Ten Novel Mutations in Chinese Patients with Megalencephalic Leukoencephalopathy with Subcortical Cysts and a Long-Term Follow-Up Research

Psychotic attack during the clinical course of megalencephalic leukoencephalopathy with subcortical cysts: a case report

OBJECTIVES

Van der Knaap disease or megalencephalic leukoencephalopathy with subcortical cysts (MLC), is a slowly progressive neurodegenerative disease with macrocephaly. We present a case of MLC with a confirmed homozygous MLC1 mutation who presented with a psychotic attack at a very young age.

CASE PRESENTATION

An 11-year-old girl was admitted to the emergency room with delusions, hallucinations, and irritability. She was diagnosed with MLC at 18 months old. Her psychotic symptoms were improved with the administration of risperidone treatment added to her valproic acid treatment for EEG abnormality.

CONCLUSION

In this case study we reported the first episode of a psychotic attack during the clinical course of MLC. This case indicates the possibility that MLC influences the onset of the psychotic attack. Further investigation with more patients is needed to identify the relationship.

Intragenic homozygous duplication in HEPACAM is associated with megalencephalic leukoencephalopathy with subcortical cysts type 2A

Disease-causing variants in HEPACAM are associated with megalencephalic leukoencephalopathy with subcortical cysts 2A (MLC2A, MIM# 613,925, autosomal recessive), and megalencephalic leukoencephalopathy with subcortical cysts 2B, remitting, with or without impaired intellectual development (MLC2B, MIM# 613,926, autosomal dominant). These disorders are characterised by macrocephaly, seizures, motor delay, cognitive impairment, ataxia, and spasticity. Brain magnetic resonance imaging (MRI) in these individuals shows swollen cerebral hemispheric white matter and subcortical cysts, mainly in the frontal and temporal regions. To date, 45 individuals from 39 families are reported with biallelic and heterozygous variants in HEPACAM, causing MLC2A and MLC2B, respectively. A 9-year-old male presented with developmental delay, gait abnormalities, seizures, macrocephaly, dysarthria, spasticity, and hyperreflexia. MRI revealed subcortical cysts with diffuse cerebral white matter involvement. Whole-exome sequencing (WES) in the proband did not reveal any clinically relevant single nucleotide variants. However, copy number variation analysis from the WES data of the proband revealed a copy number of 4 for exons 3 and 4 of HEPACAM. Validation and segregation were done by quantitative PCR which confirmed the homozygous duplication of these exons in the proband and carrier status in both parents. To the best of our knowledge, this is the first report of an intragenic duplication in HEPACAM causing MLC2A.

Megalencephalic leukoencephalopathy with subcortical cysts: a variant update and review of the literature

The leukodystrophy megalencephalic leukoencephalopathy with subcortical cysts (MLC) is characterized by infantile-onset macrocephaly and chronic edema of the brain white matter. With delayed onset, patients typically experience motor problems, epilepsy and slow cognitive decline. No treatment is available. Classic MLC is caused by bi-allelic recessive pathogenic variants in MLC1 or GLIALCAM (also called HEPACAM). Heterozygous dominant pathogenic variants in GLIALCAM lead to remitting MLC, where patients show a similar phenotype in early life, followed by normalization of white matter edema and no clinical regression. Rare patients with heterozygous dominant variants in GPRC5B and classic MLC were recently described. In addition, two siblings with bi-allelic recessive variants in AQP4 and remitting MLC have been identified. The last systematic overview of variants linked to MLC dates back to 2006. We provide an updated overview of published and novel variants. We report on genetic variants from 508 patients with MLC as confirmed by MRI diagnosis (258 from our database and 250 extracted from 64 published reports). We describe 151 unique MLC1 variants, 29 GLIALCAM variants, 2 GPRC5B variants and 1 AQP4 variant observed in these MLC patients. We include experiments confirming pathogenicity for some variants, discuss particularly notable variants, and provide an overview of recent scientific and clinical insight in the pathophysiology of MLC.

Case report: Analysis of a gene variant and prenatal diagnosis in a family with megalencephalic leukoencephalopathy with subcortical cysts

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is a rare inherited cerebral white matter disorder in children. Pathogenic variations in the causative gene MLC1 are found in approximately 76% of patients and are inherited in an autosomal recessive manner. In this study, we identified an IVS2 + 1delG variant in MLC1 in the firstborn girl of a pregnant woman who has the clinical features of MLC, including macrocephaly, motor development delay, progressive functional deterioration, and myelinopathy, whereas no obvious subcortical cysts were observed by magnetic resonance imaging of the brain. The proband is homozygous for the IVS2 + 1delG mutation, which was inherited from the parents. This variant disrupts the donor splice site, causing an abnormal transcript that results in a premature termination codon and produces a truncated protein, which was confirmed to affect splicing by MLC1 cDNA analysis. This variant was also detected in family members, and a prenatal diagnosis for the fetus was undertaken. Eventually, the couple gave birth to an unaffected baby. Furthermore, we conducted a long-term follow-up of the proband's clinical course. This report improves our understanding of the genetic and phenotypic characteristics of MLC and provides a new genetic basis for prenatal diagnosis and genetic counseling.

Prevalent MLC1 mutation causing autosomal recessive megalencephalic leukoencephalopathy in consanguineous Palestinian families

BACKGROUND

Recessive forms of megalencephalic leukoencephalopathy with subcortical cysts (MLC, OMIM 604004) is a rare early-onset leukodystrophy that presents with macrocephaly, seizures, slowly progressive gross motor deterioration, and MRI evidence of diffuse symmetric white matter swelling and subcortical cysts in the anterior temporal and frontoparietal regions. Later in the disease course, significant spasticity and ataxia develop, which may be accompanied by intellectual deterioration. This disease is caused mostly by biallelic pathogenic variants in the MLC1 gene.

METHODS

In this study, we analysed the clinical and molecular architecture of 6 individuals, belonging to 4 unrelated consanguineous Palestinian families, presenting with consistent MLC features. We sequenced the entire coding and flanking intronic regions of the MLC1 gene.

RESULTS

In all recruited individuals, we detected one recurrent homozygous splice donor mutation NM_015166.4: c.423 + 1G > A. All parents were heterozygous carriers. The mutation abolishes a highly conserved splice site in humans and other species. In silico splice predictors suggested the loss of a canonical splice donor site (CADD score 33.0. SpliceAI: 0.980). The c.423 + 1G > A variant is rare; it was detected in only 4 heterozygous carriers in gnomAD.

CONCLUSION

In this study, we identified a recurrent MLC1 variant (c.423 + 1G > A) as the cause of MLC among a group of Palestinian patients originating from a particular region of the country. Cost-effective studies should be performed to evaluate the implementation of carrier screening in adults originating from this region. Our findings have the potential to contribute to improved genetic diagnosis and carrier testing for individuals within this population and the wider community.

Clinicoradiologic Correlation in 22 Egyptian Children With Megalencephalic Leukoencephalopathy With Subcortical Cysts

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is a rare genetic form of cerebral white matter disease whose clinicoradiologic correlation has not been completely understood. In this study, we investigated the association between clinical and brain magnetic resonance imaging (MRI) features in 22 Egyptian children (median age 7 years) with MLC. Gross motor function was assessed using the Gross Motor Function Classification System, and evaluation of brain MRI followed a consistent scoring system. Each parameter of extensive cerebral white matter T2 hyperintensity, moderate-to-severe wide ventricle/enlarged subarachnoid space, and greater than 2 temporal subcortical cysts was significantly associated (P < .05) with worse Gross Motor Function Classification System score, language abnormality, and ataxia. Having >2 parietal subcortical cysts was significantly related to a worse Gross Motor Function Classification System score (P = .04). The current study indicates that patients with MLC manifest signification association between certain brain MRI abnormalities and neurologic features, but this should be confirmed in larger studies.

Transmembrane topology and oligomeric nature of an astrocytic membrane protein, MLC1

MLC1 is a membrane protein mainly expressed in astrocytes, and genetic mutations lead to the development of a leukodystrophy, megalencephalic leukoencephalopathy with subcortical cysts disease. Currently, the biochemical properties of the MLC1 protein are largely unknown. In this study, we aimed to characterize the transmembrane (TM) topology and oligomeric nature of the MLC1 protein. Systematic immunofluorescence staining data revealed that the MLC1 protein has eight TM domains and that both the N- and C-terminus face the cytoplasm. We found that MLC1 can be purified as an oligomer and could form a trimeric complex in both detergent micelles and reconstituted proteoliposomes. Additionally, a single-molecule photobleaching experiment showed that MLC1 protein complexes could consist of three MLC1 monomers in the reconstituted proteoliposomes. These results can provide a basis for both the high-resolution structural determination and functional characterization of the MLC1 protein.

Novel variants causing megalencephalic leukodystrophy in Sudanese families

Mutations in MLC1 cause megalencephalic leukoencephalopathy with subcortical cysts (MLC), a rare form of leukodystrophy characterized by macrocephaly, epilepsy, spasticity, and slow mental deterioration. Genetic studies of MLC are lacking from many parts of the world, especially in Sub-Saharan Africa. Genomic DNA was extracted for 67 leukodystrophic patients from 43 Sudanese families. Mutations were screened using the NGS panel testing 139 leukodystrophies and leukoencephalopathies causing genes (NextSeq500 Illumina). Five homozygous MLC1 variants were discovered in seven patients from five distinct families, including three consanguineous families from the same region of Sudan. Three variants were missense (c.971 T > G, p.Ile324Ser; c.344 T > C, p.Phe115Ser; and c.881 C > T, p.Pro294Leu), one duplication (c.831_838dupATATCTGT, p.Ser280Tyrfs*8), and one synonymous/splicing-site mutation (c.762 C > T, p.Ser254). The segregation pattern was consistent with autosomal recessive inheritance. The clinical presentation and brain MRI of the seven affected patients were consistent with the diagnosis of MLC1. Due to the high frequency of distinct MLC1 mutations found in our leukodystrophic Sudanese families, we analyzed the coding sequence of MLC1 gene in 124 individuals from the Sudanese genome project in comparison with the 1000-genome project. We found that Sudan has the highest proportion of deleterious variants in MLC1 gene compared with other populations from the 1000-genome project.

Astrocyte-Oligodendrocyte-Microglia Crosstalk in Astrocytopathies

Defective astrocyte function due to a genetic mutation can have major consequences for microglia and oligodendrocyte physiology, which in turn affects the white matter integrity of the brain. This review addresses the current knowledge on shared and unique pathophysiological mechanisms of astrocytopathies, including vanishing white matter, Alexander disease, megalencephalic leukoencephalopathy with subcortical cysts, Aicardi-Goutières syndrome, and oculodentodigital dysplasia. The mechanisms of disease include protein accumulation, unbalanced secretion of extracellular matrix proteins, pro- and anti-inflammatory molecules, cytokines and chemokines by astrocytes, as well as an altered gap junctional network and a changed ionic and nutrient homeostasis. Interestingly, the extent to which astrogliosis and microgliosis are present in these astrocytopathies is highly variable. An improved understanding of astrocyte-microglia-oligodendrocyte crosstalk might ultimately lead to the identification of druggable targets for these, currently untreatable, severe conditions.

A Chinese pedigree with Brown-Vialetto-Van Laere syndrome due to two novel mutations of SLC52A2 gene: clinical course and response to riboflavin

Background

Brown-Vialetto-Van Laere Syndrome (BVVLS), a rare neurological disorder characterized by motor, sensory, and cranial neuronopathies, is mainly associated with defective riboflavin transporters encoded by SLC52A2 and SLC52A3 genes. Clinical outcomes have been shown to be improved significantly by high-dose riboflavin supplementation. The aim of this study was to identify genetic causes and further evaluate the clinical course and response to riboflavin in a Chinese pedigree with BVVLS.

Case presentation

We report the novel compound heterozygous variants c.1328G>A p.(Cys443Tyr) and c.1022_1023insC p. (Leu341Profs*103) of SLC52A2 gene in a female proband who presented in our out-patient clinic at the age of one-year-old with progressive mental and motor regression, breath holding, and brain stem dysfunction including facial weakness, hearing loss, dysphagia. Following high-dose riboflavin supplementation, the respiratory insufficiency and mental, motor, and bulbar function improved. However, sensorineural hearing loss was not improved. The missense variant site was highly conserved. Both variants were not found in the population database gnomAD. The two variants were inherited from her mother and father, respectively. Both variants were predicted to be deleterious by Polyphen2, Mutation taster, and SIFT and were classified as likely pathogenic according to the ACMG guideline.

Conclusions

Two novel pathogenic variations of SLC52A2 gene were firstly found from a Chinese pedigree with BVVLS. Clinical outcomes could be improved by early diagnosis and riboflavin supplementation.

Identification in Chinese patients with GLIALCAM mutations of megalencephalic leukoencephalopathy with subcortical cysts and brain pathological study on Glialcam knock-in mouse models

BACKGROUND

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is a rare neurological degenerative disorder caused by the mutations of MLC1 or GLIALCAM with autosomal recessive or autosomal dominant inheritance and a different prognosis, characterized by macrocephaly, delayed motor and cognitive development, and bilateral abnormal signals in cerebral white matter (WM) with or without cysts on magnetic resonance imaging (MRI). This study aimed to reveal the clinical and genetic features of MLC patients with GLIALCAM mutations and to explore the brain pathological characteristics and prognosis of mouse models with different modes of inheritance.

METHODS

Clinical information and peripheral venous blood were collected from six families. Genetic analysis was performed by Sanger sequencing of GLIALCAM. Glialcam^Arg92Trp/+ and Glialcam^{Lys68Met/Thr132Asn} mouse models were generated based on mutations from patients (c.274C>T(p.Arg92Trp) (c.203A>T(p.Lys68Met), and c.395C>A (p.Thr132Asn))). Brain pathologies of the mouse models at different time points were analyzed.

RESULTS

Six patients were clinically diagnosed with MLC. Of the six patients, five (Pt1-Pt5) presented with a heterozygous mutation in GLIALCAM (c.274C>T(p.Arg92Trp) or c.275G>C(p.Arg92Pro)) and were diagnosed with MLC2B; the remaining patient (Pt6) with two compound heterozygous mutations in GLIALCAM (c.203A>T (p.Lys68Met) and c.395C>A (p.Thr132Asn)) was diagnosed with MLC2A. The mutation c.275C>G (p.Arg92Pro) has not been reported before. Clinical manifestations of the patient with MLC2A (Pt6) progressed with regression, whereas the course of the five MLC2B patients remained stable or improved. The Glialcam^Arg92Trp/+ and Glialcam^{Lys68Met/ Thr132Asn} mouse models showed vacuolization in the anterior commissural WM at 1 month of age and vacuolization in the cerebellar WM at 3 and 6 months, respectively. At 9 months, the vacuolization of the Glialcam^{Lys68Met/ Thr132Asn} mouse model was heavier than that of the Glialcam^Arg92Trp/+ mouse model. Decreased expression of Glialcam in Glialcam^Arg92Trp/+ and Glialcam^{Lys68Met/ Thr132Asn} mice may contribute to the vacuolization.

CONCLUSIONS

Clinical and genetic characterization of patients with MLC and GLIALCAM mutations revealed a novel mutation, expanding the spectrum of GLIALCAM mutations. The first Glialcam mouse model with autosomal recessive inheritance and a new Glialcam mouse model with autosomal dominant inheritance were generated. The two mouse models with different modes of inheritance showed different degrees of brain pathological features, which were consistent with the patients' phenotype and further confirmed the pathogenicity of the corresponding mutations.

Megalencephalic leukoencephalopathy with subcortical cysts: Characterization of disease variants

Objective

To provide an overview of clinical and MRI characteristics of the different variants of the leukodystrophy megalencephalic leukoencephalopathy with subcortical cysts (MLC) and identify possible differentiating features.

Methods

We performed an international multi-institutional, cross-sectional observational study of the clinical and MRI characteristics in patients with genetically confirmed MLC. Clinical information was obtained by questionnaires for physicians and retrospective chart review.

Results

We included 204 patients with classic MLC, 187 of whom had recessive mutations in MLC1 (MLC1 variant) and 17 in GLIALCAM (MLC2A variant) and 38 patients with remitting MLC caused by dominant GLIALCAM mutations (MLC2B variant). We observed a relatively wide variability in neurologic disability among patients with classic MLC. No clinical differences could be identified between patients with MLC1 and MLC2A. Patients with MLC2B invariably had a milder phenotype with preservation of motor function, while intellectual disability and autism were relatively frequent. Systematic MRI review revealed no MRI features that distinguish between MLC1 and MLC2A. Radiologic improvement was observed in all patients with MLC2B and also in 2 patients with MLC1. In MRIs obtained in the early disease stage, absence of signal abnormalities of the posterior limb of the internal capsule and cerebellar white matter and presence of only rarefied subcortical white matter instead of true subcortical cysts were suggestive of MLC2B.

Conclusion

Clinical and MRI features did not distinguish between classic MLC with MLC1 or GLIALCAM mutations. Absence of signal abnormalities of the internal capsule and cerebellar white matter are MRI findings that point to the remitting phenotype.

A Unique Mutational Spectrum of MLC1 in Korean Patients With Megalencephalic Leukoencephalopathy With Subcortical Cysts: p.Ala275Asp Founder Mutation and Maternal Uniparental Disomy of Chromosome 22

Background

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is a rare inherited disorder characterized by infantile-onset macrocephaly, slow neurologic deterioration, and seizures. Mutations in the causative gene, MLC1, are found in approximately 75% of patients and are inherited in an autosomal recessive manner. We analyzed MLC1 mutations in five unrelated Korean patients with MLC.

Methods

Direct Sanger sequencing was used to identify MLC1 mutations. A founder effect of the p.Ala275Asp variant was demonstrated by haplotype analysis using single-nucleotide polymorphic (SNP) markers. Multiple ligation-dependent probe amplification (MLPA) and comparative genomic hybridization plus SNP array were used to detect exonic deletions or uniparental disomy (UPD).

Results

The most prevalent pathogenic variant was c.824C>A (p.Ala275Asp) found in 7/10 (70%) alleles. Two pathogenic frameshift variants were found: c.135delC (p.Cys46Alafs^*12) and c.337_353delinsG (p.Ile113Glyfs^*4). Haplotype analysis suggested that the Korean patients with MLC harbored a founder mutation in p.Ala275Asp. The p.(Ile113Glyfs^*4) was identified in a homozygous state, and a family study revealed that only the mother was heterozygous for this variant. Further analysis of MLPA and SNP arrays for this patient demonstrated loss of heterozygosity of chromosome 22 without any deletion, indicating UPD. The maternal origin of both chromosomes 22 was demonstrated by haplotype analysis.

Conclusions

This study is the first to describe the mutational spectrum of Korean patients with MLC, demonstrating a founder effect of the p.Ala275Asp variant. This study also broadens our understanding of the mutational spectrum of MLC1 by demonstrating a homozygous p.(Ile113Glyfs^*4) variant resulting from UPD of chromosome 22.

Deletion of Stk40 impairs definitive erythropoiesis in the mouse fetal liver

The serine threonine kinase Stk40 has been shown to involve in mouse embryonic stem cell differentiation, pulmonary maturation and adipocyte differentiation. Here we report that targeted deletion of Stk40 leads to fetal liver hypoplasia and anemia in the mouse embryo. The reduction of erythrocytes in the fetal liver is accompanied by increased apoptosis and compromised erythroid maturation. Stk40-/- fetal liver cells have significantly reduced colony-forming units (CFUs) capable of erythroid differentiation, including burst forming unit-erythroid, CFU-erythroid (CFU-E), and CFU-granulocyte, erythrocyte, megakaryocyte and macrophage, but not CFU-granulocyte/macrophages. Purified Stk40-/- megakaryocyte-erythrocyte progenitors produce substantially fewer CFU-E colonies compared to control cells. Moreover, Stk40-/- fetal liver erythroblasts fail to form normal erythroblastic islands in association with wild type or Stk40-/- macrophages, indicating an intrinsic defect of Stk40-/- erythroblasts. Furthermore, the hematopoietic stem and progenitor cell pool is reduced in Stk40-/- fetal livers but still retains the multi-lineage reconstitution capacity. Finally, comparison of microarray data between wild type and Stk40-/- E14.5 fetal liver cells reveals a potential role of aberrantly activated TNF-α signaling in Stk40 depletion induced dyserythropoiesis with a concomitant increase in cleaved caspase-3 and decrease in Gata1 proteins. Altogether, the identification of Stk40 as a regulator for fetal erythroid maturation and survival provides new clues to the molecular regulation of erythropoiesis and related diseases.