Whole-exome sequencing identifies a novel compound heterozygous mutation of ANKS6 gene in a Chinese nephronophthisis patient

The Han:SPRD Rat: A Preclinical Model of Polycystic Kidney Disease

Autosomal Dominant Polycystic Kidney Disease (ADPKD) stands as the most prevalent hereditary renal disorder in humans, ultimately culminating in end-stage kidney disease. Animal models carrying mutations associated with polycystic kidney disease have played an important role in the advancement of ADPKD research. The Han:SPRD rat model, carrying an R823W mutation in the Anks6 gene, is characterized by cyst formation and kidney enlargement. The mutated protein, named Samcystin, is localized in cilia of tubular epithelial cells and seems to be involved in cystogenesis. The homozygous Anks6 mutation leads to end-stage renal disease and death, making it a critical factor in kidney development and function. This review explores the utility of the Han:SPRD rat model, highlighting its phenotypic similarity to human ADPKD. Specifically, we discuss its role in preclinical trials and its importance for investigating the pathogenesis of the disease and developing new therapeutic approaches.

Biallelic ANKS6 null variants cause notable extrarenal phenotypes in a nephronophthisis patient and lead to hepatobiliary abnormalities by YAP1 deficiency

The ankyrin repeat and sterile alpha motif domain containing 6 (ANKS6) gene, encoding an inversin compartment protein of the primary cilium, was recently reported as a pathogenic gene of nephronophthisis (MIM PS256100). Extrarenal manifestations are frequently observed in this disease, however, potential genotype-phenotype correlations and the underlying mechanisms remain poorly understood. Here we described an infant with kidney failure, hepatobiliary abnormalities, and heart disease, in whom whole exome sequencing identified compound heterozygous variants in ANKS6, including a novel nonsense variant p.Trp458* and a recurrent splicing variant c.2394+1G > A. mRNA expression studies showed that the splicing variant caused aberrant mRNA splicing with exon 13 skipping and the biallelic variants were predicted to cause loss of ANKS6 function. We systematically characterized the clinical and genetic spectra of the disease and revealed that biallelic null variants in ANKS6 cause more severe kidney disease and more extrarenal manifestations, thus establishing a clear genotype-phenotype correlation for the disease. Further evaluations showed that ANKS6 deficiency reduced YAP1 expression in the patient's bile duct epithelium and ANKS6 promotes YAP1 transcriptional activity in a dose-dependent manner, indicating that loss of ANKS6 function causes hepatobiliary abnormalities through YAP1 deficiency during biliary morphogenesis and development, which may offer new therapeutic targets.

A single heterozygous nonsense mutation in the TTC21B gene causes adult-onset nephronophthisis 12: A case report and review of literature

BACKGROUND

Nephronophthisis type 12 (NPHP 12) is a rare cilia-related cystic kidney disease, caused by TTC21B mutation, mainly involving the kidneys, which generally occurs in children. Our study aimed to illustrate its clinical, pathological and genetic characteristics by reporting an adult-onset case of NPHP 12 caused by a single heterozygous nonsense mutation of TTC21B confirmed by renal histology and whole exome sequencing and reviewing related literature with a comparative analysis of the clinical features of each case. It will further increase the recognition of this rare kidney genetic disease, which sometimes can manifest as an adult disease.

RESULTS

A 33-years-old man showed a chronic disease course, and he exhibited slight renal dysfunction (CKD stage 3, eGFR = 49 ml/[min* 1.73 m2]) with renal tubular proteinuria, without any extrarenal manifestations, congenital malformation history of kidney disease, or family hereditary disease. Renal histological findings showed substantial interstitial fibrosis with some irregular and tortuous tubules with complex branches and segmental thickening and splitting of the tubular basement membrane. The patient was diagnosed with chronic interstitial nephritis for an unknown reason clinically. Further genetic analysis revealed a single heterozygous nonsense mutation in the TTC21B gene and NPHP 12 was diagnosed finally.

CONCLUSION

A single heterozygous mutation in the TTC21B gene may cause atypical NPHP12, which had a relatively later onset and milder clinical symptoms without developmental abnormalities. Therefore, for unexplained adult-onset chronic interstitial nephritis with unusual changes of renal tubules and interstitial fibrosis, even without a clear history of hereditary kidney disease, genetic testing is still recommended. The correct diagnosis of this rare adult-onset hereditary nephropathy can avoid unnecessary treatment.

Potential Therapeutic Effects of Long-Term Stem Cell Administration: Impact on the Gene Profile and Kidney Function of PKD/Mhm (Cy/+) Rats

Cystic kidney disease (CKD) is a heterogeneous group of genetic disorders and one of the most common causes of end-stage renal disease. Here, we investigate the potential effects of long-term human stem cell treatment on kidney function and the gene expression profile of PKD/Mhm (Cy/+) rats. Human adipose-derived stromal cells (ASC) and human skin-derived ABCB5⁺ stromal cells (2 × 10⁶) were infused intravenously or intraperitoneally monthly, over 6 months. Additionally, ASC and ABCB5⁺-derived conditioned media were administrated intraperitoneally. The gene expression profile results showed a significant reprogramming of metabolism-related pathways along with downregulation of the cAMP, NF-kB and apoptosis pathways. During the experimental period, we measured the principal renal parameters as well as renal function using an innovative non-invasive transcutaneous device. All together, these analyses show a moderate amelioration of renal function in the ABCB5⁺ and ASC-treated groups. Additionally, ABCB5⁺ and ASC-derived conditioned media treatments lead to milder but still promising improvements. Even though further analyses have to be performed, the preliminary results obtained in this study can lay the foundations for a novel therapeutic approach with the application of cell-based therapy in CKD.