A Comprehensive Review of Bone Health in a Child: From Birth to Adulthood.

Bone health is critical for growth and development during childhood. Although fractures are common in children, fractures occurring in the absence of trauma should prompt physicians to consider underlying bone health disorders. This article provides an overview of the current definition of osteoporosis in children, highlighting its limitations and the potential for underdiagnosis. It also discusses the timing of screening initiation and various techniques used to assess bone health, along with their respective benefits and limitations. In addition, this article identifies several causes of primary and secondary osteoporosis in children, shedding light on previously overlooked disorders that can contribute to poor bone quality. The article emphasizes the importance of a multidisciplinary approach to therapeutic management and aims to optimize patient outcomes and improve the overall care of pediatric bone health disorders.

Proceedings of the 2022 Santa Fe Bone Symposium: Current Concepts in the Care of Patients with Osteoporosis and Metabolic Bone Diseases.

The 22nd Annual Santa Fe Bone Symposium (SFBS) was a hybrid meeting held August 5-6, 2022, with in-person and virtual attendees. Altogether, over 400 individuals registered, a majority of whom attended in-person, representing many states in the USA plus 7 other countries. The SFBS included 10 plenary presentations, 2 faculty panel discussions, satellite symposia, Bone Health & Osteoporosis Foundation Fracture Liaison Service Boot Camp, and a Project ECHO workshop, with lively interactive discussions for all events. Topics of interest included fracture prevention at different stages of life; how to treat and when to change therapy; skeletal health in cancer patients; advanced imaging to assess bone strength; the state of healthcare in the USA; osteosarcopenia; vitamin D update; perioperative bone health care; new guidelines for managing primary hyperparathyroidism; new concepts on bone modeling and remodeling; and an overview on the care of rare bone diseases, including hypophosphatasia, X-linked hypophosphatemia, tumor induced osteomalacia, osteogenesis imperfecta, fibrodysplasia ossificans progressiva, and osteopetrosis. The SFBS was preceded by the Santa Fe Fellows Workshop on Osteoporosis and Metabolic Bone Diseases, a collaboration of the Endocrine Fellows Foundation and the Osteoporosis Foundation of New Mexico. From the Workshop, 4 participating fellows were selected to give oral presentations at the bone symposium. These proceedings represent the clinical highlights of 2022 SFBS presentations and the discussions that followed, all with the aim of optimizing skeletal health and minimizing the consequences of fragile bones.

Best Practice Guidelines for Assessment and Management of Osteoporosis in Adult Patients Undergoing Elective Spinal Reconstruction.

STUDY DESIGN: Expert consensus study. OBJECTIVE: This expert panel was created to establish best practice guidelines to identify and treat patients with poor bone health prior to elective spinal reconstruction. SUMMARY OF BACKGROUND DATA: Currently, no guidelines exist for the management of osteoporosis and osteopenia in patients undergoing spinal reconstructive surgery. Untreated osteoporosis in spine reconstruction surgery is associated with higher complications and worse outcomes. METHODS: A multidisciplinary panel with 18 experts was assembled including orthopedic and neurological surgeons, endocrinologists, and rheumatologists. Surveys and discussions regarding the current literature were held according to Delphi method until a final set of guidelines was created with over 70% consensus. RESULTS: Panelists agreed that bone health should be considered in every patient prior to elective spinal reconstruction. All patients above 65 and those under 65 with particular risk factors (chronic glucocorticoid use, high fracture risk or previous fracture, limited mobility, and eight other key factors) should have a formal bone health evaluation prior to undergoing surgery. DXA scans of the hip are preferable due to their wide availability. Opportunistic CT Hounsfield Units of the vertebrae can be useful in identifying poor bone health. In the absence of contraindications, anabolic agents are considered first line therapy due to their bone building properties as compared with antiresorptive medications. Medications should be administered preoperatively for at least 2 months and postoperatively for minimum 8 months. CONCLUSION: Based on the consensus of a multidisciplinary panel of experts, we propose best practice guidelines for assessment and treatment of poor bone health prior to elective spinal reconstructive surgery. Patients above age 65 and those with particular risk factors under 65 should undergo formal bone health evaluation. We also established guidelines on perioperative optimization, utility of various diagnostic modalities, and the optimal medical management of bone health in this population.Level of Evidence: 5.

Somatic PIK3R1 variation as a cause of vascular malformations and overgrowth.

PURPOSE: Somatic activating variants in the PI3K-AKT pathway cause vascular malformations with and without overgrowth. We previously reported an individual with capillary and lymphatic malformation harboring a pathogenic somatic variant in PIK3R1, which encodes three PI3K complex regulatory subunits. Here, we investigate PIK3R1 in a large cohort with vascular anomalies and identify an additional 16 individuals with somatic mosaic variants in PIK3R1. METHODS: Affected tissue from individuals with vascular lesions and overgrowth recruited from a multisite collaborative network was studied. Next-generation sequencing targeting coding regions of cell-signaling and cancer-associated genes was performed followed by assessment of variant pathogenicity. RESULTS: The phenotypic and variant spectrum associated with somatic variation in PIK3R1 is reported herein. Variants occurred in the inter-SH2 or N-terminal SH2 domains of all three PIK3R1 protein products. Phenotypic features overlapped those of the PIK3CA-related overgrowth spectrum (PROS). These overlapping features included mixed vascular malformations, sandal toe gap deformity with macrodactyly, lymphatic malformations, venous ectasias, and overgrowth of soft tissue or bone. CONCLUSION: Somatic PIK3R1 variants sharing attributes with cancer-associated variants cause complex vascular malformations and overgrowth. The PIK3R1-associated phenotypic spectrum overlaps with PROS. These data extend understanding of the diverse phenotypic spectrum attributable to genetic variation in the PI3K-AKT pathway.

Fourteen-year follow-up of a child with acroscyphodysplasia with emphasis on the need for multidisciplinary management: a case report.

BACKGROUND: Acroscyphodysplasia has been described as a phenotypic variant of acrodysostosis type 2 and pseudohypoparathyroidism. In acrodysostosis, skeletal features can include brachydactyly, facial hypoplasia, cone-shaped epiphyses, short stature, and advanced bone age. To date, reports on this disorder have focused on phenotypic findings, endocrine changes, and genetic variation. We present a 14-year overview of a patient, from birth to skeletal maturity, with acroscyphodysplasia, noting the significant orthopaedic challenges and the need for a multidisciplinary team, including specialists in genetics, orthopaedics, endocrinology, and otolaryngology, to optimize long-term outcomes. CASE PRESENTATION: The patient presented as a newborn with dysmorphic facial features, including severe midface hypoplasia, malar flattening, nasal stenosis, and feeding difficulties. Radiologic findings were initially subtle, and a skeletal survey performed at age 7 months was initially considered normal. Genetic evaluation revealed a variant in PDE4D and subsequent pseudohypoparathyroidism. The patient presented to the department of orthopaedics, at age 2 years 9 months with a leg length discrepancy, right knee contracture, and severely crouched gait. Radiographs demonstrated cone-shaped epiphyses of the right distal femur and proximal tibia, but no evidence of growth plate changes in the left leg. The child developed early posterior epiphyseal arrest on the right side and required multiple surgical interventions to achieve neutral extension. Her left distal femur developed late posterior physeal arrest and secondary contracture without evidence of schypho deformity, which improved with anterior screw epiphysiodesis. The child required numerous orthopaedic surgical interventions to achieve full knee extension bilaterally. At age 13 years 11 months, she was an independent ambulator with erect posture. The child underwent numerous otolaryngology procedures and will require significant ongoing care. She has moderate intellectual disability. DISCUSSION AND CONCLUSIONS: Key challenges in the management of this case included the subtle changes on initial skeletal survey and the marked asymmetry of her deformity. While cone-shaped epiphyses are a hallmark of acrodysostosis, posterior tethering/growth arrest of the posterior distal femur has not been previously reported. Correction of the secondary knee contracture was essential to improve ambulation. Children with acroscyphodysplasia require a multidisciplinary approach, including radiology, genetics, orthopaedics, otolaryngology, and endocrinology specialties.

The Rare Bone Disease TeleECHO Program: Leveraging Telehealth to Improve Rare Bone Disease Care.

PURPOSE OF REVIEW: Rare bone diseases constitute ~ 5% of all known rare diseases and can require complex, multidisciplinary care. Advancing access to current medical knowledge is an important strategy for improving care for rare bone diseases throughout the world. To support this goal, the Rare Bone Disease Alliance launched the Rare Bone Disease TeleECHO in 2019. RECENT FINDINGS: The Rare Bone Disease TeleECHO is a monthly video teleconference that fosters a collegial community of practice and opportunities for active learning through interactive case-based learning. TeleECHO relies on a hub-and-spoke model, where medical professionals at the "hub" provide support and expertise for other healthcare providers, or the "spokes". Evidence of the global reach of the program as well as qualitative feedback from registrants supports the need for rare bone disease education and the value of the TeleECHO model. The Rare Bone Disease TeleECHO helps meet the challenge of disseminating rapidly expanding rare bone disease knowledge by leveraging telehealth.

Secondary Fracture Prevention: Consensus Clinical Recommendations from a Multistakeholder Coalition.

Osteoporosis-related fractures are undertreated, due in part to misinformation about recommended approaches to patient care and discrepancies among treatment guidelines. To help bridge this gap and improve patient outcomes, the American Society for Bone and Mineral Research assembled a multistakeholder coalition to develop clinical recommendations for the optimal prevention of secondary fractureamong people aged 65 years and older with a hip or vertebral fracture. The coalition developed 13 recommendations (7 primary and 6 secondary) strongly supported by the empirical literature. The coalition recommends increased communication with patients regarding fracture risk, mortality and morbidity outcomes, and fracture risk reduction. Risk assessment (including fall history) should occur at regular intervals with referral to physical and/or occupational therapy as appropriate. Oral, intravenous, andsubcutaneous pharmacotherapies are efficaciousandcanreduce risk of future fracture.Patientsneededucation,however, about thebenefitsandrisks of both treatment and not receiving treatment. Oral bisphosphonates alendronate and risedronate are first-line options and are generally well tolerated; otherwise, intravenous zoledronic acid and subcutaneous denosumab can be considered. Anabolic agents are expensive butmay be beneficial for selected patients at high risk.Optimal duration of pharmacotherapy is unknown but because the risk for second fractures is highest in the earlypost-fractureperiod,prompt treatment is recommended.Adequate dietary or supplemental vitaminDand calciumintake shouldbe assured. Individuals beingtreatedfor osteoporosis shouldbe reevaluated for fracture risk routinely, includingvia patienteducationabout osteoporosisandfracturesandmonitoringfor adverse treatment effects.Patients shouldbestronglyencouraged to avoid tobacco, consume alcohol inmoderation atmost, and engage in regular exercise and fall prevention strategies. Finally, referral to endocrinologists or other osteoporosis specialists may be warranted for individuals who experience repeated fracture or bone loss and those with complicating comorbidities (eg, hyperparathyroidism, chronic kidney disease).

Secondary Fracture Prevention: Consensus Clinical Recommendations from a Multistakeholder Coalition.

Osteoporosis-related fractures are undertreated, due in part to misinformation about recommended approaches to patient care and discrepancies among treatment guidelines. To help bridge this gap and improve patient outcomes, the American Society for Bone and Mineral Research assembled a multistakeholder coalition to develop clinical recommendations for the optimal prevention of secondary fracture among people aged 65 years and older with a hip or vertebral fracture. The coalition developed 13 recommendations (7 primary and 6 secondary) strongly supported by the empirical literature. The coalition recommends increased communication with patients regarding fracture risk, mortality and morbidity outcomes, and fracture risk reduction. Risk assessment (including fall history) should occur at regular intervals with referral to physical and/or occupational therapy as appropriate. Oral, intravenous, and subcutaneous pharmacotherapies are efficacious and can reduce risk of future fracture. Patients need education, however, about the benefits and risks of both treatment and not receiving treatment. Oral bisphosphonates alendronate and risedronate are first-line options and are generally well tolerated; otherwise, intravenous zoledronic acid and subcutaneous denosumab can be considered. Anabolic agents are expensive but may be beneficial for selected patients at high risk. Optimal duration of pharmacotherapy is unknown but because the risk for second fractures is highest in the early post-fracture period, prompt treatment is recommended. Adequate dietary or supplemental vitamin D and calcium intake should be assured. Individuals being treated for osteoporosis should be reevaluated for fracture risk routinely, including via patient education about osteoporosis and fractures and monitoring for adverse treatment effects. Patients should be strongly encouraged to avoid tobacco, consume alcohol in moderation at most, and engage in regular exercise and fall prevention strategies. Finally, referral to endocrinologists or other osteoporosis specialists may be warranted for individuals who experience repeated fracture or bone loss and those with complicating comorbidities (eg, hyperparathyroidism, chronic kidney disease). © 2019 American Society for Bone and Mineral Research.

Osteoporosis-related Vertebral Fragility Fractures: A Review and Analysis of the American Orthopaedic Association's Own the Bone Database.

STUDY DESIGN: Retrospective cohort study of the Own the Bone database which is a fracture liaison service designed to improve recognition and treatment of osteoporosis. OBJECTIVE: To use the Own the Bone (OTB) database to 1) examine the specific demographics of patients presenting with a low-energy clinical vertebral fracture (VFX) and 2) compare demographic and fracture-specific risk factors between patients with clinical VFX versus patients with nonvertebral low-energy fracture (NVFX). SUMMARY OF BACKGROUND DATA: Large database studies have described risk factors for developing VFX. It is well described that a history of previous VFX portends an increased risk of future VFX. Few studies have reported cohorts from a fracture liaison service such as the OTB initiative. METHODS: 35,039 unique cases of fragility fracture occurred between 2009 and 2016 and were included in analysis. VFX accounted for 3395 (9.9%) of the presenting fractures at OTB enrollment. The demographics, lifestyle factors, medication use, and fracture-specific data for patients in the OTB registry with vertebral fractures were summarized and then statistically compared to those with nonvertebral fragility fractures. RESULTS: The majority of VFX patients were Caucasian, postmenopausal women (74.4%). There was an increased likelihood of presenting with a vertebral fracture in patients who sustained a previous VFX after the age of 50, while patients who sustained a prior nonvertebral fracture (NVFX) were more likely to present with a subsequent NVFX. After controlling for patients with a history of fracture after the age of 50, VFX patients (vs. NVFX) were more likely to be age 70-79, class 1 obesity, with a history of taking anti-osteoporotic prescription medications. CONCLUSIONS: Multiple factors were associated with a significantly increased risk of VFX compared with NVFX. Understanding the risk factors unique to fragility VFX is a critical component for targeting "at-risk" patients and preventing future osteoporosis-related fractures and their consequences. LEVEL OF EVIDENCE: 4.

Assessing disease experience across the life span for individuals with osteogenesis imperfecta: challenges and opportunities for patient-reported outcomes (PROs) measurement: a pilot study.

BACKGROUND: Patient reported outcome (PRO) information is crucial for establishing better patient-provider communication, improving shared decision-making between clinicians and patients, assessing patient responses to therapeutic interventions, and increasing satisfaction with care. We used the Brittle Bones Disease Consortium (BBDC) Contact Registry for People with OI, managed by the Rare Disease Clinical Research Network (RDCRN) to (1) to evaluate the construct validity of the Patient-Reported Outcome Measurement Information System® (PROMIS®) to record important components of the disease experience among individuals with OI; and (2) explore the feasibility of using a registry to recruit individuals with OI to report on health status. Our long-term goal is to enhance communication of health and disease management findings back to the OI community, especially those who do not have access to major OI clinical centers. RESULTS: We demonstrated the construct validity of PROMIS instruments in OI. Our results confirm that the scores from most domains differ significantly from the general US population: individuals with OI have worse symptom burden and functioning. We found no excessive floor or ceiling effects. Our study demonstrates that the BBDC Contact Registry can be used to recruit participants for online health status surveys. However, there are numerous challenges that must be addressed: lack of self-knowledge of OI type, under-representation of men, limited ethnic diversity, and imperfect questionnaire completion rates. CONCLUSION: Our pilot study demonstrated the feasibility of using a contact registry to recruit respondents from the OI community and to obtain analyzable PROMIS data regarding disease experience. Because the results differ from the general population and avoid excessive floor and ceiling effects, PROMIS instruments can be used to assess response to therapeutic interventions in individuals with OI. Future directions will include (1) development and validation of an OI-specific patient-based classification system that aggregates persons with similar clinical characteristics and risks for complications to identify treatment needs; and (2) integrating these PRO tools into routine patient care and research studies.

Orthopaedic Management of Leg-length Discrepancy in Proteus Syndrome: A Case Series.

INTRODUCTION: Proteus syndrome (PS) is a rare mosaic disorder comprising asymmetric bony and soft tissue overgrowth leading to significant morbidity. Placement of growth inhibition hardware with subsequent epiphyseal arrest improves leg-length and angular deformities in pediatric patients without PS. The purpose of this study was to review the surgical approach and present outcomes, complications, and recommendations in 8 patients with PS and leg-length discrepancy (LLD). METHODS: We conducted a retrospective chart review of 8 patients with PS whose primary reason for surgery was LLD. Patients were eligible if they met clinical diagnostic criteria for PS and if the National Institutes of Health team performed at least 1 of their surgical interventions between 2005 and 2015. Surgical techniques included growth inhibition, with tension band plates, applied ≥1 times, and epiphyseal arrest. RESULTS: Eight patients, followed for an average of 4.6 years (range, 1.0 to 7.1 y) after the index procedure, were included in this analysis. Average age at first LLD surgery was 9.4 years (range, 6.1 to 13.6 y); the average LLD was 3.4 cm (range, 0.4 to 7.0 cm) at presentation, and 5.0 cm (range, 1.8 to 10.0 cm) at the time of the first LLD surgery. Participants underwent 23 total surgeries (range, 1 to 5 per patient) and 7 patients have completed surgical intervention. For the 7 patients who did not require overcorrection the average LLD at the last clinical encounter was 2.6 cm (range, 0.6 to 7.2 cm). We encountered 2 complications: 2 patients developed mild knee valgus, which responded to standard guided growth techniques. CONCLUSIONS: This case series suggests that growth inhibition and epiphyseal arrest in children with PS can reduce LLD with few complications. Careful monitoring, rapid mobilization, deep venous thrombosis prophylaxis, and sequential compression devices were also integral elements of our surgical protocol. LEVEL OF EVIDENCE: Level IV.

Genetic characterization of physical activity behaviours in university students enrolled in kinesiology degree programs.

Studies of physical activity behaviours have increasingly shown the importance of heritable factors such as genetic variation. Nonsynonymous polymorphisms of alpha-actinin 3 (ACTN3) and the ß-adrenergic receptors 1 and 3 (ADRB1 and ADRB3) have been previously associated with exercise capacity and cardiometabolic health. We thus hypothesized that these polymorphisms are also related to physical activity behaviours in young adults. To test this hypothesis we examined relationships between ACTN3 (R577X), ARDB1 (Arg389Gly), ADRB3 (Trp64Arg), and physical activity behaviours in university students. We stratified for student enrollment in kinesiology degree programs compared with nonmajors as we previously found this to be a predictor of physical activity. We did not identify novel associations between physical activity and ACTN3. However, the minor alleles of ADRB1 and ADRB3 were significantly underrepresented in kinesiology students compared with nonmajors. Furthermore, carriers of the ADRB1 minor allele reported reduced participation in moderate physical activity and increased afternoon fatigue compared with ancestral allele homozygotes. Together, these findings suggest that the heritability of physical activity behaviours in young adults may be linked to nonsynonymous polymorphisms within ß-adrenergic receptors.

A Subtrochanteric Femoral Stress Fracture following Bisphosphonate Treatment in an Adolescent Girl.

Atypical subtrochanteric and diaphyseal femoral fractures (AFFs) have emerged as a potential complication of bisphosphonate treatment in adults. Despite increasing off-label use of bisphosphonates in children and adolescents for a variety of skeletal disorders, there have been no reports of AFFs in children or adolescents outside of the osteogenesis imperfecta population. We present the case of a 16-year-old girl who developed a subtrochanteric femoral stress fracture following pamidronate treatment for idiopathic juvenile osteoporosis.

Own the Bone, a System-Based Intervention, Improves Osteoporosis Care After Fragility Fractures.

BACKGROUND: The goal of this study was to evaluate the effectiveness of the American Orthopaedic Association's Own the Bone secondary fracture prevention program in the United States. METHODS: The objective of this quality improvement cohort study was dissemination of Own the Bone and implementation of secondary prevention (osteoporosis pharmacologic and bone mineral density [BMD] test recommendations). The main outcome measures were the number of sites implementing Own the Bone and implementation of secondary prevention, i.e., orders for BMD testing and/or pharmacologic treatment. The 177 sites participating in the program were academic and community hospitals, orthopaedic surgery groups, and a health system; data were obtained from the first 125 sites utilizing its registry, between January 1, 2010, and March 31, 2015. It included all patients, aged 50 years or older, presenting with fragility fractures (n = 23,132) who were enrolled in the Own the Bone web-based registry. The interventions were education, development of program elements, dissemination, implementation, and evaluation of the Own the Bone program at participating sites. RESULTS: A growing number of institutions implemented Own the Bone (14 sites in 2005-2006 to 177 sites in 2015). After consultation, 53% of patients had a BMD test ordered and/or pharmacologic therapy for osteoporosis. CONCLUSIONS: The Own the Bone intervention has succeeded in improving the behaviors of medical professionals in the areas of osteoporosis treatment and counseling, BMD testing, initiation of pharmacotherapy, and coordination of care for patients who have experienced a fragility fracture.

Initial report of the osteogenesis imperfecta adult natural history initiative.

BACKGROUND: A better understanding of the natural history of osteogenesis imperfecta (OI) in adulthood should improve health care for patients with this rare condition. METHODS: The Osteogenesis Imperfecta Foundation established the Adult Natural History Initiative (ANHI) in 2010 to give voice to the health concerns of the adult OI community and to begin to address existing knowledge gaps for this condition. Using a web-based platform, 959 adults with self-reported OI, representing a wide range of self-reported disease severity, reported symptoms and health conditions, estimated the impact of these concerns on present and future health-related quality of life (QoL) and completed a Patient-Reported Outcomes Measurement Information System (PROMIS®) survey of health issues. RESULTS: Adults with OI report lower general physical health status (p < .0001), exhibit a higher prevalence of auditory (58% of sample versus 2-16% of normalized population) and musculoskeletal (64% of sample versus 1-3% of normalized population) concerns than the general population, but report generally similar mental health status. Musculoskeletal, auditory, pulmonary, endocrine, and gastrointestinal issues are particular future health-related QoL concerns for these adults. Numerous other statistically significant differences exist among adults with OI as well as between adults with OI and the referent PROMIS® population, but the clinical significance of these differences is uncertain. CONCLUSIONS: Adults with OI report lower general health status but are otherwise more similar to the general population than might have been expected. While reassuring, further analysis of the extensive OI-ANHI databank should help identify areas of unique clinical concern and for future research. The OI-ANHI survey experience supports an internet-based strategy for successful patient-centered outcomes research in rare disease populations.

CK-MM Polymorphism is Associated With Physical Fitness Test Scores in Military Recruits.

OBJECTIVE: Muscle-specific creatine kinase is thought to play an integral role in maintaining energy homeostasis by providing a supply of creatine phosphate. The genetic variant, rs8111989, contributes to individual differences in physical performance, and thus the purpose of this study was to determine if rs8111989 variant is predictive of Physical Fitness Test (PFT) scores in male, military infantry recruits. METHODS: DNA was extracted from whole blood, and genotyping was performed in 176 Marines. Relationships between PFT measures (run, sit-ups, and pull-ups) and genotype were determined. RESULTS: Participants with 2 copies of the T allele for rs8111989 variant had higher PFT scores for run time, pull-ups, and total PFT score. Specifically, participants with 2 copies of the TT allele (variant) (n = 97) demonstrated an overall higher total PFT score as compared with those with one copy of the C allele (n = 79) (TT: 250 ± 31 vs. CC/CT: 238 ± 31; p = 0.02), run score (TT: 82 ± 10 vs. CC/CT: 78 ± 11; p = 0.04) and pull-up score (TT: 78 ± 11 vs. CC/CT: 65 ± 21; p = 0.04) or those with the CC/CT genotype. CONCLUSION: These results demonstrate an association between physical performance measures and genetic variation in the muscle-specific creatine kinase gene (rs8111989).

Impaired osteoblast and osteoclast function characterize the osteoporosis of Snyder - Robinson syndrome.

BACKGROUND: Snyder-Robinson Syndrome (SRS) is an X-linked intellectual disability disorder also characterized by osteoporosis, scoliosis, and dysmorphic facial features. It is caused by mutations in SMS, a ubiquitously expressed gene encoding the polyamine biosynthetic enzyme spermine synthase. We hypothesized that the tissue specificity of SRS arises from differential sensitivity to spermidine toxicity or spermine deficiency. METHODS: We performed detailed clinical, endocrine, histopathologic, and morphometric studies on two affected brothers with a spermine synthase loss of function mutation (NM_004595.4:c.443A > G, p.Gln148Arg). We also measured spermine and spermidine levels in cultured human bone marrow stromal cells (hBMSCs) and fibroblasts using the Biochrom 30 polyamine protocol and assessed the osteogenic potential of hBMSCs. RESULTS: In addition to the known tissue-specific features of SRS, the propositi manifested retinal pigmentary changes, recurrent episodes of hyper- and hypoglycemia, nephrocalcinosis, renal cysts, and frequent respiratory infections. Bone histopathology and morphometry identified a profound depletion of osteoblasts and osteoclasts, absence of a trabecular meshwork, a low bone volume and a thin cortex. Comparison of cultured fibroblasts from affected and unaffected individuals showed relatively small changes in polyamine content, whereas comparison of cultured osteoblasts identified marked differences in spermidine and spermine content. Osteogenic differentiation of the SRS-derived hBMSCs identified a severe deficiency of calcium phosphate mineralization. CONCLUSIONS: Our findings support the hypothesis that cell specific alterations in polyamine metabolism contribute to the tissue specificity of SRS features, and that the low bone density arises from a failure of mineralization.

Mechanistic and therapeutic insights gained from studying rare skeletal diseases.

Rare bone diseases account for 5% of all birth defects and can cause significant morbidity throughout patients' lives. Significant progress is being made to elucidate the pathophysiological mechanisms underlying these diseases. This paper summarizes presentation highlights of a workshop on Rare Skeletal Diseases convened to explore how the study of rare diseases has influenced the field's understanding of bone anabolism and catabolism and directed the search for new therapies benefiting patients with rare conditions as well as patients with common skeletal disorders.