Multicentric Carpotarsal Osteolysis: a Contemporary Perspective on the Unique Skeletal Phenotype.

PURPOSE OF REVIEW: Multicentric carpotarsal osteolysis (MCTO) is an ultra-rare disorder characterized by osteolysis of the carpal and tarsal bones, subtle craniofacial deformities, and nephropathy. The molecular pathways underlying the pathophysiology are not well understood. RECENT FINDINGS: MCTO is caused by heterozygous mutations in MAFB, which encodes the widely expressed transcription factor MafB. All MAFB mutations in patients with MCTO result in replacement of amino acids that cluster in a phosphorylation region of the MafB transactivation domain and account for a presumed gain-of-function for the variant protein. Since 2012, fewer than 60 patients with MCTO have been described with 20 missense mutations in MAFB. The clinical presentations are variable, and a genotype-phenotype correlation is lacking. Osteolysis, via excessive osteoclast activity, has been regarded as the primary mechanism, although anti-resorptive agents demonstrate little therapeutic benefit. This paper appraises current perspectives of MafB protein action, inflammation, and dysfunctional bone formation on the pathogenesis of the skeletal phenotype in MCTO. More research is needed to understand the pathogenesis of MCTO to develop rational therapies.

A novel dominant COL11A1 mutation in a child with Stickler syndrome type II is associated with recurrent fractures.

This case describes a child with blindness, recurrent low-impact fractures, low bone mass, and intermittent joint pain who was found to have a novel missense mutation in COL11A1, consistent with Stickler syndrome type II. The case illustrates the phenotypic variability of the syndrome, which may include increased fragility in childhood. INTRODUCTION: Stickler syndrome type II is an autosomal dominant disorder caused by mutations in the gene that encodes the type XI collagen chain α1 (COL11A1). Manifestations include craniofacial dysmorphology and ocular abnormalities that may lead to blindness, hearing loss, and skeletal anomalies that range from joint pain and arthritis to scoliosis and hypermobility. METHODS: Herein, we describe a child who carried the presumed diagnosis of osteoporosis-pseudoglioma syndrome because of the combined findings of recurrent low-impact fractures due to low bone mass and blindness. The child also suffered from joint pain but had no facial dysmorphism or hearing loss. RESULTS: Targeted sequencing and deletion analysis of the LRP5, COL1A1, and COL1A2 genes failed to identify any mutations, and whole exome sequence analysis revealed a novel missense mutation (c.3032C>A:p.P1011Q) in COL11A1, consistent with Stickler type II. CONCLUSION: This case highlights the phenotypic variability of Stickler type II, broadens the list of differential diagnosis of increased bone fragility in childhood, and highlights utility of unbiased genetic testing towards establishing the correct diagnosis in children with frequent fractures.

The Internal Medicine Subinternship--Now More Important than Ever: A Joint CDIM-APDIM Position Paper.

For decades, the internal medicine (IM) subinternship has served as a critical interface between undergraduate and graduate medical education. As such, the vast majority of U.S. medical schools offer this rotation to help students prepare for post-graduate training. Historically an experiential rotation, a formal curriculum with specific learning objectives was eventually developed for this course in 2002. Since then, graduate medical education (GME) has changed significantly with the regulation of duty hours, adoption of competency-based education, and development of training milestones and entrustable professional activities. In response to these and many other changes to residency training and medical practice, in 2010, the Association of Program Directors in Internal Medicine (APDIM) surveyed its members-with input from the Clerkship Directors in Internal Medicine (CDIM) Subinternship Task Force-to determine which core skills program directors expected from new medical school graduates. The results of that survey helped to inform a joint CDIM-APDIM committee's decision to re-evaluate the goals of the IM subinternship in an effort to enhance the transition from medical school to residency. This joint committee defined the minimum expectations of what constitutes an IM subinternship rotation, proposed recommended skills for IM subinterns, and discussed challenges and future directions for this crucial course.

A randomized, phase II trial of two dose schedules of carboplatin/paclitaxel/cetuximab in stage IIIB/IV non-small-cell lung cancer (NSCLC).

BACKGROUND: This trial investigated the efficacy and safety of weekly cetuximab combined with two different schedules of paclitaxel/carboplatin for stage IIIB/IV non-small-cell lung cancer (NSCLC). METHODS: A total of 168 patients with previously untreated stage IIIB/IV NSCLC were randomized to arm A, cetuximab (400 mg/m(2) day 1 followed by weekly 250 mg/m(2)) + paclitaxel (Taxol) (225 mg/m(2))/carboplatin (AUC6) day 1 every 3 weeks or arm B, same cetuximab regimen plus paclitaxel (100 mg/m(2)) days 1, 8, and 15 every 3 weeks and carboplatin (AUC6) day 1 every 4 weeks. Treatment continued for a four-cycle maximum. Patients with a complete response, partial response, or stable disease after four cycles could receive cetuximab 250 mg/m(2)/week until disease progression or unacceptable toxicity. The primary end point was to evaluate progression-free survival (PFS). RESULTS: Median PFS was 4.7 and 4.3 months for arms A and B, respectively (6-month PFS, 27.3% versus 30.9%). Median overall survival was 11.4 versus 9.8 months for arms A and B, respectively; estimated 1-year survival, 47.7% versus 39.3%; and objective response rate, 29.6% versus 25%. The regimen was well tolerated with rash and hematologic toxicity being most common. CONCLUSIONS: This study did not meet the prespecified benchmark of 35% 6-month PFS rate; both combination schedules of cetuximab plus paclitaxel/carboplatin were feasible and equivalent for treating advanced NSCLC.

Bone marrow and spleen: dissociation of immunologic properties by cortisone.

Bone marrow and spleen cells react differently after treatment with cortisone acetate in vivo. Antibody-forming, hematopoietic, and proliferative responses of spleen cells are reduced, while bone marrow cell responses are not. The stimulation of spleen cells by phytohemagglutinin is abolished, but the response of marrow cells is enhanced. These reactions provide functional markers for the different cells involved in immunologic responses.

Familial isolated hypoparathyroidism caused by a mutation in the gene for the transcription factor GCMB.

Hypoparathyroidism is characterized by hypocalcemia, hyperphosphatemia, and absent or markedly reduced circulating concentrations of parathyroid hormone. The transcription factor GCMB is predominantly, if not exclusively, expressed in parathyroid cells and is critical for development of the parathyroid glands in mice. Thus, in the present study we examined the GCMB gene, mapped to 6p23-24, as a candidate for isolated hypoparathyroidism. We defined the boundaries of the five exons of the human GCMB gene and then identified a large intragenic mutation in the GCMB genes of the proband of an extensive kindred with isolated hypoparathyroidism. Her parents and several other unaffected relatives were heterozygous for the mutation. Despite an absence of any history of consanguinity, microsatellite analysis showed shared genotypes that flanked the GCMB gene over a span of 5 cM, suggesting that both of the proband's GCMB alleles had been derived from a single common ancestor. Analysis of additional, unrelated cases did not disclose the same mutation. We conclude that homozygous loss of function of the GCMB gene impairs normal parathyroid gland embryology and is responsible for isolated hypoparathyroidism in a subset of patients with this disease.

Deficient guanine nucleotide regulatory unit activity in cultured fibroblast membranes from patients with pseudohypoparathyroidism type I. a cause of impaired synthesis of 3',5'-cyclic AMP by intact and broken cells.

Deficient activity of the guanine nucleotide regulatory protein (G unit), an integral component of the membrane-bound adenylate cyclase complex, has been implicated as the biochemical lesion in many patients with pseudohypoparathyroidism (PHP) type I. In addition to renal resistance to parathyroid hormone in this disorder, there is decreased responsiveness of diverse tissues to hormones that act via 3',5'-cyclic AMP (cAMP). To assess whether a deficiency of G units could account for impaired adenylate cyclase activity, we studied cAMP production in intact cultured fibroblasts and fibroblast plasma membranes from five patients with PHP in response to several activators of adenylate cyclase. The number of G units in PHP fibroblast membranes, measured by cholera toxin-dependent [(32)P]ADP ribosylation of G-unit peptides, as well as the G-unit activity, determined by the ability of detergent extracts to reconstitute adenylate cyclase activity in G-unit-deficient S49 CYC(-) membranes, were found to be markedly reduced compared with control membranes (43 and 40%, respectively), The activation of fibroblast membrane adenylate cyclase by effectors that act directly through the G unit (guanosine triphosphate, guanosine 5'-0-[3-thiotriphosphate] [GTP-gamma-S], NaF) was significantly greater in control membranes than in membranes from patients with PHP. Moreover, we found that hormone (prostaglandin E(1)) stimulated adenylate cyclase activity was also greater in control membranes than in PHP membranes. Neither the apparent affinity of membrane adenylate cyclase for GTP-gamma-S (apparent K(m) =5 X 10(-8) M) nor the rate of enzyme activation by GTP-gamma-S was significantly different in fibroblast membranes from control subjects and patients with PHP. In contrast to the notable differences in hormone and G-unit-activated adenylate cyclase shown in fibroblast membranes from PHP patients and control subjects, the intrinsic catalytic activity of membranes, as determined by forskolin-stimulated adenylate cyclase, was not significantly different in the two groups. Intact fibroblasts derived from patients with PHP accumulated significantly (P 0.001) less cAMP (46+/-21 pmol cAMP/mcg DNA, n = 5) than cells from normal individuals (170+/-51 pmol cAMP/mcg DNA, n = 11) when stimulated with PGE(1). PGE(1)-stimulated accumulation of cAMP by intact fibroblast monolayers correlated closely with PGE(1) plus GTP-activated membrane adenylate cyclase activity in both patients and controls (r = 0.97, P < 0.001). Our data show that, in patients with PHP, (a) fibroblast membranes show a decreased complement of G units, (b) membrane catalytic activity is normal, but adenylate cyclase activity is reduced when stimulated by hormone or by effectors which activate the G unit, (c) the ability of cells to accumulate cAMP in response to hormone stimulation is reduced, and (d) reduced membrane adenylate cyclase activity correlates well with impaired cellular cAMP synthesis. These results, taken together, indicate that a deficiency of G-unit activity can impair synthesis of cAMP by both intact and broken cells, and may explain the resistance of multiple tissues to hormones that act via cAMP observed in PHP.

Differential expression of guanosine triphosphate binding proteins in men at high and low risk for the future development of alcoholism.

We evaluated G-proteins that are components of adenylyl cyclase (AC) signal transduction in erythrocyte and lymphocyte membranes from 26 family history positive (FHP) non-alcoholic and 26 family history negative (FHN) nonalcoholic subjects. Subjects were classified as FHP if their father met criteria for alcohol dependence; as FHN, if there was no history of alcoholism in any first or second degree relatives. Immunoblot analysis indicated that levels of erythrocyte membrane Gs alpha from FHP subjects were greater than levels in FHN subjects (171 +/- 11 vs 100 +/- 6, P < 0.001). To confirm the results of the immunoblot analysis, Gs alpha was quantitated by cholera toxin-dependent [32P]ADP-ribosylation. Levels of erythrocyte [32P]ADP-ribose-Gs alpha from FHP subjects were greater than levels in FHN subjects (236 +/- 28 vs 100 +/- 14, P < 0.001). Gs alpha levels did not correlate with age or alcohol consumption. By contrast to differences in Gs alpha, immunoblot analysis showed similar levels of Gi(2)alpha and Gi(3)alpha in erythrocyte membranes of FHP and FHN subjects. Pertussis toxin-catalyzed [32P]ADP-ribosylation of Gi-like G-proteins confirmed the immunoblot observations. Lastly, compared to FHN subjects, FHP subjects had enhanced Gs alpha expression in lymphocyte membranes as well (138 +/- 11 vs 100 +/- 5.5; P < 0.02). In summary, compared to FHN nonalcoholic men, FHP nonalcoholic men had greater levels of the stimulatory G-protein, Gs alpha, in erythrocyte and lymphocyte membranes. Enhanced expression of Gs alpha may be a marker of increased risk for the future development of alcoholism.

Deficient adenylate cyclase regulatory protein in renal membranes from a patient with pseudohypoparathyroidism.

Recent studies have established that some patients with pseudohypoparathyroidism have a deficiency of the adenylate cyclase regulatory protein (the G unit) in plasma membranes from erythrocytes, platelets, and fibroblasts. We have directly measured the activity of the G unit in renal membranes from a patient with pseudohypoparathyroidism who, in addition to parathyroid hormone resistance, has resistance to thyrotropin and gonadotropins. Erythrocyte membrane G unit activity was 57% that of control erythrocyte membranes. Lubrol PX extracts of renal membranes had only 30% of the G unit activity of control renal membrane extracts, whether assayed with sodium fluoride or guanosine-5'-O-(3-thiotriphosphate) (GTP-gamma-S). In cholate extracts, the G unit activity was 37 and 48% of control with fluoride or GTP-gamma-S, respectively. Cholera toxin-dependent incorporation of [32P]ADP-ribose into the 42,000-Mr subunit of the G unit was decreased in renal membranes from the patient compared with control renal membranes. The data demonstrate that the membrane G unit deficiency in pseudohypoparathyroidism extends to the cells of a clinically relevant parathyroid hormone target tissue.

Mutation of the signal peptide-encoding region of the preproparathyroid hormone gene in familial isolated hypoparathyroidism.

Preproparathyroid hormone (preproPTH) gene mutation has been proposed as a cause of familial isolated hypoparathyroidism (FIH). We cloned the preproPTH alleles of a patient with autosomal dominant FIH and sequenced the coding regions, 5' flanking regions, and splice junctions. The putatively abnormal (based on previous linkage studies) allele differed from the other allele's normal sequence at only one nucleotide. This T to C point mutation changes the codon for position 18 of the 31 amino acid prepro sequence from cysteine to arginine, disrupting the hydrophobic core of the signal sequence. Because the hydrophobic core is required by secreted proteins for efficient translocation across the endoplasmic reticulum, the mutant protein is likely to be inefficiently processed. Indeed, in vitro studies demonstrated dramatically impaired processing of the mutant preproPTH to proPTH. In summary, we observed a point mutation in the signal peptide-encoding region of a preproPTH gene in one FIH kindred and demonstrated a functional defect caused by the mutation. Mutation of the signal sequence constitutes a novel pathophysiologic mechanism in man, and further study may yield important insights both into this form of hormone deficiency and into the role of signal sequences in human physiology.

Urinary calcium excretion in familial hypocalciuric hypercalcemia. Persistence of relative hypocalciuria after induction of hypoparathyroidism.

Familial hypocalciuric hypercalcemia (FHH) is an autosomal dominant trait comprising hypercalcemia, hypophosphatemia, parathyroid hyperplasia, and unusually low renal clearance of calcium. We evaluated the role of parathyroid hormone in the relative hypocalciuria of FHH and characterized the renal transport of calcium in this disorder using three previously hypercalcemic FHH patients with surgical hypoparathyroidism and three controls with surgical hypoparathyroidism. Intravenous infusion of calcium chloride in two patients with FHH and in three controls increased serum calcium from a mean basal of 5.0 to a mean peak of 6.8 meq/liter in two FHH patients and from 4.2 to 5.7 in three control subjects. Urinary calcium in a third FHH patient was studied without calcium infusion during recovery from hypercalcemia of vitamin D intoxication. At all serum concentrations of calcium, calcium clearance was lower in FHH than in controls; at base-line serum calcium, the ratio of calcium clearance to inulin clearance (C(Ca)/C(IN)) in FHH subjects was 32% of that in controls and decreased to 19% during hypercalcemia. Calcium infusion increased the ratio of sodium clearance to inulin clearance in controls from a base line of 0.020 to 0.053 at peak concentrations of calcium in serum, but did not affect this parameter in FHH (0.017 at base-line serum calcium vs. 0.019 at peak). When calcium infusion studies were performed (in two patients with FHH and one control) during administration of acetazolamide, a drug whose principal renal action causes inhibition of proximal transport of solute, C(Ca)/C(IN) in the patients with FHH was 29 and 7% of that of the control at base-line and peak serum calcium, respectively. In contrast, ethacrynic acid, a diuretic that acts in the ascending limb of the loop of Henle, increased C(Ca)/C(IN) more in the FHH patients than in the control subject; C(Ca)/C(IN) was 65% at base-line and 47% at peak serum calcium, compared with that of the control subject. The greater calciuric response to ethacrynic acid than to acetazolamide or calcium infusion alone in FHH indicates that a major renal locus of abnormal calcium transport in this disorder may be the ascending limb of the loop of Henle.Decreased clearance of calcium in patients with FHH and hypoparathyroidism when compared with hypoparathyroid controls indicates that relative hypocalciuria in FHH is not dependent on hyperparathyroidism. Since the parathyroid glands in FHH are not appropriately suppressed by calcium, this implies that FHH represents a disorder of abnormal transport of, and/or response to, extracellular calcium in at least two organs, parathyroid gland and kidney.

Impaired formation of beta-adrenergic receptor-nucleotide regulatory protein complexes in pseudohypoparathyroidism.

Decreased activity of the guanine nucleotide regulatory protein (N) of the adenylate cyclase system is present in cell membranes of some patients with pseudohypoparathyrodism (PHP-Ia) whereas others have normal activity of N (PHP-Ib). Low N activity in PHP-Ia results in a decrease in hormone (H)-stimulatable adenylate cyclase in various tissues, which might be due to decreased ability to form an agonist-specific high affinity complex composed of H, receptor (R), and N. To test this hypothesis, we compared beta-adrenergic agonist-specific binding properties in erythrocyte membranes from five patients with PHP-Ia (N = 45% of control), five patients with PHP-Ib (N = 97%), and five control subjects. Competition curves that were generated by increasing concentrations of the beta-agonist isoproterenol competing with [125I]pindolol were shallow (slope factors less than 1) and were computer fit to a two-state model with corresponding high and low affinity for the agonist. The agonist competition curves from the PHP-Ia patients were shifted significantly (P less than 0.02) to the right as a result of a significant (P less than 0.01) decrease in the percent of beta-adrenergic receptors in the high affinity state from 64 +/- 22% in PHP-Ib and 56 +/- 5% in controls to 10 +/- 8% in PHP-Ia. The agonist competition curves were computer fit to a "ternary complex" model for the two-step reaction: H + R + N in equilibrium HR + N in equilibrium HRN. The modeling was consistent with a 60% decrease in the functional concentration of N, and was in good agreement with the biochemically determined decrease in erythrocyte N protein activity. These in vitro findings in erythrocytes taken together with the recent observations that in vivo isoproterenol-stimulated adenylate cyclase activity is decreased in patients with PHP (Carlson, H. E., and A. S. Brickman, 1983, J. Clin. Endocrinol. Metab. 56:1323-1326) are consistent with the notion that N is a bifunctional protein interacting with both R and the adenylate cyclase. It may be that in patients with PHP-Ia a single molecular and genetic defect accounts for both decreased HRN formation and decreased adenylate cyclase activity, whereas in PHP-Ib the biochemical lesion(s) appear not to affect HRN complex formation.

Signal-transducing G proteins: basic and clinical implications.

The pivotal role that G proteins play in transmembrane signal transduction is highlighted by the rapidly expanding list of receptors and effector molecules that are coupled through G proteins. G proteins are poised to allow discrimination and diversification of cellular signals into the cytosolic milieu. The utilization of an evolutionarily conserved "GTPase clock" by G proteins, offers insight into the fundamental role these proteins play in biology. Knowledge of the implication of altered expression or function of G proteins in human disease is now emerging. It is not surprising that deficiency or expression of altered forms of these important proteins can lead to global or restricted metabolic disturbances, depending upon the distribution and role of the G protein. Human disorders, including heart failure, alcoholism, endocrine abnormalities, and neoplasia, are now recognized as due in part to altered expression or function of G proteins.

McCune-Albright syndrome.

McCune-Albright syndrome (MAS) is characterized by the clinical triad of polyostotic fibrous dysplasia, cafe-au-lait pigmented skin lesions, and multiple endocrinopathies. The molecular basis of MAS is a mutation in G(s)alpha that results in constitutive activation of adenylyl cyclase in affected tissues. This mutation occurs during early embryogenesis, and therefore patients with MAS are mosaic. The identification of activating mutations of Gsa in liver, heart, and gastrointestinal tract of patients with MAS suggests a broader spectrum of clinical disease than previously appreciated.

Urocortin, but not corticotropin-releasing hormone (CRH), activates the mitogen-activated protein kinase signal transduction pathway in human pregnant myometrium: an effect mediated via R1alpha and R2beta CRH receptor subtypes and stimulation of Gq-proteins.

CRH and CRH-related peptides such as urocortin mediate their actions in the human myometrium via activation of two distinct classes of CRH receptors, R1 and R2. These heptahelical receptors are able to stimulate a number of different intracellular signals; one key mediator of G protein-activated intracellular signaling is the cascade of p42/p44, mitogen-activated protein kinase (MAPK). We therefore hypothesized that activation of MAPK might mediate CRH and or/urocortin actions in the myometrium. In cultured human pregnant myometrial cells, urocortin but not CRH was able to induce MAPK phosphorylation and activation, suggesting that in the human myometrium these two peptides have distinct actions and biological roles. To identify the particular receptor subtypes mediating this phenomenon, all known CRH receptors present in the human myometrial cells were stably expressed individually in HEK293 and CHO cells, and their ability to activate MAPK was tested. The R1alpha and R2beta, but not the R1beta, R1c, or R1d, receptor subtypes were able to mediate urocortin-induced MAPK activation. The signaling components were further investigated; activation of Gs, Go, or Gi proteins did not appear to be involved, but activation of Gq with subsequent production of inositol triphosphates (IP3) and protein kinase C (PKC) activation correlated with MAPK phosphorylation. Studies on Gq protein activation using [alpha-32P]-GTP-gamma-azidoanilide and IP3 production in cells expressing the R1alpha or R2beta CRH receptors demonstrated that urocortin was 10 times more potent than CRH. Moreover, urocortin (UCN) generated peak responses that were 50-70% greater than CRH in activating the Gq protein and stimulating IP3 production. In conclusion, UCN acting thought multiple receptor subtypes can stimulate myometrial MAPK via induction of the Gq/phospholipase C/IP3/PKC pathway, whereas CRH-induced activation of this pathway appears to be insufficient to achieve MAPK activation.

A novel spliced variant of the type 1 corticotropin-releasing hormone receptor with a deletion in the seventh transmembrane domain present in the human pregnant term myometrium and fetal membranes.

CRH exerts its actions via activation of specific G protein-coupled receptors, which exist in two types, CRH-R1 and CRH-R2, and arise from different genes with multiple spliced variants. RT-PCR amplification of CRH receptor sequences from human myometrium and fetal membranes yielded cDNAs that encode a novel CRH-R type 1 spliced variant. This variant (CRH-R1d) is present in the human pregnant myometrium at term only, which suggests a physiologically important role at the end of human pregnancy and labor. The amino acid sequence of CRH-R1d is identical to the CRH-R1alpha receptor except that it contains an exon deletion resulting in the absence of 14 amino acids in the predicted seventh transmembrane domain. Binding studies in HEK-293 cells stably expressing the CRH-R1d or CRH-R1alpha receptors revealed that the deletion does not change the binding characteristics of the variant receptor. In contrast, studies on the G protein activation demonstrated that CRH-R1d is not well coupled to the four subtypes of G proteins (G(s), G(i), G(o), G(q)) that CRH-R1alpha can activate. These data suggest that although the deleted segment is not important for CRH binding, it plays a crucial role in CRH receptor signal transduction. Second messenger studies of the variant receptor showed that CRH and CRH-like peptides can stimulate the adenylate cyclase system, with reduced sensitivity and potency by 10-fold compared with the CRH-R1alpha. Furthermore, CRH failed to stimulate inositol trisphosphate production. Coexpression studies between the CRH-R1d or CRH-R1alpha showed that this receptor does not play a role as a dominant negative receptor for CRH.

Deficiency of the alpha-subunit of the stimulatory G protein and severe extraskeletal ossification.

Progressive osseous heteroplasia (POH) is a rare disorder characterized by dermal ossification beginning in infancy followed by increasing and extensive bone formation in deep muscle and fascia. We describe two unrelated girls with typical clinical, radiographic, and histological features of POH who also have findings of another uncommon heritable disorder, Albright hereditary osteodystrophy (AHO). One patient has mild brachydactyly but no endocrinopathy, whereas the other manifests brachydactyly, obesity, and target tissue resistance to thyrotropin and parathyroid hormone (PTH). Levels of the alpha-subunit of the G protein (Gsalpha) were reduced in erythrocyte membranes from both girls and a nonsense mutation (Q12X) in exon 1 of the GNAS1 gene was identified in genomic DNA from the mildly affected patient. Features of POH and AHO in two individuals suggest that these conditions share a similar molecular basis and pathogenesis and that isolated severe extraskeletal ossification may be another manifestation of Gsalpha deficiency.

Pseudohypoparathyroidism with osteitis fibrosa cystica: direct demonstration of skeletal responsiveness to parathyroid hormone in cells cultured from bone.

A young girl had tibial osteotomies at age 14 for genu valgum and then had recurrent tibial cysts over a number of years. Hypocalcemia and hyperphosphatemia were first noted at age 21. The diagnosis of pseudohypoparathyroidism was made at age 28, when elevated plasma PTH was detected. Clinical and biochemical features, including a PTH response test and assay of RBC Gs, established the diagnosis of pseudohypoparathyroidism type 1b. Failure to suppress plasma PTH with vitamin D therapy led to an exacerbation of her cystic bone disease; there were widespread lytic lesions radiologically, most of which took up [99mTc]diphosphonate on bone scan. Microradioscopy revealed evidence of resorption of phalangeal tufts. Bone biopsy showed osteitis fibrosa cystica. During an orthopedic procedure, trabecular bone fragments were taken from her right humerus, and bone-derived cells cultured using an explant technique. The cultured cells were osteoblast-like in morphology, fully responsive to PTH, cholera toxin, forskolin, and PGE1 in vitro, and had an alkaline phosphatase and osteocalcin response to 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. Following this examination of skeletal responsiveness, attempts were made to suppress the elevated plasma PTH levels and symptomatic bone disease by optimizing therapy with oral 1,25-(OH)2D3. When bone pain associated with the cystic bone disease failed to resolve, the patient underwent total parathyroidectomy, following which the bone pain gradually resolved. This is the first direct demonstration of PTH responsiveness in cultured bone cells in the syndrome of pseudohypoparathyroidism with osteitis fibrosa cystica.

Normal parathyroid hormone responsiveness of bone-derived cells from a patient with pseudohypoparathyroidism.

Pseudohypoparathyroidism (PHP) is characterized by a lack of response to parathyroid hormone (PTH); however, normal skeletal responsiveness to PTH in some patients with PHP type Ia was previously suggested on the basis of clinical observations. To test this hypothesis, we measured cyclic adenosine monophosphate (cAMP) production in response to various agonists in bone-derived osteoblast-like (OBL) cells from trabecular explants obtained from an iliac crest biopsy of a 25-year-old woman with PHP. The patient was proved to have PHP type Ia on the basis of Albright's hereditary osteodystrophy and decreased activity of stimulatory guanine nucleotide-binding protein (Gs) in erythrocytes. Responsiveness of the patient's OBL cells was compared with OBL cells from eight subjects aged 18-39 years who had no evidence of metabolic bone disease. OBL cells from the patient responded to the following agonists (expressed in multiples of elevation of cAMP, stimulated/basal, mean +/- SE, n = 3): PTH, 3.8 +/- 0.3; forskolin, 8.2 +/- 0.2; and cholera toxin, 56.8 +/- 10.0. These responses were not significantly different from those of control OBL cells: PTH, 4.5 +/- 1.1 (range 2.4-7.5); forskolin, 7.7 +/- 1.4; and cholera toxin, 57.9 +/- 16.2. The normal cholera toxin response indicated the presence of functional Gs. Bone cells from patients with PHP type Ia may exhibit a normal PTH receptor-coupled adenylyl cyclase system in vitro despite clinical evidence of impaired hormone-responsive adenylyl cyclase in other tissues, including the kidney. Skeletal responsiveness to PTH may explain the long periods of spontaneous normocalcemia observed in this patient.

Two-year results of once-weekly administration of alendronate 70 mg for the treatment of postmenopausal osteoporosis.

The aim of this study was to provide confirmation that once-weekly dosing with 70 mg of alendronate (seven times the daily oral dose) and twice-weekly dosing with 35 mg is equivalent to the 10-mg once-daily regimen and to gain more extensive safety experience with this new dosing regimen. Twelve hundred fifty-eight postmenopausal women (aged 42-95 years) with osteoporosis (bone mineral density [BMD] of either lumbar spine or femoral neck at least 2.5 SDs below peak young adult mean or prior vertebral or hip fracture) were assigned to receive oral once-weekly alendronate, 70 mg (n = 519); twice-weekly alendronate, 35 mg (n = 369); or daily alendronate 10 mg (n = 370) for a total of 2 years of double-blind experience. Mean BMD increases from baseline (95% CI) at 24 months in the once-weekly, twice-weekly, and daily treatment groups, respectively, were 6.8% (6.4, 7.3), 7.0% (6.6,7.5), and 7.4% (6.9,7.8) at the lumbar spine and 4.1% (3.8,4.5), 4.3% (3.9,4.7), and 4.3% (3.9,4.7) at the total hip. These increases in BMD as well as the BMD increases at the femoral neck, trochanter, and total body and the reductions of biochemical markers of bone resorption (urinary cross-linked N-telopeptides of type I collagen [NTx]) and bone formation (serum bone-specific alkaline phosphatase [BSAP]) were similar for the three dosing regimens. All treatment regimens were well tolerated with a similar incidence of upper gastrointestinal (GI) adverse experiences. The incidence rates of clinical fractures, captured as adverse experiences, were similar among the groups. The 2-year results confirm the conclusion reached after 1 year that once-weekly alendronate is therapeutically equivalent to daily dosing, providing patients with a more convenient dosing option that may potentially enhance adherence to therapy.