The natural history and burden of illness of metachromatic leukodystrophy: a systematic literature review

BACKGROUND

Metachromatic leukodystrophy (MLD; OMIM 250100 and 249900) is a rare lysosomal storage disease caused by deficient arylsulfatase A activity, leading to accumulation of sulfatides in the nervous system. This systematic literature review aimed to explore the effect of MLD on the lives of patients.

METHODS

The Ovid platform was used to search Embase, MEDLINE, and the Cochrane Library for articles related to the natural history, clinical outcomes, and burden of illness of MLD; congress and hand searches were performed using 'metachromatic leukodystrophy' as a keyword. Of the 531 publications identified, 120 were included for data extraction following screening. A subset of findings from studies relating to MLD natural history and burden of illness (n = 108) are presented here.

RESULTS

The mean age at symptom onset was generally 16-18 months for late-infantile MLD and 6-10 years for juvenile MLD. Age at diagnosis and time to diagnosis varied widely. Typically, patients with late-infantile MLD presented predominantly with motor symptoms and developmental delay; patients with juvenile MLD presented with motor, cognitive, and behavioral symptoms; and patients with adult MLD presented with cognitive symptoms and psychiatric and mood disorders. Patients with late-infantile MLD had more rapid decline of motor function over time and lower survival than patients with juvenile MLD. Commonly reported comorbidities/complications included ataxia, epilepsy, gallbladder abnormalities, incontinence, neuropathy, and seizures.

CONCLUSIONS

Epidemiology of MLD by geographic regions, quantitative cognitive data, data on the differences between early- and late-juvenile MLD, and humanistic or economic outcomes were limited. Further studies on clinical, humanistic (i.e., quality of life), and economic outcomes are needed to help inform healthcare decisions for patients with MLD.

Metachromatic leukodystrophy: natural course of cerebral MRI changes in relation to clinical course

OBJECTIVE

Metachromatic Leukodystrophy (MLD) is a rare disorder leading to demyelination and neurological impairment. A natural history study within the German leukodystrophy network analyzed MRI changes with respect to the clinical course.

METHODS

113 MR images of 68 patients (33 late-infantile, 35 juvenile) were studied cross-sectionally and longitudinally. MRI and motor deterioration were assessed using standardized scoring systems.

RESULTS

The temporal and spatial patterns of MR severity scores differed between the late-infantile and juvenile form. Although early (involving central white matter, corpus callosum) and late signs (involving pons, cerebellum, cerebral atrophy) were similar, high MRI scores (mean 18, SD 1.2, p < 0.001) were evident in the juvenile form already at the onset of first symptoms and even in presymptomatic patients. The progression rate of the MRI score was clearly higher and more uniform in the late-infantile (on average 8 per year, p < 0.0001) than in the juvenile patients (on average 0.4 per year, p < 0.08). In late-infantile patients, MRI changes correlated highly with motor deterioration (rho = 0.73, p < 0.001), this was less remarkable in the juvenile form (rho = 0.50, p < 0.01). Severe motor dysfunction was associated with U-fiber involvement and cerebellar changes (p < 0.05).

CONCLUSIONS

MRI showed a typical spatial pattern, which evolved gradually and uniformly during disease progression in late-infantile MLD. In juvenile MLD MRI changes were already observed at disease onset and temporal patterns were more variable. As therapeutic options for MLD are evolving, these findings are not only important for patient counseling but also for the evaluation of therapeutic interventions.

Population carrier rates of pathogenic ARSA gene mutations: is metachromatic leukodystrophy underdiagnosed?

Background

Metachromatic leukodystrophy (MLD) is a severe neurometabolic disease caused mainly by deficiency of arylsulfatase A encoded by the ARSA gene. Based on epidemiological surveys the incidence of MLD per 100 000 live births varied from 0.6 to 2.5. Our purpose was to estimate the birth prevalence of MLD in Poland by determining population frequency of the common pathogenic ARSA gene mutations and to compare this estimate with epidemiological data.

Methodology

We studied two independently ascertained cohorts from the Polish background population (N∼3000 each) and determined carrier rates of common ARSA gene mutations: c.459+1G>A, p.P426L, p.I179S (cohort 1) and c.459+1G>A, p.I179S (cohort 2).

Principal Findings

Taking into account ARSA gene mutation distribution among 60 Polish patients, the expected MLD birth prevalence in the general population (assuming no selection against homozygous fetuses) was estimated as 4.0/100 000 and 4.1/100 000, respectively for the 1^st and the 2^nd cohort with a pooled estimate of 4.1/100 000 (CI: 1.8–9.4) which was higher than the estimate of 0.38 per 100 000 live births based on diagnosed cases. The p.I179S mutation was relatively more prevalent among controls than patients (OR = 3.6, P = 0.0082, for a comparison of p.I179S frequency relative to c.459+1G>A between controls vs. patients).

Conclusions/Significance

The observed discrepancy between the measured incidence of metachromatic leukodystrophy and the predicted carriage rates suggests that MLD is substantially underdiagnosed in the Polish population. The underdiagnosis rate may be particularly high among patients with p.I179S mutation whose disease is characterized mainly by psychotic symptoms.

Clinical and biochemical study of 29 Brazilian patients with metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is a lysosomal disorder caused by arylsulfatase A (ARSA) deficiency. It is classified into three forms according to the age of onset of symptoms (late infantile, juvenile, and adult). We carried out a cross-sectional and retrospective study, which aimed to determine the epidemiological, clinical, and biochemical profile of MLD patients from a national reference center for Inborn Errors of Metabolism in Brazil. Twenty-nine patients (male, 17) agreed to participate in the study (late infantile form: 22; juvenile form: 4; adult form: 1; asymptomatic: 2). Mean ages at onset of symptoms and at biochemical diagnosis were, respectively, 19 and 39 months for late infantile form and 84.7 and 161.2 months for juvenile form. The most frequently reported first clinical symptom/sign of the disease was gait disturbance and other motor abnormalities (72.7%) for late infantile form and behavioral and cognitive alterations (50%) for juvenile form. Leukocyte ARSA activity level did not present significant correlation with the age of onset of symptoms (r = -0.09, p = 0.67). Occipital white matter and basal nuclei abnormalities were not found in patients with the late infantile MLD. Our results suggest that there is a considerable delay between the age of onset of signs and symptoms and the diagnosis of MLD in Brazil. Correlation between ARSA activity and MLD clinical form was not found. Further studies on the epidemiology and natural history of this disease with larger samples are needed, especially now when specific treatments should be available in the near future.

Juvenile metachromatic leukodystrophy: understanding the disease and implications for nursing care

Hematopoietic stem cell transplants are increasingly being performed in attempt to halt the progression of juvenile metachromatic leukodystrophy, which is a rare neurodegenerative disease. Children who are diagnosed with metachromatic leukodystrophy are not commonly cared for by nurses who specialize in pediatric stem cell transplants. This article provides nurses with insight about this disease and serves as a guide for nursing care of this patient population during hematopoietic stem cell transplant. The case study highlights the complexities of care of this population while illustrating many of the unique care needs of patients with metachromatic leukodystrophy undergoing hematopoietic stem cell transplant. The article provides information about the pathophysiology of metachromatic leukodystrophy, the natural progression of symptoms, and how hematopoietic stem cell transplant may work to halt the progression of juvenile metachromatic leukodystrophy. It also focuses on the implications of nursing care, including a review of systems, the need for increased patient and family education, and the complexities of caring for a family with multiple affected children.

Molecular and phenotypic characteristics of metachromatic leukodystrophy patients from Poland

The occurrence and genotype-phenotype correlations of the eight most common mutations in the arylsulfatase A (ARSA) gene were studied in 43 unrelated Polish patients suffering from different types of metachromatic leukodystrophy (MLD). Screening for mutations p.R84Q, p.S96F, c.459+1G>A, p.I179S, p.A212V, c.1204+1G>A, p.P426L, and c.1401-1411del allowed the identification of 53.5% of the mutant alleles. In the whole investigated group of patients, mutations c.459+1G>A and p.P426L were the most frequent, 19 and 17%, respectively. The prevalence of the third most frequent mutation, i.e. p.I179S (13%), seems to be higher than that in other populations. The incidence of c.1204+1G>A was 5%, which is higher than reported earlier (2%). It seems that p.I179S and c.1204+1G>A are more prevalent in MLD patients from Poland than from other countries. In the group examined by us, mutations p.R84Q, p.S96F, p.A212V, and c.1401-1411del were not detected; thus, 46.5% of MLD alleles remained unidentified. This indicates that other, novel or already described, but rare, mutations exist in Polish population. In late infantile homozygotes for c.459+1G>A and one homozygote for c.1204+1G>A, first clinical symptom was motor deterioration. In adult homozygotes for p.P426L, the disease onset manifested as gait disturbances, followed by choreoathetotic movements, difficulties in swallowing, dysarthria, tremor, and nystagmus. In the carriers of the p.I179S mutation, the hallmark of the clinical picture was psychotic disturbances.

Prevalence of arylsulfatase A pseudodeficiency allele in metachromatic leukodystrophy patients from Poland

Arylsulfatase A (ASA) pseudodeficiency (PD) allele was searched for in 22 patients originating from Poland and suffering from different types of metachromatic leukodystrophy (MLD). Four of them carried the PD allele in a heterozygous state. The prevalence of the PD allele among investigated MLD patients was revealed to be 9%, while the frequency of the PD allele in healthy controls was estimated at 6-7%. One of the examined MLD patients was additionally a carrier of an isolated mutation leading to the loss of the N-glycosylation site. The question arises whether and how MLD mutations create a convenient milieu for PD mutations to occur (or inversely).

Arylsulfatase A pseudodeficiency incidence in Turkey

Pseudodeficiency (Pd) in arylsulfatase A (ASA) is a relatively frequent condition in healthy individuals. It produces a reduction in enzyme activity similar to that found in metachromatic leukodystrophy (MLD). A variable incidence of the Pd allele was found in different populations; it was 10-20 times higher than that of metachromatic leukodystrophy. Twelve of the 52 unrelated, healthy individuals were found to be heterozygous for the ASA Pd allele. In Turkey we estimated the incidence of the Pd allele as 11.5 percent. Out of 18 cases with MLD, one patient was found homozygous for the Pd allele and the other patient was found heterozygous.

Early thalamic and cortical hypometabolism in adult-onset dementia due to metachromatic leukodystrophy

A case of early-onset adult dementia with family history of dementia is reported, characterised by neuropsychological deficits, suggesting frontal involvement, with mild non specific white matter abnormalities on CT scan. Familial Alzheimer's disease was suspected but the neuropathological diagnosis on brain biopsy was metachromatic leukodystrophy. 18FDG-PET revealed a very peculiar pattern of metabolic impairment in thalamic areas, in medial and frontopolar regions, and in occipital lobes. Neuropsychological follow-up showed relatively stable difficulties of long-term memory and signs of frontal lobe dysfunction, similar to those observed in subcortical dementias. MRI subsequently showed periventricular leukoencephalopathy. The brain metabolic pattern observed in that case of metachromatic leukodystrophy was quite different from that reported in other types of dementia.

Leukodystrophy incidence in Germany

Through a survey of all departments of pediatrics, neurology and neuropathology in Germany, we calculated the incidence of all major forms of leukodystrophy. Only diagnoses based on specific biochemical tests in association with typical findings and/or neuroradiologically proven white matter involvement were accepted. In accordance with these strict criteria, 617 cases of leukodystrophy were found (incidence of all forms: app. 2.0/100,000). Minimal incidence was estimated at 0.8/100,000 for adrenoleukodystrophy/adrenomyeloneuropathy (ALD/AMN), 0.6/100,000 for metachromatic leukodystrophy (MLD), and 0.6/100,000 for Krabbe disease. Thus ALD/AMN is apparently underdiagnosed in Germany. A considerable proportion of leukodystrophies could not be classified in spite of adequate diagnostic procedures in experienced centers.

Arylsulfatase A pseudodeficiency--incidence in Poland

Arylsulfatase A (ASA) pseudodeficiency (Pd) was defined as the in vitro measurement of low enzyme activity in a healthy person. A variable incidence of the Pd allele was found in different populations; it was 10-20 times higher than that of metachromatic leukodystrophy (MLD). In Poland we estimated the incidence of the Pd allele at 6% and that of isolated 1788 mutation (loss of glycosylation site) at 3%. Out of 8 cases with neurological symptoms and low ASA activity, 2 were found to be homozygous for the Pd allele; 2 MLD patients had healthy siblings homozygous for the Pd allele and another patient's allele bore two mutations, Pd and that causing MLD.

[Activity of aryl sulfatase A enzyme in patients with schizophrenic disorders]

Metachromatic leukodystrophy (MLD) is a degenerative disease caused by the deficiency of aryl sulfatase (ASA). It can course with psychiatric symptoms. We determined the prevalence of ASA deficiency in a group of 23 patients with presumable schizophrenia. The median serum ASA was 53.2 nmol/mL/h (range 3.3-152.5). Six patients (26%) showed low ASA activity (< 27.5 nmol/mL/h which is the lowest value observed in 29 normal controls); five of them had clinical history of delusions of grandeur, auditive hallucinations, multiple hospitalizations, low response to neuroleptics, and abnormal evoked potentials. It is probable that the schizophrenic symptoms in these patients may be due to the enzyme deficiency. We conclude that the assay is useful in clinical practice as it may help to identify cases of MLD in patients with suspected schizophrenia.

An AT-deletion causing a frameshift in the arylsulfatase A gene of a late infantile metachromatic leukodystrophy patient

A metachromatic leukodystrophy (MLD) patient affected with the late infantile form was found to be homozygous for an AT-deletion (2324delAT) in the arylsulfatase A gene. The mutation causes a frameshift at the beginning of exon 8 leading to an early termination codon. The parents and unaffected brother of the patient were heterozygous for the microdeletion. The mutation was not detected in another 31 MLD Italian patients. No aberrant transcript caused by the mutation was revealed by the reverse transcription-polymerase chain reaction method.

Metachromatic leukodystrophy among southern Alaskan Eskimos: molecular and genetic studies

Metachromatic leukodystrophy (MLD) is an autosomal recessive disorder resulting from the inability to metabolize sulphatide, an important component of myelin. Although there is significant clinical variability between patients, most have the late-infantile form. It is one of the most common lysosomal disorders involving mental deterioration and is found throughout the world. The great majority of the cases have a deficiency of arylsulphatase A activity. Accurate diagnosis of MLD is complicated by the presence of so-called pseudodeficiency alleles and the need to receive specimens for biochemical testing within 24-48 h of collection. We report the identification of the mutation (a g-to-a transition in the first nucleotide of intron 4) in the arylsulphatase A gene causing late-infantile MLD among the Eskimo population of southern Alaska. As all patients and family members from living and deceased patients had the same mutation, a mutation-based test was developed to identify patients and carriers that can be done on dried blood spots sent via regular mail service. A possible genetic link between this population and the Navajo Indians of the southwestern United States is proposed.

Multiple mutations are responsible for the high frequency of metachromatic leukodystrophy in a small geographic area

Metachromatic leukodystrophy is a lysosomal storage disorder caused by the deficiency of arylsulfatase A. The disease occurs panethnically, with an estimated frequency of 1/40,000. Metachromatic leukodystrophy was found to be more frequent among Arabs living in two restricted areas in Israel. Ten families with affected children have been found, three in the Jerusalem region and seven in a small area in lower Galilee. Whereas all patients from the Jerusalem region are homozygous for a frequent mutant arylsulfatase A allele, five different mutations were found in the families from lower Galilee. In patients of Muslim Arab origin, we have found a G86-->D, a S96-->L, and a Q190-->H substitution. Two different defective arylsulfatase A alleles, characterized by a T274-->M and a R370-->W substitution, respectively, have been found among the Christian Arab patients. All mutations were introduced into the wild-type arylsulfatase A cDNA. No enzyme activity could be expressed from the mutagenized cDNAs after transfection into heterologous cells. In all instances, the patients were found to be homozygous for the mutations, and four of the five mutations occurred on different haplotypes. The clustering of this rare lysosomal storage disease in a small geographic area usually suggests a founder effect, so the finding of five different mutations is surprising.

Lipidoses detected in Poland through 1993

It is estimated that 70-100 children suffering from a lysosomal storage disease are born in Poland every year. From 1975 to 1993, the activity of various lysosomal enzymes was determined in the leukocytes, cultured skin fibroblasts, or hair roots from 5,594 patients, mainly children, in whom the diagnosis of a lipidosis was suspected. In that material 162 cases of a lipidosis were diagnosed. Metachromatic leukodystrophy seems to be the most frequent of the lipidoses; GM1 gangliosidosis is more frequent than GM2 gangliosidosis and Gaucher and Niemann-Pick diseases appear to be almost as frequent as the former.

Late infantile metachromatic leukodystrophy in Israel

Metachromatic Leukodystrophy (MLD) is a neurodegenerative disease in which the lysosomal enzyme, Aryl sulfatase A (ARSA) is deficient. The disease is inherited as an autosomal recessive trait and its frequency is estimated to be 1/40,000 live births. The gene of ARSA has been cloned and up to now eight mutations causing MLD have been reported. Another mutation, PD, leads to the deficiency of the enzyme in vitro (pseudodeficiency) without any known clinical effect. The PD mutation is frequent in all populations. In Israel, late infantile MLD was found to be very frequent in a small Jewish isolate, the Habbanite Jews (1/75 live births). The molecular analysis demonstrated that in the Habbanite population, the mutation occurred on an allele with the PD mutation. The loss of ARSA activity is due to a point mutation C > T leading to a change of proline to leucine. MLD is also frequent among Moslem Arabs in Jerusalem. The mutation is a transition G > A destroying the splice donor site of exon 2. This mutation has been reported in patients with the late infantile MLD from different ethnic groups. The Christian Arabs in Israel also have a high incidence of the disease (1/10,000 live births); the mutation in this population is still unknown. Knowledge of the different mutations causing MLD in these defined populations will allow a carrier screening program to be carried out and prevent the birth of additional affected children.