BACKGROUND: Mitochondrial diseases (MDs) are systemic disorders that can affect multiple organs. Renal manifestations, including renal tubular acidosis, are common because kidneys are particularly vulnerable to energy deprivation. Treatment of MDs is often complex and electrolyte replacement can be difficult especially in pediatric patients, because large and repeated amounts of oral supplements are needed but are not well tolerated.
METHODS: We describe the case of a girl affected by Kearns-Sayre disease with severe renal tubular acidosis. The management of her metabolic acidosis was challenging because she showed persistent low levels of serum bicarbonates despite a progressive incrementation of oral bicarbonates. Furthermore, as a result to the ingestion of large amounts of alkali, the girl developed an aversion to oral supplementation. After positioning a percutaneous gastrostomy (PEG) and starting enteral administration of bicarbonates (with daily boluses and continuous nocturnal infusion), she finally obtained an adequate electrolyte control, with a significant increase in her quality of life.
CONCLUSIONS: In MDs, the combination of nocturnal continuous enteral administration of alkali plus diurnal boluses may represent a valid solution to correct metabolic acidosis. It can also result in an improved patients\' quality of life, particularly in pediatric settings, where compliance to oral therapy is often lacking due to the large and repeated amounts of unpalatable bicarbonates solutions required.

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.

An 80-year-old man presented with electrolyte abnormalities, particularly hypocalcemia (3.6 mg/dL). He was diagnosed with bone and lymph node metastases from prostate cancer seven years earlier and continuously received goserelin, bicalutamide, and zoledronate. He later developed gradually worsening hypocalcemia, hypokalemia, hypophosphatemia, hypouricemia, renal dysfunction, and weight loss. Urinary potassium and phosphate loss, renal glucosuria, metabolic acidosis, and a low urine pH (5.0) were observed. Given the acquired onset and clinical course, we diagnosed the patient with zoledronate-induced proximal renal tubular acidosis. In the present case, severe hypocalcemia may have been caused by malnutrition and inappropriate long-term use of zoledronate.

Phosphate is an integral part of human cellular structure and function. Though most recognised disorders of phosphaturia are genetic in origin, phosphate loss due to acquired conditions is commonly encountered in clinical practice. Acquired hypophosphatemia is most commonly due to renal phosphate wasting and can produce significant morbidity. It also heralds future kidney damage, and continued exposure can lead to progressive kidney injury and potentially renal failure. These conditions are a diverse group of disorders with common shared mechanisms causing loss of phosphate in the urine. Renal phosphate loss can occur as an isolated entity or as a part of generalised proximal tubular dysfunction, i.e., Fanconi\'s syndrome. An insight into the pathophysiological mechanisms of acquired phosphaturia can help clinicians monitor their patients better and avoid potential harms.

We report an infant case of transient distal renal tubular acidosis and Fanconi syndrome caused by rotavirus gastroenteritis. A 10-month-old boy was admitted to the hospital because of frequent vomiting, lack of vitality, and dehydration. He was diagnosed with rotavirus gastroenteritis on account of his positive stool rotavirus antigen test. Although he presented with acidemia and severe mixed metabolic acidosis, he also had a urine pH of 6.0, indicating impaired urinary acidification. Therefore, he was diagnosed with distal renal tubular acidosis. On the third day of hospitalization, a relatively low %tubular reabsorption of phosphate level with hypophosphatemia, increased fractional excretion of uric acid with hypouricemia, and high urinary β2-microglobulin levels were observed. Moreover, he was diagnosed with Fanconi syndrome on account of multiple proximal tubular dysfunctions. After remission of rotavirus gastroenteritis, the signs of renal tubular dysfunction improved. This was a case of rotavirus gastroenteritis-caused transient distal renal tubular acidosis and Fanconi syndrome. Severe metabolic acidosis resulted from anion-gap metabolic acidosis due to acute kidney injury by rotavirus gastroenteritis and normal anion-gap acidosis due to renal tubular acidosis. When renal tubular acidosis is associated with a disease that causes anion-gap metabolic acidosis, mixed metabolic acidosis occurs and becomes exacerbated. Furthermore, it is important to consider the complications of renal tubular acidosis in the case of severe metabolic acidosis.

Fanconi\'s syndrome is a disorder that results in generalized involvement of the proximal tubule of the kidney. It is characterized by variable degrees of phosphate, glucose, and amino acid wasting in the urine and a hyperchloremic normal anion gap metabolic acidosis - secondary to defective hydrogen ion excretion and bicarbonate ion absorption. There are hereditary variants such as cystinosis (most common), hereditary fructose intolerance, galactosemia, tyrosinemia, Dents disease, and acquired variants of Fanconi\'s syndrome. Toxins, drug-induced diseases, and systemic diseases (multiple myeloma, Sjogren\'s syndrome) are the most common acquired causes of Fanconi\'s syndrome. The case report describes a middle-aged female patient, a known case of human immunodeficiency virus (HIV)-positive status who developed tenofovir disoproxil fumarate-induced Fanconi\'s syndrome, an increasingly recognized cause of acquired Fanconi\'s syndrome in HIV-positive patients.
Résumé Le syndrome de Fanconi est un trouble qui entraîne une atteinte généralisée du tubule proximal du rein. Elle se caractérise par des degrés variables de perte de phosphate, de glucose, d\'acide urique, d\'acides aminés et de bicarbonate dans l\'urine avec un trou anionique normal, une acidose métabolique hyperchlorémique. Il existe des variantes héréditaires (comme la cystinose, la tyrosinémie) et des variantes acquises du syndrome de Fanconi. Les toxines, les maladies induites par les médicaments et les maladies systémiques (myélome multiple, syndrome de Sjögren) étant la cause acquise la plus fréquente du syndrome de Fanconi. Mots-clés: Le rapport de cas décrit une patiente d\'âge moyen, un cas connu de séropositivité au VIH (virus de l\'immunodéficience humaine) qui a développé le syndrome de Fanconi induit par le ténofovir, une cause de plus en plus reconnue de syndrome de Fanconi acquis chez les patients séropositifs.

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Renal tubular acidosis (RTA) occurs when the kidneys are unable to maintain normal acid-base homeostasis because of tubular defects in acid excretion or bicarbonate ion reabsorption. Using illustrative clinical cases, this review describes the main types of RTA observed in clinical practice and provides an overview of their diagnosis and treatment. The three major forms of RTA are distal RTA (type 1; characterized by impaired acid excretion), proximal RTA (type 2; caused by defects in reabsorption of filtered bicarbonate), and hyperkalemic RTA (type 4; caused by abnormal excretion of acid and potassium in the collecting duct). Type 3 RTA is a rare form of the disease with features of both distal and proximal RTA. Accurate diagnosis of RTA plays an important role in optimal patient management. The diagnosis of distal versus proximal RTA involves assessment of urinary acid and bicarbonate secretion, while in hyperkalemic RTA, selective aldosterone deficiency or resistance to its effects is confirmed after exclusion of other causes of hyperkalemia. Treatment options include alkali therapy in patients with distal or proximal RTA and lowering of serum potassium concentrations through dietary modification and potential new pharmacotherapies in patients with hyperkalemic RTA including newer potassium binders.

Topiramate has a wide array of pharmacologic effects, including proximal renal tubular acidosis (RTA). Clinicians must be wary of the possibility for development of somnolence due to compensatory hyperventilation and cardiac dysrhythmias.

We describe a boy who presented with neonatal hypotonia, followed by delayed motor development and growth impairment. Further evaluation revealed rickets caused by proximal renal tubular dysfunction. At age 3, the boy exhibited dysmorphic features and bilateral cataract. Genetic analysis of the OCRL gene showed a novel variant in exon 13: c.1250T>A, p.Val417Asp; in silico and segregation analysis confirmed the variant to be pathogenic, compatible with the diagnosis of the oculocerebrorenal syndrome of Lowe. Lowe syndrome is a rare multisystemic disorder; the diagnostic triad requires involvement of the eye, central nervous system and the proximal renal tubule. Typical clinical features are congenital cataract, glaucoma, hypotonia, mental and behavioral problems, benign skin lesions, platelet dysfunction and dental abnormalities. Phenotypic features early in life may be nonspecific, which is illustrated by this case with a late manifestation of cataract. Because an early diagnosis can lead to better counseling and treatment, we suggest urinary testing for proteinuria as a part of the evaluation of children with unexplained hypotonia.