The health effects of vitamin D supplementation: evidence from human studies.

Vitamin D supplementation can prevent and cure nutritional rickets in infants and children. Preclinical and observational data suggest that the vitamin D endocrine system has a wide spectrum of skeletal and extra-skeletal activities. There is consensus that severe vitamin D deficiency (serum 25-hydroxyvitamin D (25OHD) concentration <30 nmol/l) should be corrected, whereas most guidelines recommend serum 25OHD concentrations of >50 nmol/l for optimal bone health in older adults. However, the causal link between vitamin D and many extra-skeletal outcomes remains unclear. The VITAL, ViDA and D2d randomized clinical trials (combined number of participants >30,000) indicated that vitamin D supplementation of vitamin D-replete adults (baseline serum 25OHD >50 nmol/l) does not prevent cancer, cardiovascular events, falls or progression to type 2 diabetes mellitus. Post hoc analysis has suggested some extra-skeletal benefits for individuals with vitamin D deficiency. Over 60 Mendelian randomization studies, designed to minimize bias from confounding, have evaluated the consequences of lifelong genetically lowered serum 25OHD concentrations on various outcomes and most studies have found null effects. Four Mendelian randomization studies found an increased risk of multiple sclerosis in individuals with genetically lowered serum 25OHD concentrations. In conclusion, supplementation of vitamin D-replete individuals does not provide demonstrable health benefits. This conclusion does not contradict older guidelines that severe vitamin D deficiency should be prevented or corrected.

Soluble Klotho causes hypomineralization in Klotho-deficient mice.

The type I transmembrane protein αKlotho (Klotho) serves as a coreceptor for the phosphaturic hormone fibroblast growth factor 23 (FGF23) in kidney, while a truncated form of Klotho (soluble Klotho, sKL) is thought to exhibit multiple activities, including acting as a hormone, but whose mode(s) of action in different organ systems remains to be fully elucidated. FGF23 is expressed primarily in osteoblasts/osteocytes and aberrantly high levels in the circulation acting via signaling through an FGF receptor (FGFR)-Klotho coreceptor complex cause renal phosphate wasting and osteomalacia. We assessed the effects of exogenously added sKL on osteoblasts and bone using Klotho-deficient (kl/kl) mice and cell and organ cultures. sKL induced FGF23 signaling in bone and exacerbated the hypomineralization without exacerbating the hyperphosphatemia, hypercalcemia and hypervitaminosis D in kl/kl mice. The same effects were seen in rodent bone models in vitro, in which we also detected formation of a sKL complex with FGF23-FGFR and decreased Phex (gene responsible for X-linked hypophosphatemic rickets (XLH)/osteomalacia) expression. Further, sKL-FGF23-dependent hypomineralization in vitro was rescued by soluble PHEX. These data suggest that exogenously added sKL directly participates in FGF23 signaling in bone and that PHEX is a downstream effector of the sKL-FGF23-FGFR axis in bone.

[Tenofovir-associated Fanconi`s syndrome and rickets in a HIV infected girl]. / Síndrome de Fanconi y raquitismo hipofosfatémico asociado al uso de tenofovir en una niña infectada con VIH.

Tenofovir (TDF) is an inhibitor of reverse transcriptase nucleotide analogue, although it has good tolerability and high anti-retroviral activity, its effect on the kidney has been a concern. OBJECTIVE: To describe a girl infected with HIV who presented Fanconi syndrome during antiretroviral therapy with TDF. CLINICAL CASE: We describe a HIV-1-infected girl, who after 18 months treatment with TDF presented loss of strength and pain of the lower extremities with functional impairment. Laboratory findings were consistent with Fanconi syndrome. Radiographs showed bilateral hip fracture and wrists. Full recovery of Fanconi syndrome was achieved four months after changing antiretroviral therapy. CONCLUSIONS: TDF-prescribing physicians must be prepared to detect signs and symptoms of renal dysfunction and immediately consider switching to another antiviral drug.

Síndrome de Fanconi y raquitismo hipofosfatémico asociado al uso de tenofovir en una niña infectada con VIH / Tenofovir-associated Fanconi`s syndrome and rickets in a HIV infected girl

El tenofovir (TDF) es un inhibidor de la transcriptasa reversa análogo de nucleótidos, aunque tiene buena tolerabilidad y alta actividad antirretroviral, su efecto sobre el riñón ha sido un motivo de preocupación. Objetivo: Describir el caso de una niña infectada por VIH que presenta síntomas y hallazgos de laboratorio compatibles con un síndrome de Fanconi durante el tratamiento con TDF como parte de su terapia antirretroviral. Caso clínico: Niña infectada por el VIH-1, que después de 18 meses con el tratamiento con TDF presentó pérdida de fuerza y dolor de las extremidades inferiores con deterioro funcional. Los hallazgos de laboratorio fueron compatibles con el síndrome de Fanconi. Las radiografías mostraron fractura bilateral de cadera y muñecas. El síndrome de Fanconi se recuperó por completo cuatro meses después del cambio de terapia antirretroviral. Conclusiones: Los médicos que prescriben TDF deben estar preparados para detectar signos y síntomas indicativos de disfunción renal y considerar de inmediato el cambio del fármaco a otro antirretroviral.

Tenofovir (TDF) is an inhibitor of reverse transcriptase nucleotide analogue, although it has good tolerability and high anti-retroviral activity, its effect on the kidney has been a concern. Objective: To describe a girl infected with HIV who presented Fanconi syndrome during antiretroviral therapy with TDF. Clinical case: We describe a HIV-1-infected girl, who after 18 months treatment with TDF presented loss of strength and pain of the lower extremities with functional impairment. Laboratory findings were consistent with Fanconi syndrome. Radiographs showed bilateral hip fracture and wrists. Full recovery of Fanconi syndrome was achieved four months after changing antiretroviral therapy. Conclusions: TDF-prescribing physicians must be prepared to detect signs and symptoms of renal dysfunction and immediately consider switching to another antiviral drug.

Anticonvulsant-induced rickets and nephrocalcinosis.

Reported here is the case of a severely disabled young girl who developed Fanconi syndrome secondary to long-term valproic acid administration, ultimately leading to hypophosphatemic rickets. Although nephrocalcinosis is not a common feature in patients with proximal tubulopathy, the patient presented also with this condition, and the concomitant use of another anticonvulsant might have potentiated this condition. The purpose of this report is to increase awareness among healthcare providers of such rare but significant complications associated with anticonvulsants.

Tenofovir-associated nephrotoxicity in two HIV-infected adolescent males.

We report two cases of tenofovir (TDF)-associated nephrotoxicity in perinatally HIV-infected adolescents. The first case, a 16-year-old African American male with an absolute CD4+ cell count of 314 cells/mm(3), presented with an abrupt rise in serum creatinine leading to irreversible renal failure while on TDF-containing highly active antiretroviral therapy (HAART). While the patient had evidence of underlying kidney disease, the timing of his renal failure indicates that TDF played a central role. The second case, a 16-year-old African-American male with an absolute CD4+ cell count of 895 cells/mm3, presented with rickets and hypophosphatemia while receiving TDF-based HAART. To our knowledge, these cases represent the first reports of TDF-associated irreversible renal failure and rickets in pediatric patients. We believe these cases highlight important and potentially irreversible side effects of this agent and emphasize the need for further studies of the renal safety of TDF in pediatric patients.

Anticonvulsant drug-induced rickets and multiple slipped epiphyses in a child treated non-operatively: a case report.

The clinical and radiographic presentation of a child with spastic tetraplegia, anticonvulsant drug-induced rickets, borderline hypothyroidism and multiple slipped epiphyses is described. While the metabolic abnormalities were being treated, the parents denied surgical treatment and have been non-compliant with bracing of the wrist, ankle and knee deformities. By two years of medical treatment, rickets had resolved and the growth plates of the lower limbs' joints had closed. Non weight-bearing, gentle physiotherapy and bracing led to good results in the hip, ankle and wrist joints and to unacceptable residual valgus angular and rotational deformity of the right knee. Severely handicapped paediatric patients with metabolic bone disorders, non-compliant with bracing and with co-existent soft tissue contractures, are probably not good candidates for conservative treatment of severe angular limb deformities. However, non-operative treatment of minimal or moderate slippage of the proximal femoral epiphysis (as well as other major epiphyses) can lead to good results.

Adverse effects of antiepileptic drugs on bone mineral density in children.

Bone mineral content (BMC) or density (BMD) may be decreased in children with epilepsy either as a consequence of the epilepsy, the condition that caused the epilepsy or the treatment for epilepsy. This paper investigates the effects of antiepileptic drugs (AEDs) on BMD in children. A systematic search of Pubmed resulted in 14 papers that described changes in BMD in children on AEDs. For phenytoin, one study failed to show a decrease in femur BMD, whereas another study reported a decrease in total body and spine BMD, but only with the use of phenytoin for > 2 years. With phenytoin combined with a ketogenic diet, a decrease in forearm BMC was seen. For phenobarbital, one study showed a decrease in spine and total body BMD, but only among those who had used phenobarbital for > 2 years. Six studies were available for carbamazepine, and none of these showed a decrease in BMD in any skeletal site. For valproate, results were diverse; two studies reported a decrease in spine BMD, whereas two other studies did not. Two studies reported a decrease in hip BMD with valproate, whereas one did not. All three studies on forearm BMD in users of valproate described a decrease. Three studies reported an improvement in BMC with vitamin D supplementation in children on AEDs. No reports on changes in BMD among users of newer AEDs are available. In conclusion, more evidence is needed for the effects on BMD in children, especially for newer AEDs. The available studies have all been cross-sectional, and longitudianal studies are needed along with studies on potential interventions in children with decreased BMD.

Metabolic concerns associated with antiepileptic medications.

Because treatment with antiepileptic drugs (AEDs) is often for years or lifelong, physicians should be aware of the metabolic changes that can be associated with AED use and the potential effects of these changes during long-term therapy. Alterations of bone metabolism leading to decreased bone mineral density, associated particularly but not exclusively with the hepatic enzyme-inducing AEDs, can worsen the risk for fractures, which is already increased in patients with epilepsy by factors such as seizure-related falls and trauma. Some AEDs are associated with weight gain, an effect that is not only distressing to many patients but may be sufficient to increase the risk for cardiovascular disease and other disorders associated with excessive body weight. The carbonic anhydrase-inhibiting properties of some AEDs can lead to metabolic acidosis. The AEDs that inhibit carbonic anhydrase are also associated with an increase in risk for renal stones, as is the ketogenic diet. Awareness of the potential metabolic disturbances associated with AED use is particularly important because many of them are subtle and may take years to become clinically apparent.

Bone disease associated with antiepileptic drugs.

Antiepileptic drugs (AEDs) are associated with bone disease. Early reports found rickets in children and osteomalacia in adults, but those reports were primarily in institutionalized persons. Studies in ambulatory adults and children taking AEDs do not reveal rickets or osteomalacia but do report abnormalities in biochemical indexes of bone mineral metabolism and density. In addition, fracture rates are increased in AED-treated patients. AEDs that induce the cytochrome P450 enzyme system are most commonly associated with abnormalities in bone. Emerging data suggest that valproate, an enzyme inhibitor, may also affect bone, and there is limited information on the newer AEDs. Several theories on the mechanism of AED-associated bone disease have been proposed, but no single one explains all the reported findings. Identifying AED-treated patients who are at risk for or have bone disease is important, as multiple therapies are available.

Bone health in pediatric epilepsy.

Childhood and adolescence are critical periods of skeletal mineralization. Peak bone mineral density achieved by the end of adolescence determines the risk for later pathological fractures and osteoporosis. Chronic disease and medication often adversely affect bone health. Epilepsy is one of the most common neurological conditions occurring in persons under the age of 21. Epilepsy may affect bone in a number of ways. Restrictions of physical activity imposed by seizures; limitations on physical activity resulting from cerebral palsy, frequently present in patients with symptomatic epilepsy; and medications used to treat seizures can all adversely affect bone health. It has long been observed that treatment with phenytoin and phenobarbital can be associated with rickets. More recently, established agents such as carbamazepine and valproate have been shown to be associated with a lowering of bone mineral density. The literature related to bone health in pediatric epilepsy is reviewed, although it should be noted that these data are limited.

An ethyl-nitrosourea-induced point mutation in phex causes exon skipping, x-linked hypophosphatemia, and rickets.

We describe the clinical, genetic, biochemical, and molecular characterization of a mouse that arose in the first generation (G(1)) of a random mutagenesis screen with the chemical mutagen ethyl-nitrosourea. The mouse was observed to have skeletal abnormalities inherited with an X-linked dominant pattern of inheritance. The causative mutation, named Skeletal abnormality 1 (Ska1), was shown to be a single base pair mutation in a splice donor site immediately following exon 8 of the Phex (phosphate-regulating gene with homologies to endopeptidases located on the X-chromosome) gene. This point mutation caused skipping of exon 8 from Phex mRNA, hypophosphatemia, and features of rickets. This experimentally induced phenotype mirrors the human condition X-linked hypophosphatemia; directly confirms the role of Phex in phosphate homeostasis, normal skeletal development, and rickets; and illustrates the power of mutagenesis in exploring animal models of human disease.

Drug-induced metabolic bone disorders.

A number of drugs, either physician prescribed or those taken without the knowledge of the physician, may have metabolic effects on, and result in abnormal changes in, the musculoskeletal system. These medications may involve the developing fetus, infant, child, or adult and may manifest as drug-induced embryopathies, osteoporosis, osteomalacia, or rickets, or a combination of these, or they may be associated with proliferative changes. Not uncommonly, the radiologist may be the first physician to identify the metabolic manifestations of these medications. The radiological changes associated with such drugs will be reviewed. Certain drugs may have teratogenic effects, nonteratogenic effects, or both. These effects, dependent solely on the timing of administration, will be discussed separately.

Antacid-induced rickets in infancy.

A 3-month-old premature infant presented with a "soft skull." Clinical and radiologic findings confirmed the diagnosis of rickets. Biochemistry revealed normal serum parathyroid hormone (PTH) and undetectable urine phosphate. These findings combined with a history of 5-6 weeks' treatment with high-dose aluminum-rich antacid established the diagnosis of antacid-induced rickets. Discontinuation of the medicine combined with phosphate and vitamin D supplementation resulted in quick resolution of all clinical, radiologic, and biochemical abnormalities. Our patient demonstrates that in premature infants antacid-induced rickets can develop within a few weeks; normal serum PTH concentration and hypophosphaturia are highly indicative of the diagnosis, and contrary to the situation in adults in whom hypercalciuria has been often described, in infants hypocalciuria is more commonly observed. Pediatricians should avoid or minimize the use of aluminum-containing antacids, and when used, carefully monitor mineral metabolism.