Multiple myeloma commonly manifests with symptoms arising from the involvement of various organs, particularly the bone and kidneys. In this report, we detail the case of a 44-year-old man who was diagnosed with multiple myeloma associated with reduced bone density. He exhibited clinical findings of osteomalacia due to Fanconi syndrome (characterized clinically by bone pain and proximal weakness and biochemically by elevated serum alkaline phosphatase, hypophosphatemia, hypouricemia, and glucosuria). With phosphate replacement, there was a notable improvement in bone pain, osteomalacia, and bone mineral density. Nevertheless, the patient continued to experience renal wasting of phosphate, uric acid, and glucose despite achieving remission from multiple myeloma for nearly 2 years. Our case highlights several important clinical features of myeloma-associated Fanconi syndrome, including the need to recognize this complication to appropriately treat the underlying bone disease while avoiding osteoclast inhibitors and the long-term persistence of the proximal renal tubulopathy despite achieving remission from myeloma and correction of osteomalacia.

OBJECTIVE: Renal dysfunction is a common complication of cirrhosis, occurring either as part of multiorgan involvement in acute illness or secondary to advanced liver disease. To date, no study has comprehensively assessed multiple renal function parameters in hospitalized patients with cirrhosis through a multiparametric analysis of renal biochemistry markers.
METHODS: We conducted a retrospective, observational study including all consecutive patients hospitalized with cirrhosis who underwent a 43-multiparametric renal function assessment between January 1, 2021, and June 30, 2023.
RESULTS: All patients showed at least one of the following renal abnormalities: Kidney Disease: Improving Global Outcomes stage G2 or higher, sodium and/or chloride excretion fraction <1%, electrolyte-free water clearance <0.4 mL/min, or tubular maximum phosphate reabsorption capacity <0.8 mmol/L. The estimated glomerular filtration rate equations significantly overestimated the measured creatinine clearance with median differences of +14 mL/min/1.73 m2 (95% CI 6-29) and +9 mL/min/1.73 m2 (95% CI 2-15) for European Kidney Function Consortium equations, respectively. Notably, 54% and 39% of patients demonstrated estimated glomerular filtration rates exceeding 30% of the measured creatinine clearance when the Chronic Kidney Disease - Epidemiology Collaboration and European Kidney Function Consortium formulas were employed, respectively. Substantial discrepancies in Kidney Disease: Improving Global Outcomes stage assignments were observed between the estimated glomerular filtration rate- and measured creatinine clearance-based assessments.
CONCLUSIONS: This study underscores the value of a multiparametric renal function assessment as a routine tool for evaluating renal function in patients with cirrhosis. A high prevalence of medically actionable renal abnormalities spanning multiple renal function modules, including alterations in glomerular function, salt and solute-free water excretion, and proximal tubule phosphate reabsorption, has been demonstrated in hospitalized patients with cirrhosis.

The efficient reabsorption of essential nutrients by epithelial cells in the proximal tubule of the kidney is crucial for maintaining homeostasis. This process relies heavily on a complex ecosystem of vesicular trafficking pathways. At the center of this network, the lysosome plays a pivotal role in processing incoming molecules, sensing nutrient availability, sorting receptors and transporters, and balancing differentiation and proliferation in the tubular epithelial cells. Disruptions in these fundamental processes can lead to proximal tubulopathy-a condition characterized by the dysfunction of the tubular cells followed by the presence of low-molecular-weight proteins and solutes in urine. If left untreated, proximal tubulopathy can progress to chronic kidney disease and severe complications. Functional studies of rare inherited disorders affecting the proximal tubule have gleaned actionable insights into fundamental mechanisms of homeostasis while revealing drug targets for therapeutic discovery and development. In this mini review, we explore hereditary proximal tubulopathies as a paradigm of kidney homeostasis disorders, discussing the factors contributing to tubular dysfunction. In addition, we shed light on the current landscape of drug discovery approaches used to identify actionable targets and summarize the preclinical pipeline of potential therapeutic agents. These efforts may ultimately lead to new treatment avenues for proximal tubulopathies, which are currently inadequately tackled by existing therapies. Through this article, our hope is to promote academia-industry partnerships and advocate for research consortia that can accelerate the effective translation of knowledge advances into innovative therapies addressing the huge unmet needs of individuals with these debilitating diseases.

UNASSIGNED: Lysozyme-associated nephropathy (LyN), a rare cause of kidney injury in patients with chronic myelomonocytic leukemia (CMML), has not been well described to date. We report the clinicopathologic spectrum of LyN from a multi-institutional series.
UNASSIGNED: We identified 37 native kidney biopsies with LyN and retrospectively obtained clinicopathologic data.
UNASSIGNED: Thirty-seven patients had a median age of 74 years and included 78% males. Their most common presentation was acute kidney injury (AKI) or AKI on chronic kidney disease (CKD) (66%) with median estimated glomerular filtration rate (eGFR) of 21.7 ml/min per 1.73 m2, and proteinuria of 1.7 g. A minority (15%) had partial Fanconi syndrome. Serum lysozyme levels were elevated in all tested. Hematologic disorder (n = 28, 76%) was the most common etiology, including CMML (n = 15), acute myeloid leukemia (n = 5), and myelodysplastic syndrome (MDS) (n = 5). Nonhematologic causes (n = 5, 14%), included metastatic neuroendocrine carcinoma (n = 3), sarcoidosis, and leprosy. Etiology was unknown in 4 (11%). Pathology showed proximal tubulopathy with abundant hypereosinophilic intracytoplasmic inclusions, with characteristic staining pattern by lysozyme immunostain. Mortality was high (8/30). However, among the 22 alive, including 85% treated, 7 had improved kidney function, including 1 who discontinued dialysis and 6 with increase in eGFR >15 ml/min per 1.73 m2 compared with eGFR at the time of biopsy.
UNASSIGNED: Increased awareness of the full clinicopathologic spectrum of LyN may lead to prompt diagnosis, earlier treatment, and potentially improved outcome of this rare entity.

Gout is recurrent inflammatory arthritis caused by the deposition of monosodium urate crystals in the joints. The risk factors that predispose to suffering from gout include non-modifiable factors such as gender, age, ethnicity and genetics, and modifiable factors such as diet and lifestyle. It has been shown that the heritability of uric acid levels in the blood is greater than 30%, which indicates that genetics play a key role in these levels. Hyperuricaemia is often a consequence of reduced renal urate excretion since more than 70% is excreted by the kidneys, mainly through the proximal tubule. The mechanisms that explain that hyperuricaemia associated with reduced renal urate excretion is, to a large extent, a proximal renal tubular disorder, have begun to be understood following the identification of two genes that encode the URAT1 and GLUT9 transporters. When they are carriers of loss-of-function mutations, they explain the two known variants of renal tubular hypouricaemia. Some polymorphisms in these genes may have an opposite gain-of-function effect, with a consequent increase in urate reabsorption. Conversely, loss-of-function polymorphisms in other genes that encode transporters involved in urate excretion (ABCG2, ABCC4) can lead to hyperuricaemia. Genome-wide association study (GWAS) methods have made it possible to locate new gout-related loci associated with reduced renal urate excretion (NIPAL1, FAM35A).

Renal proximal tubulopathy plays a crucial role in kidney disease, but its molecular mechanism is incompletely understood. Because proximal tubular cells consume a lot of energy during reabsorption, the relationship between fatty acids (FAs) and proximal tubulopathy has been attracting attention. The purpose of this study is to investigate the association between change in renal FA composition and tubulopathy.
Mice with cisplatin-induced nephrotoxicity were used as a model of AKI and 5/6-nephrectomized mice were used as a model of CKD. Renal FA composition in mice was measured by GC-MS. Human tubular epithelial cells (HK-2 cells) were used for in vitro studies.
In kidneys of AKI mice, increased stearic acid (C18:0) and decreased palmitic acid (C16:0) were observed, accompanied by increased expression of the long-chain FA elongase Elovl6. Similar results were also obtained in CKD mice. We show that C18:0 has higher tubular toxicity than C16:0 via induction of ER stress. Using adenovirus-expressing Elovl6 or siRNA for Elovl6 in HK-2 cells, we demonstrated that increased Elovl6 expression contributes to tubulopathy via increasing C18:0. Elovl6 knockout suppressed the increased serum creatinine levels, renal ER stress, and inflammation that would usually result after 5/6 nephrectomy. Advanced oxidation protein products (AOPPs), specifically an oxidized albumin, was found to induce Elovl6 via the mTORC1/SREBP1 pathway.
AOPPs may contribute to renal tubulopathy via perturbation of renal FAs through induction of Elovl6. The perturbation of renal FAs induced by the AOPPs-Elovl6 system could be a potential target for the treatment of tubulopathy.

Gout is recurrent inflammatory arthritis caused by the deposition of monosodium urate crystals in the joints. The risk factors that predispose to suffering from gout include non-modifiable factors such as gender, age, ethnicity and genetics, and modifiable factors such as diet and lifestyle. It has been shown that the heritability of uric acid levels in the blood is greater than 30%, which indicates that genetics play a key role in these levels. Hyperuricaemia is often a consequence of reduced renal urate excretion since more than 70% is excreted by the kidneys, mainly through the proximal tubule. The mechanisms that explain that hyperuricaemia associated with reduced renal urate excretion is, to a large extent, a proximal renal tubular disorder, have begun to be understood following the identification of two genes that encode the URAT1 and GLUT9 transporters. When they are carriers of loss-of-function mutations, they explain the two known variants of renal tubular hypouricaemia. Some polymorphisms in these genes may have an opposite gain-of-function effect, with a consequent increase in urate reabsorption. Conversely, loss-of-function polymorphisms in other genes that encode transporters involved in urate excretion (ABCG2, ABCC4) can lead to hyperuricaemia. Genome-wide association study (GWAS) methods have made it possible to locate new gout-related loci associated with reduced renal urate excretion (NIPAL1, FAM35A).

Oculocerebrorenal syndrome of Lowe is a rare X-linked disorder characterized by congenital cataracts, mental retardation, and proximal tubulopathy. This condition is caused by a mutation of OCRL gene (located at chromosome Xq26.1), which encodes an inositol polyphosphate 5-phosphatase.
We identified two novel OCRL mutations in two unrelated Chinese boys, each with a severe phenotype of Lowe syndrome. A novel de novo deletion (hemizygous c.659_662delAGGG, p.E220Vfs*29) was present in patient 1 and a novel splicing mutation (hemizygous c.2257-2A > T) that was maternally inherited was present in patient 2. A renal biopsy in patient 2 indicated mild mesangial proliferative glomerulonephritis, mild focal mononuclear cells infiltration, and interstitial focal fibrosis. Moreover, renal expression of OCRL-1 protein in patient 2 was significantly reduced compared to a control patient with thin basement membrane disease.
This study reports two novel OCRL variants associated with severe ocular and neurologic deficiency, despite only mild renal dysfunction. Based on our two patients and a literature review, the genotype-phenotype correlation of OCRL mutations with this severe phenotype of Lowe syndrome suggest a possible clustering of missense, deletion, and nonsense mutations in the 5-phosphatase domain and Rho-GAP domain in the Chinese population.

BACKGROUND: We report a case of light chain proximal tubulopathy associated with lupus nephritis in a patient known to have systemic lupus erythematosus. The kidney can be injured in several ways in any of these disorders. Light chain proximal tubulopathy is a rare form of renal tubular injury that may occur in and complicate plasma cell dyscrasia, characterized by cytoplasmic inclusions of the monoclonal light chain within proximal tubular cells. Lupus nephritis is a common form of renal injury as it occurs in about 25-50% of adult patients with systemic lupus erythematosus.
METHODS: We present a 57-year-old African patient known to have systemic lupus erythematosus and hypertension presented with a new complaint of microscopic hematuria. A renal biopsy was performed and revealed lupus nephritis class II concurrently associated with light chain induced proximal tubulopathy. A subsequent bone marrow biopsy was performed, which revealed multiple myeloma.
CONCLUSIONS: We report a case of coincidental lupus nephritis and proximal tubulopathy featuring a combined constellation of rare histopathological features that might add to the relationship between systemic lupus and paraproteinemia.

COVID-19 is a disease caused by the RNA virus SARS-CoV-2. It is characterised by an attack mainly affecting the respiratory system. There is renal involvement which is characterised by three main types of damage, acute tubular necrosis occurring in the most severe cases, proximal tubulopathy which is a prognostic marker of the disease and segmental and focal hyalinosis occurring in a genetically predisposed terrain. The pathophysiology of SARS-CoV-2 renal involvement is not yet defined. The direct role of the virus is debated, whereas the cytokine storm and the hypoxic and thrombotic complications seem more important. The long-term outcome of the renal damage appears to be quite good. Long-term follow-up will allow us to say whether the renal damage is part of the long COVID.