Pelizaeus-Merzbacher-like Disease Research Articles

Identification of GJC2 gene mutations in Chinese patients with Pelizaeus-Merzbacher-like disease.

Clinical and genetic features were analyzed in five pedigrees with Pelizaeus-Merzbacher-like disease (PMLD) to provide bases for genetic counseling and prenatal diagnosis. Six patients from five pedigrees were diagnosed with PMLD based on their clinical data. Six GJC2 novel mutations were found in this study, expanding the spectrum of GJC2 mutations. This is the second group of GJC2 mutations reported from six Chinese patients with PMLD. Clinical data including medical history, physical signs, and auxiliary examinations were collected from six patients and their family numbers in five pedigrees with PMLD. Polymerase chain reaction and sequence analysis were used to amplify GJC2 and PLP1 alterations, while multiplex ligation-dependent probe amplification (MLPA) was performed to detect PLP1 dosage changes. The gene mutations were diagnosed for further analysis of the genetic features. A total of seven GJC2 mutations were identified in these patients, including two novel missense mutations (c.217C>T, p.Pro73Ser; c.1199C>A, p.Ala400Glu), one nonsense mutation (c.735C>A, p.Cys245X), three novel frameshift mutations (c.579delC, p.Gly193fsX17 and c.1296_1297insG, p.Gly433fsX59; c.689delG, p.Gly230AlafsX241), and one known missense mutation (c.814T>G, p.Tyr272Asp). Compound heterozygotes were found for P1-3, while homozygotes were found for P4-6 that were inherited from their parents with normal phenotypes except for P5 and P6, respectively. The c.814T>G (p.Tyr272Asp) mutation in P5 was de novo. A c.1199C>A (p.Ala400Glu) homozygous mutation in GJC2 was identified in P6. A heterozygous variation was found in his father and the wild type was seen in his mother.

Distinct pathogenic mechanisms of various RARS1 mutations in Pelizaeus-Merzbacher-like disease.

Mutations of the genes encoding aminoacyl-tRNA synthetases are highly associated with various central nervous system disorders. Recurrent mutations, including c.5A>G, p.D2G; c.1367C>T, p.S456L; c.1535G>A, p.R512Q and c.1846_1847del, p. Y616Lfs*6 of RARS1 gene, which encodes two forms of human cytoplasmic arginyl-tRNA synthetase (hArgRS), are linked to Pelizaeus-Merzbacher-like disease (PMLD) with unclear pathogenesis. Among these mutations, c.5A>G is the most extensively reported mutation, leading to a p.D2G mutation in the N-terminal extension of the long-form hArgRS. Here, we showed the detrimental effects of R512Q substitution and ΔC mutations on the structure and function of hArgRS, while the most frequent mutation c.5A>G, p.D2G acted in a different manner without impairing hArgRS activity. The nucleotide substitution c.5A>G reduced translation of hArgRS mRNA, and an upstream open reading frame contributed to the suppressed translation of the downstream main ORF. Taken together, our results elucidated distinct pathogenic mechanisms of various RARS1 mutations in PMLD.

Rapid and Specific Immunomagnetic Isolation of Mouse Primary Oligodendrocytes.

The efficient and robust isolation and culture of primary oligodendrocytes (OLs) is a valuable tool for the in vitro study of the development of oligodendroglia as well as the biology of demyelinating diseases such as multiple sclerosis and Pelizaeus-Merzbacher-like disease (PMLD). Here, we present a simple and efficient selection method for the immunomagnetic isolation of stage three O4+ preoligodendrocytes cells from neonatal mice pups. Since immature OL constitute more than 80% of the rodent-brain white matter at postnatal day 7 (P7) this isolation method not only ensures high cellular yield, but also the specific isolation of OLs already committed to the oligodendroglial lineage, decreasing the possibility of isolating contaminating cells such as astrocytes and other cells from the mouse brain. This method is a modification of the techniques reported previously, and provides oligodendrocyte preparation purity above 80% in about 4 h.

Different Mutations of Gap Junction Connexin 47 Lead to Discrepant Activation of Unfolded Protein Response Pathway in Pelizaeus-Merzbacher-Like Disease.

Background The unfolded protein response (UPR) includes three cascade pathways, which are responsible for the elimination of overload protein that is accumulated in the endoplasmic reticulum (ER). We hypothesize that mutations in connexin 47 (Cx47) lead to abnormal retain of the protein in the ER lumen, which causes Pelizaeus–Merzbacher-like disease (PMLD), a hypomyelinating leukodystrophic disorder. Methods In this study, the influence of mutant Cx47 on the three UPR cascade pathways and discrepant UPR activation was analyzed in an oligodendrocyte cell line transfected with different mutations in the first extracellular loop of Cx47. As over activated UPR pathway would lead to cell apoptosis, cell viability and apoptosis were also compared between the different mutants. Results The elevated UPR level accompanied with higher apoptotic rates were measured in the c.138C > G or c.217C > T-transduced oligodendrocytes, but not in the c.216delGinsAA group, compared with the wild-type and empty vector groups. Cell viability was lower in oligodendrocytes transfected with the mutation of c.138C > G or c.217C > T, but not in the c.216delGinsAA group. Conclusion Different mutations in the Cx47 lead to discrepant activation of UPR pathway, which encouraged apoptotic cell death at different levels. Inappropriate activation of UPR may play important roles in the pathophysiology of PMLD.

Mutations in cardiovascular connexin genes.

Connexins (Cxs) form a family of transmembrane proteins comprising 21 members in humans. Cxs differ in their expression patterns, biophysical properties and ability to combine into homomeric or heteromeric gap junction channels between neighbouring cells. The permeation of ions and small metabolites through gap junction channels or hemichannels confers a crucial role to these proteins in intercellular communication and in maintaining tissue homeostasis. Among others, Cx37, Cx40, Cx43, Cx45 and Cx47 are found in heart, blood and lymphatic vessels. Mutations or polymorphisms in the genes coding for these Cxs have not only been implicated in cardiovascular pathologies but also in a variety of other disorders. While mutations in Cx43 are mostly linked to oculodentodigital dysplasia, Cx47 mutations are associated with Pelizaeus-Merzbacher-like disease and lymphoedema. Cx40 mutations are principally linked to atrial fibrillation. Mutations in Cx37 have not yet been described, but polymorphisms in the Cx37 gene have been implicated in the development of arterial disease. This review addresses current knowledge on gene mutations in cardiovascular Cxs systematically and links them to alterations in channel properties and disease.

New Mutation of Pelizaeus­Merzbacher-Like Disease; A Report from Iran

Pelizaeus­-Merzbacher-like disease (PMLD) is a hypomyelinating leukoencephalopathy disorder with a genetically heterogeneous pattern. Mutations in the GJA12/GJC2 gene cause one form of autosomal recessive Pelizaeus­-Merzbacher-like disease. Here, we report a new mutation in a ­10-month-old girl with nystagmus, psychomotor delay, hypotonicity, head nodding and dysmyelination from healthy second cousin parents. The genetic study showed a homozygote deletion as c902-918del in the exone 2. According to our study and recent reports from other Middle East countries, we suggest GJA12 gene mutations are common in this area, but we didnot find any previous report about this new mutation (c902-918Del).

GJC2 promoter mutations causing Pelizaeus–Merzbacher-like disease

ObjectivePelizaeus–Merzbacher-like disease is a rare hypomyelinating leukodystrophy caused by autosomal recessive mutations in GJC2, encoding a gap junction protein essential for production of a mature myelin sheath. A previously identified GJC2 mutation (c.-167G>A) in the promoter region is hypothesized to disrupt a putative SOX10 binding site; however, the lack of additional mutations in this region and contradictory functional data have limited the interpretation of this variant. MethodsWe describe two independent Pelizaeus–Merzbacher-like disease families with a novel promoter region mutation and updated in vitro functional assays. ResultsA novel GJC2 mutation (c.-170G>A) in the promoter region was identified in Pelizaeus–Merzbacher-like disease patients. In vitro functional assays using human GJC2 promoter constructs demonstrated that this mutation and the previously described c.-167G>A mutation similarly diminished the transcriptional activity driven by SOX10 and the binding affinity for SOX10. InterpretationThese findings support the role of GJC2 promoter mutations in Pelizaeus–Merzbacher-like disease. GJC2 promoter region mutation screening should be included in the evaluation of patients with unexplained hypomyelinating leukodystrophies.

A novel homozygous mutation of GJC2 derived from maternal uniparental disomy in a female patient with Pelizaeus–Merzbacher-like disease

Pelizaeus–Merzbacher-like disease (PMLD) is an autosomal recessive hypomyelinating disorder of the central nervous system characterized by nystagmus, motor developmental delay, ataxia, and progressive spasticity. The gap junction protein gamma-2 gene (GJC2), encoding the gap junction protein connexin 47, is one of the genes responsible for this condition. In this study, a novel homozygous mutation in GJC2 (c.746C>G; p.P249R) was identified in a 21-year-old female patient with PMLD. Although her mother was a carrier of this mutation, the Mendelian inheritance pattern could not be determined because the paternal sample was unavailable. Alternatively, chromosomal microarray testing together with single nucleotide polymorphism typing (CGH+SNP) was performed to determine the gene copy number and analyze the haplotype in the 1q42.13 region in which GJC2 is located. The result showed no deletion, but the GJC2 region was involved in the loss-of-heterozygosity region. Furthermore, haplotype of chromosome 1, in which GJC2 is located, revealed that both copies of chromosome 1 were derived from the patient's mother, indicating maternal uniparental disomy of chromosome 1. This study showed the advantage of the SNP genotyping microarray for detecting the origin of the mutation.

The distribution and functional properties of Pelizaeus–Merzbacher-like disease-linked Cx47 mutations on Cx47/Cx47 homotypic and Cx47/Cx43 heterotypic gap junctions

GJs (gap junctions) allow direct intercellular communication, and consist of Cxs (connexins). In the mammalian central nervous system, oligodendrocytes express Cx47, Cx32 and Cx29, whereas astrocytes express Cx43, Cx30 and Cx26. Homotypic Cx47/Cx47 GJs couple oligodendrocytes, and heterotypic Cx47/Cx43 channels are the primary GJs at oligodendrocyte/astrocyte junctions. Interestingly, autosomal recessive mutations in the gene GJC2 encoding Cx47 have been linked to a central hypomyelinating disease termed PMLD (Pelizaeus-Merzbacher-like disease). The aim of the present study was to determine the cellular distribution and functional properties of PMLD-associated Cx47 mutants (I46M, G149S, G236R, G236S, M286T and T398I). Expressing GFP (green fluorescent protein)-tagged mutant versions of Cx47in gap-junction-deficient model cells revealed that these mutants were detected at the cell-cell interface similar to that observed for wild-type Cx47. Furthermore, four of the six mutants showed no electrical coupling in both Cx47/Cx47 and Cx47/Cx43 GJ channels. These results suggest that most of the PMLD-linked Cx47 mutants disrupt Cx47/Cx47 and Cx47/Cx43 GJ function in the glial network, which may play a role in leading to PMLD symptoms.

High frequency of GJA12/GJC2 mutations in Turkish patients with Pelizaeus–Merzbacher disease

Pelizaeus-Merzbacher disease is an early onset dysmyelinating leukodystrophy. About 80% of PMD cases have been associated with duplications and mutations of the proteolipid protein 1 (PLP1) gene. Pelizaeus-Merzbacher-like disease is a genetically heterogeneous autosomal recessive disease and rarely caused by mutations in gap junction protein α12 (GJA12/GJC2) gene. The molecular basis of the disease was investigated in a cohort of 19 Turkish families. This study identified novel chromosomal rearrangements proximal and distal to, and exclusive of the PLP1 gene, showed equal frequencies of PLP1 and GJA12/GJC2 mutations at least in our cohort, and suggested further genetic heterogeneity.

A case of cerebral hypomyelination with spondylo‐epi‐metaphyseal dysplasia

We reported on a male patient with rare leukoencephalopathy and skeletal abnormalities. The condition was first noticed as a developmental delay, nystagmus and ataxia at 1 year of age. At 4 years of age, he was diagnosed as hypomyelination with skeletal abnormalities from clinical features, brain magnetic resonance imaging (MRI) and skeletal X-rays. His brain MRI revealed diffuse hypomyelination. These findings suggested the classical type of Pelizaeus-Merzbacher disease (PMD) caused by proteolipid protein (PLP)-1 gene or Pelizaeus-Merzbacher-like disease (PMLD). However, we found neither mutation nor duplication of PLP-1. The patient had severe growth retardation and general skeletal dysplasia compatible with spondylo-epi-metaphyseal dysplasia; however the mutation of discoidin domain receptor (DDR) 2 gene was absent. The co-morbidity of hypomyelination with skeletal abnormalities is rare. We performed array CGH and no causal copy number variation was recognized. Alternatively, this condition may have been caused by a mutation of the gene encoding a molecule that functions in both cerebral myelination and skeletal development.

“Pelizaeus–Merzbacher-like disease” presenting as complicated hereditary spastic paraplegia

Pelizaeus–Merzbacher-like disease (PMLD) is an autosomal recessive leukodystrophy caused by GJC2 gene mutations [1]. Clinical and genetic heterogeneity has been reported for the GJC2 gene that encodes the gap junction protein connexin 47 [1]. PMLD is typically characterized by impaired motor development, nystagmus, progressive spasticity, ataxia, and choreoathetosis in early infancy. Recently, a milder phenotype with late-onset and slowly progressive symptoms has been described [2]. Here we report an unusual case presenting with segmental dystonia and leg spasticity. This 38-year-old patient presented with involuntary head turning and tilting as well as difficulties with handwriting starting in his early twenties. At the age of 29 years, he also began to notice progressive gait slowing and leg stiffness. Of note, the patient was diagnosed with cervical neuroblastoma located anterior to the left sternocleidomastoid muscle at birth, which was operated on in the post-partum period. He was then also treated with chemotherapy (vincristine, cyclophosphamide) and radiation (total dose 19.2 Gy). Motor and language milestones were slightly delayed. He could walk at the age of 15 months and speak at 24 months. He had mild learning impairments at school but was able to complete junior high school. Family history was reported to be negative. On neurological examination, ocular pursuit was slightly saccadic but eye movements were otherwise normal. As sequelae of neuroblastoma surgery he had left Horner syndrome. He had right torticollis, left laterocollis, and dystonic posturing when holding out the arms. He also had bilateral dysdiadochokinesia and mild dysmetria. There was no weakness but marked leg spasticity with brisk deep tendon reflexes, positive Babinski sign, and a scissors-like gait (video). Neuropsychological evaluation revealed mild impairment of executive function, selective attention, and word fluency. MRI showed leukoencephalopathy with diffuse bilateral hyperintense white matter signal on T2-weighted images, which was mild in the central and occipital cerebral white matter but more marked in the posterior limbs of the internal capsule (Fig. 1), consistent with hypomyelination. In the brain stem and mesencephalon, several tracts including pyramidal tracts and medial lemniscus were hyperintense on T2-weighted images. This was also true for the middle cerebellar peduncles. The globus pallidus, red nucleus, substantia nigra, and dentate nucleus appeared relatively hypointense bilaterally. Sagittal images showed thinning of the corpus callosum. Electronic supplementary material The online version of this article (doi:10.1007/s00415-012-6617-0) contains supplementary material, which is available to authorized users.

Expanded spectrum of Pelizaeus–Merzbacher-like disease: literature revision and description of a novel GJC2 mutation in an unusually severe form

Homozygous or compound heterozygous mutations in the GJC2 gene, encoding the gap junction protein connexin47 (Cx47), cause the autosomal recessive hypomyelinating Pelizaeus-Merzbacher-like disease (PMLD1, MIM# 608804). Although clinical and neuroradiological findings resemble those of the classic Pelizaeus-Merzbacher disease, PMLD patients usually show a greater level of cognitive and motor functions. Unpredictably a homozygous missense GJC2 mutation (p.Glu260Lys) was found in a patient presenting with a very severe clinical picture characterised by congenital nystagmus and severe neurological impairment. Also magnetic resonance imaging was unusually severe, showing an abnormal supra- and infratentorial white matter involvement extending to the spinal cord. The novel p.Glu260Lys (c.778G>A) mutation, occurring in a highly conserved motif (SRPTEK) of the Cx47 extracellular loop-2 domain, was predicted, by modelling analysis, to break a 'salt bridge network', crucial for a proper connexin-connexin interaction to form a connexon, thus hampering the correct formation of the connexon pore. The same structural analysis, extended to the previously reported missense mutations, predicted that most changes were expected to have less severe impact on protein functions, correlating with the mild PMLD1 form of the patients. Our study expands the spectrum of PMLD1 and provides evidence that the extremely severe clinical and neuroradiological PMLD1 form of our patient likely correlates with the predicted impairment of gap junction channel assembly resulting from the detrimental effect of the new p.Glu260Lys mutant allele on Cx47 protein.

A Novel GJC2 Mutation Associated with Hypomyelination and Müllerian Agenesis Syndrome: Coincidence or a New Entity?

In recent years, several new white matter diseases have been identified based on magnetic resonance imaging and clinical findings. For most newly defined disorders the genetic basis has been identified. However, there is still a large group of patients without a specific diagnosis. Hypomyelinating leukodystrophies are the largest group among them. In some disorders characterized by hypomyelination only central nervous system involvement is observed, but in some disorders involvement of other organs is observed as well, such as eyes or teeth. Pelizaeus-Merzbacher-like disease (PMLD) is an autosomal recessive hypomyelinating disorder of the central nervous system characterized by nystagmus, ataxia, and progressive spasticity. The disease is caused by mutations in GJC2, the gene that encodes the gap junction protein connexin 47. Here we describe hypomyelination and Müllerian agenesis syndrome in a girl who is homozygous for a novel mutation in the GJC2 gene. It is an open question whether this is an association by chance or a feature of PMLD not previously noted.

Promoter mutation is a common variant in GJC2-associated Pelizaeus–Merzbacher-like disease

Pelizaeus–Merzbacher-like disease (PMLD) is a clinically and genetically heterogeneous neurological disorder of cerebral hypomyelination. It is clinically characterised by early onset (usually infantile) nystagmus, impaired motor development, ataxia, choreoathetoid movements, dysarthria and progressive limb spasticity. We undertook autozygosity mapping studies in a large consanguineous family of Pakistani origin in which affected children had progressive lower limb spasticity and features of cerebral hypomyelination on MR brain imaging. SNP microarray and microsatellite marker analysis demonstrated linkage to chromosome 1q42.13–1q42.2. Direct sequencing of the gap junction protein gamma-2 gene, GJC2, identified a promoter region mutation (c.-167A>G) in the non-coding exon 1. The c.-167A>G promoter mutation was identified in a further 4 individuals from two families (who were also of Pakistani origin) with clinical and radiological features of PMLD in whom previous routine diagnostic screening of GJC2 had been reported as negative. A common haplotype was identified at the GJC2 locus in the three mutation-positive families, consistent with a common origin for the mutation and likely founder effect.This promoter mutation has only recently been reported in GJC2-PMLD but it has been postulated to affect the binding of the transcription factor SOX10 and appears to be a prevalent mutation, accounting for ~29% of reported patients with GJC2-PMLD. We propose that diagnostic screening of GJC2 should include sequence analysis of the non-coding exon 1, as well as the coding regions to avoid misdiagnosis or diagnostic delay in suspected PMLD.

P27.6 Pelizaeus Merzbacher-like disease (PMLD): report of a patient with a new mutation in the GJA12/GJC2 gene

P27.6 Pelizaeus Merzbacher-like disease (PMLD): report of a patient with a new mutation in the GJA12/GJC2 gene

Pelizaeus-Merzbacher-like Disease Caused by AIMP1/p43 Homozygous Mutation

Pelizaeus-Merzbacher disease is an X-linked hypomyelinating leukodystrophy caused by PLP1 mutations. A similar autosomal-recessive phenotype, Pelizaeus-Merzbacher-like disease (PMLD), has been shown to be caused by homozygous mutations in GJC2 or HSPD1. We report a consanguineous Israeli Bedouin kindred with clinical and radiological findings compatible with PMLD in which linkage to PLP1, GJC2, and HSPD1 was excluded. Through genome-wide homozygosity mapping and mutation analysis, we demonstrated in all affected individuals a homozygous frameshift mutation that fully abrogates the main active domain of AIMP1, encoding ARS-interacting multifunctional protein 1. The mutation fully segregates with the disease-associated phenotype and was not found in 250 Bedouin controls. Our findings are in line with the previously demonstrated inability of mutant mice lacking the AIMP1/p43 ortholog to maintain axon integrity in the central and peripheral neural system.

Clinical neurophysiology for differentiation between Pelizaeus-Merzbacher Disease and Pelizaeus-Merzbacher-like Disease

Background: Hypomyelinating leukoencephalopathies constitute a large subgroup of white matter disorders with onset in childhood. Whereas a few conditions among this category are identifiable by typical clinical or neuroradiological features, Pelizaeus-Merzbacher disease (PMD) and Pelizaeus-Merzbacher-like disease (PMLD) show almost indistinguishable clinical and neuroradiological features. PMD is associated with X-linked PLP1 mutations. PMLD is genetically heterogeneous, and in about 8% of patients autosomal recessive mutations of the gap junction protein α12 (GJA12/GJC2) gene on chromosome 1q41–42 were detected. If a patient's pedigree is consistent with either an X-linked recessive or an autosomal recessive inheritance or a de novo mutation, the decision which genetic testing, PLP1 or a GJA12/GJC2, should be performed first is arbitrary. This study aimed at separating PMD from GJA12/GJC2-associated PMLD based on neurophysiologic investigations.

Elevated CSF N-acetylaspartylglutamate suggests specific molecular diagnostic abnormalities in patients with white matter diseases

Background: In order to identify biomarkers useful for the diagnosis of genetic white matter disorders we compared the metabolic profile of patients with leukodystrophies with a hypomyelinating or a non-hypomyelinating MRI pattern. Methods: We used a non-a priori method of in vitro 1H-NMR spectroscopy on CSF samples of 74 patients with leukodystrophies. Results: We found an elevation of CSF N-acetylaspartylglutamate (NAAG) in patients with Pelizaeus–Merzbacher disease (PMD)— PLP1 gene, Pelizaeus–Merzbacher-like disease— GJC2 gene and Canavan disease— ASPA gene. In the PMD group, NAAG was significantly elevated in the CSF of all patients with PLP1 duplication (19/19) but was strictly normal in 6 out of 7 patients with PLP1 point mutations. Additionally, we previously reported increased CSF NAAG in patients with SLC17A5 mutations. Conclusions: Elevated CSF NAAG is a biomarker that suggests specific molecular diagnostic abnormalities in patients with white matter diseases. Our findings also point to unique pathological functions of the overexpressed PLP in PMD patients with duplication of this gene.

Clinical neurophysiology in GJA12 -related hypomyelination vs Pelizaeus-Merzbacher disease

Among the hypomyelinating leukoencephalopathies with onset in childhood, Pelizaeus-Merzbacher disease (PMD) and Pelizaeus-Merzbacher-like disease (PMLD) constitute a large subgroup with almost indistinguishable clinical and neuroradiologic features. Whereas PMD is due to X-linked PLP1 mutations, PMLD is genetically heterogeneous, with about 8% of patients carrying autosomal recessive GJA12/GJC2 mutations. The aim of this study was to evaluate whether neurophysiologic testing may separate PMD from GJA12/GJC2-associated PMLD. Retrospective data collection study with reevaluation of evoked potentials (EP) and nerve conduction studies (NCS) in 10 patients from 7 families with PMLD due to various GJA12/GJC2 mutations and 8 boys from 7 families with classic PMD caused by a PLP1 duplication or missense mutation. In brainstem auditory EP, waves III-V were absent in all patients with PMD, but clearly recordable in 11 of 13 investigations in 8 patients with PMLD. Visual evoked potentials and somatosensory evoked potentials revealed conduction delay in both PMD and PMLD, without significant difference. NCS were normal in all patients with PMD and indicated mild peripheral neuropathy in only 2 of 10 patients with PMLD. In a patient with clinical and neuroradiologic features of Pelizaeus-Merzbacher disease/Pelizaeus-Merzbacher-like disease and a pedigree consistent with both conditions, brainstem auditory evoked potentials provide good selectivity between these disorders and point in the right direction for identifying the primary genetic defect.