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 hormone-resistant nephrotic syndrome, microcephaly, and brain abnormalities [1]. Renal alterations in GAMOS manifest in a variety of forms, ranging from isolated proteinuria to hormone-resistant nephropathy, end-stage renal disease, and multiple organ failure, leading to death [2]. Kidney biopsies also show various types of histological changes, including diffuse mesangial sclerosis, focal segmental glomerulosclerosis (FSGS), mesangial hyperplasia, increased mesangial matrix, and minimal change [3‒5].

Genetic mutations are the main cause of GAMOS. A truncating variant in the WDR73 gene is described as the first monogenic factor in GAMOS [6]. Data from Jinks et al. [6] demonstrate that in humans, WDR73 interacts through mitotic microtubules to regulate cell cycle progression, proliferation, and survival in the brain and kidney. Recently, mutations in OSGEP, TP53RK, TPRKB, and LAGE have also been identified as a cause of GAMOS [1]. These genes encode 4 subunits of the highly conserved KEOPS complex. The KEOPS complex catalyzes a universal post-transcriptional modification of transfer RNA and plays an important role in gene transcription and genome maintenance, and also plays an important role in brain and renal development [7]. Clinically, patients with KEOPS complex mutations have primary microcephaly, developmental delay, predisposition to seizures, and early-onset nephrotic syndrome [1]. Inheritance is autosomal recessive or X-linked (LAGE3).

Here, we report a patient with GAMOS carrying the newly identified LAGE3 pathogenic variants with microcephaly, severe developmental delay, and renal phenotype (large proteinuria), while normal glomerular filtration rate and serum albumin levels were maintained. Of note, this patient has never been diagnosed with nephrotic syndrome (average albumin 30 g/L).

The child was hospitalized for pneumonia at the age of 1, with abnormal urinalysis. The urinalysis showed protein 3+, occult blood+, and serum albumin 27.2 g/L. The patient showed growth retardation and delayed development in the past. Until the age of 3, he went to the doctor due to growth and development problems. The Gesell Developmental Observation-Revised (GDO-R) assessment showed gross motor development was equivalent to 11.5 months old, fine motor development was equivalent to 21 months old, adaptability development was equivalent to 15 months, language development was equivalent to 12 months, social behavior development was equivalent to 19.5 months, and the overall evaluation was low intelligence. Physical examination of the patient on admission: all fingers are short and stubby. The forehead is narrow and slanted. The patient’s cardiopulmonary examination is not special. He has weak muscle tone. Main laboratory results are shown on Table 1. The patient’s creatinine was consistently normal. A dual-energy X-ray showed low bone mass (Z-score: −3.0) and an otoacoustic emission examination indicated that the patient had normal hearing at all evaluation rates (750–8,000 Hz). Brain MRI showed extensive symmetrical abnormal signaling in the white matter with brain atrophy (significant atrophy of the cerebellar hemispheres) (Fig. 1d). The electromyography (EMG) test showed myogenic damage. There were no obvious abnormalities seen in cardiac color on Doppler ultrasound or electrocardiogram. The patient had no sensorineural ataxia or tremor, and inherited metabolic disorders were excluded by laboratory tests.

The proband undergoes kidney biopsy under general anesthesia. The pathological results suggested that 3/20 glomeruli were focal segmental sclerosis. H&E staining of renal puncture tissue suggested FSGS (Fig. 1b). Under electron microscope, the thickness of the glomerular basement membrane was ∼120–280 nm, and the foot processes were diffusely fused, with microvilli degeneration, and a small amount of electron dense deposits were seen in individual mesangial areas (Fig. 1c). The patient was diagnosed with FSGS.

In order to clarify the cause, after medical ethics review and the parents of the child signed an informed consent form, 2 mL of the peripheral blood samples of the child and the parents were collected for whole-exome genome sequencing. Whole-exome sequencing revealed a hemizygous mutation of c.290T>G (p.L97R) in the LAGE3 gene. This mutation was not detected in the patient’s father, but the patient’s mother was a heterozygous carrier. At present, the professional version of HGMD data only includes 4 variants of the LAGE3 gene, including one classic splice site (c.188+1G>A, c.317+4A>G), and two missense variant sites (c.316G>T, c.410T>C). The mutation site in our patient was close to site 316, and combined with the clinical manifestations of the patient, we speculated that the mutation was also pathogenic. The family members of the proband were verified by first-generation sequencing, and it was found that the mutation site was inherited from the mother, and the father was wild type. At the same time, mutations in the TRPC6 gene (c.2206-6G>A), and the NUP160 gene (c.562A>G) were detected. The patient’s mother was also a heterozygote for the TRPC6 variant (Fig. 1a).

Before we get the genetic sequencing results, methylprednisolone sodium succinate 10 mg b.i.d. was given for 6 days, and enalapril maleate 2.5 mg q.n. was given as a symptomatic treatment, but the proteinuria of the child did not improve, the drug was discontinued. Regular follow-up visits are currently in the outpatient clinic. Test and evaluate his urine output, blood pressure, and monitor urine routine, urine protein quantitative, kidney function, and other related indicators. The child was then admitted to the rehabilitation department and started formal rehabilitation treatment.

Galloway-Mowat syndrome (GAMOS) was first reported in 1968, describing a pair of siblings suffering from the primary nephrotic syndrome-hiatal hernia-microcephaly triad [8]. Recent studies have revealed the important role of gene mutation in the pathogenesis of GAMOS. In 2014, Colin et al. first reported that the loss of WDR73 (WD repeat domain 73) expression can lead to abnormal nuclei of glomerular podocytes, changes in microtubule networks, and cell viability [9]. Braun et al. [1] found that the subunits coded by the four genes LAGE3/OSGEP/TP53RK/TPRKB constitute a highly conserved kinase-endopeptidase and other proteins of small size complex (KEOPS), which is one of the key factors in the pathogenesis of GAMOS. Phenotypically, the patients with KEOPS subunit mutations primarily had microcephaly, developmental delay, predisposition to seizures, and early-onset nephrotic syndrome. Most affected patients die in early childhood [1]. There have been 3 cases of LAGE3 gene mutation reported so far: c188+1G>A, c.316G>T (p.val106Phe), c410T>C (p.Phe137Ser), and all have the phenotypes mentioned above [9]. CRISPR/Cas9 LAGE3 knockout mouse embryos had significantly reduced cortical length, cortical-midbrain length, and cortical width, reproducing the human microcephaly phenotype [9].

It is well known that nephrotic syndrome is an important factor in the diagnosis of GAMOS. However, the patient in this study had persistent macroalbuminuria without serum albumin below 25 g/L, which did not meet the diagnostic criteria for nephrotic syndrome. This suggests that proteinuria may not always amount to the nephrotic range, which illustrates various manifestations of LAGE3 gene mutations. The OSGEP mutation reported by Tao et al. is also an isolated case of proteinuria that did not meet the diagnostic criteria for nephrotic syndrome [10]. The mutation found in our patient was in the LAGE3 gene, and may be the first patient not diagnosed with nephrotic syndrome due to a LAGE3 mutation.

Unlike other case reports, our patient also has a mutation of the TRPC6 gene (c.2206-6G>A.TRPC6). Pathways involving this mutated gene have been implicated in the pathogenesis of kidney diseases, especially in familial nephrosis [11]. TRPC6 contributes to certain glomerular lesions as well as tubulointerstitial fibrosis [11‒14]. More recent evidence has suggested that dysregulation of wild-type TRPC6 channels cause acquired glomerular diseases, and in vitro models in which podocytes are exposed to serum or plasma samples from patients with recurrent FSGS, this dysregulation is a factor implicated in the pathogenesis of primary FSGS [12, 15, 16]. To date, we have observed a glomeruloprotective effect with TRPC6 inactivation in 3 different chronic disease models (chronic PAN nephrosis, anti-GBM autoimmune glomerulonephritis, and aging). It is possible that having this TRPC6 variant contributed to this patient not developing nephrotic syndrome. Agents that block or suppress TRPC6 may also be effective in other genetic forms of FSGS [17]. Based on the actions of putative serum “permeability factors” on TRPC6 channels in podocytes, including samples taken from patients, it is possible that TRPC6 inhibitors could be efficacious in people with primary FSGS [12, 16], and knockout studies in rats support the concept of TRPC6 inhibition in adaptive forms of FSGS, commonly seen in patients with severe uncontrolled hypertension, reduced renal mass, or a markedly reduced number of functional nephrons [13]. So we hypothesized that mutations in TPRC6 had a saving effect on FSGS in this patient.

The patient also has the NUP160 gene c.562A>G mutation. Vasu et al. [18] confirmed nucleoporins Nup160, Nup133, Nup107, and Nup96 exist as a complex in Xenopus egg extracts and in assembled pores, now termed the Nup160 complex. The nuclear pore complexes are macromolecular assemblies that play roles in nucleocytoplasmic transport in both directions, and in the regulation of transcription and chromatin organization [19]. NUP107 and NUP133 are interacting subunits of the nuclear pore complex in the nuclear envelope during interphase, and these proteins are also involved in centrosome positioning and spindle assembly during mitosis. Recently, biallelic mutations in NUP107 were identified in steroid-resistant nephrotic syndrome, 8,9 XX gonadal dysgenesis, 10 and GAMOS [20‒22]. Of note, 4 families with a homozygous NUP107 mutation (c.303G>A, p.Met101Ile) leading to exon 4 skipping were found to have GAMOS-like features such as microcephaly, intellectual disability, and steroid-resistant nephrotic syndrome [22, 23]. Fujita et al. [24] identify a homozygous NUP133 mutation in a previously described consanguineous GAMO affected family [25]. In vitro and in vivo functional analyses of the mutation will be displayed, supporting the hypothesis that the NUP133 mutation causes GAMOS [24]. Based on the above evidence, it is reasonable to speculate boldly that NUP160 mutations may cause GAMOS.

In conclusion, we reviewed the case of a 4-year-old child with GAMOS who presented with symptoms such as proteinuria, delayed language development, and delayed motor development, corresponding to clinical phenotypes such as massive proteinuria, cerebellar hypoplasia, global developmental delay, and facial deformity. Distinctive from previous reports, the patient had 2 mutations in TRPC6 (c.2206-6G>A) and NUP160 (c.562A>G), being the first time this mutation site has been discovered. This case study will provide important guidance for the future clinical diagnosis and identification of the disease. Nephrological and urological complications of LAGE gene mutations can be challenging and will require a multidisciplinary approach. The CARE Checklist has been completed by the authors for this case report, attached as online supplementary material (for all online suppl. material, see https://doi.org/10.1159/000533580).

We thank the patient and her family for participating in this study.

This study was approved by the Ethics Committee of the First Affiliated Hospital of Zhejiang University School of Medicine (No. 2020047), Hangzhou, China. Written informed consent was obtained from the parent/legal guardian of the patient for publication of the details of their medical case and any accompanying images. We have received written informed consent for the publication of these details and any accompanying images.

The authors declare no conflicts of interest.

National Natural Science Foundation of China (Grant/Award No. U20A20351), Key Research and Development Plan of Zhejiang Province (Grant/Award No. 2021C03079), the Natural Science Foundation of Zhejiang Province (LY22H050001), the key project of provincial ministry construction, Health Science and Technology Project Plan of Zhejiang Province (WKJ-ZJ-2128), and Key Laboratory of Women’s Reproductive Health Research of Zhejiang Province (No. ZDFY2020-RH-0006).

L.H., X.Z., Y.Z., Y.W., and J.M. participated in the acquisition of clinical data. Y.Z. and J.M. performed the mitochondrial DNA sequencing. L.H. wrote the manuscript and J.M. revised the manuscript. All authors have read and agreed to the published version of the manuscript.

All data generated or analyzed during this study are included in this article and its online supplementary material files. Further inquiries can be directed to the corresponding author.