Error codes at autopsy to study potential biases in diagnostic error.

OBJECTIVES: Current autopsy practice guidelines do not provide a mechanism to identify potential causes of diagnostic error (DE). We used our autopsy data registry to ask if gender or race were related to the frequency of diagnostic error found at autopsy. METHODS: Our autopsy reports include International Classification of Diseases (ICD) 9 or ICD 10 diagnostic codes for major diagnoses as well as codes that identify types of error. From 2012 to mid-2015 only 2 codes were used: UNDOC (major undocumented diagnoses) and UNCON (major unconfirmed diagnoses). Major diagnoses contributed to death or would have been treated if known. Since mid-2015, codes included specific diagnoses, i.e. undiagnosed or unconfirmed myocardial infarction, infection, pulmonary thromboembolism, malignancy, or other diagnosis as well as cause of death. Adult autopsy cases from 2012 to 2019 were assessed for DE associated with reported sex or race (nonwhite or white). 528 cases were evaluated between 2012 and 2015 and 699 between 2015 and 2019. RESULTS: Major DEs were identified at autopsy in 65.9 % of cases from 2012 to 2015 and in 72.1 % from 2015 to 2019. From 2012 to 2015, female autopsy cases showed a greater frequency in 4 parameters of DE, i.e., in the total number of cases with any error (p=0.0001), in the number of cases with UNDOC errors (p=0.0038) or UNCON errors (p=0.0006), and in the relative proportions of total numbers of errors (p=0.0001). From 2015 to 2019 undocumented malignancy was greater among males (p=0.0065); no other sex-related error was identified. In the same period some DE parameters were greater among nonwhite than among white subjects, including unconfirmed cause of death (p=0.035), and proportion of total error diagnoses (p=0.0003), UNCON diagnoses (p=0.0093), and UNDOC diagnoses (p=0.035). CONCLUSIONS: Coding for DE at autopsy can identify potential effects of biases on diagnostic error.

A Rare Case of Renal Thrombotic Microangiopathy and Focal Segmental Glomerulosclerosis Secondary to Plasma Cell Leukemia.

Plasma cell dyscrasias are a subset of hematological malignancies involving the production of monoclonal immunoglobulins. This spectrum of disorders includes asymptomatic conditions such as monoclonal gammopathy of unknown significance as well as extremely aggressive malignancies such as plasma cell leukemia. Monoclonal gammopathies are occasionally associated with renal failure, which can occur via many pathophysiological processes. The most common of these is light chain cast nephropathy, but many rare renal complications exist, including thrombotic microangiopathy (TMA) and focal segmental glomerulosclerosis (FSGS). Here, we report a patient with new renal failure with features of TMA and FSGS on biopsy and found to be secondary to plasma cell leukemia.

The Clinicopathologic Spectrum of Membranous Nephropathy with Lupus-Like Features.

INTRODUCTION: The pathologic features of membranous lupus nephritis (MLN) are occasionally encountered in secondary membranous nephropathy (sMN) without overt clinical evidence of systemic lupus erythematosus. Moreover, some sMN with lupus-like features (lupus-like membranous nephropathy [LL-MN]) have a clinical presentation more typical of primary membranous nephropathy (pMN). Based on the confounding clinical and pathologic presentation, it is unclear how to categorize and treat these patients. METHODS: We performed immunohistochemical staining for recently discovered target antigens associated with MN -NELL-1, THSD7A, and EXT1/2 and compared the clinicopathologic presentation of patients with LL-MN to those with pMN and MLN. RESULTS: From 2015 to 2020, there were 21 patients with MLN and 99 with MN, of which 59% were diagnosed pMN and 41% sMN. 44% of sMN patients showed lupus-like features (LL-fx). All LL-MN patients were negative for PLA2R and NELL1, but 12% were positive for EXT1/2. 50% of LL-MN patients had an identifiable systemic disease, of which 56% were autoimmune disease (AD) and 44% infection. Compared to pMN, LL-MN had a higher incidence of underlying AD (p = 0.02). Within pMN, 24% also had LL-fx (LL-pMN), and all but 1 were PLA2R- (78%) or NELL1-positive (15%). Only 5% of pMN patients had an AD, 66% of which showed LL-fx. Most idiopathic LL-MN were treated and behaved clinically similarly to pMN. There were no differences in outcome in terms of progression toward end-stage renal disease or mortality between LL-MN versus pMN and MLN. CONCLUSION: LL-MN appears to have a significant association with underlying AD and has a subset showing EXT1/2 positivity, whereas most LL-pMN and idiopathic LL-MN likely represent an atypical pathologic presentation of pMN.

A pilot study comparing in-person and remote outpatient substance use treatment services on quality-of-life outcomes.

Background: The widespread shift from in-person to Telehealth services during the Covid-19 pandemic irreversibly shifted the landscape of outpatient substance use treatment. This shift was necessitated by health, rather than data-driven, reasons. As we reflect on whether to continue providing Telehealth services moving forward, we require empirical support on the effectiveness of Telehealth services (compared to in-person services) in terms of patient outcomes, such as Quality of Life (QOL), to support this decision. Objective: To present data from a pilot project comparing changes in QOL across patients receiving outpatient in-person versus Telehealth substance use treatment in five clinics across New York State. Method: To retrospectively compare total self-reported QOL scores from admission to 3-months later utilizing the Quality-of-Life Enjoyment and Satisfaction scale during in-person (pre-pandemic, n = 298) and Telehealth (pandemic, n = 316) services with a mixed repeated measures ANOVA. Results: Self-reported QOL scores significantly improved across the first three months, regardless of treatment modality. Conclusion: Telehealth and in-person treatment appear comparable on QOL outcomes over the first 3 months of outpatient treatment. Both modalities are associated with improved QOL scores. Scientific significance: These preliminary findings provide evidence that Telehealth services are associated with positive patient outcomes and appear comparable to QOL outcomes among patients receiving in-person services. Future directions include further assessment of additional clinical outcomes and investigation into causal mechanisms.

Subepithelial deposits with microspherular structures in membranous glomerulonephritis.

Rare cases of membranous glomerulopathy (MGN) with subepithelial deposits consisting of microspherular structures identified by electron microscopy have been described in the literature as either MGN with spherules or podocyte infolding glomerulopathy (PIG). The paucity of available studies shows a strong association with underlying autoimmune disease. To further understand the significance of subepithelial microspherular deposits, we retrospectively identified native kidney biopsies from 10 patients diagnosed as MGN with subepithelial microspherular structures identified by ultrastructural examination at the University of Rochester Medical Center (URMC) during an 11-year period. The majority were Caucasian (80%) with a mean age of 51.3 (±12.9) years. 50% had an autoimmune disorder, of which 80% were SLE. Two SLE cases had concomitant rheumatoid arthritis and Sjogren's syndrome. One additional case had antiphospholipid syndrome and showed lupus-like features on biopsy. 40% were idiopathic and negative for PLA2R, NELL1, and THSD7A. MGN with subepithelial microspherular structures is frequently associated with an underlying autoimmune disease. The majority are negative for markers of primary MGN (PLA2R, THSD7A, and NELL1) and show features suggestive of secondary MGN.

Small Molecule Inhibitors of Nuclear Export and the Amelioration of Lupus by Modulation of Plasma Cell Generation and Survival.

OBJECTIVE: To investigate the hypothesis that selective inhibitors of nuclear export (SINE compounds), recently approved for treatment of refractory plasma cell (PC) malignancy, may have potential in the treatment of lupus. METHODS: Female NZB/NZW mice were treated with the SINE compound KPT-350 or vehicle control. Tissue specimens were harvested and analyzed by flow cytometry, using standard markers. Nephritis was monitored by determining the proteinuria score and by histologic analysis of kidney specimens. Serum anti-double-stranded DNA (anti-dsDNA) levels were measured by enzyme-linked immunosorbent assay, and total numbers of IgG-secreting and dsDNA-specific antibody-secreting cells were assessed by enzyme-linked immunospot assay. RESULTS: KPT-350 abrogated murine lupus nephritis at both early and late stages of the disease and rapidly impaired generation of autoreactive PCs in germinal centers (GCs). SINE compounds inhibited the production of NF-κB-driven homeostatic chemokines by stromal cells, altering splenic B and T cell strategic positioning and significantly reducing follicular helper T cell, GC B cell, and autoreactive PC counts. KPT-350 also decreased levels of cytokines and chemokines involved in PC survival and recruitment in the kidney of lupus-prone mice. Exportin 1, the target of SINE compounds, was detected in GCs of human tonsils, splenic B cells of lupus patients, and multiple B cell subsets in the kidneys of patients with lupus nephritis. CONCLUSION: Collectively, our results provide support for the therapeutic potential of SINE compounds, via their targeting of several molecular and cellular pathways critical in lupus pathogenesis, including autoantibody production by plasma cells.

The spectrum of renal diseases with lupus-like features: a single-center study.

BACKGROUND: A subset of patients without overt systemic lupus erythematosus (SLE) present with biopsy findings typically seen in lupus nephritis (LN). Although a minority eventually develops SLE, many do not. It remains unclear how to classify or treat these patients. Our study attempted to further understand the clinical and pathological characteristics of cases with lupus-like nephritis (LLN). METHODS: Among 2700 native kidney biopsies interpreted at University of Rochester Medical Center (URMC) from 2010 to 2019, we identified 27 patients with biopsies showing lupus-like features (LL-fx) and 96 with LN. Of those with LL-fx, 17 were idiopathic LLN and 10 were associated with a secondary etiology (e.g., infection/drugs). RESULTS: At the time of biopsy, the LLN-group tended to be slightly older (44 vs. 35), male (58.8 vs. 17.7%, p = .041), and Caucasian (47.0 vs. 28.1%, p = .005). Chronic kidney disease was the most common biopsy indication in LLN (21.4 vs. 2.8%, p = .001). Both LN and LLN presented with nephrotic-range proteinuria (mean 5.73 vs. 4.40 g/d), and elevated serum creatinine (mean 1.66 vs. 1.47 mg/dL). Tubuloreticular inclusions (TRIs; p < .001) and fibrous crescents (p = .04) were more often seen in LN, while more tubulointerstitial scarring was seen in LLN (p = .011). At mean follow-up of 1684 d (range: 31-4323), none of the LLN patients developed ESRD. A subset of both LN and cases with LL-fx overlapped with other autoimmune diseases. CONCLUSIONS: Lupus-like pathologic features are seen in a wide array of disease processes. The findings suggest that LLN may be a manifestation of an autoimmune process that overlaps with SLE.

Light chain deposition disease masquerading as smoking-associated nodular glomerulosclerosis with deposits identified by electron microscopy only.

Light chain deposition disease (LCDD) is a form of monoclonal gammopathy of renal significance. The diagnosis is based on the immunofluorescence (IF) findings of linear monoclonal light chain staining of basement membranes throughout the kidney, which appear as non-organized, granular punctate to powdery electron dense deposits by electron microscopy (EM). Although "LCDD by IF only" without EM deposits has been well-described, LCDD identified by EM with negative IF is very rare and hardly mentioned in the literature. Herein we describe a case of lambda-type LCDD that appeared negative by IF and showed light microscopic findings of nodular glomerulosclerosis, which was initially attributed to the patient's history of significant tobacco use and uncontrolled hypertension. However, EM later showed powdery electron dense material in focal glomerular and tubular basement membranes and mesangium. Subsequent bone marrow analysis revealed greater than 60% lambda-restricted plasma cells. We report this case to illustrate that within the differential diagnosis of nodular sclerosis, monoclonal immunoglobulin deposition disease (MIDD) should remain in the differential even if immunofluorescence appears negative as EM can prove to be crucial in identifying cases of MIDD.

Myeloid bodies is not an uncommon ultrastructural finding.

The presence of myeloid bodies (MBs) is classically associated with Fabry disease (FD). However, MBs are also identified in patients without clinical evidence of FD. We attempt to further understand the clinicopathologic significance of incidental MBs in those without FD. Among the 4400 renal biopsies accessioned at the University of Rochester Medical Center from 2010 to 2021, we identified 32 cases showing MBs, 6 of which had FD. Medications were compared between a non-FG and a control-group of randomly selected cases without MBs (non-MBs). Both Fabry-group (FG) and non-Fabry-group (non-FG) were predominantly middle-aged (mean 48 years vs 56, respectively). Non-FG had slight female predominance (1:4), while all in FG were female. The majority of both non-FG and non-MBs cohort were on the same medications reported to cause phospholipidosis except sertraline and hydralazine (p = .04), which were more frequent in non-FG. Ultrastructurally, non-FG tended to show focal MBs in predominantly podocytes, while FG showed more extensive MBs in not only podocytes but also parietal, tubular, endothelial, and myocyte cells (p = .03). In addition, half of FG had another superimposed renal disease including kappa-light chain deposition disease, thin-basement membrane nephropathy, and lithium-related changes. MBs are encountered not only in FD but in other settings including CADs, toxins, and other inheritable diseases. Although secondary causes of MBs typically show less extensive involvement compared to FD, these features overlap. Given the challenges in diagnosing female carriers, the finding of MBs, though not specific to FD, may be the only clue that leads to further work-up and timely diagnosis, underscoring the importance of considering FD among other etiologies in differential diagnosis.

An untapped resource: characteristics of thrombus recovered from intermediate or high risk pulmonary embolus patients.

INTRODUCTION: Response to anticoagulation varies during management of acute hospitalized pulmonary embolism. We aimed to study thrombus histology in pulmonary embolism samples removed during acute surgical embolectomy to evaluate whether thrombus morphology was similar between patients and whether there was an association with duration of symptoms and/or resolution on follow up imaging. METHODS: This was a retrospective observational single center study at the University of Rochester Medical Center. We evaluated patients that underwent acute surgical embolectomy and followed up in our clinic 2 - 4 months after the event with Ventilation/Perfusion (V/Q) scan obtained for all regardless of symptoms. Thromboemboli were formalin fixed and processed for light microscopy in the hospital histopathology laboratory. Four-micron thick sections were stained with hematoxylin and eosin, Masson trichrome, and Verhoeff elastic tissue stains. Immunohistochemistry was performed using anti-CD31 and anti-CD68. Slides were independently evaluated for time-dependent microscopic changes using Irniger's classification by two blinded pathologists. RESULTS: Sixteen patients underwent embolectomy with fifteen having V/Q imaging at follow up. The majority of patients were female. Samples showed a generally similar overall architecture that included a central core composed primarily of red blood cells and fibrin and an outer layer of platelets and monocytes. Two samples had evidence of fibrosis and recanalization. CONCLUSIONS: We found heterogeneous histopathology in samples obtained during acute embolectomy. Further prospective studies should systematically characterize clot morphology and evaluate treatment response and outcomes. Careful thrombus specimen measurement and consistent sampling for sections will be required to draw firm conclusions.

The spectrum of macrophage-predominant inflammatory myocardial disease presenting as fulminant heart failure.

BACKGROUND: Endomyocardial biopsy results are integral for diagnosis and management of myocarditis. Current diagnostic classifications of myocarditis are based on the microscopic and immunochemical characterization of inflammation do not include monocyte/macrophage-predominant (i.e. "histiocytic") myocarditis as a histologic subtype. METHODS: Endomyocardial biopsies from 6 patients with sudden heart failure were reviewed by 3 cardiac pathologists. Routine stains and immunostains to identify T cells and monocytes/macrophages, complement C4d, and endothelium were applied. Electron microscopy was performed in 2 cases. RESULTS: The 6 patients included 2 with diagnoses of systemic lupus erythematosus (SLE) and 4 without known disease. Microscopy showed space-occupying inflammation in 2 cases and interstitial inflammation in 4. No giant cell myocarditis or eosinophilic myocarditis was found. Immunostains showed infiltration predominantly by macrophages and/or monocytes with markedly fewer T cells. In 4 of 6 cases necrotic cells were immunopositive for complement C4d. Monocytes we identified immunochemically within the microvasculature in 5 cases and by electron microscopy in 2. Patients with SLE had microvascular C4d positivity or interstitial/sarcolemmal staining. Clinical outcomes ranged from spontaneous resolution to persistent heart failure requiring an internal cardioverter/defibrillator. CONCLUSIONS: (1) Heart failure with CD68 predominant inflammation ("histiocytic" myocardial inflammatory disease, HMID) occurs with variable clinical presentation and outcome; (2) HMID may be primary or secondary; (3) some cases of HMID show features suggestive of antibody and/or complement mediated myocardial injury, and (4) HMID is a diagnosis distinct from those in classification systems currently in use.

A rare case of diffuse crescents in fibrillary glomerulonephritis
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Diffuse crescentic involvement in fibrillary glomerulonephritis (FGN) is very rare. We describe a case of FGN with diffuse crescents in a patient who presented with clinical findings concerning for rapidly progressive kidney failure and pathologic findings suggestive of anti-glomerular basement membrane (GBM) disease. Serologies for anti-neutrophil cytoplasmic antibody (ANCA) and anti-GBM were negative. IgG subtyping showed IgG1 dominance, which has not been described in FGN. We present this unique case to emphasize the importance of considering FGN in biopsies showing diffuse crescentic glomerulonephritis with linear IgG staining of glomerular capillary walls, especially in the absence of other significant proliferative changes.

Social Behavior in Naked Mole-Rats: Individual Differences in Phenotype and Proximate Mechanisms of Mammalian Eusociality.

Naked mole-rats (Heterocephalus glaber) are small rodents native to east Africa, living in subterranean colonies of up to 300 individuals. Within each colony, reproduction is restricted to a single breeding female and 1-3 breeding males; all other colony members are reproductively suppressed and socially subordinate unless removed from the suppressive cues of the colony. Due to their striking reproductive skew, naked mole-rats are often considered eusocial mammals. Consistent with this idea, there are behavioral specializations and at least some evidence for morphological distinctions within and between the breeding and non-breeding members of the colony. Importantly, naked mole-rats show plasticity in their behavioral phenotype whereby changes in the social environment influence expression of both type and amount of social behavior. Thus, naked mole-rats provide the opportunity to examine the proximate mechanisms controlling individual differences in social behavior, shedding light on how mammals live in complex social groups.

Prednisone-induced sustained remission in a patient with familial fibronectin glomerulopathy (GFND).

Glomerulopathy with Fibronectin Deposits (GFND) is a rare, autosomal dominant disease characterized by proteinuria, hematuria and progressive renal failure associated with glomerular deposition of fibronectin, frequently resulting in end-stage renal disease (ESRD). There is no established treatment for this condition beyond conservative measures such as blood pressure control and the use of angiotensin-converting enzyme (ACE) inhibitors. We present a case of GFND associated with progressive chronic kidney disease (CKD) and nephrotic range proteinuria showing a sustained response to prednisone treatment. A 27-year-old G2P2 Caucasian female presented with 3 g/day of proteinuria, serum creatinine (Cr) 0.7 mg/dL, inactive urinary sediment and normotension without medication. She was part of a large family with glomerular disease, including three members who died of cerebral hemorrhage or stroke in their thirties. The patient's kidney biopsy showed mesangial deposition of fibronectin consistent with GFND. No interstitial fibrosis was seen. Genotyping revealed the Y973C FN1 gene mutation. Despite maximal tolerable ACE inhibition, proteinuria increased to 4-6 g/g Cr and serum Cr increased to 1.0 mg/dL. She was treated with prednisone 60 mg (~ 1 mg/Kg) daily for 2 mos and then tapered by ~ 0.2 mg/Kg every month for 6 mos of total therapy. Proteinuria decreased to ~ 1 g/g Cr for > 5 years and serum Cr stabilized in the 1.2 mg/dL range with treatment. No significant side effects were encountered. In conclusion, this protocol should be considered in GFND patients with nephrotic range proteinuria despite maximal angiotensin system inhibition who have relatively preserved renal function.

Segmental membranous nephropathy.

Most cases of membranous nephropathy (MGN) present with global and diffuse distribution of subepithelial deposits. However, segmental MGN, in which there is focal or diffuse segmental subepithelial deposits, are occasionally encountered. The clinical and pathologic significance of segmental MGN is not well understood and thought to be more likely due to either early or resolving phase of the global form of MGN. Several case reports and literature available suggest that it may be a manifestation of secondary causes based on pathologic features such as presence of C1q and mesangial deposits, extra-glomerular deposits involving tubular basement membranes, absence of PLA2R and THSD7A, IgG1 and IgG3 subclass dominance, and the presence of other co-existing renal disease. Other reports, however, suggest that some of these cases may be a variant of the primary form of MGN. In this review, we integrate what is known about segmental MGN in order to better direct interpretation of renal biopsies in which it is identified.

Clinical and imaging outcomes after intermediate- or high-risk pulmonary embolus.

Long-term outcomes after acute pulmonary embolism vary from complete resolution to chronic thromboembolic pulmonary hypertension (CTEPH). Guidelines after acute pulmonary embolism are generally limited to anticoagulation duration. We assessed patients with estimated prognosis >1 year in our pulmonary hypertension clinic 2-4 months after treatment for intermediate- or high-risk acute pulmonary embolism. At follow-up, ventilation-perfusion scan and echocardiogram were offered. The aim of this study was to assess for recurrent symptomatic disease, residual imaging defects or right ventricular dysfunction, and functional disability after acute management of pulmonary embolism. After treatment for acute intermediate- or high-risk pulmonary embolism, 104 patients followed up in pulmonary hypertension clinic. Of those, 55% of patients had self-reported limitation in activity. No patients had symptomatic recurrence of pulmonary embolism. Forty-eight percent of patients had residual perfusion defects on perfusion imaging, while 91% of patients had either normal or only mildly enlarged right ventricles. We identified heart failure preserved ejection fraction, iron deficiency, and obstructive sleep apnea as significant contributors to breathlessness. Treatment of these conditions was associated with improvement. Surprisingly, we diagnosed CTEPH in nine patients; for some, chronic thrombus may already have been present at the time of index evaluation. Our findings suggest that follow-up in a dedicated pulmonary hypertension clinic 2-4 months after acute intermediate- or high-risk pulmonary embolism may add value to patient care. We identified treatable comorbidities that could be contributing to post-pulmonary embolism syndrome as well as CTEPH.

Triple Thrombectomy for Trousseau Syndrome: Case Report and Review of the Literature of Stroke Intervention in Cancer-associated Thrombus.

Objective: There are few papers regarding repeat mechanical thrombectomy or thrombectomy for Trousseau's related stroke. We present a unique case of repeat thrombectomy due to Trousseau's syndrome affecting the same vessel in a patient with metastatic cancer. Case Presentation: A 47-year-old male presented with a full left middle cerebral artery syndrome and a National Institute of Health Stroke Scale of 17, despite regular apixaban use. He underwent mechanical thrombectomy successfully but developed recurrent symptoms on postoperative day (POD) 6 while on warfarin. He underwent two additional thrombectomies, the final one requiring glycoprotein IIa/IIIb inhibitor for emergent implantation of intracranial stent. Successful recanalization (thrombolysis in cerebral infarction 2b) was achieved, and the patient was discharged home on dual antiplatelet therapy and enoxaparin on POD 10 after last thrombectomy, ambulatory and independent in his activities of daily living. The patient expired as a result of his metastatic disease 109 days after the third procedure and was ambulatory for 91 of those days. Conclusion: This case illustrates the palliative aspects of mechanical thrombectomy and the complexities of anticoagulation management in patients with the metastatic disease Trousseau's syndrome.

Potassium conservation is impaired in mice with reduced renal expression of Kir4.1.

To better understand the role of the inward-rectifying K channel Kir4.1 (KCNJ10) in the distal nephron, we initially studied a global Kir4.1 knockout mouse (gKO), which demonstrated the hypokalemia and hypomagnesemia seen in SeSAME/EAST syndrome and was associated with reduced Na/Cl cotransporter (NCC) expression. Lethality by ~3 wk, however, limits the usefulness of this model, so we developed a kidney-specific Kir4.1 "knockdown" mouse (ksKD) using a cadherin 16 promoter and Cre-loxP methodology. These mice appeared normal and survived to adulthood. Kir4.1 protein expression was decreased ~50% vs. wild-type (WT) mice by immunoblotting, and immunofluorescence showed moderately reduced Kir4.1 staining in distal convoluted tubule that was minimal or absent in connecting tubule and cortical collecting duct. Under control conditions, the ksKD mice showed metabolic alkalosis and relative hypercalcemia but were normokalemic and mildly hypermagnesemic despite decreased NCC expression. In addition, the mice had a severe urinary concentrating defect associated with hypernatremia, enlarged kidneys with tubulocystic dilations, and reduced aquaporin-3 expression. On a K/Mg-free diet for 1 wk, however, ksKD mice showed marked hypokalemia (serum K: 1.5 ± 0.1 vs. 3.0 ± 0.1 mEq/l for WT), which was associated with renal K wasting (transtubular K gradient: 11.4 ± 0.8 vs. 1.6 ± 0.4 in WT). Phosphorylated-NCC expression increased in WT but not ksKD mice on the K/Mg-free diet, suggesting that loss of NCC adaptation underlies the hypokalemia. In conclusion, even modest reduction in Kir4.1 expression results in impaired K conservation, which appears to be mediated by reduced expression of activated NCC.