Extending the ophthalmological phenotype of Galloway-Mowat syndrome with distinct retinal dysfunction: a report and review of ocular findings

Assembly mechanism of Integrator's RNA cleavage module

The modular Integrator complex is a transcription regulator that is essential for embryonic development. It attenuates coding gene expression via premature transcription termination and performs 3'-processing of non-coding RNAs. For both activities, Integrator requires endonuclease activity that is harbored by an RNA cleavage module consisting of INTS4-9-11. How correct assembly of Integrator modules is achieved remains unknown. Here, we show that BRAT1 and WDR73 are critical biogenesis factors for the human cleavage module. They maintain INTS9-11 inactive during maturation by physically blocking the endonuclease active site and prevent premature INTS4 association. Furthermore, BRAT1 facilitates import of INTS9-11 into the nucleus, where it is joined by INTS4. Final BRAT1 release requires locking of the mature cleavage module conformation by inositol hexaphosphate (IP6). Our data explain several neurodevelopmental disorders caused by BRAT1, WDR73, and INTS11 mutations as Integrator assembly defects and reveal that IP6 is an essential co-factor for cleavage module maturation.

Molecular mechanisms and genetic factors contributing to the developmental dysplasia of the hip

The most prevalent hip disease in neonates is developmental dysplasia of the hip (DDH). A timely and accurate diagnosis is required to provide the most effective treatment for pediatric patients with DDH. Heredity and gene variation have been the subject of increased attention and research worldwide as one of the factors contributing to the pathogenesis of DDH. Genome-wide association studies (GWAS), genome-wide linkage analyses (GWLA), and exome sequencing (ES) have identified variants in numerous genes and single-nucleotide polymorphisms (SNPs) as being associated with susceptibility to DDH in sporadic and DDH family patients. Furthermore, the DDH phenotype can be observed in animal models that exhibit susceptibility genes or loci, including variants in CX3CR1, KANSL1, and GDF5. The dentification of noncoding RNAs and de novo gene variants in patients with DDH-related syndrome has enhanced our understanding of the genes implicated in DDH. This article reviews the most recent molecular mechanisms and genetic factors that contribute to DDH.

[Research progress on monogenic inherited glomerular diseases with central nervous system symptoms]

To date, approximately 500 monogenic inherited kidney diseases have been reported, with more than 50 genes associated with the pathogenesis of monogenic isolated or syndromic nephrotic syndrome. Most of these genes are expressed in podocytes of the glomerulus. Neurological symptoms are common extrarenal manifestations of syndromic nephrotic syndrome, and various studies have found connections between podocytes and neurons in terms of morphology and function. This review summarizes the genetic and clinical characteristics of monogenic inherited diseases with concomitant glomerular and central nervous system lesions, aiming to enhance clinicians' understanding of such diseases, recognize the importance of genetic diagnostic techniques for comorbidity screening, and reduce the rates of missed diagnosis and misdiagnosis.

Prdm15 acts upstream of Wnt4 signaling in anterior neural development of Xenopus laevis

Mutations in PRDM15 lead to a syndromic form of holoprosencephaly (HPE) known as the Galloway-Mowat syndrome (GAMOS). While a connection between PRDM15, a zinc finger transcription factor, and WNT/PCP signaling has been established, there is a critical need to delve deeper into their contributions to early development and GAMOS pathogenesis. We used the South African clawed frog Xenopus laevis as the vertebrate model organism and observed that prdm15 was enriched in the tissues and organs affected in GAMOS. Furthermore, we generated a morpholino oligonucleotide-mediated prdm15 knockdown model showing that the depletion of Prdm15 leads to abnormal eye, head, and brain development, effectively recapitulating the anterior neural features in GAMOS. An analysis of the underlying molecular basis revealed a reduced expression of key genes associated with eye, head, and brain development. Notably, this reduction could be rescued by the introduction of wnt4 RNA, particularly during the induction of the respective tissues. Mechanistically, our data demonstrate that Prdm15 acts upstream of both canonical and non-canonical Wnt4 signaling during anterior neural development. Our findings describe severe ocular and anterior neural abnormalities upon Prdm15 depletion and elucidate the role of Prdm15 in canonical and non-canonical Wnt4 signaling.

Novel LAGE3 Pathogenic Variants Combined with TRPC6 and NUP160 Variants in Galloway-Mowat Syndrome: A Case Report

Galloway-Mowat syndrome (GAMOS) is a rare autosomal recessive disorder characterized by early-onset nephrotic syndrome and microcephaly with brain anomalies in children. Researchers studying GAMOS reported the first pathogenic variant identified was the WDR73 gene, and more recently, four new pathogenic genes, OSGEP, LAGE3, TP53RK, and TPRKB, have been identified. In the present study, we report a new mutation of c.290T>G (p.L97R) LAGE3 in a 4-year-old boy with specific urological and nephrological complications. The patient presented with early-onset proteinuria, brain atrophy, delayed language and motor development, and axial hypotonia. This patient also had mutations in two other genes: TRPC6 and NUP160, make the clinical presentation of this patient more diverse. Our novel findings add to the spectrum of pathogenic variants in the LAGE3 gene. In addition, early genetic diagnosis of GAMOS is essential for genetic counseling and prenatal care.

WDR37 syndrome: identification of a distinct new cluster of disease-associated variants and functional analyses of mutant proteins

Missense variants located in the N-terminal region of WDR37 were recently identified to cause a multisystemic syndrome affecting neurological, ocular, gastrointestinal, genitourinary, and cardiac development. WDR37 encodes a WD40 repeat-containing protein of unknown function. We identified three novel WDR37 variants, two likely pathogenic de novo alleles and one inherited variant of uncertain significance, in individuals with phenotypes overlapping those previously reported but clustering in a different region of the protein. The novel alleles are C-terminal to the prior variants and located either within the second WD40 motif (c.659A>G p.(Asp220Gly)) or in a disordered protein region connecting the second and third WD40 motifs (c.778G>A p.(Asp260Asn) and c.770C>A p.(Pro257His)). The three novel mutants showed normal cellular localization but lower expression levels in comparison to wild-type WDR37. To investigate the normal interactions of WDR37, we performed co-immunoprecipitation and yeast two-hybrid assays. This revealed the ability of WDR37 to form homodimers and to strongly bind PACS1 and PACS2 phosphofurin acidic cluster sorting proteins; immunocytochemistry confirmed colocalization of WDR37 with PACS1 and PACS2 in human cells. Next, we analyzed previously reported and novel mutants for their ability to dimerize with wild-type WDR37 and bind PACS proteins. Interaction with wild-type WDR37 was not affected for any variant; however, one novel mutant, p.(Asp220Gly), lost its ability to bind PACS1 and PACS2. In summary, this study presents a novel region of WDR37 involved in human disease, identifies PACS1 and PACS2 as major binding partners of WDR37 and provides insight into the functional effects of various WDR37 variants.

Neurological involvement in monogenic podocytopathies

Genetic studies of hereditary nephrotic syndrome (NS) have identified more than 50 genes that, if mutated, are responsible for monogenic forms of steroid-resistant NS (SRNS), either isolated or syndromic. Most of these genes encode proteins expressed in the podocyte with various functions such as transcription factors, mitochondrial proteins, or enzymes, but mainly structural proteins of the slit diaphragm (SD) as well as cytoskeletal binding and regulator proteins. Syndromic NS is sometimes associated with neurological features. Over recent decades, various studies have established links between the physiology of podocytes and neurons, both morphologically (slit diaphragm and synapse) and functionally (signaling platforms). Variants in genes expressed in different compartments of the podocyte and neurons are responsible for phenotypes associating kidney lesions with proteinuria (mainly Focal and Segmental Glomerulosclerosis (FSGS) or Diffuse Mesangial Sclerosis (DMS)) and central and/or peripheral neurological disorders. The Galloway-Mowat syndrome (GAMOS, OMIM#251300) associates neurological defects, microcephaly, and proteinuria and is caused by variants in genes encoding proteins of various functions (microtubule cytoskeleton regulation (WDR73), regulation of protein synthesis via transfer RNAs (KEOPS and WDR4 complexes)). Pierson syndrome (OMIM#609049) associating congenital nephrotic syndrome and central neurological and ophthalmological anomalies is secondary to variants in LAMB2, involved in glomerular and ocular basement membranes. Finally, Charcot-Marie-Tooth-FSGS (OMIM#614455) combines peripheral sensory-motor neuropathy and proteinuria and arises from INF2 variants, resulting in cytoskeletal polymerization defects. This review focuses on genetic syndromes associating nephrotic range proteinuria and neurological involvement and provides the latest advances in the description of these neuro-renal disorders.

A patient diagnosed with Galloway-Mowat syndrome presenting with a rod-cone functional anomaly with electronegative dark-adapted ERGs

PURPOSE

Galloway-Mowat syndrome (GAMOS) is a clinically heterogenous and rare condition classically described as the combination of nephrotic syndrome associated with brain anomaly and delays in development. It was first reported in the literature in 1968 by Galloway W.H and Mowat A.P. Reports of visual anomaly in these patients are generally limited to decreased visual acuity, nystagmus and optic nerve atrophy. To this day, little is known about retinal function in this disease. Therefore, the purpose of this case report is to reveal abnormal retinal function (including light-adapted and dark-adapted retinal function) in a female patient diagnosed with GAMOS due to mutation of the WDR73 gene.

METHODS

Complete dilated pediatric ophthalmic examination and ISCEV full field standard light (10 min of light adaptation; background light: 30 cd.m^-2; flash intensity: 3.0 cd.sec.m^-2) and dark-adapted (20 min of dark adaptation; flash intensities: 0.01, 3.0 and 10.0 cd.sec.m^-2) electroretinograms were performed on a 2-year-old female patient diagnosed with GAMOS due to a biallelic mutation in the WDR73 gene.

RESULTS

Ophthalmologic evaluation under anesthesia revealed normal appearing anterior segments. Significant bilateral optic nerve pallor was noted. Fundus examination appeared to be abnormal and demonstrated mid-peripheral whitish glistening appearance with possible gliosis. Retinoscopy revealed bilateral high myopia with a refractive error of -8.00 sphere in both eyes. ISCEV standard ERG revealed residual responses under light-adapted condition. Undetectable responses were obtained after 20 min of dark adaptation when using a dim flash (DA 0.01). However, when brighter flashes were used in a dark-adapted condition (DA 3.0 and DA 10.0), the ERGs were detectable, albeit abnormal in amplitudes and of electronegative morphology.

CONCLUSIONS

The results obtained showed significant retinal functional deficit affecting both the cone and the rod photoreceptor pathways, along with the inner retina, in a patient diagnosed with GAMOS due to biallelic mutations in the WDR73 gene. Our report is limited to one patient, and additional studies are needed to verify whether retinal functional anomalies, as measured by the full field electroretinogram, present a novel biomarker in all patients affected with GAMOS or only in patients with a mutation in the WDR73 gene. Given the evidence of retinal functional changes presented in this study, it is strongly suggested to include complete ophthalmic examination, retinal imaging, including OCT, and full field ERG testing in patients affected with GAMOS.

De Novo Missense Variants in WDR37 Cause a Severe Multisystemic Syndrome

While genetic causes are known for many syndromes involving developmental anomalies, a large number of individuals with overlapping phenotypes remain undiagnosed. Using exome-sequencing analysis and review of matchmaker databases, we have discovered four de novo missense variants predicted to affect the N-terminal region of WDR37-p.Ser119Phe, p.Thr125Ile, p.Ser129Cys, and p.Thr130Ile-in unrelated individuals with a previously unrecognized syndrome. Features of WDR37 syndrome include the following: ocular anomalies such as corneal opacity/Peters anomaly, coloboma, and microcornea; dysmorphic facial features; significant neurological impairment with structural brain defects and seizures; poor feeding; poor post-natal growth; variable skeletal, cardiac, and genitourinary defects; and death in infancy in one individual. WDR37 encodes a protein of unknown function with seven predicted WD40 domains and no previously reported human pathogenic variants. Immunocytochemistry and western blot studies showed that wild-type WDR37 is localized predominantly in the cytoplasm and mutant proteins demonstrate similar protein levels and localization. CRISPR-Cas9-mediated genome editing generated zebrafish mutants with novel missense and frameshift alleles: p.Ser129Phe, p.Ser129Cys (which replicates one of the human variants), p.Ser129Tyr, p.Lys127Cysfs, and p.Gln95Argfs. Zebrafish carrying heterozygous missense variants demonstrated poor growth and larval lethality, while heterozygotes with frameshift alleles survived to adulthood, suggesting a potential dominant-negative mechanism for the missense variants. RNA-seq analysis of zebrafish embryos carrying a missense variant detected significant upregulation of cholesterol biosynthesis pathways. This study identifies variants in WDR37 associated with human disease and provides insight into its essential role in vertebrate development and possible molecular functions.

Novel homozygous OSGEP gene pathogenic variants in two unrelated patients with Galloway-Mowat syndrome: case report and review of the literature

Background

Galloway-Mowat syndrome (GAMOS) is a rare autosomal recessive disorder characterized by early-onset nephrotic syndrome and microcephaly with brain anomalies. WDR73 pathogenic variants were described as the first genetic cause of GAMOS and, very recently, four novel causative genes, OSGEP, LAGE3, TP53RK, and TPRKB, have been identified.

Case presentation

We present the clinical and genetic characteristics of two unrelated infants with clinical suspicion of GAMOS who were born from consanguineous parents. Both patients showed a similar clinical presentation, with early-onset nephrotic syndrome, microcephaly, brain atrophy, developmental delay, axial hypotonia, and early fatality. We identified two novel likely disease-causing variants in the OSGEP gene. These two cases, in conjunction with the findings of a literature review, indicate that OSGEP pathogenic variants are associated with an earlier onset of nephrotic syndrome and shorter life expectancy than WDR73 pathogenic variants.

Conclusions

Our findings expand the spectrum of pathogenic variants in the OSGEP gene and, taken in conjunction with the results of the literature review, suggest that the OSGEP gene should be considered the main known monogenic cause of GAMOS. Early genetic diagnosis of GAMOS is of paramount importance for genetic counseling and family planning.