FSGS in Chinese twins with a de novo PAX2 mutation: a case report and review of the literature

Mice with a Pax2 missense variant display impaired glomerular repair

PAX2 regulates kidney development, and its expression persists in parietal epithelial cells (PECs), potentially serving as a podocyte reserve. We hypothesized that mice with a Pax2 pathogenic missense variant (Pax2A220G/+) have impaired PEC-mediated podocyte regeneration. Embryonic wild-type mouse kidneys showed overlapping expression of PAX2/Wilms' tumor-1 (WT-1) until PEC and podocyte differentiation, reflecting a close lineage relationship. Embryonic and adult Pax2A220G/+ mice have reduced nephron number but demonstrated no glomerular disease under baseline conditions. Pax2A220G/+ mice compared with wild-type mice were more susceptible to glomerular disease after adriamycin (ADR)-induced podocyte injury, as demonstrated by worsened glomerular scarring, increased podocyte foot process effacement, and podocyte loss. There was a decrease in PAX2-expressing PECs in wild-type mice after adriamycin injury accompanied by the occurrence of PAX2/WT-1-coexpressing glomerular tuft cells. In contrast, Pax2A220G/+ mice showed no changes in the numbers of PAX2-expressing PECs after adriamycin injury, associated with fewer PAX2/WT-1-coexpressing glomerular tuft cells compared with injured wild-type mice. A subset of PAX2-expressing glomerular tuft cells after adriamycin injury was increased in Pax2A220G/+ mice, suggesting a pathological process given the worse outcomes observed in this group. Finally, Pax2A220G/+ mice have increased numbers of glomerular tuft cells expressing Ki-67 and cleaved caspase-3 compared with wild-type mice after adriamycin injury, consistent with maladaptive responses to podocyte loss. Collectively, our results suggest that decreased glomerular numbers in Pax2A220G/+ mice are likely compounded with the inability of their mutated PECs to regenerate podocyte loss, and together these two mechanisms drive the worsened focal segmental glomerular sclerosis phenotype in these mice.NEW & NOTEWORTHY Congenital anomalies of the kidney and urinary tract comprise some of the leading causes of kidney failure in children, but our previous study showed that one of its genetic causes, PAX2, is also associated with adult-onset focal segmental glomerular sclerosis. Using a clinically relevant model, our present study demonstrated that after podocyte injury, parietal epithelial cells expressing PAX2 are deployed into the glomerular tuft to assist in repair in wild-type mice, but this mechanism is impaired in Pax2A220G/+ mice.

PAX2 Gene Mutation in Pediatric Renal Disorders-A Narrative Review

The PAX2 gene is a transcription factor that is essential for the development of the urinary system among other transcription factors. The role of PAX2 is highlighted from the seventh week of gestation, when it is involved in development processes and the emergence of nephrons and collecting tubes. Being an important factor in renal development, mutations of this gene can produce severe alterations in the development of the urinary tract, namely congenital anomalies of the kidneys and urinary tract. The first reported cases described with the PAX2 mutation included both renal anomalies and the involvement of other organs, such as the eyes, producing renal coloboma syndrome. Over the years, numerous cases have been reported, including those with only renal and urinary tract anomalies. The aim of this review is to present a summary of pediatric patients described to have mutations in the PAX2 gene to contribute to a better understanding of the genetic mechanism causing anomalies of the kidneys and urinary tract. In this review, we have included only pediatric cases with renal and urinary tract disorders, without the involvement of other organs. From what we know so far from the literature, this is the first review gathering pediatric patients presenting the PAX2 mutation who have been diagnosed exclusively with renal and urinary tract disorders.

Traditional Chinese Medicine in Treating Primary Podocytosis: From Fundamental Science to Clinical Research

Podocytes form a key component of the glomerular filtration barrier. Damage to podocytes is referred to as “podocyte disease.” There are many causes of podocyte injury, including primary injury, secondary injury, and gene mutations. Primary podocytosis mostly manifests as nephrotic syndrome. At present, first-line treatment is based on glucocorticoid administration combined with immunosuppressive therapy, but some patients still progress to end-stage renal disease. In Asia, especially in China, traditional Chinese medicine (TCM) still plays an important role in the treatment of kidney diseases. This study summarizes the potential mechanism of TCM and its active components in protecting podocytes, such as repairing podocyte injury, inhibiting podocyte proliferation, reducing podocyte apoptosis and excretion, maintaining podocyte skeleton structure, and upregulating podocyte-related protein expression. At the same time, the clinical efficacy of TCM in the treatment of primary podocytosis (including idiopathic membranous nephropathy, minimal change disease, and focal segmental glomerulosclerosis) is summarized to support the development of new treatment strategies for primary podocytosis.

The KIDNEYCODE Program: Diagnostic Yield and Clinical Features of Individuals with CKD

Background

Despite increasing recognition that CKD may have underlyi ng genetic causes, genetic testing remains limited. This study evaluated the diagnostic yield and phenotypic spectrum of CKD in individuals tested through the KIDNEYCODE sponsored genetic testing program.

Methods

Unrelated individuals who received panel testing (17 genes) through the KIDNEYCODE sponsored genetic testing program were included. Individuals had to meet at least one of the following eligibility criteria: eGFR ≤90 ml/min per 1.73m² and hematuria or a family history of kidney disease; or suspected/biopsy-confirmed Alport syndrome or FSGS in tested individuals or relatives.

Results

Among 859 individuals, 234 (27%) had molecular diagnoses in genes associated with Alport syndrome (n=209), FSGS (n=12), polycystic kidney disease (n=6), and other disorders (n=8). Among those with positive findings in a COL4A gene, the majority were in COL4A5 (n=157, 72 hemizygous male and 85 heterozygous female individuals). A positive family history of CKD, regardless of whether clinical features were reported, was more predictive of a positive finding than was the presence of clinical features alone. For the 248 individuals who had kidney biopsies, a molecular diagnosis was returned for 49 individuals (20%). Most (n=41) individuals had a molecular diagnosis in a COL4A gene, 25 of whom had a previous Alport syndrome clinical diagnosis, and the remaining 16 had previous clinical diagnoses including FSGS (n=2), thin basement membrane disease (n=9), and hematuria (n=1). In total, 491 individuals had a previous clinical diagnosis, 148 (30%) of whom received a molecular diagnosis, the majority (89%, n=131) of which were concordant.

Conclusions

Although skewed to identify individuals with Alport syndrome, these findings support the need to improve access to genetic testing for patients with CKD-particularly in the context of family history of kidney disease, hematuria, and hearing loss.