Fracture Patterns and Mortality in Osteopetrosis: A 7-year Retrospective Analysis from Türkiye's National Registry

BACKGROUND

The aim of this study is to determine the demographic data, fracture treatment methods, and medical treatments of patients diagnosed with osteopetrosis in the national registry.

METHODS

Patients with International Classification of Diseases (ICD)-10 code Q78.2 for osteopetrosis between January 1, 2016 and April 11, 2023 were retrospectively reviewed. Data on sex, age at time of diagnosis, fracture history, mortality, and use of medications were evaluated for all patients. In addition, open reduction and internal fixation, closed reduction and internal fixation, closed reduction and casting, and conservative treatment methods were noted. The number of patients requiring deformity surgery was determined. The incidence and prevalence of osteopetrosis were also calculated in this cross-sectional study.

RESULTS

A total of 476 patients diagnosed with osteopetrosis were identified. The mean age at time of diagnosis of these patients was 5.79 ± 5.43 years. A total of 101 patients died. As the age at diagnosis decreased, the mortality rate of the patients increased with statistical significance ( P <0.001). A total of 192 fractures were seen in 121 osteopetrosis patients in this study. Femur fractures were most common among these patients with osteopetrosis. A history of fracture was statistically significantly less common in patients using a combination of vitamin D + calcium compared with patients not using such medication ( P <0.001). In this 7-year cross-sectional study, the incidence was found to be 1 in 416,000 and the prevalence was 0.00199% in the population under 18 years of age.

CONCLUSION

Younger age at diagnosis is associated with higher mortality in patients with osteopetrosis. In addition, the combination of vitamin D and calcium were associated with lower fracture incidence.

LEVEL OF EVIDENCE

Prognostic Level II.

Total Hip Arthroplasty in Patients With Osteopetrosis

BACKGROUND

Osteopetrosis is an inherited bone disease associated with high risk of osteoarthritis and fracture non-union, which can lead to total hip arthroplasty (THA). Bone quality and morphology are altered in these patients, and there are limited data on results of THA in these patients. The goals of this study were to describe implant survivorship, clinical outcomes, radiographic results, and complications in patients with osteopetrosis undergoing primary THA.

METHODS

We identified 7 patients (9 hips) with osteopetrosis who underwent primary THA between 1970 and 2017 utilizing our total joint registry. The mean age at index THA was 48 years and included two males and five females. The mean follow-up was 8 years.

RESULTS

The 10-year survivorship free from any revision or implant removal was 89%, with 1 revision and 1 resection arthroplasty secondary to periprosthetic femoral fractures. The 10-year survivorship free from any reoperation was 42%, with 4 additional reoperations (2 ORIFs for periprosthetic femoral fractures, 1 sciatic nerve palsy lysis of adhesions, 1 hematoma evacuation). Harris hip scores significantly increased at 5 years (P = .04). Five hips had an intraoperative acetabular fracture, and 1 had an intraoperative femur fracture. All postoperative femoral fractures occurred in patients with intramedullary diameter less than 5 mm at a level 10 cm distal to the lesser trochanter.

CONCLUSION

Primary THA in patients with osteopetrosis is associated with good 10-year implant survivorship (89%), but a very high reoperation (58%) and periprosthetic femoral fracture rate (44%). Femoral fractures appear associated with smaller intramedullary diameters.

The evolving therapeutic landscape of genetic skeletal disorders

BACKGROUND

Rare bone diseases account for 5% of all birth defects yet very few have personalised treatments. Developments in genetic diagnosis, molecular techniques and treatment technologies however, are leading to unparalleled therapeutic advance. This review explores the evolving therapeutic landscape of genetic skeletal disorders (GSDs); the key conditions and there key differentials.

METHODS

A retrospective literature based review was conducted in December 2018 using a systematic search strategy for relevant articles and trials in Pubmed and clinicaltrials.gov respectively. Over 140 articles and 80 trials were generated for review.

RESULTS

Over 20 personalised therapies are discussed in addition to several novel disease modifying treatments in over 25 GSDs. Treatments discussed are at different stages from preclinical studies to clinical trials and approved drugs, including; Burosumab for X-linked hypophosphatemia, Palovarotene for Hereditary Multiple Exostoses, Carbamazepine for Metaphyseal Chondrodysplasia (Schmid type), Lithium carbonate and anti-sclerostin therapy for Osteoporosis Pseudoglioma syndrome and novel therapies for Osteopetrosis. We also discuss therapeutic advances in Achondroplasia, Osteogenesis Imperfecta (OI), Hypophosphotasia (HPP), Fibrodysplasia Ossificans Progressiva, and RNA silencing therapies in preclinical studies for OI and HPP.

DISCUSSION

It is an exciting time for GSD therapies despite the challenges of drug development in rare diseases. In discussing emerging therapies, we explore novel approaches to drug development from drug repurposing to in-utero stem cell transplants. We highlight the improved understanding of bone pathophysiology, genetic pathways and challenges of developing gene therapies for GSDs.

Diagnosis and Management of Osteopetrosis: Consensus Guidelines From the Osteopetrosis Working Group

BACKGROUND

Osteopetrosis encompasses a group of rare metabolic bone diseases characterized by impaired osteoclast activity or development, resulting in high bone mineral density. Existing guidelines focus on treatment of the severe infantile forms with hematopoietic cell transplantation (HCT) but do not address the management of patients with less severe forms for whom HCT is not the standard of care. Therefore, our objective was to develop expert consensus guidelines for the management of these patients.

METHODS

A modified Delphi method was used to build consensus among participants of the Osteopetrosis Working Group, with responses to an anonymous online survey used to identify areas of agreement and conflict and develop a follow-up survey. The strength of recommendations and quality of evidence was graded using the Grading of Recommendations Assessment, Development and Evaluation system.

RESULTS

Consensus was found in the areas of diagnosis, monitoring, and treatment. We recommend relying on characteristic radiographic findings to make the diagnosis and found that genetic testing adds important information by identifying mutations associated with unique disease complications. We recommend ongoing monitoring for changes in mineral metabolism and other complications, including cranial nerve impingement, anemia, leukopenia, and dental disease. We suggest that calcitriol should not be used in high doses and instead recommend symptom-based supportive therapy for disease complications because noninfantile osteopetrosis has no effective treatment.

CONCLUSIONS

Scarcity of published studies on osteopetrosis reduce the ability to develop evidence-based guidelines for the management of these patients. Expert opinion-based guidelines for this rare condition are nevertheless important to enable improved care.

Autosomal dominant osteopetrosis: clinical severity and natural history of 94 subjects with a chloride channel 7 gene mutation

CONTEXT

Autosomal dominant osteopetrosis (ADO) is a sclerosing bone disorder caused by heterozygous mutations in the chloride channel 7 (ClCN7) gene. The clinical manifestations of this disease have not been well characterized since the discovery of the genetic basis of ADO.

OBJECTIVES

The primary objectives were to improve our understanding of ADO clinical characteristics and to study the natural history of the disease in the largest series of patients reported to date.

DESIGN AND SETTING

This study was primarily a retrospective cross-sectional analysis of individuals with a ClCN7 mutation that was conducted over a 4-yr period at a tertiary referral center and through family reunions. Longitudinal data on a subset of subjects were also studied.

PATIENTS AND INTERVENTIONS

We studied 311 subjects from 11 ADO families, including 62 individuals with ADO (patients with the classic clinical phenotype based on radiographs and/or biochemistry), 32 unaffected gene carriers (subjects with the gene mutation but no radiographic and/or biochemical phenotype), and 217 controls who did not harbor a ClCN7 gene mutation. Clinical data were collected through patient interviews and examinations, medical records, and/or self-reported responses on a questionnaire that was completed by all subjects.

MAIN OUTCOME MEASURES

The prevalence of fracture, osteomyelitis, visual loss, and bone marrow failure was determined. Differences in clinical manifestations were analyzed according to affected vs. carrier status, age, and underlying genotype.

RESULTS

Ninety-two percent of ADO subjects had at least one sequela of the disease. Gene carriers did not have an increased risk of disease manifestations, although they were found to have significant increases in bone mineral density (P < 0.05). Compared with controls, subjects with ADO had a significantly increased prevalence of fracture (84 vs. 36%; P < 0.0001) and osteomyelitis (16 vs. 0.9%; P < 0.0001). Severe fractures (defined as > or =10 fractures of any type and/or greater than one hip/femur fracture) were identified only in ADO subjects, and osteomyelitis typically occurred in the maxilla or mandible in older adults. Visual loss, which typically had its onset in childhood, and bone marrow failure occurred in 19 and 3% of ADO subjects, respectively. Adults were more likely to manifest an ADO clinical characteristic, but no definitive genotype-phenotype relationship could be concluded. Longitudinal data suggest that the ADO clinical phenotype worsens over time.

CONCLUSIONS

ADO caused by mutations in the CLCN7 gene is a frequently symptomatic disease manifested by a high rate of fracture, osteomyelitis, visual loss, and occasional bone marrow failure. The sequelae of ADO, which can be identified as early as infancy, appear to worsen over time. Fracture is the most prevalent consequence of ADO, although other more severe manifestations of disease can occur and should not be confused with recessive forms of osteopetrosis, particularly when identified in early childhood.

Association of an aromatase TTTA repeat polymorphism with circulating estrogen, bone structure, and biochemistry in older women

Osteoporosis is a disease that is strongly genetically determined. Aromatase converts androgens to estradiol in postmenopausal women, therefore polymorphisms of the gene for this enzyme may be associated with bone mass and fracture. We investigated the association of the TTTA microsatellite polymorphism in intron 4 of the aromatase (CYP19) gene with bone mineral density (BMD) and fracture in 1,257 women aged 70 yr and greater. The data obtained were stratified based on the presence or absence of a [TTTA]n of 7 (A2), determined from a preliminary analysis of hip dual-energy X-ray absorptiometry BMD, which was present in 27% of the population. The presence of an A2 allele was associated with a higher free estradiol index (0.52 +/- 0.49, P = 0.049) compared with the absence of an A2 allele (0.47 +/- 0.45); higher BMD at all sites of the hip (3.4% total hip, 2.3% femoral neck, 3.6% intertrochanter, 4.1% trochanter) and the lumbar spine (12.7%); higher values for the calcaneal quantitative ultrasound parameters broadband ultrasound (1.3%), speed of sound (0.4%), and stiffness (3.7%); and higher peripheral quantitative computed tomography measures for total (3.4%), trabecular (3.3%), and cortical BMD (3.3%) and the derived stress strain index (SSI) parameters SSI polar (6.4%) and SSI x (6.8%) values. A lower deoxypryridinoline creatinine ratio was observed in subjects with an A2 allele (30.3 +/- 10.4 vs. 27.1 +/- 9.1, P = 0.03). The A2 allele was associated with a lower prevalence of vertebral fracture in subjects who were osteoporotic (odds ratio 0.27, confidence interval 0.09-0.79). Therefore, a common polymorphism of the aromatase gene, perhaps in linkage disequilibrium with a functionally significant CYP19 polymorphism, is associated with bone structure and bone turnover, either by local effects or by effects on circulating bioactive estrogen.

Osteoclast diseases

Osteoclasts are the only cells capable of resorbing mineralised bone, dentine and cartilage. Osteoclasts act in close concert with bone forming osteoblasts to model the skeleton during embryogenesis and to remodel it during later life. A number of inherited human conditions are known that are primarily caused by a defect in osteoclasts. Most of these are rare monogenic disorders, but others, such as the more common Paget's disease, are complex diseases, where genetic and environmental factors combine to result in the abnormal osteoclast phenotype. Where the genetic defect gives rise to ineffective osteoclasts, such as in osteopetrosis and pycnodysostosis, the result is the presence of too much bone. However, the phenotype in many osteoclast diseases is a combination of osteosclerosis with osteolytic lesions. In such conditions, the primary defect is hyperactivity of osteoclasts, compensated by a secondary increase in osteoblast activity. Rapid progress has been made in recent years in the identification of the causative genes and in the understanding of the biological role of the proteins encoded. This review discusses the known osteoclast diseases with particular emphasis on the genetic causes and the resulting osteoclast phenotype. These human diseases highlight the critical importance of specific proteins or signalling pathways in osteoclasts.

[Autosomal-dominant osteopetrosis in Chuvashiya]

A genetic epidemiological study of osteopetrosis was carried out in Chuvashiya. The major signs of this disorder are severe anemia developed in the prenatal or early postnatal life, hepatosplenomegaly, and a progressive loss of sight and hearing. Osteopetrosis showed the autosomal recessive inheritance with a somewhat increased proportion of affected patients in families. The lowest estimate of osteopetrosis frequency in Chuvashiya was 0.00026, one affected patient per 3879 newborns. The osteopetrosis gene occurred at a frequency of 0.016; the proportion of heterozygotes was 3.15%. The gene was shown to be evenly distributed throughout the republic.

[Recessive osteopetrosis. Identification of a form of medium severity]

BACKGROUND

Several distinct forms of osteopetrosis have been identified. Some of the autosomally recessive inherited forms are benign, much like the autosomal dominant form. Others are more malignant.

PATIENTS

The clinical data, skeletal radiographs, histological features and histories of 32 children with osteopetrosis were analyzed retrospectively.

RESULTS

The 32 patients, belonging to 20 sibships were divided into two groups. The first group included 24 patients, aged 1 day-11 months (mean 4.5 months), suffering from hepatosplenomegaly, anemia, thrombocytopenia and optic atrophy in early infancy. They also had a generalized increase in bone density, abnormal bone remodeling, rachitic lesions and a "bone-within-bone" appearance. Biopsies showed severe bone resorption and myelofibrosis. 19 of the 20 patients whose outcomes were known died during the first year of life. The second group included 8 patients, aged 40 days-3 years (mean: 11 months). Hepatosplenomegaly appeared later, anemia was less severe and thrombocytopenia occurred in only 1 patient. However, all 8 patients suffered from optic atrophy and 3 were deaf. Radiographs showed bone growth without rachitic lesions. Biopsies from 2 patients showed bone resorption, but no myelofibrosis. The outcome was less severe: 6 patients, now aged 8 months to 8 years, have survived, 3 of them for over 5 years. Genetic investigation showed patterns compatible with autosomal recessive inheritance in both groups, with similar sets of features within each sibship.

CONCLUSION

This study reveals a new type of recessively inherited osteopetrosis. It can be classified as an intermediate form, distinct from both the malignant and the benign forms, and also distinct from osteopetrosis with carbonic anhydrase II deficiency.

Osteopetrosis. A genetic and epidemiological study

By a systemic search of osteopetrosis in the county of Funen, Denmark, the prevalence was 5.5/100,000 inhabitants. The study disclosed 33 patients of whom 32 had the mild, autosomal dominant form of osteopetrosis. Two obligate carriers, who had the genotype but were not phenotypically affected, were disclosed. There was a great variation in the clinical manifestations; 39% were asymptomatic. The age of first appearance of symptoms also varied widely (8-76 years), with a tendency to increasing symptoms with aging. The frequency of fractures was low. Plasma inorganic phosphate was low in 7% of the patients, and plasma acid phosphatase was increased in 39%.

Osteopetrosis in South Africa. The benign, lethal and intermediate forms

Osteopetrosis is an unusual bone disorder in which the skeleton is radiographically dense. The condition is conventionally subclassified into a benign autosomal dominant adult form and a malignant autosomal recessive variety. Among 14 affected individuals whom we have studied, 4 adults had an intermediate type of osteopetrosis in which serious complications included osteomyelitis, pathological fractures and dyshaemopoiesis. The fundamental biochemical relationship of this disorder with the classic forms of osteopetrosis is uncertain. The osteopetroses must be distinguished from other sclerosing bone conditions which have a different course and prognosis. Sclerosteosis and craniometaphyseal dysplasia, both of which occur in South Africa, are of practical importance in this context.

Osteopetrosis in children: a report of 26 cases

We have observed 26 cases of osteopetrosis among 165,594 children hospitalized over a period of 10 years in the National Children's Hospital. The hospital serves Costa Rica, a country of nearly 2,000,000 inhabitants with 60,000 live births per year. All patients had characteristic roentgenographic bony changes. Among the early manifestations of the disease, nasal obstruction and an adenoidal expression were common. The facial appearance of the patient is characteristic. Serious complications of the disease are hematologic and neurologic disorders.