Panostotic fibrous dysplasia: a congenital disorder of bone with unusual facial appearance, bone fragility, hyperphosphatasemia, and hypophosphatemia

Dental and craniofacial characteristics caused by the p.Ser40Leu mutation in IFITM5

Severe forms of osteogenesis imperfecta (OI) are usually caused by mutations in genes that code for collagen Type I and frequently are associated with craniofacial abnormalities. However, the dental and craniofacial characteristics of OI caused by the p.Ser40Leu mutation in the IFITM5 gene have not been reported. We investigated a 15-year-old girl with severe OI caused by this mutation. She had marked deformations of extremity long bones. There were no clinical or radiological signs of dentinogenesis imperfecta, but one tooth was missing and several teeth were impacted. Cone beam computed tomography revealed a generalized osteopenic appearance of the craniofacial skeleton, bilateral enlargement of mandibular bodies, and areas of cortical erosions. The cranial base and skull showed a generalized granular bone pattern with a mixture of osteosclerosis and osteolysis. Sphenoid and frontal sinuses were congenitally missing. Cephalometric analysis indicated a Class III growth pattern. In this case, the IFITM5 p.Ser40Leu mutation did not affect tooth structure but was associated with deformities in craniofacial bones that resemble those in the other parts of the skeleton.

1H-NMR analysis of the human urinary metabolome in response to an 18-month multi-component exercise program and calcium–vitamin-D3supplementation in older men

The musculoskeletal benefits of calcium and vitamin-D3supplementation and exercise have been extensively studied, but the effect on metabolism remains contentious. Urine samples were analyzed by1H-NMR spectroscopy from participants recruited for an 18-month, randomized controlled trial of a multi-component exercise program and calcium and vitamin-D3fortified milk consumption. It was shown previously that no increase in musculoskeletal composition was observed for participants assigned to the calcium and vitamin-D3intervention, but exercise resulted in increased bone mineral density, total lean body mass, and muscle strength. Retrospective metabolomics analysis of urine samples from patients involved in this study revealed no distinct changes in the urinary metabolome in response to the calcium and vitamin-D3intervention, but significant changes followed the exercise intervention, notably a reduction in creatinine and an increase in choline, guanidinoacetate, and hypoxanthine (p < 0.001, fold change > 1.5). These metabolites are intrinsically involved in anaerobic ATP synthesis, intracellular buffering, and methyl-balance regulation. The exercise intervention had a marked effect on the urine metabolome and markers of muscle turnover but none of these metabolites were obvious markers of bone turnover. Measurement of specific urinary exercise biomarkers may provide a basis for monitoring performance and metabolic response to exercise regimes.

Disrupted bone remodeling leads to cochlear overgrowth and hearing loss in a mouse model of fibrous dysplasia

Normal hearing requires exquisite cooperation between bony and sensorineural structures within the cochlea. For example, the inner ear secretes proteins such as osteoprotegrin (OPG) that can prevent cochlear bone remodeling. Accordingly, diseases that affect bone regulation can also result in hearing loss. Patients with fibrous dysplasia develop trabecular bone overgrowth resulting in hearing loss if the lesions affect the temporal bones. Unfortunately, the mechanisms responsible for this hearing loss, which could be sensorineural and/or conductive, remain unclear. In this study, we used a unique transgenic mouse model of increased G_s G-protein coupled receptor (GPCR) signaling induced by expression of an engineered receptor, Rs1, in osteoblastic cells. These ColI(2.3)⁺/Rs1⁺ mice showed dramatic bone lesions that histologically and radiologically resembled fibrous dysplasia. We found that ColI(2.3)⁺/Rs1⁺ mice showed progressive and severe conductive hearing loss. Ossicular chain impingement increased with the size and number of dysplastic lesions. While sensorineural structures were unaffected, ColI(2.3)⁺/Rs1⁺ cochleae had abnormally high osteoclast activity, together with elevated tartrate resistant acid phosphatase (TRAP) activity and receptor activator of nuclear factor kappa-B ligand (Rankl) mRNA expression. ColI(2.3)⁺/Rs1⁺ cochleae also showed decreased expression of Sclerostin (Sost), an antagonist of the Wnt signaling pathway that normally increases bone formation. The osteocyte canalicular networks of ColI(2.3)⁺/Rs1⁺ cochleae were disrupted and showed abnormal osteocyte morphology. The osteocytes in the ColI(2.3)⁺/Rs1⁺ cochleae showed increased expression of matrix metalloproteinase 13 (MMP-13) and TRAP, both of which can support osteocyte-mediated peri-lacunar remodeling. Thus, while the ossicular chain impingement is sufficient to account for the progressive hearing loss in fibrous dysplasia, the deregulation of bone remodeling extends to the cochlea as well. Our findings suggest that factors regulating bone remodeling, including peri-lacunar remodeling by osteocytes, may be useful targets for treating the bony overgrowths and hearing changes of fibrous dysplasia and other bony pathologies.

Accelerated Bone Turnover in Pregnant Women with McCune-Albright Syndrome

Bone turnover in pregnant women with McCune-Albright syndrome may be affected by both the syndrome and pregnancy. This study evaluated changes in biochemical bone turnover markers in pregnant women with the syndrome. Serum calcium, phosphorus, 1,25-dihydroxyvitamin D (1,25-(OH)2D), intact osteocalcin (I-OC) and alkaline phosphatase (ALP), and urinary pyridinoline (Pyr), deoxypyridinoline (D-Pyr) and hydroxyproline (HPR) were measured during pregnancy and postpartum in 2 women with McCune-Albright syndrome. Serum calcitonin (CT), and plasma intact parathyroid hormone (I-PTH) and parathyroid hormone-related protein (PTHrP) were also measured in 1 patient. Serum corrected Ca levels were normal or low-normal; phosphorus levels were normal, and 1,25-(OH)2D levels increased toward term and decreased thereafter, similar to normal pregnant women. Urinary Pyr, D-Pyr and HPR were elevated during pregnancy compared to normal pregnant women, peaked just after delivery, and decreased thereafter. Serum I-OC and ALP levels were high during pregnancy and postpartum. Intact PTH levels were increased during pregnancy and postpartum compared to normal pregnant women, whereas serum CT and PTHrP levels were not elevated. Both bone formation and absorption appear to be more enhanced during pregnancy and postpartum in women with McCune-Albright syndrome than in normal pregnant women. Additional or amplified cyclic AMP synthesis in bone cells through activation of the alpha subunit of G protein, independent of hormonal control, may explain the high local bone turnover.

Osteogenesis imperfecta

Osteogenesis imperfecta is a genetic disorder of increased bone fragility, low bone mass, and other connective-tissue manifestations. The most frequently used classification outlines four clinical types, which we have expanded to seven distinct types. In most patients the disorder is caused by mutations in one of the two genes encoding collagen type 1, but in some individuals no such mutations are detectable. The most important therapeutic advance is the introduction of bisphosphonate treatment for moderate to severe forms of osteogenesis imperfecta. However, at present, the best treatment regimen and the long-term outcomes of bisphosphonate therapy are unknown. Although this treatment does not constitute a cure, it is an adjunct to physiotherapy, rehabilitation, and orthopaedic care. Gene-based therapy presently remains in the early stages of preclinical research.

Effect of pamidronate treatment in children with polyostotic fibrous dysplasia of bone

Intravenous infusions with the bisphosphonate compound pamidronate decrease bone pain and reportedly can lead to refilling of dysplastic lesions in adults with fibrous dysplasia (FD) of bone. Here we describe the effects of this treatment approach in 18 children and adolescents (age at start of therapy, 6.2-17.5 yr; eight girls) with polyostotic FD, who received pamidronate for 1.2-9.1 yr (median, 3.8 yr). Treatment cycles with pamidronate (1-1.5 mg/kg.d on 3 consecutive days) were given every 4 months. Levels of serum alkaline phosphatase and urinary collagen type I N-telopeptide were elevated at baseline and decreased continuously during the first 3 yr of therapy. There was no radiographic evidence of filling of lytic lesions or thickening of the bone cortex surrounding the lesions in any patient. Histomorphometric results in dysplastic bone tissue of patients receiving pamidronate (n = 7; time of therapy, 1.4-4.8 yr) were similar to those of patients without medical therapy (n = 9). No serious side effects were noted. In conclusion, pamidronate therapy appears to be safe in children and adolescents with polyostotic FD. However, we found no clear evidence that pamidronate has an effect on dysplastic lesions in such patients.

Endocrine manifestations of stimulatory G protein alpha-subunit mutations and the role of genomic imprinting

The heterotrimeric G protein G(s) couples hormone receptors (as well as other receptors) to the effector enzyme adenylyl cyclase and is therefore required for hormone-stimulated intracellular cAMP generation. Receptors activate G(s) by promoting exchange of GTP for GDP on the G(s) alpha-subunit (G(s)alpha) while an intrinsic GTPase activity of G(s)alpha that hydrolyzes bound GTP to GDP leads to deactivation. Mutations of specific G(s)alpha residues (Arg(201) or Gln(227)) that are critical for the GTPase reaction lead to constitutive activation of G(s)-coupled signaling pathways, and such somatic mutations are found in endocrine tumors, fibrous dysplasia of bone, and the McCune-Albright syndrome. Conversely, heterozygous loss-of-function mutations may lead to Albright hereditary osteodystrophy (AHO), a disease characterized by short stature, obesity, brachydactyly, sc ossifications, and mental deficits. Similar mutations are also associated with progressive osseous heteroplasia. Interestingly, paternal transmission of GNAS1 mutations leads to the AHO phenotype alone (pseudopseudohypoparathyroidism), while maternal transmission leads to AHO plus resistance to several hormones (e.g., PTH, TSH) that activate G(s) in their target tissues (pseudohypoparathyroidism type IA). Studies in G(s)alpha knockout mice demonstrate that G(s)alpha is imprinted in a tissue-specific manner, being expressed primarily from the maternal allele in some tissues (e.g., renal proximal tubule, the major site of renal PTH action), while being biallelically expressed in most other tissues. Disrupting mutations in the maternal allele lead to loss of G(s)alpha expression in proximal tubules and therefore loss of PTH action in the kidney, while mutations in the paternal allele have little effect on G(s)alpha expression or PTH action. G(s)alpha has recently been shown to be also imprinted in human pituitary glands. The G(s)alpha gene GNAS1 (as well as its murine ortholog Gnas) has at least four alternative promoters and first exons, leading to the production of alternative gene products including G(s)alpha, XLalphas (a novel G(s)alpha isoform that is expressed only from the paternal allele), and NESP55 (a chromogranin-like protein that is expressed only from the maternal allele). A fourth alternative promoter and first exon (exon 1A) located approximately 2.5 kb upstream of the G(s)alpha promoter is normally methylated on the maternal allele and transcriptionally active on the paternal allele. In patients with isolated renal resistance to PTH (pseudohypoparathyroidism type IB), the exon 1A promoter region has a paternal-specific imprinting pattern on both alleles (unmethylated, transcriptionally active), suggesting that this region is critical for the tissue-specific imprinting of G(s)alpha. The GNAS1 imprinting defect in pseudohypoparathyroidism type IB is predicted to decrease G(s)alpha expression in renal proximal tubules. Studies in G(s)alpha knockout mice also demonstrate that this gene is critical in the regulation of lipid and glucose metabolism.

[Effect of pamidronate on clinical symptoms and bone metabolism in fibrous dysplasia and McCune-Albright syndrome]

BACKGROUND

Patients with fibrous dysplasia and the McCune-Albright syndrome which is characterized by additional endocrine dysfunctions, such as pubertas precox, suffer from a regional impairment in the differentiation of osteoblasts that is acquired during early embryogenesis and results in fibrous bone lesions. These lesions may cause bone deformities, fractures and chronical pain in the affected skeletal regions. We here report about our experience with a systemic treatment of the bisphosphonate pamidronate.

PATIENTS

We treated 3 patients with fibrous dysplasia and 5 patients with McCune-Albright syndrome over a cumulative period of 37 patient-years.

RESULTS

In all patients who suffered from painful lesions, intravenous infusions of 60 mg pamidronate resulted in an improvement of pain that lasted up to 6 months. In 2 patients we also observed a reduction in the size of some of the osteolytic lesions. Side effects were limited to asymptomatical fever and a small decline in total serum calcium within the physiological limits during the infusions.

CONCLUSION

Pamidronate appears to be an effective and well tolerable treatment option for patients with fibrous dysplasia.

Increased expression of the c-fos proto-oncogene in bone from patients with fibrous dysplasia

BACKGROUND

Fibrous dysplasia is characterized by intense marrow fibrosis and increased rates of bone turnover. The lesions of fibrous dysplasia resemble those described in the long bones of transgenic mice overexpressing the c-fos proto-oncogene. Activating mutations in the alpha subunit of the stimulatory guanine-nucleotide-binding protein (GS alpha) linked to adenylate cyclase have recently been described in bone cells from patients with the McCune-Albright syndrome and fibrous dysplasia.

METHODS

We used in situ hybridization to determine the level of expression of c-fos in bone-biopsy specimens from two normal subjects, eight patients with fibrous dysplasia, and six patients with other bone disorders characterized by high rates of bone turnover. The probe used corresponded to the fourth exon of the c-fos gene.

RESULTS

High levels of c-fos expression were detected in the bone lesions from all eight patients with fibrous dysplasia. No expression of c-fos was detected in bone specimens from the normal subjects or from specimens of normal bone obtained from patients with fibrous dysplasia. The cells that expressed c-fos in the dysplastic lesions were fibroblastic and populated the marrow space. A very low level of c-fos expression was detected in the biopsy specimens from the patients with other bone diseases. One patient with polyostotic fibrous dysplasia and one patient with the McCune-Albright syndrome were tested for the previously described GS alpha gene mutations and were found to express these mutations in bone.

CONCLUSIONS

Increased expression of the c-fos proto-oncogene, presumably a consequence of increased adenylate cyclase activity, may be important in the pathogenesis of the bone lesions in patients with fibrous dysplasia.

Long-term effects of intravenous pamidronate in fibrous dysplasia of bone

Nine patients with symptomatic and severe fibrous dysplasia were treated with intravenous pamidronate (60 mg per day over 3 days every sixth month), and were followed up for 18-48 months. The major effect was decreased bone pain (complete remission in 12 of 14 sites). Radiological changes were seen in four patients, with thickening of cortices, refilling of osteolytic lesions, or both. The initial increased bone remodelling was reduced, as shown by decrease of raised serum alkaline phosphatase and urinary hydroxyproline. The treatment was well tolerated, but a 13-year-old patient showed widening of knee growth-plates which is consistent with a transient mineralisation defect.