Glycosyltransferase POMGNT1 deficiency strengthens N-cadherin-mediated cell-cell adhesion.

Defects in protein O-mannosylation lead to severe congenital muscular dystrophies collectively known as α-dystroglycanopathy. A hallmark of these diseases is the loss of the O-mannose-bound matriglycan on α-dystroglycan, which reduces cell adhesion to the extracellular matrix. Mutations in protein O-mannose ß1,2-N-acetylglucosaminyltransferase 1 (POMGNT1), which is crucial for the elongation of O-mannosyl glycans, have mainly been associated with muscle-eye-brain (MEB) disease. In addition to defects in cell-extracellular matrix adhesion, aberrant cell-cell adhesion has occasionally been observed in response to defects in POMGNT1. However, specific molecular consequences of POMGNT1 deficiency on cell-cell adhesion are largely unknown. We used POMGNT1 knockout HEK293T cells and fibroblasts from an MEB patient to gain deeper insight into the molecular changes in POMGNT1 deficiency. Biochemical and molecular biological techniques combined with proteomics, glycoproteomics, and glycomics revealed that a lack of POMGNT1 activity strengthens cell-cell adhesion. We demonstrate that the altered intrinsic adhesion properties are due to an increased abundance of N-cadherin (N-Cdh). In addition, site-specific changes in the N-glycan structures in the extracellular domain of N-Cdh were detected, which positively impact on homotypic interactions. Moreover, in POMGNT1-deficient cells, ERK1/2 and p38 signaling pathways are activated and transcriptional changes that are comparable with the epithelial-mesenchymal transition (EMT) are triggered, defining a possible molecular mechanism underlying the observed phenotype. Our study indicates that changes in cadherin-mediated cell-cell adhesion and other EMT-related processes may contribute to the complex clinical symptoms of MEB or α-dystroglycanopathy in general and suggests that the impact of changes in O-mannosylation on N-glycosylation has been underestimated.

Decreased expression of protein O-linked mannose ß-1,2-N-acetylglucosaminyltransferase 1 contributes to Alzheimer's disease-like pathologies.

Alzheimer's disease (AD) is pathologically characterized by senile plaques and neurofibrillary tangles composed of ß-amyloid peptide (Aß) and tau hyperphosphorylation, respectively. Mannosylation, a particular type of posttranslational modification, may be involved in the pathogenesis of AD. However, its underlying mechanism remains unclear. Protein O-linked mannose ß-1,2-N-acetylglucosaminyltransferase 1 (POMGnT1) catalyzes the formation of the N-acetylglucosamine ß-1,2-Man linkage of O-mannosylglycan, which can increase the protein posttranslational mannosylation level. The defective POMGnT1 gene leads to the hypomannosylation of proteins, which may cause cognitive decline in aged people. This study aimed to investigate whether POMGnT1 participated in the pathogenesis of AD and explore its underlying role using AD mouse and cell models. In this study, the expression of POMGnT1 was measured in AD models [ß-amyloid precursor protein (APP)/presenilin-1 (PS1) transgenic mice, an AD mouse model; N2a cells stably transfected with Swedish mutant APP (N2a/APP), an AD cell model]. The results revealed that the expression of POMGnT1 decreased in AD mouse and cell models. In addition, POMGnT1-overexpressing N2a/APP cells were built by retroviral transfection. POMGnT1 overexpression may lower Aß levels by reducing APP production and downregulating ß- and γ-secretase activities. It also promoted clearance of Aß by upregulating insulin-degrading enzymes and ameliorated tau hyperphosphorylation. Hence, it was concluded that POMGnT1 was involved in the pathogenic process of AD. The decreased expression of POMGnT1 contributes to AD-like pathologies.NEW & NOTEWORTHY This study explored the role of mannosylation in the pathogenesis of AD through a mannosyltransferase-POMGnT1. Results demonstrated that target gene overexpression could ameliorate pathologies of Aß and tau hyperphosphorylation. This study is the first to examine the relationship between mannosylation and AD.

Two middle-aged women with the Finnish variant of muscle-eye-brain disease (MEB).

Muscle-eye-brain disease (MEB) is a recessively inherited rare disease. Sixteen different gene mutations are known, with the most common mutations in the POMGNT1 gene. The disease is now called congenital muscular dystrophy-dystroglycanopathy type A3 (MDDGA3). It manifests itself as muscular dystrophy with eye and brain anomalies and intellectual disability. Previous clinical reports describe young patients. We have been able to follow two patients for almost 40 years. Their clinical picture has remained quite stable since adolescence, appearing as severe intellectual and motor disability, extremely limited communication skills, visual impairment, epilepsy, joint contractures, repeated bowel obstructions, teeth abrasion due to bruxism, an irregular sleep pattern and as a previously unreported feature hypothermic periods manifesting as excessive sleepiness.

Synthetic glycopeptides reveal specific binding pattern and conformational change at O-mannosylated position of α-dystroglycan by POMGnT1 catalyzed GlcNAc modification.

Structural and functional effects of core M1 type glycan modification catalyzed by protein O-linked mannose ß1,2-N-acetylglucosaminyltransferase 1 (POMGnT1) were investigated using a core M1 glycoform focused library of an α-dystroglycan fragment, 372TRGAIIQTPTLGPIQPTRV390. Evanescent-field fluorescence-assisted microarray system illuminated the specific binding pattern of plant lectins that can discriminate the glycan structure of core M1 glycan of the library. The comparative NMR analysis of synthetic glycopeptide having different length of the O-mannosylated glycans revealed a conformational change of the peptide backbone along with core M1 disaccharide formation. No long-range NOE signals of glycan-amino acid nor inter amino acid indicate the conformational change is induced by steric hindrance of core M1, the sole 1,2-O-modified form among protein binding sugar residue found in mammals.

Compound heterozygous POMGNT1 mutations leading to muscular dystrophy-dystroglycanopathy type A3: a case report.

BACKGROUND: Dystroglycanopathies, which are caused by reduced glycosylation of alpha-dystroglycan, are a heterogeneous group of neurodegenerative disorders characterized by variable brain and skeletal muscle involvement. Muscle-eye-brain disease (or muscular dystrophy-dystroglycanopathy type 3 A) is an autosomal recessive disorder characterized by congenital muscular dystrophy, ocular abnormalities, and lissencephaly. CASE PRESENTATION: We report clinical and genetic characteristics of a 6-year-old boy affected by muscular dystrophy-dystroglycanopathy. He has severe a delay in psychomotor and speech development, muscle hypotony, congenital myopia, partial atrophy of the optic nerve disc, increased level of creatine kinase, primary-muscle lesion, polymicrogyria, ventriculomegaly, hypoplasia of the corpus callosum, cysts of the cerebellum. Exome sequencing revealed compound heterozygous mutations in POMGNT1 gene (transcript NM_001243766.1): c.1539 + 1G > A and c.385C > T. CONCLUSIONS: The present case report shows diagnostic algorithm step by step and helps better understand the clinical and genetic features of congenital muscular dystrophy.

Neurons and glia modify receptor protein-tyrosine phosphatase ζ (RPTPζ)/phosphacan with cell-specific O-mannosyl glycans in the developing brain.

Protein O-mannosylation is a glycan modification that is required for normal nervous system development and function. Mutations in genes involved in protein O-mannosyl glycosylation give rise to a group of neurodevelopmental disorders known as congenital muscular dystrophies (CMDs) with associated CNS abnormalities. Our previous work demonstrated that receptor protein-tyrosine phosphatase ζ (RPTPζ)/phosphacan is hypoglycosylated in a mouse model of one of these CMDs, known as muscle-eye-brain disease, a disorder that is caused by loss of an enzyme (protein O-mannose ß-1,2-N-acetylglucosaminyltransferase 1) that modifies O-mannosyl glycans. In addition, monoclonal antibodies Cat-315 and 3F8 were demonstrated to detect O-mannosyl glycan modifications on RPTPζ/phosphacan. Here, we show that O-mannosyl glycan epitopes recognized by these antibodies define biochemically distinct glycoforms of RPTPζ/phosphacan and that these glycoforms differentially decorate the surface of distinct populations of neural cells. To provide a further structural basis for immunochemically based glycoform differences, we characterized the O-linked glycan heterogeneity of RPTPζ/phosphacan in the early postnatal mouse brain by multidimensional mass spectrometry. Structural characterization of the O-linked glycans released from purified RPTPζ/phosphacan demonstrated that this protein is a significant substrate for protein O-mannosylation and led to the identification of several novel O-mannose-linked glycan structures, including sulfo-N-acetyllactosamine containing modifications. Taken together, our results suggest that specific glycan modifications may tailor the function of this protein to the unique needs of specific cells. Furthermore, their absence in CMDs suggests that hypoglycosylation of RPTPζ/phosphacan may have different functional consequences in neurons and glia.

Mining the O-mannose glycoproteome reveals cadherins as major O-mannosylated glycoproteins.

The metazoan O-mannose (O-Man) glycoproteome is largely unknown. It has been shown that up to 30% of brain O-glycans are of the O-Man type, but essentially only alpha-dystroglycan (α-DG) of the dystrophin-glycoprotein complex is well characterized as an O-Man glycoprotein. Defects in O-Man glycosylation underlie congenital muscular dystrophies and considerable efforts have been devoted to explore this O-glycoproteome without much success. Here, we used our SimpleCell strategy using nuclease-mediated gene editing of a human cell line (MDA-MB-231) to reduce the structural heterogeneity of O-Man glycans and to probe the O-Man glycoproteome. In this breast cancer cell line we found that O-Man glycosylation is primarily found on cadherins and plexins on ß-strands in extracellular cadherin and Ig-like, plexin and transcription factor domains. The positions and evolutionary conservation of O-Man glycans in cadherins suggest that they play important functional roles for this large group of cell adhesion glycoproteins, which can now be addressed. The developed O-Man SimpleCell strategy is applicable to most types of cell lines and enables proteome-wide discovery of O-Man protein glycosylation.

Production of sialylated O-linked glycans in Pichia pastoris.

The methylotrophic yeast, Pichia pastoris, is an important organism used for the production of therapeutic proteins. Previously, we have reported the glycoengineering of this organism to produce human-like N-linked glycans but up to now no one has addressed engineering the O-linked glycosylation pathway. Typically, O-linked glycans produced by wild-type P. pastoris are linear chains of four to five α-linked mannose residues, which may be capped with ß- or phospho-mannose. Previous genetic engineering of the N-linked glycosylation pathway of P. pastoris has eliminated both of these two latter modifications, resulting in O-linked glycans which are linear α-linked mannose structures. Here, we describe a method for the co-expression of an α-1,2-mannosidase, which reduces these glycans to primarily a single O-linked mannose residue. In doing so, we have reduced the potential of these glycans to interact with carbohydrate-binding proteins, such as dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin. Furthermore, the introduction of the enzyme protein-O-linked-mannose ß-1,2-N-acetylglucosaminyltransferase 1, resulted in the capping of the single O-linked mannose residues with N-acetylglucosamine. Subsequently, this glycoform was extended into human-like sialylated glycans, similar in structure to α-dystroglycan-type glycoforms. As such, this represents the first example of sialylated O-linked glycans being produced in yeast and extends the utility of the P. pastoris production platform beyond N-linked glycosylated biotherapeutics to include molecules possessing O-linked glycans.

Case Series on Autosomal Recessive Non-Syndromic Retinitis Pigmentosa Caused by POMGNT1 Mutations with a Report of a New Variant.

Recessive Protein O-linked-mannose beta-1,2-N-acetylglucosaminyltransferase 1 (POMGNT1) mutations can cause early onset muscle-eye-brain disease but have also more recently been associated with non-syndromic Retinitis Pigmentosa. In this case series, we describe three sisters affected by non-syndromic autosomal recessive POMGNT1 retinopathy with a report of a new variant. The three patients received care at West Virginia University Eye Institute, including full ophthalmic examination with additional fundus imaging, optical coherence tomography (OCT), electroretinogram (ERG), and visual field testing. Diagnostic panel testing of 330 genes was also obtained. The proband was seen for cataract evaluation at age 42, and her fundus examination was suggestive of retinitis pigmentosa. Her oldest sister had been treated for acute anterior uveitis with retinal vasculitis. Another sister was diagnosed with multiple sclerosis (MS) and peripheral retinal degeneration. Posterior subcapsular cataracts were diagnosed between age 42 and 55 in all three sisters, each with constricted fields with preserved central vision. We identified one pathogenic POMGNT1 variant (c.751 + 1G > A) and one likely pathogenic variant (c.1010T > C p.Ile337Thr) in all three sisters. A thorough family history and examination of the siblings with genotyping might have led to an earlier diagnosis of retinal inherited disease and avoidance of immunomodulatory treatment in the oldest sibling.

Uniparental disomy for chromosome 1 with POMGNT1 splice-site variant causes muscle-eye-brain disease.

POMGNT1, encoding protein O-mannose beta-1,2-N-acetylglucosaminyltransferase 1, is one of the genes responsible for dystroglycanopathy (DGP), which includes multiple phenotypes such as muscle-eye-brain disease (MEB), congenital muscular dystrophy with intellectual disability, and limb-girdle muscular dystrophy Here, we report a case of MEB that is the result of a homozygous variant of POMGNT1 that is revealed through uniparental disomy (UPD). An 8-month-old boy was admitted with mental and motor retardation, hypotonia, esotropia, early onset severe myopia, and structural brain abnormalities. A panel testing of genetic myopathy-related genes was used to identify a homozygous c.636C>T (p.Phe212Phe) variant in exon 7 of POMGNT1 in the patient, a heterozygous c.636C>T variant in the father, and the wild type in the mother. Quantitative polymerase chain reaction (q-PCR) revealed no abnormal copy numbers in exon 7. Trio-based whole-exome sequencing (trio-WES) revealed a possible paternal UPD on chromosome 1 of the patient. Chromosomal microarray analysis (CMA) revealed a 120,451 kb loss of heterozygosity (LOH) on 1p36.33-p11.2, encompassing POMGNT1, and a 99,319 kb loss of heterozygosity on 1q21.2-q44, which indicated UPD. Moreover, RNA sequencing (RNA-seq) verified that the c.636C>T variant was a splice-site variant, leading to skipping of exon 7 (p.Asp179Valfs*23). In conclusion, to the best of our knowledge, we present the first case of MEB caused by UPD, providing valuable insights into the genetic mechanisms underlying this condition.

Analysis of the expression and distribution of protein O-linked mannose ß1,2-N-acetylglucosaminyltransferase 1 in the normal adult mouse brain.

Introduction: Protein O-linked mannose ß1,2-N-acetylglucosaminyltransferase 1 (POMGNT1) is crucial for the elongation of O-mannosyl glycans. Mutations in POMGNT1 cause muscle-eye-brain (MEB) disease, one of the main features of which is anatomical aberrations in the brain. A growing number of studies have shown that defects in POMGNT1 affect neuronal migration and distribution, disrupt basement membranes, and misalign Cajal-Retzius cells. Several studies have examined the distribution and expression of POMGNT1 in the fetal or neonatal brain for neurodevelopmental studies in the mouse or human brain. However, little is known about the neuroanatomical distribution and expression of POMGNT1 in the normal adult mouse brain. Methods: We analyzed the expression of POMGNT1 mRNA and protein in the brains of various neuroanatomical regions and spinal cords by western blotting and RT-qPCR. We also detected the distribution profile of POMGnT1 in normal adult mouse brains by immunohistochemistry and double-immunofluorescence. Results: In the present study, we found that POMGNT1-positive cells were widely distributed in various regions of the brain, with high levels of expression in the cerebral cortex and hippocampus. In terms of cell type, POMGNT1 was predominantly expressed in neurons and was mainly enriched in glutamatergic neurons; to a lesser extent, it was expressed in glial cells. At the subcellular level, POMGNT1 was mainly co-localized with the Golgi apparatus, but expression in the endoplasmic reticulum and mitochondria could not be excluded. Discussion: The present study suggests that POMGNT1, although widely expressed in various brain regions, may has some regional and cellular specificity, and the outcomes of this study provide a new laboratory basis for revealing the possible involvement of POMGNT1 in normal physiological functions of the brain from a morphological perspective.

Human FAM3C restores memory-based thermotaxis of Caenorhabditis elegans famp-1/m70.4 loss-of-function mutants.

The family with sequence similarity 3 (FAM3) superfamily represents a distinct class of signaling molecules that share a characteristic structural feature. Mammalian FAM3 member C (FAM3C) is abundantly expressed in neuronal cells and released from the synaptic vesicle to the extracellular milieu in an activity-dependent manner. However, the neural function of FAM3C has yet to be fully clarified. We found that the protein sequence of human FAM3C is similar to that of the N-terminal tandem domains of Caenorhabditis elegans FAMP-1 (formerly named M70.4), which has been recognized as a tentative ortholog of mammalian FAM3 members or protein-O-mannose ß-1,2-N-acetylglucosaminyltransferase 1 (POMGnT1). Missense mutations in the N-terminal domain, named Fam3L2, caused defects in memory-based thermotaxis but not in chemotaxis behaviors; these defects could be restored by AFD neuron-specific exogenous expression of a polypeptide corresponding to the Fam3L2 domain but not that corresponding to the Fam3L1. Moreover, human FAM3C could also rescue defective thermotaxis behavior in famp-1 mutant worms. An in vitro assay revealed that the Fam3L2 and FAM3C can bind with carbohydrates, similar to the stem domain of POMGnT1. The athermotactic mutations in the Fam3L2 domain caused a partial loss-of-function of FAMP-1, whereas the C-terminal truncation mutations led to more severe neural dysfunction that reduced locomotor activity. Overall, we show that the Fam3L2 domain-dependent function of FAMP-1 in AFD neurons is required for the thermotaxis migration of C. elegans and that human FAM3C can act as a substitute for the Fam3L2 domain in thermotaxis behaviors.

Congenital Mirror Movements Associated With Brain Malformations.

BACKGROUND: Congenital mirror movements are involuntary movements of a side of the body imitating intentional movements on the opposite side, appearing in early childhood and persisting beyond 7 years of age. Congenital mirror movements are usually idiopathic but have been reported in association with various brain malformations. METHODS: We describe clinical, genetic, and radiologic features in 9 individuals from 5 families manifesting congenital mirror movements. RESULTS: The brain malformations associated with congenital mirror movements were: dysplastic corpus callosum in father and daughter with a heterozygous p.Met1* mutation in DCC; hypoplastic corpus callosum, dysgyria, and malformed vermis in a mother and son with a heterozygous p.Thr312Met mutation in TUBB3; dysplastic corpus callosum, dysgyria, abnormal vermis, and asymmetric ventricles in a father and 2 daughters with a heterozygous p.Arg121Trp mutation in TUBB; hypoplastic corpus callosum, dysgyria, malformed basal ganglia and abnormal vermis in a patient with a heterozygous p.Glu155Asp mutation in TUBA1A; hydrocephalus, hypoplastic corpus callosum, polymicrogyria, and cerebellar cysts in a patient with a homozygous p.Pro312Leu mutation in POMGNT1. CONCLUSION: DCC, TUBB3, TUBB, TUBA1A, POMGNT1 cause abnormal axonal guidance via different mechanisms and result in congenital mirror movements associated with brain malformations.

Identification of a novel missense c.386G > A variant in a boy with the POMGNT1-related muscular dystrophy-dystroglycanopathy.

Muscular dystrophy-dystroglycanopathies are autosomal recessive neurologic disorders, caused by homozygous or compound heterozygous mutations in the POMGNT1 gene-encoding protein O-mannose beta-1,2-N-acetylglucosaminyl transferase. This type of muscular dystrophy is characterized by early-onset muscle weakness, gait ataxia, microcephaly, and developmental delay.We performed whole-exome sequencing to detect the disease-causing variants in a 4 year-old boy. Afterwards, Sanger sequencing was performed to confirm the detected variant in the patient and his family. We evaluated a 4 year-old Iranian boy presented with delayed speech and language development, gait ataxia, global developmental delay, motor delay, neurodevelopmental delay, postnatal microcephaly and strabismus. His parents were first cousins, and the mother had a history of spontaneous abortion. In this study, we report a novel missense c.386G > A; p.(Arg129Gln) variant in the POMGNT1 gene which was confirmed by Sanger sequencing in the patient and segregated with the disease in the family.

FAM3B/PANDER-Like Carbohydrate-Binding Domain in a Glycosyltransferase, POMGNT1.

Protein O-mannose ß1,2-N-acetylglucosaminyltransferase 1 (POMGNT1) is one of the gene products responsible for α-dystroglycanopathy, which is a type of congenital muscular dystrophy caused by O-mannosyl glycan defects. The originally identified function of POMGNT1 was as a glycosyltransferase that catalyzes the formation of the GlcNAcß1-2Man linkage of O-mannosyl glycan, but the enzyme function is not essential for α-dystroglycanopathy pathogenesis. Our recent study revealed that the stem domain of POMGNT1 has a carbohydrate-binding ability, which recognizes the GalNAcß1-3GlcNAc structure. This carbohydrate-binding activity is required for the formation of the ribitol phosphate (RboP)-3GalNAcß1-3GlcNAc structure by fukutin. This protocol describes methods to assess the carbohydrate-binding activity of the POMGNT1 stem domain.

Role of glycosyltransferase PomGnT1 in glioblastoma progression.

BACKGROUND: Glioblastoma multiforme (GBM) is the most aggressive and invasive brain tumor, for which novel prognostic markers and predictors of therapeutic response are urgently needed. We reported previously that levels of peptide-O-linked mannose ß-1,2-N-acetylglucosaminyltransferase 1 (PomGnT1) in glioma specimens correlated with tumor grade. However, the prognostic significance of PomGnT1 in glioma patients and its function in GBM progression remain unknown. METHODS: Clinical relevance of PomGnT1 in GBM patients' prognosis was analyzed both in a clinically annotated expression dataset of 446 GBM tumor specimens and in 82 GBM tumor samples collected at our institution. The function of PomGnT1 in glioma growth and invasion, and the underlying mechanisms of PomGnT1 regulation were explored in vitro and in vivo. RESULTS: PomGnT1 expression in GBM tissues was closely associated with poor prognosis in GBM patients. Forced overexpression of PomGnT1 in glioblastoma cells impaired cell adhesion and increased their proliferation and invasion in vitro. Subsequent in vivo experiments showed that overexpression of PomGnT1 promoted tumor growth and shortened the survival time of tumor-bearing mice in an orthotopic model. Conversely, stable short hairpin RNA-mediated knockdown of PomGnT1 expression produced opposite effects both in vitro and in vivo. Mechanistic studies revealed that activation of epidermal growth factor receptor (EGFR) resulted in EGFR/extracellular signal-regulated kinase-dependent upregulation of PomGnT1, downregulation of receptor-type protein tyrosine phosphatase ß, and activation of ß-catenin pathway signaling. CONCLUSION: These findings suggest that PomGnT1 promotes GBM progression via activation of ß-catenin and may serve as a prognostic factor for glioma patient survival as well as a novel molecular target for anticancer therapy in malignant glioma.

Clinical features and molecular characterization of a patient with muscle-eye-brain disease: a novel mutation in the POMGNT1 gene.

Muscle-eye-brain disease is a congenital muscular dystrophy characterized by structural brain and eye defects. Here, we describe a 12-year-old boy with partial agenesis of corpus callosum, ventriculomegaly, flattened brain stem, diffuse pachygyria, blindness, profound cognitive deficiencies, and generalized muscle weakness, yet without a clear dystrophic pattern on muscle biopsy. There was no glycosylation of α-dystroglycan and the genetic screening revealed a novel truncating mutation, c.1545delC (p.Tyr516Thrfs*21), and a previously identified missense mutation, c.1469G>A (p.Cys490Tyr), in the protein O-mannose beta-1,2-N-acetylglucosaminyltransferase 1 (POMGNT1) gene. These findings broaden the clinical spectrum of muscle-eye-brain disease to include pronounced hypotonia with severe brain and eye malformations, yet with mild histopathologic changes in the muscle specimen, despite the absence of glycosylated α-dystroglycan.

Clinical, radiological, and genetic survey of patients with muscle-eye-brain disease caused by mutations in POMGNT1.

BACKGROUND: To evaluate clinical, genetic, and radiologic features of our patients with muscle-eye-brain disease. METHODS: The data of patients who were diagnosed with muscle-eye-brain disease from a cohort of patients with congenital muscular dystrophy in the Division of Pediatric Neurology of Dokuz Eylül University School of Medicine and Gaziantep Children's Hospital between 2005 and 2013 were analyzed retrospectively. RESULTS: From a cohort of 34 patients with congenital muscular dystrophy, 12 patients from 10 families were diagnosed with muscle-eye-brain disease. The mean age of the patients was 9 ± 5.5 years (2-19 years). Mean serum creatine kinase value was 2485.80 ± 1308.54 IU/L (700-4267 IU/L). All patients presented with muscular hypotonia at birth followed by varying degrees of spasticity and exaggerated deep tendon reflexes in later stages of life. Three patients were able to walk. The most common ophthalmologic and radiologic abnormalities were cataracts, retinal detachment, periventricular white matter abnormalities, ventriculomegaly, pontocerebellar hypoplasia, and multiple cerebellar cysts. All of the patients had mutations in the POMGNT1 gene. The most common mutation detected in 66% of patients was c.1814 G > A (p.R605H). Two novel mutations were identified. CONCLUSIONS: We suggest that muscle-eye-brain disease is a relatively common muscular dystrophy in Turkey. It should be suspected in patients with muscular hypotonia, increased creatine kinase, and structural eye and brain abnormalities. The c.1814 G > A mutation in exon 21 of the POMGNT1 gene is apparently a common mutation in the Turkish population. Individuals with this mutation show classical features of muscle-eye-brain disease, but others may exhibit a milder phenotype and retain the ability to walk independently. Congenital muscular dystrophy patients from Turkey carrying the clinical and radiologic features of muscle-eye-brain disease should be evaluated for mutations in POMGNT1 gene.