Collapsing glomerulopathy in Galloway–Mowat syndrome: A case report and review of the literature

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.

WDR73 Depletion Destabilizes PIP4K2C Activity and Impairs Focal Adhesion Formation in Galloway–Mowat Syndrome

Simple Summary

Galloway–Mowat syndrome is a rare genetic disease, classically characterized by a combination of various neurological symptoms and nephrotic syndrome. WDR73 is the pathogenic gene responsible for Galloway–Mowat syndrome. However, the pathological and molecular mechanisms of Galloway–Mowat syndrome, especially nephrotic syndrome caused by WDR73 deficiency, remains unknown. In this study, we knocked out the WDR73 in human embryonic kidney 293 cells to observe the morphological characteristics of the cells and elucidate the functions of WDR73. Additionally, we used a combination of proteomics, transcriptomics, and biochemical assays to identify the regulated targets of WDR73. We aimed to discover directly interacting molecules and the regulatory pathway of WDR73 and to illustrate the molecular mechanism between the WDR73 pathway and nephrotic disease in Galloway–Mowat syndrome. From the molecular mechanism we found in vitro, we draw a hypothesis that the damage to focal adhesion of podocytes caused by WDR73 defect is the key issue of kidney dysfunction. Finally, we verified the hypothesis in a podocyte-specific conditional knockout Wdr73 mouse model.

Abstract

(1) Background: Galloway–Mowat syndrome (GAMOS) is a rare genetic disease, classically characterized by a combination of various neurological symptoms and nephrotic syndrome. WDR73 is the pathogenic gene responsible for GAMOS1. However, the pathological and molecular mechanisms of GAMOS1, especially nephrotic syndrome caused by WDR73 deficiency, remain unknown. (2) Methods and Results: In this study, we first observed remarkable cellular morphological changes including impaired cell adhesion, decreased pseudopodia, and G2/M phase arrest in WDR73 knockout (KO) HEK 293 cells. The differentially expressed genes in WDR73 KO cells were enriched in the focal adhesion (FA) pathway. Additionally, PIP4K2C, a phospholipid kinase also involved in the FA pathway, was subsequently validated to interact with WDR73 via protein microarray and GST pulldown. WDR73 regulates PIP4K2C protein stability through the autophagy–lysosomal pathway. The stability of PIP4K2C was significantly disrupted by WDR73 KO, leading to a remarkable reduction in PIP2 and thus weakening the FA formation. In addition, we found that podocyte-specific conditional knockout (Wdr73 CKO) mice showed high levels of albuminuria and podocyte foot process injury in the ADR-induced model. FA formation was impaired in primary podocytes derived from Wdr73 CKO mice. (3) Conclusions: Since FA has been well known for its critical roles in maintaining podocyte structures and function, our study indicated that nephrotic syndrome in GAMOS1 is associated with disruption of FA caused by WDR73 deficiency.

Further delineation of the clinical spectrum of de novo TRIM8 truncating mutations

De novo mutations of the TRIM8 gene, which codes for a tripartite motif protein, have been identified using whole exome sequencing (WES) in two patients with epileptic encephalopathy (EE), but these reports were not sufficient to conclude that TRIM8 was a novel gene responsible for EE. Here we report four additional patients presenting with EE and de novo truncating mutations of TRIM8 detected by WES, and give further details of the patient previously reported by the Epi4K consortium. Epilepsy of variable severity was diagnosed in children aged 2 months to 3.5 years of age. All patients had developmental delay of variable severity with no or very limited language, often associated with behavioral anomalies and unspecific facial features or MRI brain abnormalities. The phenotypic variability observed in these patients appeared related to the severity of the epilepsy. One patient presented pharmacoresistant EE with regression, recurrent infections and nephrotic syndrome, compatible with the brain and kidney expression of TRIM8. Interestingly, all mutations were located at the highly conserved C-terminus section of TRIM8. This collaborative study confirms that TRIM8 is a novel gene responsible for EE, possibly associated with nephrotic syndrome. This report brings new evidence on the pathogenicity of TRIM8 mutations and highlights the value of data-sharing to delineate the phenotypic characteristics and biological basis of extremely rare disorders.

Collapsing Glomerulopathy in a Child with Galloway-Mowat Syndrome

Galloway-Mowat syndrome (GMS) is an autosomal recessive disorder with a poor prognosis that was first defined as a triad of central nervous system involvement, hiatal hernia, and nephrotic syndrome. However, this syndrome is now known to have a heterogeneous clinical presentation. The nephrotic syndrome is steroid resistant and is responsible for the outcome. The combination of collapsing glomerulopathy and GMS is very rare. A 26-month-old boy presented with steroid-resistant nephrotic syndrome associated with neurologic findings, including microcephaly, psychomotor retardation, and nystagmus. Magnetic resonance imaging showed marked cerebral atrophy, optic atrophy, and hypomyelination. A renal biopsy was consistent with collapsing glomerulopathy. If collapsing glomerulopathy is associated with neurological abnormalities, especially with microcephaly, clinicians should consider GMS as a possible underlying cause.

Extending the mutation spectrum for Galloway-Mowat syndrome to include homozygous missense mutations in the WDR73 gene

Galloway-Mowat syndrome is a rare autosomal-recessive disorder classically described as the combination of microcephaly and nephrotic syndrome. Recently, homozygous truncating mutations in WDR73 (WD repeat domain 73) were described in two of 31 unrelated families with Galloway-Mowat syndrome which was followed by a report of two sibs in an Egyptian consanguineous family. In this report, seven affecteds from four families showing biallelic missense mutations in WDR73 were identified by exome sequencing and confirmed to follow a recessive model of inheritance. Three-dimensional modeling predicted conformational alterations as a result of the mutation, supporting pathogenicity. An additional 13 families with microcephaly and renal phenotype were negative for WDR73 mutations. Missense mutations in the WDR73 gene are reported for the first time in Galloway-Mowat syndrome. A detailed phenotypic comparison of all reported WDR73-linked Galloway-Mowat syndrome patients with WDR73 negative patients showed that WDR73 mutations are limited to those with classical Galloway-Mowat syndrome features, in addition to cerebellar atrophy, thin corpus callosum, brain stem hypoplasia, occasional coarse face, late-onset and mostly slow progressive nephrotic syndrome, and frequent epilepsy.

Loss-of-function mutations in WDR73 are responsible for microcephaly and steroid-resistant nephrotic syndrome: Galloway-Mowat syndrome

Galloway-Mowat syndrome is a rare autosomal-recessive condition characterized by nephrotic syndrome associated with microcephaly and neurological impairment. Through a combination of autozygosity mapping and whole-exome sequencing, we identified WDR73 as a gene in which mutations cause Galloway-Mowat syndrome in two unrelated families. WDR73 encodes a WD40-repeat-containing protein of unknown function. Here, we show that WDR73 was present in the brain and kidney and was located diffusely in the cytoplasm during interphase but relocalized to spindle poles and astral microtubules during mitosis. Fibroblasts from one affected child and WDR73-depleted podocytes displayed abnormal nuclear morphology, low cell viability, and alterations of the microtubule network. These data suggest that WDR73 plays a crucial role in the maintenance of cell architecture and cell survival. Altogether, WDR73 mutations cause Galloway-Mowat syndrome in a particular subset of individuals presenting with late-onset nephrotic syndrome, postnatal microcephaly, severe intellectual disability, and homogenous brain MRI features. WDR73 is another example of a gene involved in a disease affecting both the kidney glomerulus and the CNS.

Genetic causes of focal segmental glomerulosclerosis: implications for clinical practice

Focal segmental glomerulosclerosis (FSGS) is a common cause of steroid-resistant nephrotic syndrome in children and adults. Although FSGS is considered a podocyte disease, the aetiology is diverse. In recent years, many inheritable genetic forms of FSGS have been described, caused by mutations in proteins that are important for podocyte function. In the present commentary, we review these genetic causes of FSGS and describe their prevalence in familial and sporadic FSGS. In routine clinical practice, the decision to perform the costly DNA analysis should be based on the assessment if the results affect the care of the individual patient with respect to the evaluation of extra-renal manifestations, treatment decisions, transplantation and genetic counselling.

Pathogenesis of focal segmental glomerular sclerosis in a girl with the partial deletion of chromosome 6p

Focal segmental glomerular sclerosis (FSGS) is a leading cause of the nephrotic syndrome and characterized by the sclerosing lesions that affect one or more segments of some glomeruli. We encountered a female patient with a partial deletion of chromosome 6p, who presented proteinuria at age 3 years. Detailed chromosomal analysis disclosed an interstitial deletion of 6p: del(6)(p22.1p22.3). No abnormality such as hydronephrosis or renal agenesis was disclosed by imaging, but FSGS was present in a renal biopsy specimen. The patient is currently 11 years old and shows mental retardation with mild deterioration in the renal function. To address the defective genes in the present patient, we carried out comparative genomic hybridization (CGH), showing that E2F3 on chromosome 6p is absent in this patient. E2F3, a member of the E2F family transcription factors, inhibits expression of vascular endothelial growth factor (VEGF) and induces apoptosis during vascular development. The deletion of E2F3 was also detected by employing a PCR method, suggesting that glomerular architecture had been compromised in this patient. Serum VEGF concentrations were elevated to 177 ± 21.4 pg/mL (upper limit of 33.3 pg/mL), when she was 6 years old, associated with the enhanced expression of VEGF in glomeruli. These findings suggest that the dysregulation of VEGF synthesis caused by the deletion of E2F3 may be associated with development of FSGS. In conclusion, among patients with idiopathic FSGS, an abnormality of E2F3 may exist on chromosome 6p. Therefore, one might consider chromosomal analyses in children with FSGS who have mental retardation.

Neuropathological homology in true Galloway-Mowat syndrome

Galloway-Mowat syndrome is a rare condition that is likely hereditary though the underlying offending gene has not been identified, and is characterized by microcephaly and severe nephrotic syndrome culminating in childhood death. Some of the reported cases have abnormalities in neuronal migration and intractable seizures, but many of the described cases focus on the renal pathology and emphasize a diversity of clinical and pathological features. The case described herein includes a thorough neuropathological description, and when the neuroradiology and neuropathology of the previously published cases is scrutinized, a fairly consistent clinical and neuropathological phenotype emerges.

Molecular genetic analysis of podocyte genes in focal segmental glomerulosclerosis--a review

This review deals with podocyte proteins that play a significant role in the structure and function of the glomerular filter. Genetic linkage studies has identified several genes involved in the development of nephrotic syndrome and contributed to the understanding of the pathophysiology of glomerular proteinuria and/or focal segmental glomerulosclerosis. Here, we describe already well-characterized genetic diseases due to mutations in nephrin, podocin, CD2AP, alpha-actinin-4, WT1, and laminin beta2 chain, as well as more recently identified genetic abnormalities in TRPC6, phospholipase C epsilon, and the proteins encoded by the mitochondrial genome. In addition, the role of the proteins which have shown to be important for the structure and functions by gene knockout studies in mice, are also discussed. Furthermore, some rare syndromes with glomerular involvement, in which molecular defects have been recently identified, are briefly described. In summary, this review updates the current knowledge of genetic causes of congenital and childhood nephrotic syndrome and provides new insights into mechanisms of glomerular dysfunction.