantation

Metachromatic leukodystrophy refers to a group of genetic neurologic diseases caused by deficiencies of the enzyme arylsulfatase A and the resulting accumulation of sulfatides in white matter. Bone marrow transplantation has been advocated as a treatment in an attempt to correct the enzyme deficiency. Such a transplant was performed in 1991 in a 16-year-old girl with a form of late juvenile metachromatic leukodystrophy caused by a homozygous P426L mutation in the arylsulfatase A gene. Engraftment was prompt and resulted in constant enzymatic normalization of circulating lymphocytes. The elevated urinary excretion of sulfatides remained unaffected. Clinical findings up until transplantation consisted of gait disturbances, impairment of cognitive functioning, and deterioration in school performance over several years. During a 6-year follow-up period, the patient's condition was subject to major fluctuations but, on the whole, findings showed slow neurologic and neurophysiologic deterioration. The clinical course observed after bone marrow transplantation probably more or less reflects the natural course expected in this form of late-onset metachromatic leukodystrophy.