Creatine kinase brain isoenzyme (BB-CK) presence in serum distinguishes osteopetroses among the sclerosing bone disorders

Patient-Reported Outcomes in Autosomal Dominant Osteopetrosis: Findings from the Osteopetrosis Registry Study

CONTEXT

Autosomal dominant osteopetrosis (ADO) is a rare sclerotic bone disease characterized by impaired osteoclast activity, resulting in high bone mineral density and skeletal fragility. The full phenotype and disease burden on patients' daily lives has not been systematically measured.

OBJECTIVE

We developed an online registry to ascertain population-based data on the spectrum and rate of progression of disease and to identify relevant patient centered outcomes that could be used to measure treatment effects and guide the design of future clinical trials.

DESIGN

Cross-sectional data from participants with osteopetrosis were collected using an online REDCap-based database.

PARTICIPANTS

Thirty-four participants with a confirmed diagnosis of ADO, aged 4-84 years.

MAIN OUTCOME MEASURES

Participants aged 18 years and older completed the PROMIS 57, participants aged 8 to 17 years completed the PROMIS Pediatric 49, and parents of participants aged <18 years completed the PROMIS Parent Proxy 49.

RESULTS

Based on the PROMIS 57, relative to the general population, adults with ADO reported low physical function and low ability to participate in social roles and activities, and high levels of anxiety, fatigue, sleep problems, and pain interference. Daily pain medications were reported by 24% of the adult population. In contrast, neither pediatric participants, nor their parent proxy reported a negative impact on health-related quality of life.

CONCLUSIONS

Data from this registry demonstrate the broad spectrum of ADO disease severity and high impact on health-related quality of life in adults with ADO.

Pilot study protocol of a randomized controlled trial for the potential effects of creatine monohydrate on persistent post-concussive symptoms

Background

Mild traumatic brain injury or concussion is a global public concern, with an estimated annual incidence between 48 million and 96 million worldwide. It is a socioeconomical problem, and almost one-third of individuals with concussion suffer from severe persistent post-concussive symptoms (PPCS), with an increased risk of unemployment or terminating their studies. To date, no single treatment is available with guaranteed success. Creatine monohydrate (CrM) has shown potential as a treatment for post-concussive symptoms, having a positive impact on cognitive function, chronic fatigue, depression, and anxiety. The aim of this study is to examine the effect of CrM on PPCS assessed using the Rivermead Post-Concussion Symptoms Questionnaire (RPQ).

Methods

The study is designed as a double-blinded randomised controlled trial. Study participants are found through neurological outpatient clinics in Denmark or through social media. They will be between 25 and 35 years of age, will have suffered from PPCS for 6-12 months prior to inclusion, and will have no comorbidities. The participants will be randomly allocated to either an intervention group (INT), placebo group (PLA), or control group (CG). Baseline data will be collected immediately after inclusion, and the study period will be 7 weeks. Follow-up data will be collected 1 week after the end of the study period. The primary outcome of the study is changes in RPQ score. Changes in weight and training status will be adjusted for as potential confounders.

Ethics and dissemination

This protocol is approved by the National Committee on Health Research (97508) and by the Danish Data Protection Agency 11.651. The investigators intend to submit their study findings for publication in peer-reviewed journals and disseminate the findings via presentation at academic meetings/conferences.Clinical Trial registration: NCT05562232, registered September 30, 2022.

Drug-induced osteopetrosis

Osteopetrosis (OPT) denotes the consequences from failure of osteoclasts to resorb bone and chondroclasts to remove calcified physeal cartilage throughout growth. Resulting impairment of skeletal modeling, remodeling, and growth compromises widening of medullary spaces, formation of the skull, and expansion of cranial foramina. Thus, myelophthisic anemia, raised intracranial pressure, and cranial nerve palsies complicate OPT when severe. Osteopetrotic bones fracture due to misshaping, failure of remodeling to weave the collagenous matrix of cortical osteons and trabeculae, persistence of mineralized growth plate cartilage, "hardening" of hydroxyapatite crystals, and delayed healing of skeletal microcracks. Teeth may fail to erupt. Now it is widely appreciated that OPT is caused by germline loss-of-function mutation(s) usually of genes involved in osteoclast function, but especially rarely of genes necessary for osteoclast formation. Additionally, however, in 2003 we published a case report demonstrating that prolonged excessive dosing during childhood of the antiresorptive aminobisphosphonate pamidronate can sufficiently block osteoclast and chondroclast activity to recapitulate the skeletal features of OPT. Herein, we include further evidence of drug-induced OPT by illustrating osteopetrotic skeletal changes from repeated administration of high doses of the aminobisphosphonate zoledronic acid (zoledronate) given to children with osteogenesis imperfecta.

Case report: Gene mutations and clinical characteristics of four patients with osteopetrosis

Osteopetrosis is characterized by increased bone density caused by decreased osteoclasts or dysfunction of their differentiation and absorption properties, usually caused by biallelic variants of the TCIRG1(OMIM:604592)and CLCN7(OMIM:602727) genes. Herein, the clinical, biochemical, and radiological manifestations of osteopetrosis in four Chinese children are described. Whole-exome sequencing identified compound heterozygous variants of the CLCN7 and TCIRG1 genes in these patients. In Patient 1, two novel variants were identified in CLCN7:c.880T > G(p.F294V) and c.686C > G(p.S229X). Patient 2 harbored previously reported a single gene variant c.643G > A(p.G215R) in CLCN7. Patient 3 had a novel variant c.569A > G(p.N190S) and a novel frameshift variant c.1113dupG(p.N372fs) in CLCN7. Patient 4 had a frameshift variant c.43delA(p.K15fs) and variant c.C1360T in TCIRG1, resulting in the formation of a premature termination codon (p.R454X), both of which were reported previously. Our results expand the spectrum of identified genetic variation in osteopetrosis and provide a deeper understanding of the relations between genotype and clinical characteristics of this disorder.

Autosomal dominant osteopetrosis type II resulting from a de novo mutation in the CLCN7 gene: A case report

BACKGROUND

Osteopetrosis is a family of extremely rare diseases caused by failure of osteoclasts and impaired bone resorption. Among them, autosomal dominant osteopetrosis type II (ADO II), related to the chloride channel 7 (CLCN7) gene, is the most frequent form of osteopetrosis. In this study, we report a de novo mutation of CLCN7 in a patient without the family history of ADO II.

CASE SUMMARY

A 5-year-old Chinese boy with ADO II was found to have a de novo mutation in the CLCN7 gene [c.746C>T (p.P249L)]. Typical clinical manifestations, including thickening of the cortex of spinal bones and long bones, non-traumatic fracture of the femoral neck, and femoral head necrosis, were found in this patient. The patient is the first reported case of ADO II with the missense mutation c.746C>T (p.P249L) of the CLCN7 gene reported in China. We also review the available literature on ADO II-related CLCN7 mutations, including baseline patient clinical features, special clinical significance, and common mutations.

CONCLUSION

Our report will enrich the understanding of mutations in ADO II patients. The possibility of a de novo mutation should be considered in individuals who have no family history of osteopetrosis.

High bone mass from mutation of low-density lipoprotein receptor-related protein 6 (LRP6)

Wnt/β-catenin signaling is important for skeletal development and health. Eleven heterozygous gain-of-function missense mutations within the first β-propeller of low-density lipoprotein receptor-related protein 5 (LRP5) are known to cause the autosomal dominant disorder called high bone mass (HBM). In 2019, different heterozygous LRP6 missense mutations were identified in two American families with the HBM phenotype but including absent lateral maxillary and mandibular incisors. We report a 19-year-old Argentinian man referred for "osteopetrosis" and nine years of generalized, medium-intensity bone pain and arthralgias of both knees. His jaw and nasal bridge were broad and several teeth were missing. Routine biochemical testing, including of mineral homeostasis, was normal. Urinary deoxypyridinoline and serum CTX were slightly increased. Radiographic skeletal survey showed diffusely increased radiodensity. DXA revealed substantially elevated BMD Z-scores. Digital orthopantomography confirmed agenesis of his maxillary and mandibular lateral incisors and his second left superior premolar. Cranial magnetic resonance imaging showed diffuse thickening of the calvarium and skull base, dilation of the sheath of the optic nerves containing increased fluid and associated with subtle stenosis of the optic canal, and narrow internal auditory canals. Mutation analyses identified a heterozygous indel mutation in exon 4 of LRP6 involving a single nucleotide change and 6-nucleotide deletion (c.678T>Adel679-684, p.His226Gln-del227-228ProPhe) leading to a missense change and 2-amino acid deletion that would compromise the first β-propeller of LRP6. Experience to date indicates LRP6 HBM is indistinguishable from LRP5 HBM without mutation analysis, although in LRP6 HBM absence of adult lateral incisors may prove to be a unique feature.

Juvenile Paget's Disease From Heterozygous Mutation of SP7 Encoding Osterix (Specificity Protein 7, Transcription Factor SP7)

Juvenile Paget's disease (JPD) became in 1974 the commonly used name for ultra-rare heritable occurrences of rapid bone remodeling throughout of the skeleton that present in infancy or early childhood as fractures and deformity hallmarked biochemically by marked elevation of serum alkaline phosphatase (ALP) activity (hyperphosphatasemia). Untreated, JPD can kill during childhood or young adult life. In 2002, we reported that homozygous deletion of the gene called tumor necrosis factor receptor superfamily, member 11B (TNFRSF11B) encoding osteoprotegerin (OPG) explained JPD in Navajos. Soon after, other bi-allelic loss-of-function TNFRSF11B defects were identified in JPD worldwide. OPG inhibits osteoclastogenesis and osteoclast activity by decoying receptor activator of nuclear factor κ-B (RANK) ligand (RANKL) away from its receptor RANK. Then, in 2014, we reported JPD in a Bolivian girl caused by a heterozygous activating duplication within TNFRSF11A encoding RANK. Herein, we identify mutation of a third gene underlying JPD. An infant girl began atraumatic fracturing of her lower extremity long-bones. Skull deformity and mild hearing loss followed. Our single investigation of the patient, when she was 15 years-of-age, showed generalized osteosclerosis and hyperostosis. DXA revealed a Z-score of +5.1 at her lumbar spine and T-score of +3.3 at her non-dominant wrist. Biochemical studies were consistent with positive mineral balance and several markers of bone turnover were elevated and included striking hyperphosphatasemia. Iliac crest histopathology was consistent with rapid skeletal remodeling. Measles virus transcripts, common in classic Paget's disease of bone, were not detected in circulating mononuclear cells. Then, reportedly, she responded to several months of alendronate therapy with less skeletal pain and correction of hyperphosphatasemia but had been lost to our follow-up. After we detected no defect in TNFRSF11A or B, trio exome sequencing revealed a de novo heterozygous missense mutation (c.926C>G; p.S309W) within SP7 encoding the osteoblast transcription factor osterix (specificity protein 7, transcription factor SP7). Thus, mutation of SP7 represents a third genetic cause of JPD.

Hyperphosphatemia with low FGF7 and normal FGF23 and sFRP4 levels in the circulation characterizes pediatric hypophosphatasia

Hypophosphatasia (HPP) is the inborn-error-of-metabolism caused by loss-of-function mutation(s) of the ALPL gene that encodes the tissue-nonspecific isoenzyme of alkaline phosphatase (TNSALP). TNSALP in healthy individuals is on cell surfaces richly in bone, liver, and kidney. Thus, TNSALP natural substrates accumulate extracellularly in HPP, including inorganic pyrophosphate (PPi), a potent inhibitor of hydroxyapatite crystal formation and growth. Superabundance of extracellular PPi (ePPi) in HPP impairs mineralization of bones and teeth, often leading to rickets during childhood and osteomalacia in adult life and to tooth loss at any age. HPP's remarkably broad-ranging severity is largely explained by nearly four hundred typically missense mutations throughout the ALPL gene that are transmitted as an autosomal dominant or autosomal recessive trait. In the clinical laboratory, the biochemical hallmark of HPP is low serum ALP activity (hypophosphatasemia). However, our experience indicates that hyperphosphatemia from increased renal reclamation of filtered inorganic phosphate (Pi) is also common. Herein, from our prospective single-center study, we document throughout the clinical spectrum of non-lethal pediatric HPP that hyperphosphatemia reflects increased renal tubular threshold maximum for phosphorus adjusted for the glomerular filtration rate (TmP/GFR). To explore its pathogenesis, we studied mineral metabolism and quantitated circulating levels of three phosphatonins [fibroblast growth factor 23 (FGF23), secreted frizzled-related protein 4 (sFRP4), and fibroblast growth factor 7 (FGF7)] in 41 pediatric patients with HPP, 73 with X-linked hypophosphatemia (XLH), and 15 healthy pediatric control (CTR) subjects. The HPP and XLH cohorts had normal serum total and ionized calcium and parathyroid hormone levels (Ps > 0.10) and uncompromised glomerular filtration. In XLH, serum FGF23 was characteristically elevated (P < 0.0001) and despite hypophosphatemia sFRP4 was normal (P > 0.4) while FGF7 was low (P < 0.0001). In HPP, despite hyperphosphatemia serum FGF23 and sFRP4 were normal (Ps > 0.8) while FGF7 was low (P < 0.0001). Subsequently, in rats, we confirmed that FGF7 is phosphaturic. Thus, hyperphosphatemia in non-lethal pediatric HPP is associated with phosphatonin insufficiency together with, as we discuss, ePPi excess and diminished renal TNSALP activity.

New explanation for autosomal dominant high bone mass: Mutation of low-density lipoprotein receptor-related protein 6

LRP5 encodes low-density lipoprotein receptor-related protein 5 (LRP5). When LRP5 with a Frizzled receptor join on the surface of an osteoblast and bind a member of the Wnt family of ligands, canonical Wnt/β-catenin signaling occurs and increases bone formation. Eleven heterozygous gain-of-function missense mutations within LRP5 are known to prevent the LRP5 inhibitory ligands sclerostin and dickkopf1 from attaching to LRP5's first β-propeller, and thereby explain the rare autosomal dominant (AD) skeletal disorder "high bone mass" (HBM). LRP6 is a cognate co-receptor of LRP5 and similarly controls Wnt signaling in osteoblasts, yet the consequences of increased LRP6-mediated signaling remain unknown. We investigated two multi-generational American families manifesting the clinical and routine laboratory features of LRP5 HBM but without an LRP5 defect and instead carrying a heterozygous LRP6 missense mutation that would alter the first β-propeller of LRP6. In Family 1 LRP6 c.602C>T, p.A201V was homologous to LRP5 HBM mutation c.641C>T, p.A214V, and in Family 2 LRP6 c.553A>C, p.N185H was homologous to LRP5 HBM mutation c.593A>G, p.N198S but predicting a different residue at the identical amino acid position. In both families the LRP6 mutation co-segregated with striking generalized osteosclerosis and hyperostosis. Clinical features shared by the seven LRP6 HBM family members and ten LRP5 HBM patients included a broad jaw, torus palatinus, teeth encased in bone and, reportedly, resistance to fracturing and inability to float in water. For both HBM disorders, all affected individuals were taller than average for Americans (Ps < 0.005), but with similar mean height Z-scores (P = 0.7606) and indistinguishable radiographic skeletal features. Absence of adult maxillary lateral incisors was reported by some LRP6 HBM individuals. In contrast, our 16 patients with AD osteopetrosis [i.e., Albers-Schönberg disease (A-SD)] had an unremarkable mean height Z-score (P = 0.9401) lower than for either HBM group (Ps < 0.05). DXA mean BMD Z-scores in LRP6 HBM versus LRP5 HBM were somewhat higher at the lumbar spine (+7.8 vs +6.5, respectively; P = 0.0403), but no different at the total hip (+7.9 vs +7.7, respectively; P = 0.7905). Among the three diagnostic groups, only the LRP6 HBM DXA BMD values at the spine seemed to increase with subject age (R = +0.7183, P = 0.0448). Total hip BMD Z-scores were not significantly different among the three disorders (Ps > 0.05), and showed no age effect (Ps > 0.1). HR-pQCT available only for LRP6 HBM revealed indistinct corticomedullary boundaries, high distal forearm and tibial total volumetric BMD, and finite element analysis predicted marked fracture resistance. Hence, we have discovered mutations of LRP6 that cause a dento-osseous disorder indistinguishable without mutation analysis from LRP5 HBM. LRP6 HBM seems associated with generally good health, providing some reassurance for the development of anabolic treatments aimed to enhance LRP5/LRP6-mediated osteogenesis.

Unique Variant of NOD2 Pediatric Granulomatous Arthritis With Severe 1,25-Dihydroxyvitamin D-Mediated Hypercalcemia and Generalized Osteosclerosis

Pediatric granulomatous arthritis (PGA) refers to two formerly separate entities: autosomal dominant Blau syndrome (BS) and its sporadic phenocopy early-onset sarcoidosis (EOS). In 2001 BS and in 2005 EOS became explained by heterozygous mutations within the gene that encodes nucleotide-binding oligomerization domain-containing protein 2 (NOD2), also called caspase recruitment domain-containing protein 15 (CARD15). NOD2 is a microbe sensor in leukocyte cytosol that activates and regulates inflammation. PGA is characterized by a triad of autoinflammatory problems (dermatitis, uveitis, and arthritis) in early childhood, which suggests the causal NOD2/CARD15 mutations are activating defects. Additional complications of PGA were recognized especially when NOD2 mutation analysis became generally available. However, in PGA, hypercalcemia is only briefly mentioned, and generalized osteosclerosis is not reported, although NOD2 regulates NF-κB signaling essential for osteoclastogenesis and osteoclast function. Herein, we report a 4-year-old girl with PGA uniquely complicated by severe 1,25(OH)₂ D-mediated hypercalcemia, nephrocalcinosis, and compromised renal function together with radiological and histopathological features of osteopetrosis (OPT). The classic triad of PGA complications was absent, although joint pain and an antalgic gait accompanied wrist, knee, and ankle swelling and soft non-tender masses over her hands, knees, and feet. MRI revealed tenosynovitis in her hands and suprapatellar effusions. Synovial biopsy demonstrated reactive synovitis without granulomas. Spontaneous resolution of metaphyseal osteosclerosis occurred while biochemical markers indicated active bone turnover. Anti-inflammatory medications suppressed circulating 1,25(OH)₂ D, corrected the hypercalcemia, and improved her renal function, joint pain and swelling, and gait. Mutation analysis excluded idiopathic infantile hypercalcemia, type 1, and known forms of OPT, and identified a heterozygous germline missense mutation in NOD2 common in PGA (c.1001G>A, p.Arg334Gln). Thus, radiological and histological findings of OPT and severe hypercalcemia from apparent extrarenal production of 1,25(OH)₂ D can complicate NOD2-associated PGA. Although the skeletal findings seem inconsequential, treatment of the hypercalcemia is crucial to protect the kidneys. © 2018 American Society for Bone and Mineral Research.

Gnathodiaphyseal dysplasia: Severe atypical presentation with novel heterozygous mutation of the anoctamin gene (ANO5)

Gnathodiaphyseal dysplasia (GDD; OMIM #166260) is an ultra-rare autosomal dominant disorder caused by heterozygous mutation in the anoctamin 5 (ANO5) gene and features fibro-osseous lesions of the jawbones, bone fragility with recurrent fractures, and bowing/sclerosis of tubular bones. The physiologic role of ANO5 is unknown. We report a 5-year-old boy with a seemingly atypical and especially severe presentation of GDD and unique ANO5 mutation. Severe osteopenia was associated with prenatal femoral fractures, recurrent postnatal fractures, and progressive bilateral enlargement of his maxilla and mandible beginning at ~2months-of-age that interfered with feeding and speech and required four debulking operations. Histopathological analysis revealed benign fibro-osseous lesions resembling cemento-ossifying fibromas of the jaw without psammomatoid bodies. A novel, de novo, heterozygous, missense mutation was identified in exon 15 of ANO5 (c.1553G>A; p.Gly518Glu). Our findings broaden the phenotypic and molecular spectra of GDD. Fractures early in life with progressive facial swelling are key features. We assessed his response to a total of 7 pamidronate infusions commencing at age 15months. Additional reports must further elucidate the phenotype, explore any genotype-phenotype correlation, and evaluate treatments.

Clinical Significance of DXA and HR-pQCT in Autosomal Dominant Osteopetrosis (ADO II)

The main hallmark of high bone mass (HBM) disorders is increased bone mineral density, potentially visible in conventional radiographs and quantifiable by other radiographic methods. While one of the most common forms of HBM is CLCN7-related autosomal dominant osteopetrosis type II (ADO II), there is no consensus on diagnostic thresholds. We therefore wanted to assess whether CLCN7-osteopetrosis patients differ from benign HBM cases in terms of (1) bone mineral density, (2) bone structure, and (3) microarchitectural abnormalities. 16 patients meeting the criteria of HBM (DXA T/Z-score ≥ 2.5 at all sites) were included in this retrospective study. Osteologic assessment using dual-energy X-ray absorptiometry (DXA), high-resolution peripheral quantitative computed tomography (HR-pQCT), and serum analyses was performed. The presence of CLCN7 and/or other HBM gene mutations affecting bone mass were tested using a custom designed bone panel. While a DXA threshold for ADO II could be implemented (DXA Z-score ≥ + 6.0), the differences in bone microarchitecture were of lesser extent compared to the benign HBM group. All adult patients with ADO II suffered from elevated fracture rates independent from Z-score. In HR-pQCT, structural alterations, such as bone islets were found only inconsistently. In cases of HBM, a DXA Z-score ≥ 6 may be indicative for an inheritable HBM disorder, such as ADO II. Microarchitectural bone alterations might represent local microfracture repair or accumulation of cartilage remnants due to impaired osteoclast function, but seem not to be correlated with fracture risk.

Osteopetroses, emphasizing potential approaches to treatment

Osteopetroses are a heterogeneous group of rare genetic bone diseases sharing the common hallmarks of reduced osteoclast activity, increased bone mass and high bone fragility. Osteoclasts are bone resorbing cells that contribute to bone growth and renewal through the erosion of the mineralized matrix. Alongside the bone forming activity by osteoblasts, osteoclasts allow the skeleton to grow harmonically and maintain a healthy balance between bone resorption and formation. Osteoclast impairment in osteopetroses prevents bone renewal and deteriorates bone quality, causing atraumatic fractures. Osteopetroses vary in severity and are caused by mutations in a variety of genes involved in bone resorption or in osteoclastogenesis. Frequent signs and symptoms include osteosclerosis, deformity, dwarfism and narrowing of the bony canals, including the nerve foramina, leading to hematological and neural failures. The disease is autosomal, with only one extremely rare form associated so far to the X-chromosome, and can have either recessive or dominant inheritance. Recessive ostepetroses are generally lethal in infancy or childhood, with a few milder forms clinically denominated intermediate osteopetroses. Dominant osteopetrosis is so far associated only with mutations in the CLCN7 gene and, although described as a benign form, it can be severely debilitating, although not at the same level as recessive forms, and can rarely result in reduced life expectancy. Severe osteopetroses due to osteoclast autonomous defects can be treated by Hematopoietic Stem Cell Transplant (HSCT), but those due to deficiency of the pro-osteoclastogenic cytokine, RANKL, are not suitable for this procedure. Likewise, it is unclear as to whether HSCT, which has high intrinsic risks, results in clinical improvement in autosomal dominant osteopetrosis. Therefore, there is an unmet medical need to identify new therapies and studies are currently in progress to test gene and cell therapies, small interfering RNA approach and novel pharmacologic treatments.

Raine Syndrome (OMIM #259775), Caused By FAM20C Mutation, Is Congenital Sclerosing Osteomalacia With Cerebral Calcification (OMIM 259660)

In 1985, we briefly reported infant sisters with a unique, lethal, autosomal recessive disorder designated congenital sclerosing osteomalacia with cerebral calcification. In 1986, this condition was entered into Mendelian Inheritance In Man (MIM) as osteomalacia, sclerosing, with cerebral calcification (MIM 259660). However, no attestations followed. Instead, in 1989 Raine and colleagues published an affected neonate considering unprecedented the striking clinical and radiographic features. In 1992, "Raine syndrome" entered MIM formally as osteosclerotic bone dysplasia, lethal (MIM #259775). In 2007, the etiology emerged as loss-of-function mutation of FAM20C that encodes family with sequence similarity 20, member C. FAM20C is highly expressed in embryonic calcified tissues and encodes a kinase (dentin matrix protein 4) for most of the secreted phosphoproteome including FGF23, osteopontin, and other regulators of skeletal mineralization. Herein, we detail the clinical, radiological, biochemical, histopathological, and FAM20C findings of our patients. Following premortem tetracycline labeling, the proposita's non-decalcified skeletal histopathology after autopsy indicated no rickets but documented severe osteomalacia. Archival DNA revealed the sisters were compound heterozygotes for a unique missense mutation and a novel deletion in FAM20C. Individuals heterozygous for the missense mutation seemed to prematurely fuse their metopic suture and develop a metopic ridge sometimes including trigonocephaly. Our findings clarify FAM20C's role in hard tissue formation and mineralization, and show that Raine syndrome is congenital sclerosing osteomalacia with cerebral calcification. © 2016 American Society for Bone and Mineral Research.

Serum creatine kinase isoenzymes in children with osteogenesis imperfecta

This study evaluates serum creatine kinase isoenzyme activity in children with osteogenesis imperfecta to determine its usefulness as a biochemical marker during treatment with bisphosphonate. The changes of creatine kinase (CK) isoenzyme activity during and after discontinuation therapy were observed. These results could be useful in addressing over-treatment risk prevention.

INTRODUCTION

The brain isoenzyme of creatine kinase (CKbb) is highly expressed in mature osteoclasts during osteoclastogenesis, thus plays an important role in bone resorption. We previously identified high serum CKbb levels in 18 children with osteogenesis imperfect (OI) type 1 treated for 1 year with bisphosphonate (neridronate). In the present study, serum CK isoenzymes were evaluated in the same children with continuous versus discontinued neridronate treatment over a further 2-year follow-up period.

METHODS

This study included 18 children with OI type 1, 12 with continued (group A) and 6 with ceased (group B) neridronate treatment. Auxological data, serum biochemical markers of bone metabolism, bone mineral density z-score, and serum total CK and isoenzyme activities were determined in both groups.

RESULTS

Serum CKbb was progressively and significantly increased in group A (p < 0.004) but rapidly decreased to undetectable levels in group B. In both groups, the cardiac muscle creatine kinase isoenzyme (CKmb) showed a marked decrease, while serum C-terminal telopeptide (CTx) levels were almost unchanged.

CONCLUSIONS

This study provides evidence of the cumulative effect of neridronate administration in increasing serum CKbb levels and the reversible effect after its discontinuation. This approach could be employed for verifying the usefulness of serum CKbb as a biochemical marker in patients receiving prolonged bisphosphonate treatment. Moreover, the decreased serum CKmb levels suggest a systemic effect of these drugs.

Lenz-Majewski hyperostotic dwarfism with hyperphosphoserinuria from a novel mutation in PTDSS1 encoding phosphatidylserine synthase 1

Lenz-Majewski hyperostotic dwarfism (LMHD) is an ultra-rare Mendelian craniotubular dysostosis that causes skeletal dysmorphism and widely distributed osteosclerosis. Biochemical and histopathological characterization of the bone disease is incomplete and nonexistent, respectively. In 2014, a publication concerning five unrelated patients with LMHD disclosed that all carried one of three heterozygous missense mutations in PTDSS1 encoding phosphatidylserine synthase 1 (PSS1). PSS1 promotes the biosynthesis of phosphatidylserine (PTDS), which is a functional constituent of lipid bilayers. In vitro, these PTDSS1 mutations were gain-of-function and increased PTDS production. Notably, PTDS binds calcium within matrix vesicles to engender hydroxyapatite crystal formation, and may enhance mesenchymal stem cell differentiation leading to osteogenesis. We report an infant girl with LMHD and a novel heterozygous missense mutation (c.829T>C, p.Trp277Arg) within PTDSS1. Bone turnover markers suggested that her osteosclerosis resulted from accelerated formation with an unremarkable rate of resorption. Urinary amino acid quantitation revealed a greater than sixfold elevation of phosphoserine. Our findings affirm that PTDSS1 defects cause LMHD and support enhanced biosynthesis of PTDS in the pathogenesis of LMHD.

Induction of creatine kinase release from cultured osteoclasts via the pharmacological action of aminobisphosphonates

An increase of serum creatine kinase (CK) has been observed in clinical studies of nitrogen-containing aminobisphosphonates (N-BPs). Osteoclasts are thought to be the source of the CK, but there is no clear evidence for the hypothesis. In this study, CK release from rabbit osteoclasts induced by N-BPs was examined in an in vitro culture system. Rabbit bone-derived cells were cultured for 3 days on the N-BPs pretreated cortical bone slices. CK activity in the culture medium was measured at 3 days of culture. The CK activity was increased with all N-BPs at concentrations at which showed antiresorptive activity over 60% inhibition of C-terminal cross-linking telopeptide of type I collagen (CTX-1) release. The maximum induction of CK activity was 2.6 times the control level. The lowest N-BP concentration inducing CK release was 3 times lower than that required to decrease the osteoclast number. Bafilomycin A1, an inhibitor of vacuolar H⁺-ATPase, abrogated all N-BP actions, including CK release. Bone-derived cells except osteoclasts were insensitive to bafilomycin A1, suggesting that osteoclasts were the source of CK. Regarding the time course, CK release occurred after a 1 day lag time and increased steadily until day 3 of culture. These results show that CK release is induced by N-BPs from osteoclasts at concentrations at which N-BPs show antiresorptive activity over 60% inhibition of CTX-1 release in vitro. These findings explain the mechanism of the CK increase induced by clinical use of N-BPs.

Rapid skeletal turnover in a radiographic mimic of osteopetrosis

Among the high bone mass disorders, the osteopetroses reflect osteoclast failure that prevents skeletal resorption and turnover, leading to reduced bone growth and modeling and characteristic histopathological and radiographic findings. We report an 11-year-old boy with a new syndrome that radiographically mimics osteopetrosis (OPT), but features rapid skeletal turnover. He presented at age 21 months with a parasellar, osteoclast-rich giant cell granuloma. Radiographs showed a dense skull, generalized osteosclerosis and cortical thickening, medullary cavity narrowing, and diminished modeling of tubular bones. His serum alkaline phosphatase was >5000 IU/L (normal <850 IU/L). After partial resection, the granuloma re-grew but then regressed and stabilized during 3 years of uncomplicated pamidronate treatment. His hyperphosphatasemia transiently diminished, but all bone turnover markers, especially those of apposition, remained elevated. Two years after pamidronate therapy stopped, bone mineral density (BMD) Z-scores reached +9.1 and +5.8 in the lumbar spine and hip, respectively, and iliac crest histopathology confirmed rapid bone remodeling. Serum multiplex biomarker profiling was striking for low sclerostin. Mutation analysis was negative for activation of lipoprotein receptor-related protein 4 (LRP4), LRP5, or TGFβ1, and for defective sclerostin (SOST), osteoprotegerin (OPG), RANKL, RANK, SQSTM1, or sFRP1. Microarray showed no notable copy number variation. Studies of his nonconsanguineous parents were unremarkable. The etiology and pathogenesis of this unique syndrome are unknown.

Serum brain-type creatine kinase increases in children with osteogenesis imperfecta during neridronate treatment

BACKGROUND

Creatine kinase (Ck) catalyzes the reversible transfer of high-energy phosphate groups between adenosine triphosphate and phosphocreatine. The brain isoform (Ckbb) is greatly induced in mature osteoclasts, playing an important role in bone-resorbing function during osteoclastogenesis. High Ckbb serum level has been found in patients with osteopetrosis and in patients with bisphosphonate (BP)-induced osteopetrosis. BPs are considered the treatment of choice for children with osteogenesis imperfecta (OI), acting as potent inhibitors of bone resorption by suppressing the activity of osteoclasts.

METHODS

We determined total serum Ck and isoform activity in 18 prepubertal children with type I OI, before and during treatment with the BP neridronate infusions.

RESULTS

Basal serum Ckbb levels were slightly elevated with respect to controls (mean ± SD = 3.0 ± 2.7 vs. 2.0 ± 2.2) and progressively increased after neridronate treatment (t0 vs. t4: mean ± SD = 3.0 ± 2.7 to 10.8 ± 8.1), with significant increment after first, second, and fourth infusions (P < 0.01). An inverse correlation was found between serum Ckbb and serum CTx at basal level.

CONCLUSION

Our results support previous observations that increased serum Ckbb reflects failure of osteoclasts or, at least, suppression of osteoclasts. Upon considering that BPs are long acting, this information could be useful to prevent the risk of overtreatment after long-term BP exposure in pediatric patients with OI.

Severe skeletal toxicity from protracted etidronate therapy for generalized arterial calcification of infancy

Generalized arterial calcification (AC) of infancy (GACI) is an autosomal recessive disorder that features hydroxyapatite deposition within arterial elastic fibers. Untreated, approximately 85% of GACI patients die by 6 months of age from cardiac ischemia and congestive heart failure. The first-generation bisphosphonate etidronate (EHDP; ethane-1-hydroxy-1,1-diphosphonic acid, also known as 1-hydroxyethylidene-bisphosphonate) inhibits bone resorption and can mimic endogenous inorganic pyrophosphate by blocking mineralization. With EHDP therapy for GACI, AC may resolve without recurrence upon treatment cessation. Skeletal disease is not an early characteristic of GACI, but rickets can appear from acquired hypophosphatemia or prolonged EHDP therapy. We report a 7-year-old boy with GACI referred for profound, acquired, skeletal disease. AC was gone after 5 months of EHDP therapy during infancy, but GACI-related joint calcifications progressed. He was receiving EHDP, 200 mg/day orally, and had odynodysphagia, diffuse opioid-controlled pain, plagiocephaly, facial dysmorphism, joint calcifications, contractures, and was wheelchair bound. Biochemical parameters of mineral homeostasis were essentially normal. Serum osteocalcin was low and the brain isoform of creatine kinase and tartrate-resistant acid phosphatase 5b (TRAP-5b) were elevated as in osteopetrosis. Skeletal radiographic findings resembled pediatric hypophosphatasia with pancranial synostosis, long-bone bowing, widened physes, as well as metaphyseal osteosclerosis, cupping and fraying, and "tongues" of radiolucency. Radiographic features of osteopetrosis included osteosclerosis and femoral Erlenmeyer flask deformity. After stopping EHDP, he improved rapidly, including remarkable skeletal healing and decreased joint calcifications. Profound, but rapidly reversible, inhibition of skeletal mineralization with paradoxical calcifications near joints can occur in GACI from protracted EHDP therapy. Although EHDP treatment is lifesaving in GACI, surveillance for toxicity is crucial.

The virulence gene and clinical phenotypes of osteopetrosis in the Chinese population: six novel mutations of the CLCN7 gene in twelve osteopetrosis families

Osteopetrosis is a heritable bone disorder resulting from a deficiency of or a functional defect in osteoclasts. We aimed to characterize the molecular defects and clinical manifestations in Chinese patients with osteopetrosis by studying 12 unrelated osteopetrosis families. The entire coding region and adjacent splice sites of the CLCN7, TCIRG1, LRP5 and SOST genes were amplified and directly sequenced. X-rays of hip and lumbar spine, bone mineral density and bone turnover markers were examined simultaneously. Family history and fracture history were collected using a questionnaire. Among 12 unrelated families, 10 families were diagnosed with autosomal dominant osteopetrosis type II (ADOII) with 10 probands and 3 affected subjects. Two individuals in the other two families were diagnosed with uncategorized osteopetrosis because no mutations were detected in any of the four studied genes. Eight mutations, including two reported mutations (R767W and E798FS) and six novel mutations (E313K, A316G, R743W, G741R, W127G and S290F), were detected in the CLCN7 gene from 12 living ADOII patients. Among them, R767W and R743W mutations were two common mutations that were each found in 20% of 10 ADOII probands. In CLCN7-related ADOII patients, long bone fractures and elevated serum CK level were two major clinical phenotypes, especially in patients younger than 18 years. Further functional studies of the above eight mutations in the CLCN7 gene are needed in the future.

Elevated serum lactate dehydrogenase isoenzymes and aspartate transaminase distinguish Albers-Schönberg disease (Chloride Channel 7 Deficiency Osteopetrosis) among the sclerosing bone disorders

Osteopetrosis (OPT) refers to the consequences of generalized failure of skeletal resorption during growth. Most cases are explained by loss-of-function mutation within the genes that encode either chloride channel 7 (CLCN7) or a vacuolar proton pump subunit (TCIRG1), each compromising acid secretion by osteoclasts. Patients suffer fractures and sometimes cranial nerve entrapment and insufficient medullary space for hematopoiesis. In 1996, we reported that a high serum level of the brain isoenzyme of creatine kinase (BB-CK), the CK of osteoclasts, characterizes OPT dueamong the sclerosing bone disorders (J Clin Endocrinol Metab. 1996;11:1438). Now, we show that elevation in serum of multiple lactate dehydrogenase (LDH) isoenzymes with aspartate transaminase (AST) distinguishes autosomal dominant OPT due to loss-of-function mutation in CLCN7 [Albers-Schönberg disease (A-SD)] among these conditions. Serum total LDH and AST levels as high as 3× and 2×, respectively, the upper limits of normal for age-appropriate controls, were persistent and essentially concordant in A-SD. Serum LDH was elevated in 7 of 9 children and in the 2 adults studied with A-SD. LDH isoenzyme quantitation showed excesses of LDH-2, -3, and -4. Neither total LDH nor AST increases were found in other forms of OPT, including bisphosphonate-induced OPT, or in 41 children and 6 adults representing 20 additional sclerosing bone disorders. Serum TRACP-5b and BB-CK also were markedly elevated in A-SD. Hence, high serum levels of several enzymes characterize A-SD. Elevated serum LDH isoenzymes and AST indicate a disturbance (of uncertain clinical significance) within multiple extraosseous tissues when there is CLCN7 deficiency.

Dysosteosclerosis presents as an "osteoclast-poor" form of osteopetrosis: comprehensive investigation of a 3-year-old girl and literature review

Dysosteosclerosis (DSS), an extremely rare dense bone disease, features short stature and fractures and sometimes optic atrophy, cranial nerve palsy, developmental delay, and failure of tooth eruption in infancy or early childhood consistent with osteopetrosis (OPT). Bone histology during childhood shows unresorbed primary spongiosa from deficient osteoclast action. Additionally, there is remarkable progressive flattening of all vertebrae and, by adolescence, paradoxical metaphyseal osteopenia with thin cortical bone. Reports of consanguinity indicate autosomal recessive inheritance, yet more affected males than females suggest X-linked recessive inheritance. We investigated a nonconsanguineous girl with DSS. Osteosclerosis was discovered at age 7 months. Our studies, spanning ages 11 to 44 months, showed weight at approximately 50th percentile, and length diminishing from approximately 30th percentile to -2.3 SD. Head circumference was +4 SD. The patient had frontal bossing, blue sclera, normal teeth, genu valgum, and unremarkable joints. Radiographs showed orbital and facial sclerosis, basilar thickening, bone-in-bone appearance of the pelvis, sclerotic long bone ends, and fractures of ribs and extremities. Progressive metaphyseal widening occurred as vertebrae changed from ovoid to flattened and became beaked anteriorly. A hemogram was normal. Consistent with OPT, serum parathyroid hormone (PTH) concentrations reflected dietary calcium levels. Serum bone alkaline phosphatase, osteocalcin, and TRACP-5b were subnormal. The iliac crest contained excessive primary spongiosa and no osteoclasts. No mutations were identified in the splice sites or exons for the genes encoding chloride channel 7, T-cell immune regulator 1, OPT-associated transmembrane protein 1, and monocyte colony-stimulating factor (M-CSF) and its receptor C-FMS, ANKH, OPG, RANK, and RANKL. Genomic copy-number microarray was unrevealing. Hence, DSS is a distinctive OPT of unknown etiology featuring osteoclast deficiency during early childhood. How osteopenia follows is an enigma of human skeletal pathobiology.

Maxillofacial aspects in malignant osteopetrosis

OBJECTIVE

Malignant osteopetrosis (MO) is a rare hereditary disease that affects young children. Its physiopathology is explained by a basic defect in osteoclast precursor cells, with a radiographic image of diffuse sclerosis and increased bone density. The bone contains an increased number of structurally abnormal osteoclasts. Infections commonly occur because the neutrophils exhibit reduced chemotactic response and decreased ability of bacterial phagocytosis.

PATIENT

A white female patient aged 9 months, of mixed descent, was diagnosed at birth as having MO after bone marrow biopsy. Dental examination revealed the presence of four teeth, all of which had enamel hypoplasia and no carious lesions. After bone marrow transplantation (BMT), an erythematous lesion appeared on the alveolar ridge on day 2, with signs of tooth exfoliation. On day 7, there was gingival bleeding, edema, and erythema at the region of the maxillary incisors with grade 3 mobility, without changes in food intake.

RESULTS

Concerning the oral cavity, the patient maintained grade 1 tooth mobility without tooth exfoliation or other oral alterations.

CONCLUSION

Accurate diagnosis and careful therapeutic planning are important to avoid the secondary complications of the disease.

Bisphosphonate-induced osteopetrosis: novel bone modeling defects, metaphyseal osteopenia, and osteosclerosis fractures after drug exposure ceases

In 2003, we reported on a 12-yr-old boy who had developed osteopetrosis (OPT) while receiving pamidronate (PMD) for idiopathic bone pain and enigmatic elevation in circulating bone alkaline phosphatase. Now 17 yr of age, he was re-evaluated 6.5 yr after PMD exposure stopped. Our patient described less bone pain but further limb fractures. His growth plates were fused, yet hyperphosphatasemia persisted. Radiographs documented interval fractures of a metacarpal, an osteosclerotic distal radius, and a dense diaphyseal segment of an ulna where a "chalkstick" break remained incompletely healed after 2 yr. There was new L(4) spondylolysis, and previous L(5) spondylolysis had caused spondylolisthesis. Modeling disturbances of OPT persisted, but partial recovery was shown by metaphyseal surfaces with a unique concave shape. Metaphyseal osteosclerosis had remodeled imperfectly to become focal areas of dense, diaphyseal bone. Newer metaphyseal bone was unexpectedly osteopenic, especially in his distal femurs where cortices were thin and a paucity of trabeculae was documented by CT. Femoral necks had become short and wide with an abnormal contour. A "bone-within-bone" configuration was now present throughout his skeleton. In vertebrae, endplates were thin, and trabecular osteopenia was present central and peripheral to the bands of osteosclerosis. BMD Z-scores assessed by DXA had decreased into the normal range in his spine, hip, and whole body. Iliac crest biopsy showed active bone formation, with much less accumulated primary spongiosa than during the PMD infusions. Osteoclasts that had been dysmorphic, round cells without polarization and off of bone surfaces were now unremarkable in number, location, and appearance. In conclusion, bisphosphonate toxicity during childhood can impair skeletal modeling and remodeling with structural changes that evolve and carry into adult life.

Recovery from skeletal fluorosis (an enigmatic, American case)

A 52-year-old man presented with severe neck immobility and radiographic osteosclerosis. Elevated fluoride levels in serum, urine, and iliac crest bone revealed skeletal fluorosis. Nearly a decade of detailed follow-up documented considerable correction of the disorder after removal of the putative source of fluoride (toothpaste).

INTRODUCTION

Skeletal fluorosis, a crippling bone disorder, is rare in the United States, but affects millions worldwide. There are no data regarding its reversibility.

MATERIALS AND METHODS

A white man presented in 1996 with neck immobility and worsening joint pains of 7-year duration. Radiographs revealed axial osteosclerosis. Bone markers were distinctly elevated. DXA of lumbar spine (LS), femoral neck (FN), and distal one-third radius showed Z scores of +14.3, +6.6, and -0.6, respectively. Transiliac crest biopsy revealed cancellous volume 4.5 times the reference mean, cortical width 3.2 times the reference mean, osteoid thickness 25 times the reference mean, and wide and diffuse tetracycline uptake documenting osteomalacia. Fluoride (F) was elevated in serum (0.34 and 0.29 mg/liter [reference range: <0.20]), urine (26 mg/liter [reference range: 0.2-1.1 mg/liter]), and iliac crest (1.8% [reference range: <0.1%]). Tap and bottled water were negative for F. Surreptitious ingestion of toothpaste was the most plausible F source.

RESULTS

Monitoring for a decade showed that within 3 months of removal of F toothpaste, urine F dropped from 26 to 16 mg/liter (reference range: 0.2-1.1 mg/liter), to 3.9 at 14 months, and was normal (1.2 mg/liter) after 9 years. Serum F normalized within 8 months. Markers corrected by 14 months. Serum creatinine increased gradually from 1.0 (1997) to 1.3 mg/dl (2006; reference range: 0.5-1.4 mg/dl). Radiographs, after 9 years, showed decreased sclerosis of trabeculae and some decrease of sacrospinous ligament ossification. DXA, after 9 years, revealed 23.6% and 15.1% reduction in LS and FN BMD with Z scores of +9.3 and +4.8, respectively. Iliac crest, after 8.5 years, had normal osteoid surface and thickness with distinct double labels. Bone F, after 8.5 years, was 1.15% (reference range, <0.1), which was a 36% reduction (still 10 times the reference value). All arthralgias resolved within 2 years, and he never fractured, but new-onset nephrolithiasis occurred within 9 months and became a chronic problem.

CONCLUSIONS

With removal of F exposure, skeletal fluorosis is reversible, but likely impacts for decades. Patients should be monitored for impending nephrolithiasis.

Hepatitis C-associated osteosclerosis (HCAO): report of a new case with involvement of the OPG/RANKL system

We report a new case of hepatitis C-associated osteosclerosis (HCAO). The clinical presentation of the patient was an acquired deep severe bone pain with increased serum bone alkaline phosphatase activity (up to 12 times the upper limit of normal), and generalized bone sclerosis, temporally related to the hepatitis C-virus (HCV) infection. We documented in this patient an increase of circulating osteoprotegerin (OPG), and a concentration of circulating receptor activator for nuclear factor-kB ligand (RANKL) below the lower limit of the reference range. The observed abnormalities of the OPG/RANKL system may contribute to the maintenance of the positive balance of bone remodeling that characterizes patients with HCAO.

Characterization of osteoclasts from patients harboring a G215R mutation in ClC-7 causing autosomal dominant osteopetrosis type II

Autosomal dominant osteopetrosis II (ADOII) is a relatively benign disorder caused by a missense mutation in the ClCN7 gene. In this study, we characterize the osteoclasts from patients with ADOII, caused by a G215R mutation, and investigate the effect on osteoclast function in vitro. Osteoclasts from ADOII patients and healthy age- and sex-matched controls, were used to evaluate osteoclastogenesis, cell fusion, acidification, and resorptive activity. ADOII osteoclasts in vivo have increased number and size. However, in vitro we observed no significant changes in the osteoclast formation rate, the morphology, and the expression of markers, such as cathepsin K and tartrate-resistant acid phosphatase. When mature ADOII osteoclasts were investigated on mineralized bone, they degraded the bone material, however only to 10 to 20% of the level in controls. We show by acridine orange, that the reduced chloride transport leads to reduced acidification. We show that the residual activity is sensitive to inhibitors of cathepsins and chloride channels, confirming that resorption is reduced but present. In conclusion, this is the first functional in vitro study of human ADOII osteoclasts. We show normal osteoclastogenesis in ADOII osteoclasts. However, the residual activity of the ClC-7 channel in ADOII osteoclasts does not allow sufficient acidification and thereby resorption.

High bone density due to a mutation in LDL-receptor-related protein 5

BACKGROUND

Osteoporosis is a major public health problem of largely unknown cause. Loss-of-function mutations in the gene for low-density lipoprotein receptor-related protein 5 (LRP5), which acts in the Wnt signaling pathway, have been shown to cause osteoporosis-pseudoglioma.

METHODS

We performed genetic and biochemical analyses of a kindred with an autosomal dominant syndrome characterized by high bone density, a wide and deep mandible, and torus palatinus.

RESULTS

Genetic analysis revealed linkage of the syndrome to chromosome 11q12-13 (odds of linkage, >1 million to 1), an interval that contains LRP5. Affected members of the kindred had a mutation in this gene, with valine substituted for glycine at codon 171 (LRP5V171). This mutation segregated with the trait in the family and was absent in control subjects. The normal glycine lies in a so-called propeller motif that is highly conserved from fruit flies to humans. Markers of bone resorption were normal in the affected subjects, whereas markers of bone formation such as osteocalcin were markedly elevated. Levels of fibronectin, a known target of signaling by Wnt, a developmental protein, were also elevated. In vitro studies showed that the normal inhibition of Wnt signaling by another protein, Dickkopf-1 (Dkk-1), was defective in the presence of LRP5V171 and that this resulted in increased signaling due to unopposed Wnt activity.

CONCLUSIONS

The LRP5V171 mutation causes high bone density, with a thickened mandible and torus palatinus, by impairing the action of a normal antagonist of the Wnt pathway and thus increasing Wnt signaling. These findings demonstrate the role of altered LRP5 function in high bone mass and point to Dkk as a potential target for the prevention or treatment of osteoporosis.

Serum creatine kinase isoenzyme BB in mammalian osteopetrosis

In mammalian osteopetrosis the different mutations exemplify reduced bone resorption leading to net accumulation of bone. Recently, high blood levels of creatine kinase-BB have been reported in some human forms, suggesting it as a marker of osteopetrosis. In the current study serum creatine kinase-BB was evaluated in relation to known osteoclastic pathophysiology in two human types of autosomal dominant osteopetrosis at baseline and after stimulation with triiodothyronine and in four different rodent mutations. Creatine kinase-BB was increased markedly in Type 2 autosomal dominant osteopetrosis and in the incisors absent rat, both characterized by large numbers of giant osteoclasts, and did not change significantly after stimulation. Although creatine kinase-BB was unchanged in Type 1 autosomal dominant osteopetrosis at baseline and after stimulation, the rodent counterparts characterized by small osteoclasts, microphthalmic and osteopetrotic mice and toothless rats, had significantly decreased levels. Similar differences were observed in both types of autosomal dominant osteopetrosis compared with controls concerning tartrate resistant acid phosphatase. Creatine kinase-BB in mammalian osteopetrosis is related to osteoclastic number and size, where it probably reflects the differentiation and maturation of inactive bone resorbing cells. The isoenzyme does not seem to be a valuable screening marker for osteopetrosis.

Bone mineral density and laboratory evaluation of a type II autosomal dominant osteopetrosis carrier

Type II autosomal dominant osteopetrosis (ADO2) is an inherited disorder characterized by increased skeletal mass and characteristic abnormalities evident on radiography. Although previous investigators have described nonpenetrant individuals (carriers), it is not known whether carriers manifest subtle abnormalities. We hypothesized that ADO2 carriers would have an abnormality of osteoclast function that would lead to changes in bone mineral density (BMD), in serum tartrate-resistant acid phosphatase (TRAP), or in creatine kinase isoenzyme BB (CK-BB) levels that would permit carrier recognition. We identified a female carrier in a well-established ADO2 family and measured BMD, serum TRAP, and CK-BB concentrations. She had normal BMD, serum TRAP, and CK-BB concentrations. Thus, these measurements cannot be used to exclude carrier status in individuals who are seen for genetic counseling. However, measurements in other asymptotic carriers are necessary before concluding that these measurements are normal in all or most nonpenetrant individuals.

Locus heterogeneity of autosomal dominant osteopetrosis (ADO)

Autosomal dominant osteopetrosis (ADO), is a heritable disorder that results from a failure of osteoclast-mediated bone resorption. The etiology of the disorder is unknown. A previous linkage study of one Danish family mapped an ADO locus to chromosome 1p21. We have studied two families from Indiana with ADO. The present study sought to determine if the ADO gene in these families was also linked to chromosome 1p21. We used six microsatellite repeat markers, which demonstrated linkage to the 1p21 ADO locus in the Danish study, to perform linkage analysis in the new kindreds. Multipoint analysis excluded linkage of ADO to chromosome 1p21 (logarithm of the odds score < -7.00) in both families. In addition, no haplotype segregated with the disorder in either family. In summary, the present investigation ruled out linkage of ADO to chromosome 1p21 in two families from Indiana. Our results demonstrate that there is locus heterogeneity of this disorder; therefore, mutations in at least two different genes can give rise to the ADO phenotype.