OCRL1 Deficiency Affects the Intracellular Traffic of ApoER2 and Impairs Reelin-Induced Responses.

Lowe Syndrome (LS) is a rare X-linked disorder characterized by renal dysfunction, cataracts, and several central nervous system (CNS) anomalies. The mechanisms underlying the neurological dysfunction in LS remain unclear, albeit they share some phenotypic characteristics similar to the deficiency or dysfunction of the Reelin signaling, a relevant pathway with roles in CNS development and neuronal functions. In this study, we investigated the role of OCRL1, an inositol polyphosphate 5-phosphatase encoded by the OCRL gene, mutated in LS, focusing on its impact on endosomal trafficking and receptor recycling in human neuronal cells. Specifically, we tested the effects of OCRL1 deficiency in the trafficking and signaling of ApoER2/LRP8, a receptor for the ligand Reelin. We found that loss of OCRL1 impairs ApoER2 intracellular trafficking, leading to reduced receptor expression and decreased levels at the plasma membrane. Additionally, human neurons deficient in OCRL1 showed impairments in ApoER2/Reelin-induced responses. Our findings highlight the critical role of OCRL1 in regulating ApoER2 endosomal recycling and its impact on the ApoER2/Reelin signaling pathway, providing insights into potential mechanisms underlying the neurological manifestations of LS.

Atypical phenotypes and novel OCRL variations in southern Chinese patients with Lowe syndrome.

BACKGROUND: Lowe syndrome is characterized by the presence of congenital cataracts, psychomotor retardation, and dysfunctional proximal renal tubules. This study presents a case of an atypical phenotype, investigates the genetic characteristics of eight children diagnosed with Lowe syndrome in southern China, and performs functional analysis of the novel variants. METHODS: Whole-exome sequencing was conducted on eight individuals diagnosed with Lowe syndrome from three medical institutions in southern China. Retrospective collection and analysis of clinical and genetic data were performed, and functional analysis was conducted on the five novel variants. RESULTS: In our cohort, the clinical symptoms of the eight Lowe syndrome individuals varied. One patient was diagnosed with Lowe syndrome but did not present with congenital cataracts. Common features among all patients included cognitive impairment, short stature, and low molecular weight proteinuria. Eight variations in the OCRL gene were identified, encompassing three previously reported and five novel variations. Among the novel variations, three nonsense mutations were determined to be pathogenic, and two patients harboring novel missense variations of uncertain significance exhibited severe typical phenotypes. Furthermore, all novel variants were associated with altered protein expression levels and impacted primary cilia formation. CONCLUSION: This study describes the first case of an atypical Lowe syndrome patient without congenital cataracts in China and performs a functional analysis of novel variants in the OCRL gene, thereby expanding the understanding of the clinical manifestations and genetic diversity associated with Lowe syndrome.

Base editing correction of OCRL in Lowe syndrome: ABE-mediated functional rescue in patient-derived fibroblasts.

Lowe syndrome, a rare X-linked multisystem disorder presenting with major abnormalities in the eyes, kidneys, and central nervous system, is caused by mutations in OCRL gene (NG_008638.1). Encoding an inositol polyphosphate 5-phosphatase, OCRL catalyzes the hydrolysis of PI(4,5)P2 into PI4P. There are no effective targeted treatments for Lowe syndrome. Here, we demonstrate a novel gene therapy for Lowe syndrome in patient fibroblasts using an adenine base editor (ABE) that can efficiently correct pathogenic point mutations. We show that ABE8e-NG-based correction of a disease-causing mutation in a Lowe patient-derived fibroblast line containing R844X mutation in OCRL gene, restores OCRL expression at mRNA and protein levels. It also restores cellular abnormalities that are hallmarks of OCRL dysfunction, including defects in ciliogenesis, microtubule anchoring, α-actinin distribution, and F-actin network. The study indicates that ABE-mediated gene therapy is a feasible treatment for Lowe syndrome, laying the foundation for therapeutic application of ABE in the currently incurable disease.

Overlap between ophthalmology and psychiatry - A narrative review focused on congenital and inherited conditions.

A number of congenital and inherited diseases present with both ocular and psychiatric features. The genetic inheritance and phenotypic variants play a key role in disease severity. Early recognition of the signs and symptoms of those disorders is critical to earlier intervention and improved prognosis. Typically, the associations between these two medical subspecialties of ophthalmology and psychiatry are poorly understood by most practitioners so we hope to provide a narrative review to improve the identification and management of these disorders. We conducted a comprehensive review of the literature detailing the diseases with ophthalmic and psychiatric overlap that were more widely represented in the literature. Herein, we describe the clinical features, pathophysiology, molecular biology, diagnostic tests, and the most recent approaches for the treatment of these diseases. Recent studies have combined technologies for ocular and brain imaging such as optical coherence tomography (OCT) and functional imaging with genetic testing to identify the genetic basis for eye-brain connections. Additional work is needed to further explore these potential biomarkers. Overall, accurate, efficient, widely distributed and non-invasive tests that can help with early recognition of these diseases will improve the management of these patients using a multidisciplinary approach.

A missense mutant of ocrl1 promotes apoptosis of tubular epithelial cells and disrupts endocytosis and the cell cycle of podocytes in Dent-2 Disease.

BACKGROUND: This study aimed to identify an orcl1 mutation in a patient with Dent-2 Disease and investigate the underlying mechanisms. METHODS: The ocrl1 mutation was identified through exome sequencing. Knockdown of orcl1 and overexpression of the orcl1 mutant were performed in HK-2 and MPC5 cells to study its function, while flow cytometry measured reactive oxygen species (ROS), phosphatidylserine levels, and cell apoptosis. Scanning electron microscopy observed crystal adhesion, while transmission electron microscopy examined kidney tissue pathology. Laser scanning confocal microscopy was used to examine endocytosis, and immunohistochemical and immunofluorescence assays detected protein expression. Additionally, podocyte-specific orcl1 knockout mice were generated to investigate the role of orcl1 in vivo. RESULTS: We identified a mutation resulting in the replacement of Histidine with Arginine at position 318 (R318H) in ocrl1 in the proband. orcl1 was widely expressed in the kidney. In vitro experiments showed that knockdown of orcl1 and overexpression of ocrl1 mutant increased ROS, phosphatidylserine exocytosis, crystal adhesion, and cell apoptosis in HK-2 cells. Knockdown of orcl1 in podocytes reduced endocytosis and disrupted the cell cycle while increasing cell migration. In vivo studies in mice showed that conditional deletion of orcl1 in podocytes caused glomerular dysfunction, including proteinuria and fibrosis. CONCLUSION: This study identified an R318H mutation in orcl1 in a patient with Dent-2 Disease. This mutation may contribute to renal injury by promoting ROS production and inducing cell apoptosis in tubular cells, while disrupting endocytosis and the cell cycle, and promoting cell migration of podocytes. Video Abstract.

A Case of Hidradenitis Suppurativa in a Genetically Confirmed Lowe Syndrome Patient.

Lowe syndrome (LS), also known as oculocerebrorenal syndrome, is an X-linked multisystemic disorder caused by mutations in OCRL1, which encodes a member of the inositol-5-phosphatase family. As implied by its name, congenital cataracts, defects in the central nervous system, and renal manifestations are the main symptoms. Early hidradenitis suppurativa (HS) occurrence in Dent disease 2 (DD2), which is a mild variant of LS and shares the OCRL1 gene mutation, has been reported, although not in LS patients. Here, we report a case of HS in a 17-year-old boy with genetically confirmed LS, which suggests that defects in the OCRL1 gene may contribute to HS pathogenesis.

Initial Effect of Recombinant Human Growth Hormone Treatment in a Patient with Löwe Syndrome.

OBJECTIVES: Löwe syndrome (the oculocerebrorenal syndrome of Löwe, OCRL, OMIM #309000, ORPHA: 534) is a very rare multisystem X-linked disorder characterized by ocular, kidney and nervous system anomalies. CASE PRESENTATION: We present the first Bulgarian genetically confirmed patient with OCRL. The patient had facial dysmorphism, cryptorchidism, congenital cataracts, nystagmus, delayed physical and mental development, and poor nutritional status. He had severe rickets, metabolic acidosis, hypokalaemia, hypophosphataemia, and low IGF-1 levels at the age of three, in addition to his developmental delay. The molecular-genetic analysis reported a pathogenic variant c.1124A>G, p.H375R in the OCRL gene. This variant was inherited from the mother, who was a carrier. Following the diagnosis of OCRL, treatment with potassium citrate, phosphate, and calcitriol was initiated, along with an increase in caloric intake. Following general physical and biochemical improvement, therapy with rhGH started 4 years ago, and current results are presented. CONCLUSIONS: The patient with Löwe syndrome who was presented with a 6-year follow-up demonstrates the complexity of rare disease cases and the value of multidisciplinary care together with growth hormone treatment for better results in these patients.

Heterogeneity in Lowe Syndrome: Mutations Affecting the Phosphatase Domain of OCRL1 Differ in Impact on Enzymatic Activity and Severity of Cellular Phenotypes.

Lowe Syndrome (LS) is a condition due to mutations in the OCRL1 gene, characterized by congenital cataracts, intellectual disability, and kidney malfunction. Unfortunately, patients succumb to renal failure after adolescence. This study is centered in investigating the biochemical and phenotypic impact of patient's OCRL1 variants (OCRL1VAR). Specifically, we tested the hypothesis that some OCRL1VAR are stabilized in a non-functional conformation by focusing on missense mutations affecting the phosphatase domain, but not changing residues involved in binding/catalysis. The pathogenic and conformational characteristics of the selected variants were evaluated in silico and our results revealed some OCRL1VAR to be benign, while others are pathogenic. Then we proceeded to monitor the enzymatic activity and function in kidney cells of the different OCRL1VAR. Based on their enzymatic activity and presence/absence of phenotypes, the variants segregated into two categories that also correlated with the severity of the condition they induce. Overall, these two groups mapped to opposite sides of the phosphatase domain. In summary, our findings highlight that not every mutation affecting the catalytic domain impairs OCRL1's enzymatic activity. Importantly, data support the inactive-conformation hypothesis. Finally, our results contribute to establishing the molecular and structural basis for the observed heterogeneity in severity/symptomatology displayed by patients.

Oculocerebrorenal syndrome of Lowe protein controls cytoskeletal reorganisation during human platelet spreading.

Lowe syndrome (LS) is a rare, X-linked disorder characterised by numerous symptoms affecting the brain, the eyes, and the kidneys. It is caused by mutations in the oculocerebrorenal syndrome of Lowe (OCRL) protein, a 5-phosphatase localised in different cellular compartments that dephosphorylates phosphatidylinositol-4,5-bisphosphate into phosphatidylinositol-4-monophosphate. Some patients with LS also have bleeding disorders, with normal to low platelet (PLT) count and impaired PLT function. However, the mechanism of PLT dysfunction in patients with LS is not completely understood. The main function of PLTs is to activate upon vessel wall injury and stop the bleeding by clot formation. PLT activation is accompanied by a shape change that is a result of massive cytoskeletal rearrangements. Here, we show that OCRL-inhibited human PLTs do not fully spread, form mostly filopodia, and accumulate actin nodules. These nodules co-localise with ARP2/3 subunit p34, vinculin, and sorting nexin 9. Furthermore, OCRL-inhibited PLTs have a retained microtubular coil with high levels of acetylated tubulin. Also, myosin light chain phosphorylation is decreased upon OCRL inhibition, without impaired degranulation or integrin activation. Taken together, these results suggest that OCRL contributes to cytoskeletal rearrangements during PLT activation that could explain mild bleeding problems in patients with LS.

Lipid Polarization during Cytokinesis.

The plasma membrane of eukaryotic cells is composed of a large number of lipid species that are laterally segregated into functional domains as well as asymmetrically distributed between the outer and inner leaflets. Additionally, the spatial distribution and organization of these lipids dramatically change in response to various cellular states, such as cell division, differentiation, and apoptosis. Division of one cell into two daughter cells is one of the most fundamental requirements for the sustenance of growth in all living organisms. The successful completion of cytokinesis, the final stage of cell division, is critically dependent on the spatial distribution and organization of specific lipids. In this review, we discuss the properties of various lipid species associated with cytokinesis and the mechanisms involved in their polarization, including forward trafficking, endocytic recycling, local synthesis, and cortical flow models. The differences in lipid species requirements and distribution in mitotic vs. male meiotic cells will be discussed. We will concentrate on sphingolipids and phosphatidylinositols because their transbilayer organization and movement may be linked via the cytoskeleton and thus critically regulate various steps of cytokinesis.

Prenatal diagnosis of Lowe syndrome in a male fetus with isolated bilateral cataract.

Background: Lowe syndrome is a rare disease characterized by the association of congenital cataract, hypotonia, followed by global psychomotor delay and intellectual disability, as well as progressive renal dysfunction, and renal failure occurring at around 20 years of age. Case presentation: We discuss the case of a male fetus diagnosed with isolated bilateral cataract on the sonography performed at 21 + 5 weeks of gestation, confirmed by a fetal MRI at 23 weeks of gestation.After ruling out infectious etiologies, a genetic consult was conducted at 26 weeks of gestation, and an amniocentesis was realized to search for a chromosomal cause, Norrie's disease and Lowe syndrome by Sanger analysis. A c.1351G > A (p.Asp451Asn) hemizygous mutation in OCRL gene was identified, inherited from the mother, which led to the diagnosis of Lowe syndrome in the fetus. Conclusions: This is the first case of Lowe syndrome diagnosed prenatally on an isolated cataract, which allows the discussion of a more extensive etiological research when a male fetus is diagnosed with isolated bilateral cataract, by including notably a systematic analysis of the OCRL gene.

Participation of OCRL1, and APPL1, in the expression, proteolysis, phosphorylation and endosomal trafficking of megalin: Implications for Lowe Syndrome.

Megalin/LRP2 is the primary multiligand receptor for the re-absorption of low molecular weight proteins in the proximal renal tubule. Its function is significantly dependent on its endosomal trafficking. Megalin recycling from endosomal compartments is altered in an X-linked disease called Lowe Syndrome (LS), caused by mutations in the gene encoding for the phosphatidylinositol 5-phosphatase OCRL1. LS patients show increased low-molecular-weight proteins with reduced levels of megalin ectodomain in the urine and accumulation of the receptor in endosomal compartments of the proximal tubule cells. To gain insight into the deregulation of megalin in the LS condition, we silenced OCRL1 in different cell lines to evaluate megalin expression finding that it is post-transcriptionally regulated. As an indication of megalin proteolysis, we detect the ectodomain of the receptor in the culture media. Remarkably, in OCRL1 silenced cells, megalin ectodomain secretion appeared significantly reduced, according to the observation in the urine of LS patients. Besides, the silencing of APPL1, a Rab5 effector associated with OCRL1 in endocytic vesicles, also reduced the presence of megalin's ectodomain in the culture media. In both silencing conditions, megalin cell surface levels were significantly decreased. Considering that GSK3ß-mediated megalin phosphorylation reduces receptor recycling, we determined that the endosomal distribution of megalin depends on its phosphorylation status and OCRL1 function. As a physiologic regulator of GSK3ß, we focused on insulin signaling that reduces kinase activity. Accordingly, megalin phosphorylation was significantly reduced by insulin in wild-type cells. Moreover, even though in cells with low activity of OCRL1 the insulin response was reduced, the phosphorylation of megalin was significantly decreased and the receptor at the cell surface increased, suggesting a protective role of insulin in a LS cellular model.

Management of cataract surgery in Lowe syndrome.

AIM: To evaluate the ophthalmic and anesthesiologic management of cataract surgery in children with Lowe syndrome receiving lens removal, the development and management of secondary glaucoma. METHODS: This retrospective case series included 12 eyes of 6 children with genetically verified Lowe syndrome receiving cataract removal. Information regarding the type and duration of surgery and total anesthesia time were recorded. Additionally, intra- and postoperative complications were noted as well as clinical examinations such as visual acuity and funduscopy. RESULTS: All children received simultaneous bilateral cataract surgery at the mean age of 8.98±3.58wk. Lensectomy combined with posterior capsulotomy and anterior vitrectomy was performed in all children. The mean time for cataract surgery per eye was 35.83±8.86min, whereas the total time of surgery was 153.33±22.11min. The mean extubation time and duration at recovery room was 42.33±22.60min and 130.00±64.37min, respectively. During surgery, a decrease of oxygen saturation below 93% was found in only one child. During the postoperative follow-up, nystagmus (6 children) and strabismus (5 children) was commonly found in contrast to no case of visual axis opacification. Secondary glaucoma developed in five eyes of three children, which was treated with topical eye drops in only one child. A trabeculectomy was performed in both eyes of one child, whereas removal of syechia and an iridectomy in one eye of one child. CONCLUSION: Bilateral simultaneous cataract surgery under general anesthesia is a safe surgical procedure in Lowe syndrome children. The glaucoma screening with intraocular pressure measurements is crucial in the postoperative management of Lowe syndrome patients to avoid additional visual impairment.

Assessment of endocytic traffic and Ocrl function in the developing zebrafish neuroepithelium.

Endocytosis allows cells to internalise a wide range of molecules from their environment and to maintain their plasma membrane composition. It is vital during development and for maintenance of tissue homeostasis. The ability to visualise endocytosis in vivo requires suitable assays to monitor the process. Here, we describe imaging-based assays to visualise endocytosis in the neuroepithelium of living zebrafish embryos. Injection of fluorescent tracers into the brain ventricles followed by live imaging was used to study fluid-phase or receptor-mediated endocytosis, for which we used receptor-associated protein (RAP, encoded by Lrpap1) as a ligand for low-density lipoprotein receptor-related protein (LRP) receptors. Using dual-colour imaging combined with expression of endocytic markers, it is possible to track the progression of endocytosed tracers and to monitor trafficking dynamics. Using these assays, we reveal a role for the Lowe syndrome protein Ocrl in endocytic trafficking within the neuroepithelium. We also found that the RAP-binding receptor Lrp2 (encoded by lrp2a) appears to contribute only partially to neuroepithelial RAP endocytosis. Altogether, our results provide a basis to track endocytosis within the neuroepithelium in vivo and support a role for Ocrl in this process. This article has an associated First Person interview with the first author of the paper.

Case Report: Combined Cataract Surgery and Minimally Invasive Glaucoma Surgery Provide an Alternative Treatment Approach for Lowe Syndrome.

We describe the case of a 4-month-old boy who presented with bilateral congenital cataract and high intraocular pressure (IOP) in the left eye, followed by mental retardation and delayed motor development. Genetic investigation revealed the boy had a splicing variant (c.940-11G>A) of the oculocerebrorenal syndrome of Lowe (OCRL) gene. The boy underwent a lensectomy for congenital cataract in his right eye, and lensectomy combined with a 360° suture trabeculotomy to remove the clouded lens and to control IOP of the left eye. During postoperative one-and-a-half-year follow-up, the boy exhibited an improved visual acuity and a well-controlled IOP without the use of topical IOP-lowering medications. Lowe syndrome is a rare multisystemic disorder that is diagnosed through clinical manifestation and genetic testing. The possibility of Lowe syndrome should be considered in patients presenting with typical triad, and genetic analysis should be performed in time to confirm the diagnosis. We recommend combined cataract surgery and minimally invasive glaucoma surgery (MIGS) as a safe, feasible, and efficient method to treat congenital cataract and glaucoma in Lowe syndrome patients.

X-Linked Kidney Disorders in Women.

A number of genes that cause inherited kidney disorders reside on the X chromosome. Given that males have only a single active X chromosome, these disorders clinically manifest primarily in men and boys. However, phenotypes in female carriers of X-linked kidney conditions are becoming more and more recognized. This article reviews the biology of X inactivation as well as the kidney phenotype in women and girls with a number of X-linked kidney disorders including Alport syndrome, Fabry disease, nephrogenic diabetes insipidus, X-linked hypophosphatemic rickets, Dent disease, and Lowe syndrome.

A human stem cell resource to decipher the biochemical and cellular basis of neurodevelopmental defects in Lowe syndrome.

Human brain development is a complex process where multiple cellular and developmental events are coordinated to generate normal structure and function. Alteration in any of these events can impact brain development, manifesting clinically as neurodevelopmental disorders. Human genetic disorders of lipid metabolism often present with features of altered brain function. Lowe syndrome (LS) is an X-linked recessive disease with features of altered brain function. LS results from mutations in OCRL1, which encodes a phosphoinositide 5-phosphatase enzyme. However, the cellular mechanisms by which loss of OCRL1 leads to brain defects remain unknown. Human brain development involves several cellular and developmental features not conserved in other species and understanding such mechanisms remains a challenge. Rodent models of LS have been generated but failed to recapitulate features of the human disease. Here we describe the generation of human stem cell lines from LS patients. Further, we present biochemical characterization of lipid metabolism in patient cell lines and demonstrate their use as a 'disease-in-a-dish' model for understanding the mechanism by which loss of OCRL1 leads to altered cellular and physiological brain development. This article has an associated First Person interview with the first author of the paper.

A case of Dent disease type 2 with large deletion of OCRL diagnosed after close examination of a school urinary test.

A 7-year-old boy visited our hospital for a detailed examination of proteinuria identified in a school urinary test. He had short stature, misaligned teeth, and mild intellectual disability. A urinary examination identified mild proteinuria and extremely high levels of beta-2 microglobulin. On blood examination, his protein, albumin, and creatinine levels were found to be normal; however, his lactate dehydrogenase and creatinine phosphokinase levels were slightly elevated. Upon histological examination, no abnormalities in glomeruli or tubules were found. Considering these results, we diagnosed our patient with Dent disease type 2 (DD2). Although the whole exome sequencing revealed large deletion of OCRL, which was seen only in Lowe syndrome and not in DD2 previously, our final diagnosis for the patient is DD2. A phenotypic continuum exists between Dent disease and Lowe syndrome, and several factors modify the phenotypes caused by defects in OCRL. Although patients have thus far been diagnosed with DD2 or Lowe syndrome on the basis of their symptoms, accumulation and analysis of cases with OCRL defects may hereafter enable more accurate diagnoses.

Identification of novel OCRL isoforms associated with phenotypic differences between Dent disease-2 and Lowe syndrome.

BACKGROUND: Although Lowe syndrome and Dent disease-2 are caused by Oculocerebrorenal syndrome of Lowe (OCRL) mutations, their clinical severities differ substantially and their molecular mechanisms remain unclear. Truncating mutations in OCRL exons 1-7 lead to Dent disease-2, whereas those in exons 8-24 lead to Lowe syndrome. Herein we identified the mechanism underlying the action of novel OCRL protein isoforms. METHODS: Messenger RNA samples extracted from cultured urine-derived cells from a healthy control and a Dent disease-2 patient were examined to detect the 5' end of the OCRL isoform. For protein expression and functional analysis, vectors containing the full-length OCRL transcripts, the isoform transcripts and transcripts with truncating mutations detected in Lowe syndrome and Dent disease-2 patients were transfected into HeLa cells. RESULTS: We successfully cloned the novel isoform transcripts from OCRL exons 6-24, including the translation-initiation codons present in exon 8. In vitro protein-expression analysis detected proteins of two different sizes (105 and 80 kDa) translated from full-length OCRL, whereas only one protein (80 kDa) was found from the isoform and Dent disease-2 variants. No protein expression was observed for the Lowe syndrome variants. The isoform enzyme activity was equivalent to that of full-length OCRL; the Dent disease-2 variants retained >50% enzyme activity, whereas the Lowe syndrome variants retained <20% activity. CONCLUSIONS: We elucidated the molecular mechanism underlying the two different phenotypes in OCRL-related diseases; the functional OCRL isoform translated starting at exon 8 was associated with this mechanism.