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Osteoclasts are essential for bone resorption, playing a crucial role in skeletal development, homeostasis, and remodeling. Their differentiation depends on the RANK receptor encoded by the TNFRSF11A gene, with defects in this gene linked to osteoclast-poor sclerosing skeletal dysplasias. This report presents a 37-yr-old woman with normal height, valgus deformities that were treated surgically, frequent fractures, scoliosis, mildly elevated BMD, sclerotic diaphyseal bone, and metaphyseal widening. Initially suspected of having dysosteosclerosis, her diagnosis shifted toward Pyle disease due to the valgus deformity and prominent metaphyseal widening and translucency. Genetic analysis identified 2 pathogenic TNFRSF11A variants: a nonsense mutation c.1093G>T, p.(Glu365 * ) and a frameshift mutation c.1266_1268delinsCC, p.(Leu422Phefs * 104). Thus, genetic and clinical assessment converged on the diagnosis of a mild form of dysosteosclerosis. Both mutations introduced premature stop codons but escaped complete nonsense-mediated decay, potentially permitting residual protein function. Analysis of patient-derived osteoclasts cultured on glass surfaces showed partial differentiation. However, in vitro resorptive function was strongly impaired, which was clinically reflected by reduced serum concentration of the bone resorption marker CTx. Despite this impairment, the retained residual resorptive function likely explains the patient's relatively mild clinical presentation. These findings underscore the complex genetic interactions that affect osteoclast function, leading to a spectrum of phenotypes in osteoclast-related bone disorders., Competing Interests: All authors declare no conflict of interest and no competing financial interests., (© The Author(s) 2025. Published by Oxford University Press on behalf of the American Society for Bone and Mineral Research.)

Case: A 27-year-old woman with increasing bilateral thigh pain and underlying diagnosis of dysosteosclerosis was diagnosed with bilateral impending pathological femur fractures. Both femurs exhibited abnormal morphology with bowing, thickened cortices, and narrow intramedullary canals. We planned minimally invasive prophylactic plate osteosynthesis. Computed tomography scans of both femora were obtained and used to generate 3-dimensional (3D) printed models. Osteosynthesis plates were precontoured to fit the 3D models and sterilized, and prophylactic fixation was performed using a minimally invasive submuscular technique. Conclusion: 3D printed models aided in precontouring fixation plates in a case with challenging bony anatomy, enabling minimally invasive surgery. [ABSTRACT FROM AUTHOR]

The role of colony‐stimulating factor‐1 receptor (CSF‐1R) in macrophage and organismal development has been extensively studied in mouse. Within the last decade, mutations in the CSF1R have been shown to cause rare diseases of both pediatric (Brain Abnormalities, Neurodegeneration, and Dysosteosclerosis, OMIM #618476) and adult (CSF1R‐related leukoencephalopathy, OMIM #221820) onset. Here we review the genetics, penetrance, and histopathological features of these diseases and discuss to what extent the animal models of Csf1r deficiency currently available provide systems in which to study the underlying mechanisms involved. [ABSTRACT FROM AUTHOR]

Dysosteosclerosis (DOS) is a rare sclerosing bone dysplasia characterized by unique osteosclerosis of the long tubular bones and platyspondyly. DOS is inherited in an autosomal recessive manner and is genetically and clinically heterogeneous. To date, four individuals with DOS who have five different TNFRSF11A mutations have been reported. Based on their data, it is hypothesized that mutations producing aberrant mutant RANK proteins (missense or truncated or elongated) cause DOS, while null mutations lead to osteopetrosis, autosomal recessive 7 (OPTB7). Herein, we present the fifth case of TNFRSF11A -associated DOS with a novel homozygous frame-shift mutation (c.19_31del; p.[Arg7CysfsTer172]). The mutation is predicted to cause nonsense mutation-mediated mRNA decay (NMD) in all RANK isoform transcripts, resulting in totally null allele. Our findings suggest genotype-phenotype relationship in TNFRSF11A -associated OPTB7 and DOS remains unclear, and that the deficiency of TNFRSF11A functions might cause DOS, rather than osteopetrosis. More data are necessary to understand the phenotypic spectrum caused by TNFRSF11A mutations. [ABSTRACT FROM AUTHOR]

Dysosteosclerosis (DOS) is a rare sclerosing bone dysplasia characterized by unique osteosclerosis of the long tubular bones and platyspondyly. DOS is inherited in an autosomal recessive manner and is genetically and clinically heterogeneous. To date, four individuals with DOS who have five different TNFRSF11A mutations have been reported. Based on their data, it is hypothesized that mutations producing aberrant mutant RANK proteins (missense or truncated or elongated) cause DOS, while null mutations lead to osteopetrosis, autosomal recessive 7 (OPTB7). Herein, we present the fifth case of TNFRSF11A-associated DOS with a novel homozygous frame-shift mutation (c.19_31del; p.[Arg7CysfsTer172]). The mutation is predicted to cause nonsense mutation-mediated mRNA decay (NMD) in all RANK isoform transcripts, resulting in totally null allele. Our findings suggest genotype-phenotype relationship in TNFRSF11A-associated OPTB7 and DOS remains unclear, and that the deficiency of TNFRSF11A functions might cause DOS, rather than osteopetrosis. More data are necessary to understand the phenotypic spectrum caused by TNFRSF11A mutations.

Colony stimulating factor 1 receptor (CSF1R, MIM# 164770) encodes a tyrosine‐kinase receptor playing an important role in development of osteoclasts and microglia. Heterozygous CSF1R variants have been known to cause hereditary diffuse leukoencephalopathy with spheroids (HDLS, MIM# 221820), an adult‐onset leukoencephalopathy characterized by loss of motor functions and cognitive decline. Recently, a new phenotype characterized by brain abnormalities, neurodegeneration, and dysosteosclerosis (BANDDOS) with biallelic CSF1R pathogenic variants in the etiology has been described. BANDDOS differs from HDLS by early‐onset neurodegenerative changes with additional structural brain abnormalities and skeletal findings resembling dysosteosclerosis (DOS). Described skeletal findings of the disease are highly variable ranging from absence of a skeletal phenotype and milder Pyle disease‐like to osteopetrosis and DOS. To date, only a few patients carrying biallelic CSF1R variants have been reported. In this clinical report, we describe three siblings with variable skeletal findings along with neurological symptoms ranging from mild to severe in whom exome sequencing revealed a novel homozygous splice site variant in canonical splice donor site of intron 21 adjacent to an exon, which encoding part of kinase domain of CSF1R along with a review of the literature. [ABSTRACT FROM AUTHOR]

Colony stimulating factor 1 receptor (CSF1R) plays key roles in regulating development and function of the monocyte/macrophage lineage, including microglia and osteoclasts. Mono-allelic mutations of CSF1R are known to cause hereditary diffuse leukoencephalopathy with spheroids (HDLS), an adult-onset progressive neurodegenerative disorder. Here, we report seven affected individuals from three unrelated families who had bi-allelic CSF1R mutations. In addition to early-onset HDLS-like neurological disorders, they had brain malformations and skeletal dysplasia compatible to dysosteosclerosis (DOS) or Pyle disease. We identified five CSF1R mutations that were homozygous or compound heterozygous in these affected individuals. Two of them were deep intronic mutations resulting in abnormal inclusion of intron sequences in the mRNA. Compared with Csf1r- null mice, the skeletal and neural phenotypes of the affected individuals appeared milder and variable, suggesting that at least one of the mutations in each affected individual is hypomorphic. Our results characterized a unique human skeletal phenotype caused by CSF1R deficiency and implied that bi-allelic CSF1R mutations cause a spectrum of neurological and skeletal disorders, probably depending on the residual CSF1R function. [ABSTRACT FROM AUTHOR]

Abstract The osteopetroses and related sclerosing bone dysplasias can have a broad range of manifestations. Especially in the milder forms, sandwich vertebrae are an easily recognizable and reliable radiological hallmark. We report on four patients from three families presenting with sandwich vertebrae and platyspondyly. The long bone phenotypes were discordant with one patient showing modeling defects and patchy osteosclerosis, while the second displayed only metaphyseal sclerotic bands, and the third and fourth had extreme metaphyseal flaring with uniform osteosclerosis. Two of the four patients had experienced pathological fractures, two had developmental delay, but none showed cranial nerve damage, hepatosplenomegaly, or bone marrow failure. According to these clinical features the diagnoses ranged between intermediate autosomal recessive osteopetrosis and dysosteosclerosis. After exclusion of mutations in CLCN7 we performed gene panel and exome sequencing. Two novel mutations in SLC29A3 were found in the first two patients. In the third family a TCIRG1 C-terminal frameshift mutation in combination with a mutation at position +4 in intron 2 were detected. Our study adds two cases to the small group of individuals with SLC29A3 mutations diagnosed with dysosteosclerosis, and expands the phenotypic variability. The finding that intermediate autosomal recessive osteopetrosis due to TCIRG1 splice site mutations can also present with platyspondyly further increases the molecular heterogeneity of dysosteosclerosis-like sclerosing bone dysplasias. Highlights • We describe sclerotic bone dysplasia due to SLC29A3 mutations with a hitherto unrecognized phenotypic variability. • Intermediate autosomal recessive osteopetrosis with dramatic metaphyseal flaring can be due to TCIRG1 mutations. • Intermediate autosomal recessive osteopetrosis due to TCIRG1 mutations can present like dysosteosclerosis. • Dysosteosclerosis is clinically and molecularly more heterogeneous and less malignant than previously thought. [ABSTRACT FROM AUTHOR]

Dysosteosclerosis (DSS) refers to skeletal dysplasias that radiographically feature focal appendicular osteosclerosis with variable platyspondyly. Genetic heterogeneity is increasingly reported for the DSS phenotype and now involves mutations of SLC29A3 , TNFRSF11A , TCIRG1 , LRRK1 , and CSF1R. Typical radiological findings are widened radiolucent long bones with thin cortices yet dense irregular metaphyses, flattened vertebral bodies, dense ribs, and multiple fractures. However, the radiographic features of DSS evolve, and the metaphyseal and/or appendicular osteosclerosis variably fades with increasing patient age, likely due to some residual osteoclast function. Fractures are the principal presentation of DSS, and may even occur in infancy with SLC29A3 -associated DSS. Cranial base sclerosis can lead to cranial nerve palsies such as optic atrophy, and may be the initial presentation, though not observed with SLC29A3- associated DSS. Gene-specific extra-skeletal features can be the main complication in some forms of DSS such as CSF1R- associated DSS. Further genetic heterogeneity is likely, especially for X-linked recessive DSS and cases currently with an unknown genetic defect. Distinguishing DSS can be challenging due to variable clinical and radiological features and an evolving phenotype. However, defining the DSS phenotype is important for predicting complications, prognosis, and instituting appropriate health surveillance and treatment. [ABSTRACT FROM AUTHOR]

Dysosteosclerosis is a sclerosing bone dysplasia with skeletal changes resembling those of osteopetrosis. The disorder is associated with dental anomalies and occasionally mental retardation. Because of the rarity and phenotypic diversity of dysosteosclerosis, it remains unsolved whether or not the disorder is heterogeneous. We report here on an affected boy associated with brain calcification and epilepsy with developmental delay. Prenatal ultrasound revealed ventriculomegaly, and brain CT in the neonatal period showed periventricular calcifications. At 13 mo of age, he presented with generalized convulsion with developmental delay. Metaphyseal sclerosis, metaphyseal undermodeling, and oval-shaped vertebral bodies on skeletal survey warranted a diagnosis of dysosteosclerosis. Retrospective review of radiographs as a neonate showed metaphyseal radiolucency, but not metaphyseal sclerosis. Since then, neither the bone changes nor neurological symptom has progressively worsened up to 4 yr of age. Thus, it is thought that the clinical and radiological manifestations of the sclerotic disorder become obvious during infancy. Brain calcification of prenatal onset may be an essential syndromic constituent of the disorder. [ABSTRACT FROM AUTHOR]

Four Spanish children with clinical and radiological features corresponding to dysosteosclerosis are presented. All the children were male and belonged to the same family. The first known carrier is the maternal grand-mother, who had three daughters by three different fathers who in turn had one or more sons with the disease. The four carriers were normal. Consanguinity did not occur in any case and the disorder was transmitted as a sex-linked recessive condition. [ABSTRACT FROM AUTHOR]

SUMMARY A 5 year old boy presented with delayed development and loss of vision. A skeletal survey showed osteosclerosis consistent with dysosteosclerosis. Some unusual features of dysosteosclerosis are discussed. [ABSTRACT FROM AUTHOR]