Identification of mutations in TMEM5 and ISPD as a cause of severe cobblestone lissencephaly

Walker-Warburg syndrome: A case report of congenital muscular dystrophy with hydrocephalus

Walker-Warburg Syndrome is a genetically heterogeneous disease with autosomal recessive inheritance characterized by brain and eye deformities, profound mental retardation, congenital muscular dystrophy, and early death. This case study demonstrates a mutation on chromosome 12q14 in the TMEM5 gene (RXYLT1; 605862), which encodes a transmembrane protein with glycosyltransferase function. We present a case of a full-term male baby delivered by Cesarean section due to macrocephaly. At birth, the newborn had hypotonia and respiratory distress, requiring mechanical ventilation. On examination the patient was found to have macrocephaly, generalized hypotonia, hyporeflexia, and retinal degeneration. Genetic testing revealed a homozygous variant in the RXYLT1 gene, consistent with the diagnosis of autosomal recessive muscular dystrophy-dystroglycanopathy (congenital with brain and eye anomalies) type A10. The patient underwent a ventriculoperitoneal shunt and received supportive management. WWS is a fatal disease, and most affected children do not survive beyond the age of 3. Prenatal screening, ultrasonography and magnetic resonance imaging can aid in the detection and confirmation of abnormal brain development in WWS cases.

Characterization and Engineered U1 snRNA Rescue of Splicing Variants in a Turkish Neurodevelopmental Disease Cohort

Although they are rare in the population, rare neurodevelopmental disorders (RNDDs) constitute a significant portion of all rare diseases. While advancements in sequencing technologies led to improvements in diagnosing and managing rare neurodevelopmental diseases, accurate pathogenicity classification of the identified variants is still challenging. Sequence variants altering pre-mRNA splicing make up a significant part of pathogenic variants. Despite advances in the in silico prediction tools, noncanonical splice site variants are one of the groups of variants that pose a challenge in their clinical interpretation. In this study, we analyzed the effects of seven splicing variants we had previously proposed as disease-causing and demonstrated that all but one of the seven variants had a strong or moderate effect on splicing, as assessed by a minigene assay. Next, applying U1 snRNAs engineered for different splicing variants in the corresponding genes and expressed with minigene plasmids in HeLa cells provided a partial correction in four of the studied genes to varying degrees. Findings from our study highlight the importance of in vitro minigene-based assays for the reclassification of putative splice-altering variants of uncertain significance and the therapeutic potential of modified U1 snRNAs in RNDDs.

RETINAL MANIFESTATIONS OF WALKER-WARBURG SYNDROME IN TWO SIBLINGS WITH RXYLT1 MUTATIONS

PURPOSE

We report two siblings with genetically confirmed Walker-Warburg syndrome (WWS), studied with multimodal imaging, who presented with different retinal manifestations.

METHODS

This is a retrospective report of two WWS cases with ultra-widefield fundus photography, fluorescein angiography, and ultrasound. Molecular diagnosis was achieved using panel testing and targeted variant testing.

RESULTS

Two siblings, one male and one female, born 17 months apart with a diagnosis of WWS underwent retinal examination with imaging. The 3-month-old female infant exhibited microphthalmia, persistent hyaloidal arteries, and retrolental membranes with total tractional retinal detachments on ultrasound in both eyes. The 22-day-old male newborn exhibited persistent hyaloidal arteries and extensive peripheral avascular retina on angiography in both eyes. Both were found to be positive for the same two pathogenic variants in the RXYLT1/TMEM5 gene, which accounts for approximately 9% of cases of genetically confirmed WWS.

CONCLUSION

Siblings with genetically confirmed WWS can have variable presentations despite identical genotype. This highlights the phenotypic disease spectrum of WWS, which may be similar to that seen in familial exudative vitreoretinopathy.

Protein O-mannosylation: one sugar, several pathways, many functions

Recent research has unveiled numerous important functions of protein glycosylation in development, homeostasis, and diseases. A type of glycosylation taking the center stage is protein O-mannosylation, a posttranslational modification conserved in a wide range of organisms, from yeast to humans. In animals, protein O-mannosylation plays a crucial role in the nervous system, whereas protein O-mannosylation defects cause severe neurological abnormalities and congenital muscular dystrophies. However, the molecular and cellular mechanisms underlying protein O-mannosylation functions and biosynthesis remain not well understood. This review outlines recent studies on protein O-mannosylation while focusing on the functions in the nervous system, summarizes the current knowledge about protein O-mannosylation biosynthesis, and discusses the pathologies associated with protein O-mannosylation defects. The evolutionary perspective revealed by studies in the Drosophila model system are also highlighted. Finally, the review touches upon important knowledge gaps in the field and discusses critical questions for future research on the molecular and cellular mechanisms associated with protein O-mannosylation functions.

An adhesion signaling axis involving Dystroglycan, β1-Integrin, and Cas adaptor proteins regulates the establishment of the cortical glial scaffold

The mature mammalian cortex is composed of 6 architecturally and functionally distinct layers. Two key steps in the assembly of this layered structure are the initial establishment of the glial scaffold and the subsequent migration of postmitotic neurons to their final position. These processes involve the precise and timely regulation of adhesion and detachment of neural cells from their substrates. Although much is known about the roles of adhesive substrates during neuronal migration and the formation of the glial scaffold, less is understood about how these signals are interpreted and integrated within these neural cells. Here, we provide in vivo evidence that Cas proteins, a family of cytoplasmic adaptors, serve a functional and redundant role during cortical lamination. Cas triple conditional knock-out (Cas TcKO) mice display severe cortical phenotypes that feature cobblestone malformations. Molecular epistasis and genetic experiments suggest that Cas proteins act downstream of transmembrane Dystroglycan and β1-Integrin in a radial glial cell-autonomous manner. Overall, these data establish a new and essential role for Cas adaptor proteins during the formation of cortical circuits and reveal a signaling axis controlling cortical scaffold formation.

Classification of domains in predicted structures of the human proteome

Recent advances in protein structure prediction have generated accurate structures of previously uncharacterized human proteins. Identifying domains in these predicted structures and classifying them into an evolutionary hierarchy can reveal biological insights. Here, we describe the detection and classification of domains from the human proteome. Our classification indicates that only 62% of residues are located in globular domains. We further classify these globular domains and observe that the majority (65%) can be classified among known folds by sequence, with a smaller fraction (33%) requiring structural data to refine the domain boundaries and/or to support their homology. A relatively small number (966 domains) cannot be confidently assigned using our automatic pipelines, thus demanding manual inspection. We classify 47,576 domains, of which only 23% have been included in experimental structures. A portion (6.3%) of these classified globular domains lack sequence-based annotation in InterPro. A quarter (23%) have not been structurally modeled by homology, and they contain 2,540 known disease-causing single amino acid variations whose pathogenesis can now be inferred using AF models. A comparison of classified domains from a series of model organisms revealed expansions of several immune response-related domains in humans and a depletion of olfactory receptors. Finally, we use this classification to expand well-known protein families of biological significance. These classifications are presented on the ECOD website (http://prodata.swmed.edu/ecod/index_human.php).

A novel pathogenic deletion in ISPD causes Walker-Warburg syndrome in a Chinese family

BACKGROUND

Walker-Warburg syndrome (WWS) is a genetically heterogeneous disease that often presents with complex brain and eye malformations and congenital muscular dystrophy. Mutations of the ISPD gene have been identified as one of the most frequent causes of WWS.

OBJECTIVE

The current study aimed to identify the cause of severe congenital hydrocephalus and brain dysplasia in our subject.

METHODS

Genomic DNA was extracted from the fetus's umbilical cord blood and peripheral venous blood of the parents. The genetic analysis included whole-exome sequencing and qPCR. Additionally, in silico analysis and cellular experiments were performed.

RESULTS

We identified a novel homozygous deletion of exons 7 to 9 in the ISPD gene of the fetus with WWS. In silico analysis revealed a defective domain structure in the C-terminus domain of the ISPD. Analysis of the electrostatic potential energy showed the formation of a new binding pocket formation on the surface of the mutant ISPD gene (ISPD-del ex7-9). Cellular study of the mutant ISPD revealed a significant change in its cellular localization, with the ISPD-del ex7-9 protein translocating from the cytoplasm to the nucleus compared to wild-type ISPD, which is mostly present in the cytoplasm.

CONCLUSION

The present study expands the mutational spectrum of WWS caused by ISPD mutations. Importantly, our work suggests that whole-exome sequencing could be considered as a diagnostic option for fetuses with congenital hydrocephalus and brain malformations when karyotype or chromosomal microarray analysis fails to provide a definitive diagnosis.

Childhood muscular dystrophies

Infancy- and childhood-onset muscular dystrophies are associated with a characteristic distribution and progression of motor dysfunction. The underlying causes of progressive childhood muscular dystrophies are heterogeneous involving diverse genetic pathways and genes that encode proteins of the plasma membrane, extracellular matrix, sarcomere, and nuclear membrane components. The prototypical clinicopathological features in an affected child may be adequate to fully distinguish it from other likely diagnoses based on four common features: (1) weakness and wasting of pelvic-femoral and scapular muscles with involvement of heart muscle; (2) elevation of serum muscle enzymes in particular serum creatine kinase; (3) necrosis and regeneration of myofibers; and (4) molecular neurogenetic assessment particularly utilizing next-generation sequencing of the genome of the likeliest candidates genes in an index case or family proband. A number of different animal models of therapeutic strategies have been developed for gene transfer therapy, but so far these techniques have not yet entered clinical practice. Treatment remains for the most part symptomatic with the goal of ameliorating locomotor and cardiorespiratory manifestations of the disease.

A missense mutation in ISPD contributes to maintain muscle fiber stability

Background

Results

Conclusion

Seizures and EEG characteristics in a cohort of pediatric patients with dystroglycanopathies

PURPOSE

To delineate the seizure type, phenotype and V-EEG patterns of dystroglycanopathy (DGP) and correlate them with the neuroradiological and genetic results.

METHODS

Patients with seizures were screened from our dystroglycanopathy database from January 2010 to March 2021. Detailed clinical information, including seizure type, brain magnetic resonance imaging (MRI), EEG and genetic analysis, was collected.

RESULTS

Thirteen patients (15.1%, 13/86) had seizures. Most patients had a severe phenotype. The mean age at first seizure onset was 2 years and 8 months. The most common seizure type was generalized tonic-clonic seizure (GTCS), with 92.3% (12/13) induced by fever. Three patients were diagnosed with epilepsy. Most patients did not take any medicine. A few patients had irregular use of antiseizure medications (ASMs). Of the 13 patients, seven patients were diagnosed with MEB, four patients with POMGNT1 mutations, two with ISPD mutations, and one with POMT1 mutation. Three patients were diagnosed with FCMD with FKTN mutations. Two patients were diagnosed with CMD-MR, one patient with ISPD mutation, and one with POMT1 mutation. One patient was diagnosed with LGMD with FKRP mutation. Nine patients underwent EEG examination, and eight patients had abnormal EEG results, including abnormal background activities in three patients, abnormal background activities combined with paroxysmal discharges in three patients, pure paroxysmal discharges in one patient and positive phase sharp waves in the occipital region in one patient. For radiology, brain MRI was available for 12 patients. The brain MRI of nine patients showed type II lissencephaly. Two patients showed cerebellar hypoplasia and brainstem hypoplasia. One patient had a normal brain MRI result. Patients with type II lissencephaly usually had abnormal background activities and paroxysmal discharges.

CONCLUSION

The seizure phenotype of dystroglycanopathy (DGP) is characterized by GTCS, which was the most common seizure type, while focal seizures and epileptic spasms could also occur in DGP patients. Most seizures were induced by fever. Seizures were relatively more frequent in severe phenotypes of DGP, such as FCMD and MEB. Abnormal background activities were the most common EEG patterns, which were closely related to type II lissencephaly.

Whole-genome sequencing reveals de-novo mutations associated with nonsyndromic cleft lip/palate

The majority (85%) of nonsyndromic cleft lip with or without cleft palate (nsCL/P) cases occur sporadically, suggesting a role for de novo mutations (DNMs) in the etiology of nsCL/P. To identify high impact protein-altering DNMs that contribute to the risk of nsCL/P, we conducted whole-genome sequencing (WGS) analyses in 130 African case-parent trios (affected probands and unaffected parents). We identified 162 high confidence protein-altering DNMs some of which are based on available evidence, contribute to the risk of nsCL/P. These include novel protein-truncating DNMs in the ACTL6A, ARHGAP10, MINK1, TMEM5 and TTN genes; as well as missense variants in ACAN, DHRS3, DLX6, EPHB2, FKBP10, KMT2D, RECQL4, SEMA3C, SEMA4D, SHH, TP63, and TULP4. Many of these protein-altering DNMs were predicted to be pathogenic. Analysis using mouse transcriptomics data showed that some of these genes are expressed during the development of primary and secondary palate. Gene-set enrichment analysis of the protein-altering DNMs identified palatal development and neural crest migration among the few processes that were significantly enriched. These processes are directly involved in the etiopathogenesis of clefting. The analysis of the coding sequence in the WGS data provides more evidence of the opportunity for novel findings in the African genome.

Fetal phenotypes of Mendelian disorders: A descriptive study from India

OBJECTIVE

Exome sequencing(ES) based diagnosis of Mendelian diseases in the fetus is limited by paucity of phenotypic information. This study reports the comprehensive phenotypes of some fetuses with Mendelian disorders.

METHODS

Next generation technology based sequencing of all coding regions of the genome(Exome sequencing) or targeted gene sequencing using Sanger or next generation platforms was performed in a cohort of deeply phenotyped, cytogenetically normal fetuses with morphological defects. Prenatal ultrasonographic phenotypes and Postmortem details including dysmorphology, histopathology, radiography were ascertained. Novel candidate genes, novel/ unusual findings and unusual genotypes in cases with confirmed Mendelian disorders are described.

RESULTS

Of the 102 fetuses sequenced, 45 (44%) achieved definitive diagnosis of a Mendelian disorder with 50 pathogenic/likely pathogenic variants. The majority (87%) were autosomal recessive, 69% families were consanguineous and 54% variants were novel. Dysmorphic syndromes, skeletal dysplasias and metabolic disorders were the commonest disease categories, ciliopathies and dystroglycanopathies commonest molecular categories. We describe the first fetal description of six monogenic diseases, and nine cases with novel histological findings. Nineteen cases had novel/ unusual findings.

CONCLUSION

This cohort demonstrates how deep fetal phenotypes of some Mendelian disorders can show novel/unusual findings which have important implications for prenatal diagnosis of these conditions. This article is protected by copyright. All rights reserved.

CDP-ribitol prodrug treatment ameliorates ISPD-deficient muscular dystrophy mouse model

Ribitol-phosphate modification is crucial for the functional maturation of α-dystroglycan. Its dysfunction is associated with muscular dystrophy, cardiomyopathy, and central nervous system abnormalities; however, no effective treatments are currently available for diseases caused by ribitol-phosphate defects. In this study, we demonstrate that prodrug treatments can ameliorate muscular dystrophy caused by defects in isoprenoid synthase domain containing (ISPD), which encodes an enzyme that synthesizes CDP-ribitol, a donor substrate for ribitol-phosphate modification. We generated skeletal muscle-selective Ispd conditional knockout mice, leading to a pathogenic reduction in CDP-ribitol levels, abnormal glycosylation of α-dystroglycan, and severe muscular dystrophy. Adeno-associated virus-mediated gene replacement experiments suggested that the recovery of CDP-ribitol levels rescues the ISPD-deficient pathology. As a prodrug treatment strategy, we developed a series of membrane-permeable CDP-ribitol derivatives, among which tetraacetylated CDP-ribitol ameliorated the dystrophic pathology. In addition, the prodrug successfully rescued abnormal α-dystroglycan glycosylation in patient fibroblasts. Consequently, our findings provide proof-of-concept for supplementation therapy with CDP-ribitol and could accelerate the development of therapeutic agents for muscular dystrophy and other diseases caused by glycosylation defects.

Malformations of cerebral development and clues from the peripheral nervous system: A systematic literature review

Clinical manifestations of malformations of cortical development (MCD) are variable and can range from mild to severe intellectual disability, cerebral palsy and drug-resistant epilepsy. Besides common clinical features, non-specific or more subtle clinical symptoms may be present in association with different types of MCD. Especially in severely affected individuals, subtle but specific underlying clinical symptoms can be overlooked or overshadowed by the global clinical presentation. To facilitate the interpretation of genetic variants detailed clinical information is indispensable. Detailed (neurological) examination can be helpful in assisting with the diagnostic trajectory, both when referring for genetic work-up as well as when interpreting data from molecular genetic testing. This systematic literature review focusses on different clues derived from the neurological examination and potential further work-up triggered by these signs and symptoms in genetically defined MCDs. A concise overview of specific neurological findings and their associations with MCD subtype and genotype are presented, easily applicable in daily clinical practice. The following pathologies will be discussed: neuropathy, myopathy, muscular dystrophies and spastic paraplegia. In the discussion section, tips and pitfalls are illustrated to improve clinical outcome in the future.

Protein O-mannosylation across kingdoms and related diseases: From glycobiology to glycopathology

The post-translational glycosylation of proteins by O-linked α-mannose is conserved from bacteria to humans. Due to advances in high-throughput mass spectrometry-based approaches, a variety of glycoproteins are identified to be O-mannosylated. Various proteins with O-mannosylation are involved in biological processes, providing essential necessity for proper growth and development. In this review, we summarize the process and regulation of O-mannosylation. The multi-step O-mannosylation procedures are quite dynamic and complex, especially when considering the structural and functional inspection of the involved enzymes. The widely studied O-mannosylated proteins in human include α-Dystroglycan (α-DG), cadherins, protocadherins, and plexin, and their aberrant O-mannosylation are associated with many diseases. In addition, O-mannosylation also contributes to diverse functions in lower eukaryotes and prokaryotes. Finally, we present the relationship between O-mannosylation and gut microbiota (GM), and elucidate that O-mannosylation in microbiome is of great importance in the dynamic balance of GM. Our study provides an overview of the processes of O-mannosylation in mammalian cells and other organisms, and also associated regulated enzymes and biological functions, which could contribute to the understanding of newly discovered O-mannosylated glycoproteins.

Roots of the Malformations of Cortical Development in the Cell Biology of Neural Progenitor Cells

The cerebral cortex is a structure that underlies various brain functions, including cognition and language. Mammalian cerebral cortex starts developing during the embryonic period with the neural progenitor cells generating neurons. Newborn neurons migrate along progenitors’ radial processes from the site of their origin in the germinal zones to the cortical plate, where they mature and integrate in the forming circuitry. Cell biological features of neural progenitors, such as the location and timing of their mitoses, together with their characteristic morphologies, can directly or indirectly regulate the abundance and the identity of their neuronal progeny. Alterations in the complex and delicate process of cerebral cortex development can lead to malformations of cortical development (MCDs). They include various structural abnormalities that affect the size, thickness and/or folding pattern of the developing cortex. Their clinical manifestations can entail a neurodevelopmental disorder, such as epilepsy, developmental delay, intellectual disability, or autism spectrum disorder. The recent advancements of molecular and neuroimaging techniques, along with the development of appropriate in vitro and in vivo model systems, have enabled the assessment of the genetic and environmental causes of MCDs. Here we broadly review the cell biological characteristics of neural progenitor cells and focus on those features whose perturbations have been linked to MCDs.

Roles, molecular mechanisms, and signaling pathways of TMEMs in neurological diseases

Transmembrane protein family members (TMEMs) span the entire lipid bilayer and act as channels that allow the transport of specific substances through biofilms. The functions of most TMEMs are unexplored. Numerous studies have shown that TMEMs are involved in the pathophysiological processes of various nervous system diseases, but the specific mechanisms of TMEMs in the pathogenesis of diseases remain unclear. In this review, we discuss the expression, physiological functions, and molecular mechanisms of TMEMs in brain tumors, psychiatric disorders, abnormal motor activity, cobblestone lissencephaly, neuropathic pain, traumatic brain injury, and other disorders of the nervous system. Additionally, we propose that TMEMs may be used as prognostic markers and potential therapeutic targets in patients with various neurological diseases.

An Early Diagnostic Clue for COL18A1- and LAMA1-Associated Diseases: High Myopia With Alopecia Areata in the Cranial Midline

Background

High myopia with alopecia areata in the occipital region has been observed in patients with Knobloch syndrome caused by COL18A1 mutations. This study investigated other possible genetic causes of high myopia in patients with alopecia areata in the cranial midline.

Methods

Six patients with early onset high myopia and alopecia areata in the cranial midline were recruited. Targeted high-throughput sequencing was performed on the proband’s DNA to detect potential pathogenic variants. Cosegregation analysis was performed for available family members. Minigene assay and RNA Sequencing were used to validate the abnormality of possible splicing change and gross deletion. Ophthalmological and neuroimaging examinations were performed.

Results

Eight novel and one known loss-of-function mutants were detected in all six patients, including a gross deletion detected by RNA sequencing. Four COL18A1 mutants in three patients with scalp leisure in the occipital region; and five LAMA1 mutations in three patients with scalp leisure in the parietal region. Further assessments indicated that patients with COL18A1 mutations had Knobloch syndrome, and the patients with LAMA1 mutations had Poretti–Boltshauser syndrome.

Conclusion

Our study found that early onset high myopia with midline alopecia areata could be caused not only by mutations of the COL18A1 gene but also by mutations in the LAMA1 gene. To our knowledge, we are the first to observe scalp defects in patients with LAMA1 mutations. High myopia with alopecia areata in the cranial midline could be treated as an early diagnostic clue for ophthalmologists to consider the two kinds of rare diseases.

Neuroimaging manifestations and genetic heterogeneity of Walker-Warburg syndrome in Saudi patients

BACKGROUND

Walker-Warburg syndrome (WWS), an autosomal recessive disease, is the most severe phenotype of congenital muscular dystrophies. Its diagnosis remains primarily clinical and radiological. Identification of its causative variants will assist genetic counseling. We aim to describe genetic and neuroimaging findings of WWS and investigate the correlation between them.

METHODS

We retrospectively reviewed the clinical, genetic and neuroimaging findings of eleven Saudi neonates diagnosed with WWS between April 2012 and December 2018 in a single tertiary care center. Correlation between neuroimaging and genetic findings was investigated.

RESULTS

All patients had macrocephaly except one who had intrauterine growth restriction. Dysmorphic features were identified in nearly half of the patients. Creatine kinase levels were available in nine patients and were always elevated. Homozygous pathogenic variants were identified in all patients spanning POMT1 (n = 5), TMEM5 (n = 3), ISPD (n = 2) and POMT2 (n = 1) including one patient who had a dual molecular diagnosis of ISPD and PGAP2. On neuroimaging, all patients showed cobblestone cortex, classical infratentorial findings, and hydrocephalus. Other cerebral cortical malformations included subependymal heterotopia, polymicrogyria and open-lip schizencephaly in four, two and one patients, respectively. Buphthalmos and microphthalmia were the most prevalent orbital findings and found in all patients either unilaterally or bilaterally.

CONCLUSION

WWS is a genetically heterogeneous disorder among Saudis. The case with an additional PGAP2-related phenotype exemplifies the increased risk of dual autosomal recessive disorders in consanguineous populations. MRI is excellent in demonstrating spectrum of WWS brain and orbital malformations; however, no definite correlation could be found between the MRI findings and the genetic variant.

Neuropathology of genetically defined malformations of cortical development-A systematic literature review

AIMS

Malformations of cortical development (MCD) include a heterogeneous spectrum of clinical, imaging, molecular and histopathological entities. While the understanding of genetic causes of MCD has improved with the availability of next-generation sequencing modalities, genotype-histopathological correlations remain limited. This is the first systematic review of molecular and neuropathological findings in patients with MCD to provide a comprehensive overview of the literature.

METHODS

A systematic review was performed between November 2019 and February 2020. A MEDLINE search was conducted for 132 genes previously linked to MCD in order to identify studies reporting macroscopic and/or microscopic findings in patients with a confirmed genetic cause.

RESULTS

Eighty-one studies were included in this review reporting neuropathological features associated with pathogenic variants in 46 genes (46/132 genes, 34.8%). Four groups emerged, consisting of (1) 13 genes with well-defined histological-genotype correlations, (2) 27 genes for which neuropathological reports were limited, (3) 5 genes with conflicting neuropathological features, and (4) 87 genes for which no histological data were available. Lissencephaly and polymicrogyria were reported most frequently. Associated brain malformations were variably present, with abnormalities of the corpus callosum as most common associated feature.

CONCLUSIONS

Neuropathological data in patients with MCD with a defined genetic cause are available only for a small number of genes. As each genetic cause might lead to unique histopathological features of MCD, standardised thorough neuropathological assessment and reporting should be encouraged. Histological features can help improve the understanding of the pathogenesis of MCD and generate hypotheses with impact on further research directions.

Case Report: ISPD Gene Mutation Leads to Dystroglycanopathies: Genotypic Phenotype Analysis and Treatment Exploration

ISPD gene mutation-related diseases have high clinical and genetic heterogeneity, and no studies have yet reported any effective treatments. We describe six patients with dystroglycanopathies caused by ISPD gene mutations and analyze their genotypes and phenotypes to explore possible effective treatments. Our results confirm that the phenotype of limb-girdle muscular dystrophies can be easily misdiagnosed as Duchenne muscular dystrophy and that exon deletions of ISPD gene are relatively common. Moreover, low-dose prednisone therapy can improve patients' exercise ability and prolong survival and may be a promising new avenue for ISPD therapy.

Genetic cause of heterogeneous inherited myopathies in a cohort of Greek patients

Inherited muscle disorders are caused by pathogenic changes in numerous genes. Herein, we aimed to investigate the etiology of muscle disease in 24 consecutive Greek patients with myopathy suspected to be genetic in origin, based on clinical presentation and laboratory and electrophysiological findings and absence of known acquired causes of myopathy. Of these, 16 patients (8 females, median 24 years-old, range 7 to 67 years-old) were diagnosed by Whole Exome Sequencing as suffering from a specific type of inherited muscle disorder. Specifically, we have identified causative variants in 6 limb-girdle muscular dystrophy genes (6 patients; ANO5, CAPN3, DYSF, ISPD, LAMA2, SGCA), 3 metabolic myopathy genes (4 patients; CPT2, ETFDH, GAA), 1 congenital myotonia gene (1 patient; CLCN1), 1 mitochondrial myopathy gene (1 patient; MT-TE) and 3 other myopathy-associated genes (4 patients; CAV3, LMNA, MYOT). In 6 additional family members affected by myopathy, we reached genetic diagnosis following identification of a causative variant in an index patient. In our patients, genetic diagnosis ended a lengthy diagnostic process and, in the case of Multiple acyl-CoA dehydrogenase deficiency and Pompe's disease, it enabled specific treatment to be initiated. These results further expand the genotypic and phenotypic spectrum of inherited myopathies.

Extracellular Control of Radial Glia Proliferation and Scaffolding During Cortical Development and Pathology

During the development of the cortex, newly generated neurons migrate long-distances in the expanding tissue to reach their final positions. Pyramidal neurons are produced from dorsal progenitors, e.g., radial glia (RGs) in the ventricular zone, and then migrate along RG processes basally toward the cortex. These neurons are hence dependent upon RG extensions to support their migration from apical to basal regions. Several studies have investigated how intracellular determinants are required for RG polarity and subsequent formation and maintenance of their processes. Fewer studies have identified the influence of the extracellular environment on this architecture. This review will focus on extracellular factors which influence RG morphology and pyramidal neuronal migration during normal development and their perturbations in pathology. During cortical development, RGs are present in different strategic positions: apical RGs (aRGs) have their cell bodies located in the ventricular zone with an apical process contacting the ventricle, while they also have a basal process extending radially to reach the pial surface of the cortex. This particular conformation allows aRGs to be exposed to long range and short range signaling cues, whereas basal RGs (bRGs, also known as outer RGs, oRGs) have their cell bodies located throughout the cortical wall, limiting their access to ventricular factors. Long range signals impacting aRGs include secreted molecules present in the embryonic cerebrospinal fluid (e.g., Neuregulin, EGF, FGF, Wnt, BMP). Secreted molecules also contribute to the extracellular matrix (fibronectin, laminin, reelin). Classical short range factors include cell to cell signaling, adhesion molecules and mechano-transduction mechanisms (e.g., TAG1, Notch, cadherins, mechanical tension). Changes in one or several of these components influencing the RG extracellular environment can disrupt the development or maintenance of RG architecture on which neuronal migration relies, leading to a range of cortical malformations. First, we will detail the known long range signaling cues impacting RG. Then, we will review how short range cell contacts are also important to instruct the RG framework. Understanding how RG processes are structured by their environment to maintain and support radial migration is a critical part of the investigation of neurodevelopmental disorders.

Fetal Anomalies Associated with Novel Pathogenic Variants in TMEM94

Background: Intellectual developmental disorder with cardiac defects and dysmorphic facies (IDDCDF, MIM 618316) is a newly described disorder. It is characterized by global developmental delay, intellectual disability and speech delay, congenital cardiac malformations, and dysmorphic facial features. Biallelic pathogenic variants of TMEM94 are associated with IDDCDF. Methods and Results: In a prenatal setting, where fetal abnormalities were detected using antenatal sonography, we used trio-exome sequencing (trio-ES) in conjunction with chromosomal microarray analysis (CMA) to identify two novel homozygous loss of function variants in the TMEM94 gene (c.606dupG and c.2729-2A>G) in two unrelated Saudi Arabian families. Conclusions: This study provides confirmation that TMEM94 variants may cause IDDCDF. For the first time we describe the pathogenicity of TMEM94 defects detected during the prenatal period.

COG6-CDG: Expanding the phenotype with emphasis on glycosylation defects involved in the causation of male disorders of sex development

COG6-congenital disorder of glycosylation (COG6-CDG) is caused by biallelic mutations in COG6. To-date, 12 variants causing COG6-CDG in less than 20 patients have been reported. Using whole exome sequencing we identified two siblings with a novel homozygous deletion of 26 bp in COG6, creating a splicing variant (c.518_540 + 3del) and a shift in the reading frame. The phenotype of COG6-CDG includes growth and developmental retardation, microcephaly, liver and gastrointestinal disease, hypohydrosis and recurrent infections. We report two patients with novel phenotypic features including bowel malrotation and ambiguous genitalia, directing attention to the role of glycoprotein metabolism in the causation of disorders of sex development (DSD). Searching the glycomic literature, we identified 14 CDGs including males with DSD, a feature not previously accentuated. This study broadens the genetic and phenotypic spectrum of COG6-CDG and calls for increasing awareness to the central role of glycosylation processes in development of human sex and genitalia.

Profiling of the muscle-specific dystroglycan interactome reveals the role of Hippo signaling in muscular dystrophy and age-dependent muscle atrophy

BACKGROUND

Dystroglycanopathies are a group of inherited disorders characterized by vast clinical and genetic heterogeneity and caused by abnormal functioning of the ECM receptor dystroglycan (Dg). Remarkably, among many cases of diagnosed dystroglycanopathies, only a small fraction can be linked directly to mutations in Dg or its regulatory enzymes, implying the involvement of other, not-yet-characterized, Dg-regulating factors. To advance disease diagnostics and develop new treatment strategies, new approaches to find dystroglycanopathy-related factors should be considered. The Dg complex is highly evolutionarily conserved; therefore, model genetic organisms provide excellent systems to address this challenge. In particular, Drosophila is amenable to experiments not feasible in any other system, allowing original insights about the functional interactors of the Dg complex.

METHODS

To identify new players contributing to dystroglycanopathies, we used Drosophila as a genetic muscular dystrophy model. Using mass spectrometry, we searched for muscle-specific Dg interactors. Next, in silico analyses allowed us to determine their association with diseases and pathological conditions in humans. Using immunohistochemical, biochemical, and genetic interaction approaches followed by the detailed analysis of the muscle tissue architecture, we verified Dg interaction with some of the discovered factors. Analyses of mouse muscles and myocytes were used to test if interactions are conserved in vertebrates.

RESULTS

The muscle-specific Dg complexome revealed novel components that influence the efficiency of Dg function in the muscles. We identified the closest human homologs for Dg-interacting partners, determined their significant enrichment in disease-associations, and verified some of the newly identified Dg interactions. We found that Dg associates with two components of the mechanosignaling Hippo pathway: the WW domain-containing proteins Kibra and Yorkie. Importantly, this conserved interaction manages adult muscle size and integrity.

CONCLUSIONS

The results presented in this study provide a new list of muscle-specific Dg interactors, further analysis of which could aid not only in the diagnosis of muscular dystrophies, but also in the development of new therapeutics. To regulate muscle fitness during aging and disease, Dg associates with Kibra and Yorkie and acts as a transmembrane Hippo signaling receptor that transmits extracellular information to intracellular signaling cascades, regulating muscle gene expression.

A new patient-derived iPSC model for dystroglycanopathies validates a compound that increases glycosylation of α-dystroglycan

Dystroglycan, an extracellular matrix receptor, has essential functions in various tissues. Loss of α-dystroglycan-laminin interaction due to defective glycosylation of α-dystroglycan underlies a group of congenital muscular dystrophies often associated with brain malformations, referred to as dystroglycanopathies. The lack of isogenic human dystroglycanopathy cell models has limited our ability to test potential drugs in a human- and neural-specific context. Here, we generated induced pluripotent stem cells (iPSCs) from a severe dystroglycanopathy patient with homozygous FKRP (fukutin-related protein gene) mutation. We showed that CRISPR/Cas9-mediated gene correction of FKRP restored glycosylation of α-dystroglycan in iPSC-derived cortical neurons, whereas targeted gene mutation of FKRP in wild-type cells disrupted this glycosylation. In parallel, we screened 31,954 small molecule compounds using a mouse myoblast line for increased glycosylation of α-dystroglycan. Using human FKRP-iPSC-derived neural cells for hit validation, we demonstrated that compound 4-(4-bromophenyl)-6-ethylsulfanyl-2-oxo-3,4-dihydro-1H-pyridine-5-carbonitrile (4BPPNit) significantly augmented glycosylation of α-dystroglycan, in part through upregulation of LARGE1 glycosyltransferase gene expression. Together, isogenic human iPSC-derived cells represent a valuable platform for facilitating dystroglycanopathy drug discovery and therapeutic development.

Clinical long-time course, novel mutations and genotype-phenotype correlation in a cohort of 27 families with POMT1-related disorders

Background

The protein O-mannosyltransferase 1, encoded by the POMT1 gene, is a key enzyme in the glycosylation of α-dystroglycan. POMT1–related disorders belong to the group of dystroglycanopathies characterized by a proximally pronounced muscular dystrophy with structural or functional involvement of the brain and/or the eyes. The phenotypic spectrum ranges from the severe Walker-Warburg syndrome (WWS) to milder forms of limb girdle muscular dystrophy (LGMD). The phenotypic severity of POMT1-related dystroglycanopathies depends on the residual enzyme activity. A genotype-phenotype correlation can be assumed.

Results

The clinical, neuroradiological, and genetic findings of 35 patients with biallelic POMT1 mutations (15 WWS, 1 MEB (muscle-eye-brain disease), 19 LGMD) from 27 independent families are reported. The representative clinical course of an infant with WWS and the long-term course of a 32 years old patient with LGMD are described in more detail. Specific features of 15 patients with the homozygous founder mutation p.Ala200Pro are defined as a distinct and mildly affected LGMD subgroup. Ten previously reported and 8 novel POMT1 mutations were identified. Type and location of each of the POMT1 mutations are evaluated in detail and a list of all POMT1 mutations reported by now is provided. Patients with two mutations leading to premature protein termination had a WWS phenotype, while the presence of at least one missense mutation was associated with milder phenotypes. In the patient with MEB-like phenotype two missense mutations were observed within the catalytic active domain of the enzyme.

Conclusions

Our large cohort confirms the importance of type and location of each POMT1 mutation for the individual clinical manifestation and thereby expands the knowledge on the genotype-phenotype correlation in POMT1-related dystroglycanopathies. This genotype-phenotype correlation is further supported by the observation of an intrafamiliar analogous clinical manifestation observed in all affected 13 siblings from 5 independent families. Our data confirm the progressive nature of the disease also in milder LGMD phenotypes, ultimately resulting in loss of ambulation at a variable age. Our data define two major clinical POMT1 phenotypes, which should prompt genetic testing including the POMT1 gene: patients with a severe WWS manifestation predominantly present with profound neonatal muscular hypotonia and a severe and progressive hydrocephalus with involvement of brainstem and/or cerebellum. The presence of an occipital encephalocele in a WWS patient might point to POMT1 as causative gene within the different genes associated with WWS. The milder LGMD phenotypes constantly show markedly elevated creatine kinase values in combination with microcephaly and cognitive impairment.

Electronic supplementary material

The online version of this article (10.1186/s13023-019-1119-0) contains supplementary material, which is available to authorized users.

Muscular Dystrophy with Ribitol-Phosphate Deficiency: A Novel Post-Translational Mechanism in Dystroglycanopathy

Muscular dystrophy is a group of genetic disorders characterized by progressive muscle weakness. In the early 2000s, a new classification of muscular dystrophy, dystroglycanopathy, was established. Dystroglycanopathy often associates with abnormalities in the central nervous system. Currently, at least eighteen genes have been identified that are responsible for dystroglycanopathy, and despite its genetic heterogeneity, its common biochemical feature is abnormal glycosylation of alpha-dystroglycan. Abnormal glycosylation of alpha-dystroglycan reduces its binding activities to ligand proteins, including laminins. In just the last few years, remarkable progress has been made in determining the sugar chain structures and gene functions associated with dystroglycanopathy. The normal sugar chain contains tandem structures of ribitol-phosphate, a pentose alcohol that was previously unknown in humans. The dystroglycanopathy genes fukutin, fukutin-related protein (FKRP), and isoprenoid synthase domain-containing protein (ISPD) encode essential enzymes for the synthesis of this structure: fukutin and FKRP transfer ribitol-phosphate onto sugar chains of alpha-dystroglycan, and ISPD synthesizes CDP-ribitol, a donor substrate for fukutin and FKRP. These findings resolved long-standing questions and established a disease subgroup that is ribitol-phosphate deficient, which describes a large population of dystroglycanopathy patients. Here, we review the history of dystroglycanopathy, the properties of the sugar chain structure of alpha-dystroglycan, dystroglycanopathy gene functions, and therapeutic strategies.

O-glycosylation disorders pave the road for understanding the complex human O-glycosylation machinery

Over 100 human Congenital Disorders of Glycosylation (CDG) have been described. Of these, about 30% reside in the O-glycosylation pathway. O-glycosylation disorders are characterized by a high phenotypic variability, reflecting the large diversity of O-glycan structures. In contrast to N-glycosylation disorders, a generic biochemical screening test is lacking, which limits the identification of novel O-glycosylation disorders. The emergence of next generation sequencing (NGS) and O-glycoproteomics technologies have changed this situation, resulting in significant progress to link disease phenotypes with underlying biochemical mechanisms. Here, we review the current knowledge on O-glycosylation disorders, and discuss the biochemical lessons that we can learn on 1) novel glycosyltransferases and metabolic pathways, 2) tissue-specific O-glycosylation mechanisms, 3) O-glycosylation targets and 4) structure-function relationships. Additionally, we provide an outlook on how genetic disorders, O-glycoproteomics and biochemical methods can be combined to answer fundamental questions regarding O-glycan synthesis, structure and function.

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.

Developmental biology of the meninges

The meninges are membranous layers surrounding the central nervous system. In the head, the meninges lie between the brain and the skull, and interact closely with both during development. The cranial meninges originate from a mesenchymal sheath on the surface of the developing brain, called primary meninx, and undergo differentiation into three layers with distinct histological characteristics: the dura mater, the arachnoid mater, and the pia mater. While genetic regulation of meningeal development is still poorly understood, mouse mutants and other models with meningeal defects have demonstrated the importance of the meninges to normal development of the calvaria and the brain. For the calvaria, the interactions with the meninges are necessary for the progression of calvarial osteogenesis during early development. In later stages, the meninges control the patterning of the skull and the fate of the sutures. For the brain, the meninges regulate diverse processes including cell survival, cell migration, generation of neurons from progenitors, and vascularization. Also, the meninges serve as a stem cell niche for the brain in the postnatal life. Given these important roles of the meninges, further investigation into the molecular mechanisms underlying meningeal development can provide novel insights into the coordinated development of the head.

Malformations of Cerebral Cortex Development: Molecules and Mechanisms

Malformations of cortical development encompass heterogeneous groups of structural brain anomalies associated with complex neurodevelopmental disorders and diverse genetic and nongenetic etiologies. Recent progress in understanding the genetic basis of brain malformations has been driven by extraordinary advances in DNA sequencing technologies. For example, somatic mosaic mutations that activate mammalian target of rapamycin signaling in cortical progenitor cells during development are now recognized as the cause of hemimegalencephaly and some types of focal cortical dysplasia. In addition, research on brain development has begun to reveal the cellular and molecular bases of cortical gyrification and axon pathway formation, providing better understanding of disorders involving these processes. New neuroimaging techniques with improved resolution have enhanced our ability to characterize subtle malformations, such as those associated with intellectual disability and autism. In this review, we broadly discuss cortical malformations and focus on several for which genetic etiologies have elucidated pathogenesis.

Keeping an eye on congenital disorders of O-glycosylation: A systematic literature review

Congenital disorders of glycosylation (CDG) are a rapidly growing family comprising >100 genetic diseases. Some 25 CDG are pure O-glycosylation defects. Even among this CDG subgroup, phenotypic diversity is broad, ranging from mild to severe poly-organ/system dysfunction. Ophthalmic manifestations are present in 60% of these CDG. The ophthalmic manifestations in N-glycosylation-deficient patients have been described elsewhere. The present review documents the spectrum and incidence of eye disorders in patients with pure O-glycosylation defects with the aim of assisting diagnosis and management and promoting research.

The roles of dystroglycan in the nervous system: insights from animal models of muscular dystrophy

Dystroglycan is a cell membrane protein that binds to the extracellular matrix in a variety of mammalian tissues. The α-subunit of dystroglycan (αDG) is heavily glycosylated, including a special O-mannosyl glycoepitope, relying upon this unique glycosylation to bind its matrix ligands. A distinct group of muscular dystrophies results from specific hypoglycosylation of αDG, and they are frequently associated with central nervous system involvement, ranging from profound brain malformation to intellectual disability without evident morphological defects. There is an expanding literature addressing the function of αDG in the nervous system, with recent reports demonstrating important roles in brain development and in the maintenance of neuronal synapses. Much of these data are derived from an increasingly rich array of experimental animal models. This Review aims to synthesize the information from such diverse models, formulating an up-to-date understanding about the various functions of αDG in neurons and glia of the central and peripheral nervous systems. Where possible, we integrate these data with our knowledge of the human disorders to promote translation from basic mechanistic findings to clinical therapies that take the neural phenotypes into account.

Summary: Dystroglycan is a ubiquitous matrix receptor linked to brain and muscle disease. Unraveling the functions of this protein will inform basic and translational research on neural development and muscular dystrophies.

Modeling methylation data as an additional genetic variance component

High-throughput platforms allow the characterization of thousands of previously known methylation sites. These platforms have great potential for investigating the epigenetic effects that are partially responsible for gene expression control. Methylation sites provide a bridge for the investigation of real-time environmental contributions on genomic events by the alteration of methylation status of those sites. Using the data provided by GAW20's organization committee, we calculated the heritability estimates of each cytosine-phosphate-guanine (CpG) island before and after the use of fenofibrate, a lipid-control drug. Surprisingly, we detected substantially high heritability estimates before drug usage. This somewhat unexpected high sample correlation was corrected by the use of principal components and the distributions of heritability estimates before and after fenofibrate treatment, which made the distributions comparable. The methylation sites located near a gene were collected and a genetic relationship matrix estimated to represent the overall correlation between samples. We implemented a random-effect association test to screen genes whose methylation patterns partially explain the observable high-density lipoprotein (HDL) heritability. Our leading association was observed for the TMEM52 gene that encodes a transmembrane protein, and is largely expressed in the liver, had not been previously associated with HDL until this manuscript. Using a variance component decomposition framework with the linear mixed model allows the integration of data from different sources, such as methylation, gene expression, metabolomics, and proteomics. The decomposition of the genetic variance component decomposition provides a flexible analytical approach for the challenges of this new omics era.

A new case expanding the mutation and phenotype spectrum of TMEM5-related alpha-dystroglycanopathy

Dystroglycanopathies are a diverse group of neuromuscular disorders caused by aberrant glycosylation of alpha-dystroglycan. TMEM5 is one of many glycosyltransferases recently described to be associated with alpha-dystroglycanopathies. We report the case of a 15-year-old boy suffering from a congenital muscular dystrophy with elevated serum creatine kinase levels and an almost complete absence of alpha-dystroglycan in muscle biopsy. The clinical course was milder than any previously reported case and did not include brain or eye defects. Standard next-generation sequencing analysis revealed a homozygous mutation in the donor splice site region of exon 5 in TMEM5 (c.914+6 T>G). Available in-silico prediction tools anticipated a reduced efficiency of the splice site. Subsequent cDNA sequencing confirmed the expression of a truncated transcript of TMEM5 lacking exon 5, hence leading to an in-frame deletion in the exostosin domain of the protein. This report expands the clinical and mutation spectrum of alpha-dystroglycanopathies.

Perspectives on Glycosylation and Its Congenital Disorders

Congenital disorders of glycosylation (CDG) are a rapidly expanding group of metabolic disorders that result from abnormal protein or lipid glycosylation. They are often difficult to clinically diagnose because they broadly affect many organs and functions and lack clinical uniformity. However, recent technological advances in next-generation sequencing have revealed a treasure trove of new genetic disorders, expanded the knowledge of known disorders, and showed a critical role in infectious diseases. More comprehensive genetic tools specifically tailored for mammalian cell-based models have revealed a critical role for glycosylation in pathogen-host interactions, while also identifying new CDG susceptibility genes. We highlight recent advancements that have resulted in a better understanding of human glycosylation disorders, perspectives for potential future therapies, and mysteries for which we continue to seek new insights and solutions.

Cell endogenous activities of fukutin and FKRP coexist with the ribitol xylosyltransferase, TMEM5

Dystroglycanopathies are a group of muscular dystrophies that are caused by abnormal glycosylation of dystroglycan; currently 18 causative genes are known. Functions of the dystroglycanopathy genes fukutin, fukutin-related protein (FKRP), and transmembrane protein 5 (TMEM5) were most recently identified; fukutin and FKRP are ribitol-phosphate transferases and TMEM5 is a ribitol xylosyltransferase. In this study, we show that fukutin, FKRP, and TMEM5 form a complex while maintaining each of their enzyme activities. Immunoprecipitation and immunofluorescence experiments demonstrated protein interactions between these 3 proteins. A protein complex consisting of endogenous fukutin and FKRP, and exogenously expressed TMEM5 exerts activities of each enzyme. Our data showed for the first time that endogenous fukutin and FKRP enzyme activities coexist with TMEM5 enzyme activity, and suggest the possibility that formation of this enzyme complex may contribute to specific and prompt biosynthesis of glycans that are required for dystroglycan function.

Distinct expression of functionally glycosylated alpha-dystroglycan in muscle and non-muscle tissues of FKRP mutant mice

The glycosylation of alpha-dystroglycan (α-DG) is crucial in maintaining muscle cell membrane integrity. Dystroglycanopathies are identified by the loss of this glycosylation leading to a breakdown of muscle cell membrane integrity and eventual degeneration. However, a small portion of fibers expressing functionally glycosylated α-DG (F-α-DG) (revertant fibers, RF) have been identified. These fibers are generally small in size, centrally nucleated and linked to regenerating fibers. Examination of different muscles have shown various levels of RFs but it is unclear the extent of which they are present. Here we do a body-wide examination of muscles from the FKRP-P448L mutant mouse for the prevalence of RFs. We have identified great variation in the distribution of RF in different muscles and tissues. Triceps shows a large increase in RFs and together with centrally nucleated fibers whereas the pectoralis shows a reduction in revertant but increase in centrally nucleated fibers from 6 weeks to 6 months of age. We have also identified that the sciatic nerve with near normal levels of F-α-DG in the P448Lneo- mouse with reduced levels in the P448Lneo+ and absent in LARGE^myd. The salivary gland of LARGE^myd mice expresses high levels of F-α-DG. Interestingly the same glands in the P448Lneo-and to a lesser degree in P448Lneo+ also maintain considerable amount of F-α-DG, indicating the non-proliferating epithelial cells have a molecular setting permitting glycosylation.

Insight into the molecular genetics of myopia

Myopia is the most common cause of visual impairment worldwide. Genetic and environmental factors contribute to the development of myopia. Studies on the molecular genetics of myopia are well established and have implicated the important role of genetic factors. With linkage analysis, association studies, sequencing analysis, and experimental myopia studies, many of the loci and genes associated with myopia have been identified. Thus far, there has been no systemic review of the loci and genes related to non-syndromic and syndromic myopia based on the different approaches. Such a systemic review of the molecular genetics of myopia will provide clues to identify additional plausible genes for myopia and help us to understand the molecular mechanisms underlying myopia. This paper reviews recent genetic studies on myopia, summarizes all possible reported genes and loci related to myopia, and suggests implications for future studies on the molecular genetics of myopia.

The evolution of cortical development: the synapsid-diapsid divergence

The cerebral cortex covers the rostral part of the brain and, in higher mammals and particularly humans, plays a key role in cognition and consciousness. It is populated with neuronal cell bodies distributed in radially organized layers. Understanding the common and lineage-specific molecular mechanisms that orchestrate cortical development and evolution are key issues in neurobiology. During evolution, the cortex appeared in stem amniotes and evolved divergently in two main branches of the phylogenetic tree: the synapsids (which led to present day mammals) and the diapsids (reptiles and birds). Comparative studies in organisms that belong to those two branches have identified some common principles of cortical development and organization that are possibly inherited from stem amniotes and regulated by similar molecular mechanisms. These comparisons have also highlighted certain essential features of mammalian cortices that are absent or different in diapsids and that probably evolved after the synapsid-diapsid divergence. Chief among these is the size and multi-laminar organization of the mammalian cortex, and the propensity to increase its area by folding. Here, I review recent data on cortical neurogenesis, neuronal migration and cortical layer formation and folding in this evolutionary perspective, and highlight important unanswered questions for future investigation.