The burden of inherited leukodystrophies in children

Disease specific therapies in leukodystrophies and leukoencephalopathies

Leukodystrophies are a heterogeneous, often progressive group of disorders manifesting a wide range of symptoms and complications. Most of these disorders have historically had no etiologic or disease specific therapeutic approaches. Recently, a greater understanding of the pathologic mechanisms associated with leukodystrophies has allowed clinicians and researchers to prioritize treatment strategies and advance research in therapies for specific disorders, some of which are on the verge of pilot or Phase I/II clinical trials. This shifts the care of leukodystrophy patients from the management of the complex array of symptoms and sequelae alone to targeted therapeutics. The unmet needs of leukodystrophy patients still remain an overwhelming burden. While the overwhelming consensus is that these disorders collectively are symptomatically treatable, leukodystrophy patients are in need of advanced therapies and if possible, a cure.

A novel autosomal dominant leukodystrophy with specific MRI pattern

Etiologic diagnosis of adulthood leukodystrophy is challenging in neurologic practice. We describe here the clinico-radiological features of a novel autosomal dominant leukodystrophy in a single family. Clinical and MRI features were recorded in a three generation family. Exome sequencing was performed in two affected relatives and one healthy member. Four total relatives (3 women and 1 man, mean age at onset: 45, range 32-59) were followed: 2 for migraine and 2 for cognitive loss. MRI features were homogeneous in the four affected relatives: extensive and symmetrical white matter hyperintensities on T2-weighted images, with a posterior predominance, involvement of the middle cerebellar peduncles, corpus callosum and the posterior limb of the internal capsules. An extensive metabolic screening was negative. In addition, sequencing of pathogenic genes involved in dominant leukodystrophies (NOTCH3, LMNB1, GFAP, CSF1R) was negative. No mutation has been identified yet with exome sequencing. This report is peculiar because of dominant inheritance, adult onset, highly homogeneous white matter hyperintensities on T2-weighted MR images, predominant in the middle cerebellar peduncles and posterior part of internal capsule and absence of mutation of the genes involved in dominant leukodystrophies.

MRI pattern approach of adult-onset inherited leukoencephalopathies

White matter hyperintensities are frequently encountered in clinical practice. In adulthood, white matter hyperintensities are generally related to acquired disorders, such as vascular, inflammatory, or demyelinating diseases. Symmetrical and confluent white matter abnormalities on the first available MRI suggest a genetic disorder. In this article, we provide keys to recognize and classify the adult-onset forms of inherited leukoencephalopathies and to identify their causes by targeting specific biochemical or molecular biomarkers.

Clinical exome sequencing identifies a novel TUBB4A mutation in a child with static hypomyelinating leukodystrophy

BACKGROUND

Leukodystrophies are a large group of inherited diseases of central nervous system myelin. There are few treatments, and most patients do not receive a final genetic diagnosis.

PATIENT

We report a novel presentation of a female child with hypotonia, global developmental delay, and rotatory nystagmus. Brain MRI demonstrated profound hypomyelination and minimal or no atrophy in the brain stem or cerebellum.

RESULTS

Extensive testing failed to yield a diagnosis until clinical whole-exome sequencing revealed a novel pathogenic mutation in the β-tubulin gene TUBB4A. TUBB4A is a cause of hereditary dystonia type 4 and has recently been reported to cause hypomyelination with atrophy of the basal ganglia and cerebellum.

CONCLUSIONS

This report expands the phenotypic spectrum of TUBB4A-associated neurological diseases to include static hypomyelinating leukodystrophy and supports the clinical relevance of next-generation sequencing diagnosis approaches.

Imaging manifestations of the leukodystrophies, inherited disorders of white matter

The leukodystrophies are a diverse set of inherited white matter disorders and are uncommonly encountered by radiologists in everyday practice. As a result, it is challenging to recognize these disorders and to provide a useful differential for the referring physician. In this article, leukodystrophies are reviewed from the perspective of 4 imaging patterns: global myelination delay, periventricular/deep white matter predominant, subcortical white matter predominant, and mixed white/gray matter involvement patterns. Special emphasis is placed on pattern recognition and unusual combinations of findings that may suggest a specific diagnosis.

Preventable Infections in Children with Leukodystrophy

Children with inherited leukodystrophies have high hospitalization rates, often associated with infection. We studied whether potentially modifiable risk factors (pre-existing in-dwelling central intravenous access, urinary catheter, hardware, or mechanical ventilation; and influenza vaccine) were associated with infection-related hospitalization in children with leukodystrophy. Central intravenous access was associated with sepsis (odds ratio (OR) 9.8); urinary catheter was associated with urinary tract infections (OR 9.0); lack of seasonal vaccination was associated with influenza (OR 6.4); and mechanical ventilation was associated with pneumonia (OR 2.7). We conclude that potentially modifiable risk factors are significantly associated with infection and hospitalization in children with leukodystrophies.

White matter changes in an untreated, newly diagnosed case of classical homocystinuria

The authors report the case of a 4-year-old boy who developed progressive unilateral weakness and developmental delays prior to his diagnosis of classical homocystinuria. Magnetic resonance imaging (MRI) of the brain demonstrated diffuse white matter changes, raising the concern for a secondary diagnosis causing leukoencephalopathy, since classical homocystinuria is not typically associated with these changes. Other inborn errors of the transsulfuration pathway have been reported as causing these changes. Once begun on therapy for his homocystinuria, his neurologic deficits resolved and his delays rapidly improved. Repeat MRI performed one year after instating therapy showed resolution of his white matter abnormalities. This case illustrates the need to consider homocystinuria and other amino acidopathies in the differential diagnosis of childhood white matter diseases and lends weight to the hypothesis that hypermethioninemia may induce white matter changes.

National variation in costs and mortality for leukodystrophy patients in US children's hospitals

BACKGROUND

Inherited leukodystrophies are progressive, debilitating neurological disorders with few treatment options and high mortality rates. Our objective was to determine national variation in the costs for leukodystrophy patients and to evaluate differences in their care.

METHODS

We developed an algorithm to identify inherited leukodystrophy patients in deidentified data sets using a recursive tree model based on International Classification of Disease, 9th Edition, Clinical Modification, diagnosis and procedure charge codes. Validation of the algorithm was performed independently at two institutions, and with data from the Pediatric Health Information System (PHIS) of 43 US children's hospitals, for a 7-year period between 2004 and 2010.

RESULTS

A recursive algorithm was developed and validated, based on six International Classification of Disease, 9th Edition, Clinical Modification, codes and one procedure code that had a sensitivity up to 90% (range 61-90%) and a specificity up to 99% (range 53-99%) for identifying inherited leukodystrophy patients. Inherited leukodystrophy patients comprise 0.4% of admissions to children's hospitals and 0.7% of costs. During 7 years, these patients required $411 million of hospital care, or $131,000/patient. Hospital costs for leukodystrophy patients varied at different institutions, ranging from two to 15 times more than the average pediatric patient. There was a statistically significant correlation between higher volume and increased cost efficiency. Increased mortality rates had an inverse relationship with increased patient volume that was not statistically significant.

CONCLUSIONS

We developed and validated a code-based algorithm for identifying leukodystrophy patients in deidentified national datasets. Leukodystrophy patients account for $59 million of costs yearly at children's hospitals. Our data highlight potential to reduce unwarranted variability and improve patient care.

Lamin B1 mediates cell-autonomous neuropathology in a leukodystrophy mouse model

Adult-onset autosomal-dominant leukodystrophy (ADLD) is a progressive and fatal neurological disorder characterized by early autonomic dysfunction, cognitive impairment, pyramidal tract and cerebellar dysfunction, and white matter loss in the central nervous system. ADLD is caused by duplication of the LMNB1 gene, which results in increased lamin B1 transcripts and protein expression. How duplication of LMNB1 leads to myelin defects is unknown. To address this question, we developed a mouse model of ADLD that overexpresses lamin B1. These mice exhibited cognitive impairment and epilepsy, followed by age-dependent motor deficits. Selective overexpression of lamin B1 in oligodendrocytes also resulted in marked motor deficits and myelin defects, suggesting these deficits are cell autonomous. Proteomic and genome-wide transcriptome studies indicated that lamin B1 overexpression is associated with downregulation of proteolipid protein, a highly abundant myelin sheath component that was previously linked to another myelin-related disorder, Pelizaeus-Merzbacher disease. Furthermore, we found that lamin B1 overexpression leads to reduced occupancy of Yin Yang 1 transcription factor at the promoter region of proteolipid protein. These studies identify a mechanism by which lamin B1 overexpression mediates oligodendrocyte cell-autonomous neuropathology in ADLD and implicate lamin B1 as an important regulator of myelin formation and maintenance during aging.

Lifetime risk estimators in epidemiological studies of Krabbe Disease: Review and Monte Carlo comparison

This review addresses difficulties arising in estimating epidemiological parameters of leukodystrophies and lysosomal storage disorders, with special focus on Krabbe disease. Although multiple epidemiological studies of Krabbe disease have been published, these studies are difficult to reconcile since they have used different study populations and varying methods of calculation. Confusion exists regarding which epidemiological parameters have been estimated; the current review shows that most previous estimates can be properly interpreted as lifetime risk at birth. One of the most common estimation methods is shown to be inaccurate, while two other methods are shown to be approximately accurate. Based on the results of the current paper, recommendations are made that are expected to improve the quality of future studies of Krabbe disease. It is anticipated that these recommendations will be applicable to epidemiological studies of other lysosomal storage disorders, as well as any other rare diseases diagnosed with enzymatic screening.

Determinants of health care use in a population-based leukodystrophy cohort

OBJECTIVES

To determine the costs for children with leukodystrophies and whether high costs are associated with characteristic clinical features or resources use.

STUDY DESIGN

We determined health care costs in a population cohort of 122 patients with leukodystrophies, including inpatient, outpatient, and emergency department use, during a 9-year period. We analyzed differences in patients with high costs (>85th percentile) and their health care use.

RESULTS

Patients with leukodystrophy had significant variability in resource use, with the top 15th percentile of patients accounting for 73% of costs ($9.6 million). The majority of costs, 81% ($10.8 million), arose from inpatient hospitalization. High-cost patients had more and longer hospitalizations, increased requirements for intensive unit care and mechanical ventilation, and significantly more infections. Importantly, bone marrow transplantation did not solely account for the difference between high-cost and low-cost groups.

CONCLUSION

Inpatient hospitalization is the greatest source of health care resource use in patients with leukodystrophies. A minority of patients account for the majority of costs, primarily attributable to an increased volume of hospitalization. Strategies to improve care and reduce costs will need to reduce inpatient stays and target modifiable reasons for hospitalization.

The lived experience of Taiwanese mothers of a child diagnosed with adrenoleukodystrophy

This research was conducted to describe Taiwanese mothers' lived experience of caring for their child diagnosed with adrenoleukodystrophy. Analysis of eight interviews by Colaizzi's method revealed six themes: (1) difficulty confirming the diagnosis; (2) powerlessness toward unsatisfactory treatment; (3) struggles with decisions around carrier testing; (4) guilt about being a carrier; (5) support from family, other parents, and religion; and (6) lack of integrated resources and support. The results suggest the need to raise public and physician awareness about adrenoleukodystrophy via the media and medical education. A central organization to provide parents with comprehensive information is needed.

Relative incidence of inherited white matter disorders in childhood to acquired pediatric demyelinating disorders

Epidemiologic frequencies of pediatric white matter disorders as a class have not been well defined. This is particularly true of genetic disorders of the white matter of the brain. In this study, ICD-9 codes were used to estimate relative incidence rates and descriptive statistics of leukodystrophies, other genetic leukoencephalopathies and acquired demyelinating disease among children residing in the Washington, D.C. metropolitan area. Children being treated at US children's hospitals between January 1, 2004, and December 31, 2009, for acquired demyelinating disease or genetic white matter disorders were captured using the Pediatric Health Information System and the Physician Practice Management system and validated with local electronic medical records. Comparisons were made between genetic white matter disorders and acquired demyelinating disorders, to determine differences in incidence, age, gender, ethnicity, and mortality. Genetic causes of white matter disease identified with ICD-9 codes had an estimated incidence of 1.2/100,000 children in the Washington, DC area. What was of interest was nearly 5 out of 10 cases of pediatric white matter disease of any etiology were attributable to genetic causes. When only progressive white matter diseases were considered, 7 out of 10 cases were attributable to genetic causes, and only 3 out of 10 to progressive acquired demyelinating disease such as multiple sclerosis. These findings signify the important contribution of heritable white matter disorders to pediatric neurologic disease in the Washington, DC, metro area as well as throughout the United States. Continued research of these understudied disorders should compare disease incidence and determinants to validate these findings in different populations.

Advances and pitfalls of cell therapy in metabolic leukodystrophies

Leukodystrophies are a group of disorders characterized by myelin dysfunction, either at the level of myelin formation or maintenance, that affect the central nervous system (CNS) and also in some cases, to a lesser extent, the peripheral nervous system (PNS). Although these genetic-based disorders are generally rare, all together they have a significant impact in the society, with an estimated overall incidence of 1 in 7,663 live births. Currently, there is no cure for leukodystrophies, and the development of effective treatments remains challenging. Not only leukodystrophies generally progress very fast, but also most are multifocal needing the simultaneous targeting at multiple sites. Moreover, as the CNS is affected, the blood-brain barrier (BBB) limits the efficacy of treatment. Recently, interest on cell therapy has increased, and the leukodystrophies for which metabolic correction is needed have become first-choice candidates for cell-based clinical trials. In this review, we present and discuss the available cell transplantation therapies in metabolic leukodystrophies including fucosidosis, X-linked adrenoleukodystrophy, metachromatic leukodystrophy, Canavan disease, and Krabbe's disease. We will discuss the latest advances of cell therapy and its pitfalls in this group of disorders, taking into account, among others, the limitations imposed by reduced cell migration in multifocal conditions, the need to achieve corrective enzyme threshold levels, and the growing awareness that not only myelin but also the associated axonopathy needs to be targeted in some leukodystrophies.

Leukodystrophies

Leukodystrophies comprise a broad group of progressive, inherited disorders affecting mainly myelin. They often present after a variable period of normalcy with a variety of neurologic problems. Though the ultimate diagnosis is not found in many patients with leukodystrophies, distinctive features unique to them aid in diagnosis, treatment and prognostication. The clinical characteristics, etiologies, diagnostic testing and treatment options are reviewed in detail for some of the major leukodystrophies: X-linked adrenoleukodystrophy, Krabbe disease, metachromatic leukodystrophy, Pelizaeus-Merzbacher disease, Alexander disease, Canavan disease, megalencephalic leukoencephalopathy with subcortical cysts and vanishing white matter disease.

Targeted metabolomic analyses of cellular models of pelizaeus-merzbacher disease reveal plasmalogen and myo-inositol solute carrier dysfunction

Background

Leukodystrophies are devastating diseases characterized by dys- and hypo-myelination. While there are a number of histological and imaging studies of these disorders, there are limited biochemical data available. We undertook targeted lipidomic analyses of Pelizaeus-Merzbacher disease (PMD) fibroblasts, PMD lymphocytes, and 158JP oligodendrocytes, a murine model of PMD, to define the lipid changes in these cell models. Further targeted metabolomics analyses were conducted to obtain a preliminary evaluation of the metabolic consequences of lipid changes and gene mutations in these cell models.

Results

In both PMD fibroblasts and lymphocytes, and 158JP oligodendrocytes, ethanolamine plasmalogens were significantly decreased. Labeling studies with 158JP oligodendrocytes further demonstrated a decreased rate of lipid remodeling at sn-2. Targeted metabolomics analyses of these cells revealed dramatic increases in cellular levels of myo-inositol. Further uptake studies demonstrated increased rates of myo-inositol uptake by PMD lymphocytes.

Conclusions

Our data demonstrating PlsEtn decrements, support previous studies indicating leukodystrophy cells possess significant peroxisomal deficits. Our data for the first time also demonstrate that decrements in peroxisomal function coupled with the PLP1 gene defects of PMD, result in changes in the function of membrane myo-inositol solute carriers resulting in dramatic increases in cellular myo-inositol levels.