Although some dietary supplements have been reported to cause renal dysfunction, there have been few reports of supplement-induced Fanconi syndrome. We present the case of a 56-year-old woman with Fanconi syndrome that developed after she consumed a red yeast rice supplement. She was referred to our hospital because of renal dysfunction, and was found to have electrolyte abnormalities, including hypophosphatemia and hypouricemia, renal diabetes, and hyperchloremic metabolic acidosis, and was, therefore, diagnosed with Fanconi syndrome. Renal biopsy revealed proximal tubular injury characterized by severely degenerated tubular epithelial cells as well as mild hypocellular fibrosis. We speculated that the red yeast rice supplement, which the patient had been consuming for approximately 1 year, might be a cause of her syndrome, because reports of renal dysfunction associated with the consumption of red yeast rice supplements have emerged in Japan since 2024. After the supplement was discontinued and oral prednisolone treatment was initiated, the patient\'s renal function improved and her electrolyte abnormalities were ameliorated. Furthermore, even after tapering off and discontinuing the prednisolone over approximately 12 weeks, her renal function remained. Because Fanconi syndrome may be caused by various exogenous substances, the taking of a thorough medical history is crucial, including with respect to the use not only of prescription medications, but also other substances, including supplements.

Patients with ifosfamide-induced renal damage present with Fanconi syndrome. Karyomegalic nephropathy/interstitial nephritis (KNIN) is a rare form of chronic tubulo-interstitial nephritis that was initially considered a type of familial nephropathy. However, several reports of drug-induced KNIN, i.e., KNIN-like nephropathy, have been reported in recent years. We present the case of an 18-year-old man who presented with Fanconi syndrome and progressive renal dysfunction after receiving chemotherapy including ifosfamide and cisplatin for right femoral osteosarcoma. Renal biopsy revealed numerous atrophied tubular epithelial cells with large, polymorphic nuclei, and the definitive diagnosis was KNIN. Most patients with KNIN-like nephropathy who receive ifosfamide are concomitantly treated with cisplatin, indicating that ifosfamide and cisplatin might act synergistically to increase the risk for KNIN-like nephropathy. Further investigation in case series is warranted to reveal potential treatment approaches and to evaluate prognosis.

Subtrochanteric femoral fracture is rare and intractable due to the possible association with low bone formation. Retrospective analysis of 38 patients with subtrochanteric femoral fractures revealed that four patients suffered from disorders related to low bone formation and there were specific treatments for two of them.
OBJECTIVE: The main aim of this study was to detect latent metabolic bone diseases and skeletal dysplasia associated with low bone formation among patients with morphologic atypical femoral fracture (AFF). A second aim was to evaluate the frequency of recognized risk factors, such as antiresorptive agents, glucocorticoids, and age.
METHODS: Clinical information was retrospectively analyzed among 38 Japanese patients who were admitted to the Department of Orthopedic Surgery and Spinal Surgery and the Division of Emergency and Critical Care Medicine at the University of Tokyo Hospital with diagnoses of subtrochanteric fractures between February 2012 and March 2022.
RESULTS: Among 38 patients (including 30 females), 21 patients were aged 75 and over. Ten patients had past oral glucocorticoid use, and 18 had past antiresorptive agent use. Two patients were diagnosed with hypophosphatemic osteomalacia after the development of fractures. One patient was suspected to be a carrier of a loss-of-function variant of alkaline phosphatase, biomineralization associated (ALPL), and one other patient had previously been genetically diagnosed with pycnodysostosis. Among four patients with a diagnosis or suspicion of these metabolic bone diseases and skeletal dysplasia, four had past clinical fractures, two had past subtrochanteric femoral fractures, and two had subtrochanteric femoral fractures on both sides.
CONCLUSIONS: If clinicians encounter patients with morphologic AFF, latent diseases related to low bone formation should be carefully differentiated because appropriate treatment may prevent delayed union and recurrent fractures. Additionally, it may be desirable to exclude these bone diseases in advance before initiating long-term use of antiresorptive agents in osteoporotic patients by screening with serum alkaline phosphatase levels to reduce the risk of morphologic AFF.

Fanconi syndrome (FS) can present with hypophosphatemia, renal glycosuria, hypouricemia and aminoaciduria. Phosphate depletion is the most critical clinical aspect of FS as it leads to osteomalacia. Some patients present with symptoms and signs related to hypophosphatemic osteomalacia (HO). Thus, these patients present with these symptoms and are misdiagnosed. From an investigation of the published literature, HO symptoms are found to be non-specific and were thus misdiagnosed in various centers. The present study describes the case of a a 46-year-old male with FS who suffered from joint pain and was first misdiagnosed. After he was referred to the authors\' hospital, his case was evaluated and following a consideration of the results of this evaluation, he was diagnosed with idiopathic FS with multiple osteoporotic fractures. Furthermore, the present study performs a brief literature review other cases of patients that were misdiagnosed and whose symptoms were later found to be due to HO are also discussed. It is hoped that the present study may increase the awareness of HO among physicians and may help to draw attention to such cases of patients presenting with non-specific symptoms.

Twenty-eight individuals who experienced proximal renal tubulopathy (PRT, Fanconi syndrome) while receiving tenofovir disoproxil initiated tenofovir alafenamide (TAF) and were followed for 5 years. None developed recurrent PRT or experienced significant changes in estimated glomerular filtration rate (by creatinine or cystatin-C), albuminuria, proteinuria, retinol-binding proteinuria, fractional excretion of phosphate, alkaline phosphatase, or bone mineral density at the lumbar spine. These data suggest that TAF is a well tolerated treatment option for individuals vulnerable to developing PRT.

A 62-year-old man visited his primary care physician with the complaints of loss of appetite and fatigue. He was admitted to our hospital based on a diagnosis of acute kidney injury, Fanconi syndrome as indicated by hypokalemia, hypouricemia, hypophosphatemia, elevated glucose levels in urine, and aminoaciduria. He had been taking multiple supplements, including Red Yeast Rice Cholesterol Help®, for one and a half years. After admission, all the supplements were stopped. Blood samples were collected; however, the samples were negative for diseases that could cause Fanconi syndrome. Renal biopsy revealed renal proximal tubular damage, mainly characterized by simplification of the proximal tubular epithelium. The mycotoxin, citrinin, which is reported to be produced by the mold used for producing red yeast rice, but not the mold Monascus pilosus used for Red Yeast Rice Cholesterol Help®, reportedly causes proximal tubular damage. However, although the causative agent has not been identified, it was thought that a substance similar to citrinin, produced by the mold used for Red Yeast Rice Cholesterol Help®, caused proximal tubular damage, leading to acute kidney injury and Fanconi syndrome. Hence, all supplements were stopped, and the patient was treated with oral potassium and phosphorus preparations, leading to gradual recovery of his kidney function. We herein report the first case of acute kidney injury and Fanconi syndrome in a patient taking multiple health supplements, including Red Yeast Rice Cholesterol Help®. Early discontinuation of the oral supplements was probably useful in improving the patient\'s kidney function.

GATM-related Fanconi renotubular syndrome 1 (FRTS1) is a form of renal Fanconi syndrome (RFS), which is a disorder of solute and water reabsorption caused by defects in the function of the entire proximal tubule. Recent findings reveal the molecular basis of FRTS1: Intramitochondrial fiber aggregation triggered by mutant GATM provides a starting point for proximal tubule damage and drives disease progression. As a rare and newly recognized inherited kidney disease, the complex manifestations of FRTS1 are easily underdiagnosed or misdiagnosed. We discuss the complex phenotype of a 26-year-old woman with onset in infancy and a long history of hypophosphatemic rickets. We also identified a novel heterozygous missense variant in the GATM gene in this patient. The novel variant and phenotype we report expand the disease spectrum of FRTS1. We recommend screening for GATM in children with RFS, especially in patients with resistant rickets who have previously had negative genetic testing. In addition, we found pathological deposition of mutant GATM proteins within mitochondria in the patient\'s urinary sediment cells by a combination of electron microscopy and immunofluorescence. This unique urine cytology experiment has the potential to be a valuable tool for identifying patients with RRTS1.

X-linked proximal tubulopathies are rare diseases that predominantly affect men. Women are generally carriers and clinical or biochemical manifestations are usually absent or mild. We present the case of a young woman who presented with a full phenotype of Dent disease type 1 due to a de novo mutation in the CLCN5 gene and a skewed X-chromosome inactivation. Although cases of overt Dent disease type 2 and Lowe syndrome in women have been described in the literature, to our knowledge this is the first case of overt Dent disease type 1.

This case presentation highlights the need to routinely monitor renal function in patients on Tenofovir Disoproxil Fumarate (TDF) due to its side effect of proximal tubule dysfunction.
UNASSIGNED: This is a case presentation of a 50-year-old African female who had been on a Tenofovir based regimen for 12 years and developed Fanconi syndrome. She recovered after discontinuation of the Tenofovir Disoproxil Fumarate (TDF).

OBJECTIVE: Cryoglobulinemia is a pathological condition characterized by the presence of cryoglobulins in the blood, with cryoglobulinemic glomerulonephritis being the most frequent form of renal involvement. Fanconi syndrome presents as a generalized dysfunction of the proximal tubule, characterized by the presence of polyuria, phosphaturia, glycosuria, proteinuria, proximal renal tubular acidosis, and osteomalacia. We aimed to present five cases co-occurring with Fanconi syndrome and cryoglobulinemia.
METHODS: We retrospectively summarized the cases of five patients with Fanconi syndrome and cryoglobulinemia at Peking Union Medical College Hospital from January 2012 to June 2022. The clinical features, diagnosis, treatment, and prognosis were systematically analyzed.
RESULTS: All five patients exhibited typical features of Fanconi syndrome, and cryoglobulinemia was concurrently detected in all cases. These patients also exhibit positive anti-nuclear antibody spectrum and hyperglobulinemia, and IgM constitutes the predominant monoclonal component in cryoglobulins. In addition to supplemental treatment, timely immunosuppressive therapy may potentially benefit the long-term renal prognosis of patients with this condition.
CONCLUSIONS: Our findings highlight the rare co-occurrence of Fanconi syndrome and cryoglobulinemia in clinical practice. Despite the lack of causal evidence, the coexistence of Fanconi syndrome and tubulointerstitial injury is also noteworthy in patients with cryoglobulinemia, underscoring the importance of thorough evaluation and tailored management in patients presenting with overlapping renal manifestations. Key Points • Patients with mixed cryoglobulinemia can clinically present with tubulointerstitial injury, specifically manifesting as Fanconi syndrome. • In addition to typical symptoms of Fanconi syndrome, these patients also exhibit positive anti-nuclear antibody spectrum and hyperglobulinemia, while IgM constitutes the monoclonal component in cryoglobulins. • Timely immunosuppressive therapy may improve long-term renal prognosis in these patients.