Case Report: Novel compound heterozygous TPRKB variants cause Galloway-Mowat syndrome

Background

Galloway-Mowat syndrome (GAMOS) is a rare genetic disease characterized by early-onset nephrotic syndrome and microcephaly with central nervous system abnormalities. Pathogenic variants in genes encoding kinase, endopeptidase, and other proteins of small size (KEOPS) complex subunits cause GAMOS. The subunit TPRKB (TP53RK binding protein) has been reported in only two patients with GAMOS with homozygous missense variants.

Clinical report

Herein, we described a three-year-old male with GAMOS. He exhibited developmental delay, developmental regression, microcephaly, distinctive facial features, skeletal abnormalities, and epilepsy. Brain magnetic resonance imaging revealed progressive brain atrophy, delayed myelination, T2-hypointense signals in the thalamus, and multiple intracranial abnormal signals on diffusion-weighted imaging. He presented with relapsing nephrotic proteinuria exacerbated by upper respiratory tract infections and progressive renal function decline. Exome sequencing identified compound heterozygous missense and frameshift variants in TPRKB: c.224dup, p.(Ser76IlefsTer3) and c.247C>T, p.(Leu83Phe).

Conclusions

Our study supports that pathogenic TPRKB variants cause KEOPS complex-related GAMOS.

Diagnosis delay a family of Galloway-Mowat Syndrome caused by a classical splicing mutation of Lage3

BACKGROUND

Galloway-Mowat syndrome (GAMOS) is a group of rare hereditary diseases by the combination of early onset steroid-resistant nephrotic syndrome (SRNS) and microcephaly with brain anomalies caused by WDR73, LAGE3, OSGEP, TP53RK, TPRKB, GON7, WDR4 or NUP133 mutations.

CASE PRESENTATION

We present the clinical and genetic features of a two-year-old boy with early nephrotic syndrome, microcephaly, growth retardation hypotonia and hypothyroidism. Genetic testing showed the presence of a canonical-splice mutation in the LAGE3 gene (NM_006014: c.188 + 1C > T). A total of nine female members of the family carried the variant. Seven male members died prematurely, and three of them suffered from nephrotic syndrome, which is consistent with the x-linked gene map of the disease. The overall symptoms of the disease due to the LAGE3 mutation were mild compared to other pathogenic genes.

CONCLUSION

As far as we know, this is the largest family case of GAMOS2 caused by LAGE3 mutation found so far. We also compared other subtypes of GAMOS. Due to the heterogeneity of the renal phenotype, regular proteinuria screening is recommended for all patients diagnosed with GAMOS.

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.

A suite of in vitro and in vivo assays for monitoring the activity of the pseudokinase Bud32

Bud32 is a member of the protein kinase superfamily that is invariably conserved in all eukaryotic and archaeal organisms. In both of these kingdoms, Bud32 forms part of the KEOPS (Kinase, Endopeptidase and Other Proteins of Small size) complex together with the three other core subunits Kae1, Cgi121 and Pcc1. KEOPS functions to generate the universal and essential tRNA post-transcriptional modification N⁶-theronylcarbamoyl adenosine (t⁶A), which is present at position A37 in all tRNAs that bind to codons with an A in the first position (ANN decoding tRNAs) and is essential for the fidelity of translation. Mutations in KEOPS genes in humans underlie the severe genetic disease Galloway-Mowat syndrome, which results in childhood death. KEOPS activity depends on two major functions of Bud32. Firstly, Bud32 facilitates efficient tRNA substrate recruitment to KEOPS and helps in positioning the A37 site of the tRNA in the active site of Kae1, which carries out the t⁶A modification reaction. Secondly, the enzymatic activity of Bud32 is required for the ability of KEOPS to modify tRNA. Unlike conventional protein kinases, which employ their enzymatic activity for phosphorylation of protein substrates, Bud32 employs its enzymatic activity to function as an ATPase. Herein, we present a comprehensive suite of assays to monitor the activity of Bud32 in KEOPS in vitro and in vivo. We present protocols for the purification of the archaeal KEOPS proteins and of a tRNA substrate, as well as protocols for monitoring the ATPase activity of Bud32 and for analyzing its role in tRNA binding. We further present a complementary protocol for monitoring the role Bud32 has in cell growth in yeast.

Galloway-Mowat Syndrome Type 3 Caused by OSGEP Gene Variants: A Case Report and Literature Review

BACKGROUND

Galloway-Mowat syndrome type 3 (GAMOS3) is an extremely rare and severe autosomal-recessive disease characterized by early-onset nephrotic syndrome (NS), microcephaly and neurological impairment. Reported GAMOS cases have gradually increased since pathogenic OSGEP variants were identified as the aetiology in 2017.

METHODS

Using whole-exome sequencing and a data analysis process established by Children's Hospital of Fudan University, the clinical and molecular features of 3 infants with OSGEP mutations were summarized. Literature regarding the clinical features of GAMOS3 caused by OSGEP variants was reviewed.

RESULTS

Thirty-seven individuals (3 from this study) from 34 families were included. Twenty-two different OSGEP variants were identified. The c.740G>A (p.Arg247Gln) variant in OSGEP was detected in 15 families (44%), all from Asia. Most affected individuals (including patients I and II in this study) showed a typical phenotype, including microcephaly (92%) with brain anomalies (97%), developmental delay (81%), congenital NS (54%), and craniofacial (94%) and skeletal dysmorphism (84%). Renal manifestations varied from proteinuria (94%, median onset = 1.5 months) to NS (83%) and end-stage renal disease (48%, 11 months) during follow-up. Patients with congenital NS had a lower survival probability (median survival time = 3 months) than those without congenital NS (78 months) (P < 0.01, log-rank test).

CONCLUSION

GAMOS3 is a progressive renal-neurological syndrome with a poor prognosis, especially with congenital NS. Microcephaly with dysmorphic features are vital clues to further evaluate renal impairment and brain anomalies. Timely molecular diagnosis is crucial for clinical decision-making, appropriate treatment and genetic counselling.

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.

Novel variants in OSGEP leading to Galloway-Mowat syndrome by altering its subcellular localization

Galloway-Mowat syndrome (GAMOS) is an extremely rare clinically heterogeneous autosomal or X-linked inherited recessive disease characterized by early-onset steroid-resistant nephrotic syndrome (SRNS), microcephaly and neurological impairment. In this study, two siblings mainly presenting with decreased head circumference, hypotonia, gross motor delay, and dysmorphic features were initially detected without pathogenic variants by karyotyping, SNP-array and WES. After a 3 year's follow-up, the proband manifested additional proteinuria, hematuria and "deeper sulci" with a sign of brain atrophy. By reanalysis on the proband's previous WES data, two novel compound heterozygous variants of OSGEP (c.133dupA; c.608C > T) were identified. Furthermore, functional studies showed that the variants reduced the expression of OSGEP protein and activated the DNA damage response (DDR) signaling in the lymphoblastoid cell lines (LCLs) obtained from the patient. The analysis of protein localization with confocal microscopy revealed that the EGFP-tagged/HA-tagged mutant OSGEP proteins were abnormal aggregation or retained inside the cytosol, respectively. Our study not only expanded the pathogenic variant spectrum of OSGEP but also carried on regular follow-up for kidney involvement and established a strategy for evaluation on the function of mutant OSGFP by subcellular localization assay.

Galloway-Mowat syndrome: New insights from bioinformatics and expression during Xenopus embryogenesis

Galloway-Mowat syndrome (GAMOS) is a rare developmental disease. Patients suffer from congenital brain anomalies combined with renal abnormalities often resulting in an early-onset steroid-resistant nephrotic syndrome. The etiology of GAMOS has a heterogeneous genetic contribution. Mutations in more than 10 different genes have been reported in GAMOS patients. Among these are mutations in four genes encoding members of the human KEOPS (kinase, endopeptidase and other proteins of small size) complex, including OSGEP, TP53RK, TPRKB and LAGE3. Until now, these components have been functionally mainly investigated in bacteria, eukarya and archaea and in humans in the context of the discovery of its role in GAMOS, but the KEOPS complex members' expression and function during embryogenesis in vertebrates is still unknown. In this study, in silico analysis showed that both gene localization and the protein sequences of the three core KEOPS complex members Osgep, Tp53rk and Tprkb are highly conserved across different species including Xenopus laevis. In addition, we examined the spatio-temporal expression pattern of osgep, tp53rk and tprkb using RT-PCR and whole mount in situ hybridization approaches during early Xenopus development. We observed that all three genes were expressed during early embryogenesis and enriched in tissues and organs affected in GAMOS. More precisely, KEOPS complex genes are expressed in the pronephros, but also in neural tissue such as the developing brain, eye and cranial cartilage. These findings suggest that the KEOPS complex plays an important role during vertebrate embryonic development.

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.

Galloway-Mowat syndrome in Taiwan: OSGEP mutation and unique clinical phenotype

Background

Galloway-Mowat syndrome (GAMOS) is a rare autosomal recessive disease characterized by the combination of glomerulopathy with early-onset nephrotic syndrome and microcephaly with central nervous system anomalies. Given its clinical heterogeneity, GAMOS is believed to be a genetically heterogenous group of disorders. Recently, it has been reported that mutations in KEOPS-encoding genes, including the OSGEP gene, were responsible for GAMOS.

Results

Overall, 6 patients from 5 different Taiwanese families were included in our study; the patients had an identical OSGEP gene mutation (c.740G > A transition) and all exhibited a uniform clinical phenotype with early-onset nephrotic syndrome, craniofacial and skeletal dysmorphism, primary microcephaly with pachygyria, and death before 2 years of age. We reviewed their clinical manifestations, the prenatal and postnatal presentations and ultrasound findings, results of imaging studies, associated anomalies, and outcome on follow-up. All individuals were found to have an “aged face” comprising peculiar facial dysmorphisms. Arachnodactyly or camptodactyly were noted in all patients. Neurological findings consisted of microcephaly, hypotonia, developmental delay, and seizures. Brain imaging studies all showed pachygyria and hypomyelination. All patients developed early-onset nephrotic syndrome. The proteinuria was steroid-resistant and eventually resulted in renal function impairment. Prenatal ultrasound findings included microcephaly, intrauterine growth restriction, and oligohydramnios. Fetal MRI in 2 patients confirmed the gyral and myelin abnormalities.

Conclusions

Our study suggests that a careful review of the facial features can provide useful clues for an early and accurate diagnosis. Prenatal ultrasound findings, fetal MRI, genetic counseling, and mutation analysis may be useful for an early prenatal diagnosis.

Nephrological and urological complications of homozygous c.974G>A (p.Arg325Gln) OSGEP mutations

BACKGROUND

Galloway-Mowat syndrome (GAMOS) (OMIM #251300) is a severe autosomal recessive disease characterized by the combination of early-onset steroid-resistant nephrotic syndrome (SRNS) and microcephaly with brain anomalies caused by WDR73 as well as OSGEP, TP53RK, TPRKB, or LAGE3 mutations.

OBJECTIVE

We report on the hitherto undescribed urological and nephrological complications of the homozygous c.974G>A (p.Arg325Gln) OSGEP mutations in a 7-year-old Caucasian girl.

CASE DIAGNOSIS

The patient came to the attention of pediatric nephrology at the age of 3 years and 11 months, when she presented with status epilepticus due to profound hypomagnesemia (0.31 mmol/L, normal 0.65-1.05). A 24-h urine demonstrated a magnesium loss of 0.6 mmol/kg/day with associated proteinuria suggesting renal tubulopathy. Subsequently, she developed recurrent urinary tract infections (UTIs) and was diagnosed with neurogenic bladder dysfunction. The patient continued to have UTIs associated with seizures and sequential cultures growing multi-drug-resistant organisms despite of antibiotic prophylaxis. In addition, the proteinuria (median microalbumin/creatinine ratio 647 mg/mmol) increased, and she developed partial Fanconi syndrome. At age 7, she developed a large bladder calculus (3.3 × 3.2 cm) and three left non-obstructing renal calculi associated with elevated urinary cystine, hypercalciuria, and ongoing hypomagnesemia and required surgical intervention. Glomerular filtration rate (GFR) remained normal and she never developed frank nephrotic syndrome (average albumin 31 g/L).

CONCLUSIONS

It is unclear if patients with OSGEP mutations with tubular symptoms rather than nephrotic syndrome should be considered a different entity. Nephrological and urological complications of OSGEP mutations can be challenging and require a multidisciplinary approach.

Mutations in WDR4 as a new cause of Galloway-Mowat syndrome

Galloway-Mowat syndrome (GAMOS) is a phenotypically heterogeneous disorder characterized by neurodevelopmental defects combined with renal-glomerular disease, manifesting with proteinuria. To identify additional monogenic disease causes, we here performed whole exome sequencing (WES), linkage analysis, and homozygosity mapping in three affected siblings of an Indian family with GAMOS. Applying established criteria for variant filtering, we identify a novel homozygous splice site mutation in the gene WDR4 as the likely disease-causing mutation in this family. In line with previous reports, we observe growth deficiency, microcephaly, developmental delay, and intellectual disability as phenotypic features resulting from WDR4 mutations. However, the newly identified allele additionally gives rise to proteinuria and nephrotic syndrome, a phenotype that was never reported in patients with WDR4 mutations. Our data thus expand the phenotypic spectrum of WDR4 mutations by demonstrating that, depending on the specific mutated allele, a renal phenotype may be present. This finding suggests that GAMOS may occupy a phenotypic spectrum with other microcephalic diseases. Furthermore, WDR4 is an additional example of a gene that encodes a tRNA modifying enzyme and gives rise to GAMOS, if mutated. Our findings thereby support the recent observation that, like neurons, podocytes of the renal glomerulus are particularly vulnerable to cellular defects resulting from altered tRNA modifications.

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

Background

Galloway-Mowat syndrome (GMS) is a rare autosomal recessive condition first described in 1968 and characterized by microcephaly and infantile onset of central nervous system (CNS) abnormalities resulting in severely delayed psychomotor development, cerebellar atrophy, epilepsy, and ataxia, as well as renal abnormalities such as nephrotic syndrome, proteinuria, end-stage renal disease (ESRD), and hiatal hernia.

Case presentation

We describe a GMS case diagnosed with homozygous missense mutation in the WDR73 gene, with absence of renal abnormalities. We expanded the clinical phenotype of GMS with WDR73 gene defect to include retinal dysfunction with missense mutation and developmental dysplasia of the hip. We compared eye findings of our case to previously reported cases, and we present an electroretinogram (ERG) picture for the first time in the literature.

Conclusion

We recommend that clinicians screen patients with GM syndrome for retinal dysfunction and that a skeletal survey should be done to detect developmental dysplasia of the hip (DDH) so as to provide for early intervention.

Homozygous mutation in NUP107 leads to microcephaly with steroid-resistant nephrotic condition similar to Galloway-Mowat syndrome

BACKGROUND

Microcephaly with nephrotic syndrome is a rare co-occurrence, constituting the Galloway-Mowat syndrome (GAMOS), caused by mutations in WDR73 (OMIM: 616144). However, not all patients harbour demonstrable WDR73 deleterious variants, suggesting that there are other yet unidentified factors contributing to GAMOS aetiology.

METHODS

Autozygosity mapping and candidate analysis was used to identify deleterious variants in consanguineous families. Analysis of patient fibroblasts was used to study splicing and alterations in cellular function.

RESULTS

In two consanguineous families with five affected individuals from Turkey with a GAMOS-like presentation, we identified a shared homozygous variant leading to partial exon 4 skipping in nucleoporin, 107-KD (NUP107). The founder mutation was associated with concomitant reduction in NUP107 protein and in the obligate binding partner NUP133 protein, as well as density of nuclear pores in patient cells.

CONCLUSION

Recently, NUP107 was suggested as a candidate in a family with nephrotic syndrome and developmental delay. Other NUP107-reported cases had isolated renal phenotypes. With the addition of these individuals, we implicate an allele-specific critical role for NUP107 in the regulation of brain growth and a GAMOS-like presentation.

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.

Seizures Related to Hypomagnesemia: A Case Series and Review of the Literature

OBJECTIVE

Childhood seizures have various nonneurological etiologies. The patient's magnesium levels should be measured when evaluating afebrile seizures. The purpose of the current case series is to describe a systematic approach for diagnosing hypomagnesemia using 3 recent patient cases.

METHODS

This case series describes 3 patients with unprovoked hypomagnesemia-associated seizures. The authors describe the differential diagnosis, pathophysiology, and the workup of hypomagnesemia-associated seizures.

RESULTS

Hypomagnesemia contributed to the cause of the seizures in all 3 cases. Various causes of hypomagnesemia were investigated, including genetic etiologies. All 3 patients were maintained at a magnesium level >0.65 mmol/L, which improved or eliminated the seizures.

SIGNIFICANCE

Magnesium levels should always be measured when trying to determine the etiology of seizures. Hypomagnesemia and afebrile seizures should be treated with the goal of maintaining a magnesium concentration >0.65 mmol/L. Although rare, genetic causes of hypomagnesemia should be considered, once common causes of hypomagnesemia are ruled out.