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Purpose Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome of abnormal phosphate and vitamin D metabolism caused by typically small endocrine tumors that secrete fibroblast growth factor 23 (FGF23). TIO is characterized clinically by progressive musculoskeletal pain, fatigue, proximal muscle weakness, and multiple fractures, leading to long-term disability. Misdiagnosis and delayed diagnosis are common because of the nonspecific symptoms, and several years may elapse before patients receive an accurate diagnosis and appropriate treatment. Thus, it is vital that awareness of the appropriate recognition and management of TIO is increased among healthcare professionals who may encounter patients with suspected TIO. Methods A roundtable meeting was held on 10 January 2020 in Dallas, TX, USA, to gather perspectives on the diagnosis and treatment of TIO. The following topics were considered: clinical presentation, patient history, differential diagnosis, laboratory assessment, imaging, venous sampling, and treatment. Results This report provides a summary of our collective experiences in the management of TIO. Main conclusions Laboratory tests are mandatory to expedite TIO diagnosis and should include measurement of fasting serum phosphorus, renal phosphate reabsorption, serum 1,25-dihydroxyvitamin D, and serum FGF23 levels. Functional and anatomical imaging are essential to locate the FGF23-secreting tumor(s) causing TIO. Surgical resection is often a curative treatment when the tumor can be localized; however, better management of patients who cannot be operated on with targeted therapies is needed. Further efforts to increase awareness of TIO within the medical community, and education on recommended diagnostic and treatment pathways are required to improve the management of this debilitating disease.

Background: Osteogenesis imperfecta (OI) is characterized by bone fragility and increased fracture susceptibility. Most mutations occur in COL1A1 and COL1A2 genes. Rarely, mutations in BMP1 have been reported in association with OI type XIII. Disease severity is generally more severe when the mutation affects both gene products encoded by BMP1 that serve as procollagenases: bone morphogenic protein 1 and mammalian tolloid (mTLD) [1]. Clinical Case: A 7-year-old Hispanic boy, with speech and gross motor delays, sustained five bilateral tibial fractures with minimal trauma since age 2.5 years. At age 6 years, he developed severe back pain after a minor fall. Diffuse spinal osteopenia and multiple vertebral compression fractures (VCF) at T9, L1, L3 were identified radiographically, with progressive vertebral height loss in the ensuing 9 months. Fatigue was reported after walking >10 min, with difficulty running and climbing stairs. There was no family history of musculoskeletal disorders. Stature was consistently between 10-15th% for age. Subtle facial dysmorphism included micrognathia and small chin, with patchy blue-gray sclerae, and normal dentition. The lumbar spine was tender to percussion. Gait was slow and antalgic with external rotation of the right hip. Laboratory evaluation revealed normal serum calcium, iPTH, magnesium, phosphate, 25-hydroxyvitamin D and alkaline phosphatase for age. P1NP was slightly high (193 µg/L, 30-110 µg/L) and CTX was slightly low (554 pg/mL, n: 574-1849 pg/mL), the latter being atypical for OI. Total hip BMD (adjusted for height Z-score) was normal (Z-score = 1.76) and adjusted femoral neck BMD was high (Z-score = 2.67). VCFs precluded assessment of lumbar spine BMD. Genomic analysis revealed a homozygous missense mutation in exon 4 of BMP1 resulting in an amino acid substitution (c. C505T; p.Arg169Cys) in both the bone morphogenetic protein 1 and mTLD gene products of BMP1. The mutation is predicted to be damaging to both proteins, and associated with this rare form of OI. Conclusion: We report a novel homozygous mutation in BMP1 identified in a child with autosomal recessive OI. Unlike most forms of OI, patients with type XIII often have normal or increased BMD [1], making a correlation between BMD and fracture risk difficult. While bisphosphonates (BP) may help reduce recurrent fractures and provide symptomatic relief, the broad phenotypic spectrum and concern for further increasing BMD complicate management. A high resolution peripheral quantitative CT scan to assess bone microarchitecture and quality may aid in the decision of BP therapy. As evidence is limited on the effectiveness of BP in this rare form of OI, it is important to consider each case individually. 1. Sangsin, A., et al., Two novel compound heterozygous BMP1 mutations in a patient with osteogenesis imperfecta: a case report. BMC Med Genet, 2017. 18(1): p. 25.

Pediatric allogeneic hematopoietic stem cell transplantation (AHSCT) recipients with chronic graft-versus-host disease (cGVHD) are at high risk for endocrinopathies, particularly impaired bone mineral density (BMD). However, rates of BMD impairment in pediatric AHSCT recipients with cGVHD have not been well documented. We report 33 patients with cGVHD who were referred to the National Institutes of Health (NIH) for the Natural History of Clinical and Biological Factors Determining Outcomes in Chronic Graft-versus-Host Disease Study (NCT 0092235) and underwent formal BMD assessment via dual-energy X-ray absorptiometry (DEXA). Not surprisingly, we found much higher rates of BMD impairment than previously reported for pediatric AHSCT recipients who were not stratified by the presence or absence of cGVHD. Most of these patients (73%) had a z-score ≤−2 in at least 1 anatomic site. Although we expected the rate to be higher than that observed for pediatric AHSCT recipients in studies that did not analyze patients with cGVHD separately, this rate is nonetheless extremely high. Furthermore, the overall rate of occult vertebral compression fractures (VCFs) in our cohort was 17%, and the rate was 23% in patients with at least 1 z-score of ≤−2. The rates of BMD impairment and VCF in our pediatric cohort were significantly higher than those seen in the adult AHSCT recipients who were concurrently enrolled on the same study at the NIH and had similar cGVHD severity. We found that older age at cGVHD diagnosis and a greater number of systemic therapies were associated with occult VCF. Moreover, the intensity of current immunosuppression negatively impacted lumbar spine and total hip BMD in this cohort. Our study, although limited by small patient numbers and lack of a control AHSCT recipient group without cGVHD, indicates that children with cGVHD are at a greater risk for BMD impairment than previously appreciated. Given the rising incidence of cGVHD in AHSCT recipients and our findings, we recommend that pre-AHSCT DEXA be incorporated into routine pediatric pretransplantation screening studies. A baseline DEXA study could facilitate longitudinal monitoring of BMD in children, who may be more susceptible than adults to the negative effects of AHSCT on BMD. In addition, given the high risk of BMD impairment in pediatric AHSCT recipients with cGVHD, such patients should undergo BMD evaluation upon developing cGVHD, with continued monitoring thereafter to allow intervention before progression of the BMD impairment to its severe manifestation, VCF.