Increased lysosomal proteolysis counteracts protein accumulation in the proximal tubule during focal segmental glomerulosclerosis.

Focal segmental glomerulosclerosis (FSGS) is a prevalent cause of end-stage renal disease, but the mechanisms underlying progression are unresolved. Lysosomal protein accumulation in the proximal tubule, mediated by megalin and cubilin endocytosis of increased amounts of filtered protein, is thought to result in inflammation and fibrosis. Here we determine whether release of inflammatory and fibrotic mediators in response to protein overload in the proximal tubule is caused by lysosomal enzyme deficits and insufficient proteolysis. As a model of FSGS, we used inducible podocyte-specific podocin-knockout mice analyzed at different time points. The content of megalin and cubilin ligands increased in the lysosomes after onset of proteinuria; however, protein and mRNA levels of megalin and cubilin showed only minor changes. To determine if the elevated lysosomal ligand content was caused by deficiency of enzymes, we analyzed protein and mRNA levels of lysosomal enzymes and found increased endogenous synthesis. Injection of dye-quenched fluorescent and iodinated albumin showed that proteolytic turnover in lysosomes of knockout mice adapted to the increased protein load. Inflammatory and fibrotic signals were increased early in disease, although the majority of lysosomes degraded endocytosed proteins effectively. Thus, insufficient lysosomal degradation in FSGS is not the cause of the inflammation and fibrosis during kidney disease.

Transitioning preclinical students into clerkships amidst curricular disruptions from the COVID-19 pandemic.

The COVID-19 pandemic resulted in significant disruptions to medical education. The patient care space was unavailable as a learning environment, which compounded the complexity of preparing students for clerkships with a traditional transition to clerkship (TTC) curriculum. We developed a multimodal, structured approach to re-introduce students to the clinical space prior to the start of clerkships. 105 second year medical students completed a 4-week clinical enhancement course. A modified Delphi method was used to select core topics, which were then anchored to key Entrustable Professional Activities (EPAs). Students participated in 9 virtual problem-based cases, workshops and multiple supervised patient encounters. Students were surveyed before, during, and after the course; responses were compared with paired t-tests. 25.9% rated the course as excellent, 44.2% as very good, and 19.5% as good. Compared to baseline, self-perceived efficacy grew significantly (P < 0.05) across all EPAs. Improvements in key competencies were sustained when students were surveyed 2 weeks into their first clerkship. This was a well-received, novel course, focused on helping students transition back into the clinical space through a multimodal teaching approach. This framework may be used by other institutions seeking to restructure their TTC initiatives.

Podocin inactivation in mature kidneys causes focal segmental glomerulosclerosis and nephrotic syndrome.

Podocin is a critical component of the glomerular slit diaphragm, and genetic mutations lead to both familial and sporadic forms of steroid-resistant nephrotic syndrome. In mice, constitutive absence of podocin leads to rapidly progressive renal disease characterized by mesangiolysis and/or mesangial sclerosis and nephrotic syndrome. Using established Cre-loxP technology, we inactivated podocin in the adult mouse kidney in a podocyte-specific manner. Progressive loss of podocin in the glomerulus recapitulated albuminuria, hypercholesterolemia, hypertension, and renal failure seen in nephrotic syndrome in humans. Lesions of FSGS appeared after 4 wk, with subsequent development of diffuse glomerulosclerosis and tubulointerstitial damage. Interestingly, conditional inactivation of podocin at birth resulted in a gradient of glomerular lesions, including mesangial proliferation, demonstrating a developmental stage dependence of renal histologic patterns of injury. The development of significant albuminuria in this model occurred only after early and focal foot process effacement had progressed to diffuse involvement, with complete absence of podocin immunolabeling at the slit diaphragm. Finally, we identified novel potential mediators and perturbed molecular pathways, including cellular proliferation, in the course of progression of renal disease leading to glomerulosclerosis, using global gene expression profiling.

AAIM Recommendations for the 2020-2021 Internal Medicine Residency Application Cycle in Response to the COVID-19 Pandemic.

This statement was released in June 2020 by the Alliance for Academic Internal Medicine to provide guidance for the 2020-2021 residency application cycle in light of the COVID-19 pandemic. While many of the recommendations are specific to this cycle, others, such as the Department Summary Letter of Evaluation, are meant to be an enduring change to the internal medicine residency application process. AAIM realizes that some schools may not yet have the tools or resources to implement the template fully this cycle and look toward collaboration within the internal medicine education community to facilitate adoption in the cycles to come.

Maternal environment interacts with modifier genes to influence progression of nephrotic syndrome.

Mutations in the NPHS2 gene, which encodes podocin, are responsible for some cases of sporadic and familial autosomal recessive steroid-resistant nephrotic syndrome. Inter- and intrafamilial variability in the progression of renal disease among patients bearing NPHS2 mutations suggests a potential role for modifier genes. Using a mouse model in which the podocin gene is constitutively inactivated, we sought to identify genetic determinants of the development and progression of renal disease as a result of the nephrotic syndrome. We report that the evolution of renal disease as a result of nephrotic syndrome in Nphs2-null mice depends on genetic background. Furthermore, the maternal environment significantly interacts with genetic determinants to modify survival and progression of renal disease. Quantitative trait locus mapping suggested that these genetic determinants may be encoded for by genes on the distal end of chromosome 3, which are linked to proteinuria, and on the distal end of chromosome 7, which are linked to a composite trait of urea, creatinine, and potassium. These loci demonstrate epistatic interactions with other chromosomal regions, highlighting the complex genetics of renal disease progression. In summary, constitutive inactivation of podocin models the complex interactions between maternal and genetically determined factors on the progression of renal disease as a result of nephrotic syndrome in mice.

Nephrin mutations can cause childhood-onset steroid-resistant nephrotic syndrome.

Classically, infants with mutations in NPHS1, which encodes nephrin, present with nephrotic syndrome within the first 3 mo of life (congenital nephrotic syndrome of the Finnish-type), and children with mutations in NPHS2, which encodes podocin, present later with steroid-resistant nephrotic syndrome. Recently, however, NPHS2 mutations have been identified in children with congenital nephrotic syndrome. Whether NPHS1 mutations similarly account for some cases of childhood steroid-resistant nephrotic syndrome is unknown. In this study, 160 patients who belonged to 142 unrelated families and presented with nephrotic syndrome at least 3 mo after birth were screened for NPHS1 variants once mutations in NPHS2 had been excluded. Compound heterozygous NPHS1 mutations were identified in one familial case and nine sporadic cases. Mutations included protein-truncating nonsense and frameshift mutations, as well as splice-site and missense variants. Mutations were classified as "severe" or "mild" using prediction algorithms and functional assays. Most missense variants trafficked normally to the plasma membrane and maintained the ability to form nephrin homodimers and to heterodimerize with NEPH1, suggesting retained function. The presence of at least one "mild" mutation in these patients likely explains the later onset and milder course of disease. These results broaden the spectrum of renal disease related to nephrin mutations.

Impact of diagnostic bone biopsies on the management of non-vertebral osteomyelitis: A retrospective cohort study.

Optimal antibiotic management of patients with osteomyelitis remains a challenge for many clinicians. Although image-guided bone biopsy (IGB) remains the gold standard, its role in confirming diagnosis and guiding antibiotic management is not clear in patients with non-vertebral osteomyelitis.To determine the diagnostic yield of IGB and its impact on antibiotic management in non-vertebral osteomyelitis.Retrospective cohort study.Urban academic medical center.Patients admitted for non-vertebral osteomyelitis who underwent image-guided bone biopsy.Primary outcomes were microbiologic and histopathological results. We evaluated the impact of IGB on clinician-initiated changes in antibiotic regimen before and after biopsy.We evaluated 203 bone biopsies in 185 patients with clinical suspicion of osteomyelitis. 79% of patient received antibiotics prior to biopsy. Bone cultures were positive in 28% and histopathology confirmed osteomyelitis in 29%, but concordance was poor. Furthermore, clinical suspicion of infection was much higher, given that 68% received empiric antibiotics. Leukocytosis was significantly associated with positive cultures in multivariate analysis. There was no statistically significant correlation between antibiotic management and bone culture results. When culture yielded an organism, empiric regimens were kept the same, broadened or narrowed with equal frequency; targeted regimens were chosen only in 4 cases. Despite negative cultures in 98/138 cases having received empiric treatment, antibiotics were discontinued in only 8 cases. Even when empiric treatment was not given, negative cultures did not dissuade clinicians from eventual antibiotic use in a significant number of cases (17/48). In 46/71 patients whose final regimen included vancomycin, there was no evidence of current or past infection with MRSA.In patients with non-vertebral osteomyelitis, the diagnostic yield of image-guided bone biopsy is low, and clinicians frequently make decisions regarding antibiotic management that are not aligned with culture results.

Top Qualifications Hospitalist Leaders Seek in Candidates: Results from a National Survey.

Despite rapidly growing interest in Hospital Medicine (HM), no prior research has examined the factors that may be most beneficial or detrimental to candidates during the HM hiring process. We developed a survey instrument to assess how those involved in the HM hiring process assess HM candidate attributes, skills and behaviors. The survey was distributed electronically to nontrainee physician Society of Hospital Medicine members. Respondents ranked the top five qualifications of HM candidates and the top five qualities an HM candidate should demonstrate on interview day to be considered for hiring. In thematic analysis of free-response questions, several themes emerged relating to interview techniques and recruitment strategies, including heterogeneous approaches to long-term versus short-term applicants. These findings represent the first published assessment in the area of HM hiring and should inform HM candidates and their mentors.

Biliary and pancreatic dysgenesis in mice harboring a mutation in Pkhd1.

Autosomal recessive polycystic kidney disease is a hereditary fibrocystic disease that involves the kidneys and the biliary tract. Mutations in the PKHD1 gene are responsible for typical forms of autosomal recessive polycystic kidney disease. We have generated a mouse model with targeted mutation of Pkhd1 by disrupting exon 4, resulting in a mutant transcript with deletion of 66 codons and expression at approximately 30% of wild-type levels. Pkhd1(del4/del4) mice develop intrahepatic bile duct proliferation with progressive cyst formation and associated periportal fibrosis. In addition, these mice exhibit extrahepatic manifestations, including pancreatic cysts, splenomegaly, and common bile duct dilation. The kidneys are unaffected both histologically and functionally. Fibrocystin is expressed in the apical membranes and cilia of bile ducts and distal nephron segments but is absent from the proximal tubule. This pattern is unchanged in orthologous models of autosomal dominant polycystic kidney disease due to mutation in Pkd1 or Pkd2. Mutant fibrocystin in Pkhd1(del4/del4) mice also retains this expression pattern. The hypomorphic Pkhd1(del4/del4) mouse model provides evidence that reduced functional levels of fibrocystin are sufficient for cystogenesis and fibrosis in the liver and pancreas, but not the kidney, and supports the hypothesis of species-dependent differences in susceptibility of tissues to Pkhd1 mutations.

NPHS2 mutation analysis shows genetic heterogeneity of steroid-resistant nephrotic syndrome and low post-transplant recurrence.

BACKGROUND: Mutations of NPHS2 are causative in familial autosomal-recessive (AR) and sporadic steroid-resistant nephrotic syndrome (SRNS). This study aimed to determine the spectrum of NPHS2 mutations and to establish genotype-phenotype correlations. METHODS: NPHS2 mutation analysis was performed in 338 patients from 272 families with SRNS: 81 families with AR SRNS, 172 patients with sporadic SRNS, and 19 patients with diffuse mesangial sclerosis (DMS). RESULTS: Twenty-six different pathogenic NPHS2 mutations were detected, including 13 novel mutations. The mutation detection rate was 43% for familial AR and 10.5% for sporadic SRNS, confirming genetic heterogeneity. No pathogenic NPHS2 mutations were found in DMS patients. Age at onset in patients with two pathogenic mutations was earlier, especially in cases with frameshift, truncating, and the R138Q missense mutations. Patients with only one NPHS2 mutation or variant had late-onset NS. Triallelic inheritance was observed in one patient with a homozygous R138Q mutation and a de novo NPHS1 mutation. Among 32 patients with two NPHS2 mutations who underwent kidney transplantation, only one developed late recurrence of focal segmental glomerulosclerosis (FSGS). Among 25 patients with sporadic SRNS and post-transplantation recurrence, we detected a heterozygous NPHS2 mutation in one case, and heterozygous variants/polymorphisms in 3 cases. CONCLUSION: Patients with two pathogenic NPHS2 mutations present with early-onset SRNS and very low incidence of post-transplantation recurrence. Heterozygous NPHS2 variants may play a role in atypical cases with mild, late-onset course, and recurrence after transplantation.

Milder presentation of recessive polycystic kidney disease requires presence of amino acid substitution mutations.

Autosomal recessive polycystic kidney disease (ARPKD; MIM 263200) is a hereditary and severe form of polycystic disease affecting the kidneys and biliary tract with an estimated incidence of 1 in 20,000 live births. The clinical spectrum is widely variable: up to 50% of affected neonates die shortly after birth, whereas others survive to adulthood. Mutations at a single locus, polycystic kidney and hepatic disease 1 (PKHD1), are responsible for all typical forms of ARPKD. Mutation detection was performed in PKHD1 by DHPLC in 85 affected, unrelated individuals. Seventy-four amplicons were amplified and analyzed from the PKHD1 genomic locus. Sequence variants were considered pathogenic when they were not observed in 160 control individuals (320 chromosomes). For purposes of genotype-phenotype comparisons, families were stratified by clinical presentation into two groups: the severe perinatal group, in which at least one affected child presented with perinatal disease and neonatal demise, and the less severe, nonperinatal group, in which none of the affected children died in the neonatal period. Forty-one mutations were found in 55 affected disease chromosomes; 32 of these mutations have not been reported previously. Mutations were distributed throughout the portions of gene encoding the predicted extracellular portion of the protein product. The most commonly encountered mutation, T36M, was found in 8 of 55 disease chromosomes. Amino acid substitutions were found to be more commonly associated with a nonlethal presentation, whereas chain terminating mutations were more commonly associated with neonatal demise (chi(2) = 11.54, P = 0.003). All patients who survive the neonatal period have at least one amino acid substitution mutation, suggesting that such substitutions produce milder disease through production of partially functional protein products. The nature of the germline mutations in ARPKD plays a significant role in determining clinical outcome.