De novo TRIM8 variants impair its protein localization to nuclear bodies and cause developmental delay, epilepsy, and focal segmental glomerulosclerosis.

Focal segmental glomerulosclerosis (FSGS) is the main pathology underlying steroid-resistant nephrotic syndrome (SRNS) and a leading cause of chronic kidney disease. Monogenic forms of pediatric SRNS are predominantly caused by recessive mutations, while the contribution of de novo variants (DNVs) to this trait is poorly understood. Using exome sequencing (ES) in a proband with FSGS/SRNS, developmental delay, and epilepsy, we discovered a nonsense DNV in TRIM8, which encodes the E3 ubiquitin ligase tripartite motif containing 8. To establish whether TRIM8 variants represent a cause of FSGS, we aggregated exome/genome-sequencing data for 2,501 pediatric FSGS/SRNS-affected individuals and 48,556 control subjects, detecting eight heterozygous TRIM8 truncating variants in affected subjects but none in control subjects (p = 3.28 × 10-11). In all six cases with available parental DNA, we demonstrated de novo inheritance (p = 2.21 × 10-15). Reverse phenotyping revealed neurodevelopmental disease in all eight families. We next analyzed ES from 9,067 individuals with epilepsy, yielding three additional families with truncating TRIM8 variants. Clinical review revealed FSGS in all. All TRIM8 variants cause protein truncation clustering within the last exon between residues 390 and 487 of the 551 amino acid protein, indicating a correlation between this syndrome and loss of the TRIM8 C-terminal region. Wild-type TRIM8 overexpressed in immortalized human podocytes and neuronal cells localized to nuclear bodies, while constructs harboring patient-specific variants mislocalized diffusely to the nucleoplasm. Co-localization studies demonstrated that Gemini and Cajal bodies frequently abut a TRIM8 nuclear body. Truncating TRIM8 DNVs cause a neuro-renal syndrome via aberrant TRIM8 localization, implicating nuclear bodies in FSGS and developmental brain disease.

Identification of Potential Modulators of a Pathogenic G Protein-Gated Inwardly Rectifying K+ Channel 4 Mutant: In Silico Investigation in the Context of Drug Discovery for Hypertension.

Genetic abnormalities have been associated with primary aldosteronism, a major cause of secondary hypertension. This includes mutations in the KCNJ5 gene, which encodes G protein-gated inwardly rectifying K+ channel 4 (GIRK4). For example, the substitution of glycine with glutamic acid gives rise to the pathogenic GIRK4G151E mutation, which alters channel selectivity, making it more permeable to Na+ and Ca2+. While tertiapin and tertiapin-Q are well-known peptide inhibitors of the GIRK4WT channel, clinically, there is a need for the development of selective modulators of mutated channels, including GIRK4G151E. Using in silico methods, including homology modeling, protein-peptide docking, ligand-binding site prediction, and molecular docking, we aimed to explore potential modulators of GIRK4WT and GIRK4G151E. Firstly, protein-peptide docking was performed to characterize the binding site of tertiapin and its derivative to the GIRK4 channels. In accordance with previous studies, the peptide inhibitors preferentially bind to the GIRK4WT channel selectivity filter compared to GIRK4G151E. A ligand-binding site analysis was subsequently performed, resulting in the identification of two potential regions of interest: the central cavity and G-loop gate. Utilizing curated chemical libraries, we screened over 700 small molecules against the central cavity of the GIRK4 channels. Flavonoids, including luteolin-7-O-rutinoside and rutin, and the macrolides rapamycin and troleandomycin bound strongly to the GIRK4 channels. Similarly, xanthophylls, particularly luteoxanthin, bound to the central cavity with a strong preference towards the mutated GIRK4G151E channel compared to GIRK4WT. Overall, our findings suggest potential lead compounds for further investigation, particularly luteoxanthin, that may selectively modulate GIRK4 channels.

The role of novel COQ8B mutations in glomerulopathy and related kidney defects.

BACKGROUND AND OBJECTIVES: Glomerulopathies affect kidney glomeruli and can lead to end-stage renal disease if untreated. Clinical and experimental evidence have identified numerous (>20) genetic mutations in the mitochondrial coenzyme Q8B protein (COQ8B) primarily associated with nephrotic syndrome. Yet, little else is understood about COQ8B activity in renal pathogenesis and its role in mitochondrial dysfunction. We identified additional novel COQ8B mutations in a glomerulopathy patient and aimed to define the potential structural and functional defects of COQ8B mutations. DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS: Whole exome sequencing was performed on a Hispanic female presenting with proteinuria. Novel mutations in the COQ8B gene were identified. The effects of mutation on protein function, mitochondrial morphology, and disease progression were investigated by histopathology, transmission electron microscopy, homology modeling, and in silico structural analysis. RESULTS: We have characterized the pathophysiology of novel COQ8B mutations, compound heterozygous for two alterations c.1037T>G (p.I346S), and c.1560G>A (p.W520X), in the progression of proteinuria in a Hispanic female. Histopathology revealed defects in podocyte structure and mitochondrial morphology. In silico and computation analyses highlight possible structural origins of COQ8B dysfunction in the presence of mutations. CONCLUSIONS: Novel mutations in COQ8B present promising biomarkers for the early detection and therapeutic targeting of mitochondrial glomerulopathy. Insights from structural modeling suggest roles of mutation-dependent alterations in COQ8B allosteric regulation, protein folding, or stability in renal pathogenesis.

Congenital nephrotic syndrome.

Congenital nephrotic syndrome (CNS), a challenging form of nephrotic syndrome, is characterized by massive proteinuria, hypoalbuminemia, and edema. Extensive leakage of plasma proteins is the main feature of CNS. Patients can be diagnosed in utero or during the first few weeks of life, usually before three months. The etiology of CNS can be related to either genetic or nongenetic etiologies. Pathogenic variants in NPHS1, NPHS2, LAMB2, WT1, and PLCE1 genes have been implicated in this disease. The clinical course is complicated by significant edema, infections, thrombosis, hypothyroidism, failure to thrive, and others. Obtaining vascular access, frequent intravenous albumin infusions, diuretic use, infection prevention, and nutritional support are the mainstay management during their first month of life. The best therapy for these patients is kidney transplantation. CNS diagnosis and treatment continue to be a challenge for clinicians. This review increases the awareness about the pathogenesis, diagnosis, and management of CNS patients.