Dynll1 is essential for development and promotes endochondral bone formation by regulating intraflagellar dynein function in primary cilia.

Mutations in subunits of the cilia-specific cytoplasmic dynein-2 (CD2) complex cause short-rib thoracic dystrophy syndromes (SRTDs), characterized by impaired bone growth and life-threatening perinatal respiratory complications. Different SRTD mutations result in varying disease severities. It remains unresolved whether this reflects the extent of retained hypomorphic protein functions or relative importance of the affected subunits for the activity of the CD2 holoenzyme. To define the contribution of the LC8-type dynein light chain subunit to the CD2 complex, we have generated Dynll1-deficient mouse strains, including the first-ever conditional knockout (KO) mutant for any CD2 subunit. Germline Dynll1 KO mice exhibit a severe ciliopathy-like phenotype similar to mice lacking another CD2 subunit, Dync2li1. Limb mesoderm-specific loss of Dynll1 results in severe bone shortening similar to human SRTD patients. Mechanistically, loss of Dynll1 leads to a partial depletion of other SRTD-related CD2 subunits, severely impaired retrograde intra-flagellar transport, significant thickening of primary cilia and cilia signaling defects. Interestingly, phenotypes of Dynll1-deficient mice are very similar to entirely cilia-deficient Kif3a/Ift88-null mice, except that they never present with polydactyly and retain relatively higher signaling outputs in parts of the hedgehog pathway. Compared to complete loss of Dynll1, maintaining very low DYNLL1 levels in mice lacking the Dynll1-transcription factor ASCIZ (ATMIN) results in significantly attenuated phenotypes and improved CD2 protein levels. The results suggest that primary cilia can maintain some functionality in the absence of intact CD2 complexes and provide a viable animal model for the analysis of the underlying bone development defects of SRTDs.

CREB activation in hypertrophic chondrocytes is involved in the skeletal overgrowth in epiphyseal chondrodysplasia Miura type caused by activating mutations of natriuretic peptide receptor B.

Natriuretic peptide receptor B (NPRB) produces cyclic guanosine monophosphate (cGMP) when bound by C-type natriuretic peptide (CNP). Activating mutations in NPRB cause a skeletal overgrowth disorder, which has been named epiphyseal chondrodysplasia, Miura type (ECDM; OMIM #615923). Here we explored the cellular and molecular mechanisms for the skeletal overgrowth in ECDM using a mouse model in which an activating mutant NPRB is specifically expressed in chondrocytes. The mutant mice (NPRB[p.V883M]-Tg) exhibited postnatal skeletal overgrowth and increased cGMP in cartilage. Both endogenous and transgene-derived NPRB proteins were localized at the plasma membrane of hypertrophic chondrocytes. The hypertrophic zone of growth plate was thickened in NPRB[p.V883M]-Tg. An in vivo BrdU-labeling assay suggested that some of the hypertrophic chondrocytes in NPRB[p.V883M]-Tg mice continued to proliferate, although wild-type (WT) chondrocytes stopped proliferating after they became hypertrophic. In vitro cell studies revealed that NPRB activation increased the phosphorylation of cyclic AMP-responsive element binding protein (CREB) and expression of cyclin D1 in matured chondrocytes. Treatment with cell-permeable cGMP also enhanced the CREB phosphorylation. Inhibition of cyclic adenosine monophosphate (cAMP)/protein kinase A pathway had no effects on the CREB phosphorylation induced by NPRB activation. In immunostaining of the growth plates for the proliferation marker Ki67, phosphorylated CREB and cyclin D1, most signals were similarly observed in the proliferating zone in both genotypes, but some cells in the hypertrophic zone of NPRB[p.V883M]-Tg were also positively stained. These results suggest that NPRB activation evokes its signal in hypertrophic chondrocytes to induce CREB phosphorylation and make them continue to proliferate, leading to the skeletal overgrowth in ECDM.

Detailed clinical and radiological features of the first patient with Elsahy-Waters syndrome in East Asia.

Elsahy-Waters syndrome (EWS; OMIM#211380) is a rare autosomal recessive disorder that is caused by loss-of-function variants in CDH11, which encodes cadherin 11. EWS is characterized by brachycephaly, midface hypoplasia, characteristic craniofacial morphology, cervical fusion, cutaneous syndactyly in 2-3 digits, genitourinary anomalies, and intellectual disability. To the best of our knowledge, there have been only six patients of molecularly confirmed EWS. We report the first patient of EWS in East Asia in a Japanese man with a novel splice site homozygous variant of CDH11. We reviewed the clinical and molecular findings in previously reported individuals and the present patient. In addition to the previously reported clinical features of EWS, the present patient had unreported findings of atlantoaxial instability due to posterior displacement of dens, thoracic fusion, thoracic butterfly vertebra, sacralization of the lumbar vertebra (L5), and multiple perineural cysts. The spinal findings in this patient could represent a new spectrum of skeletal phenotypes of EWS. It remains to be clarified whether the multiple perineural cysts in the patient were associated with EWS or coincidental. The current observation might contribute to an expanded understanding of the clinical consequences of loss-of-function of cadherin 11.

Trevor's disease of the distal radioulnar joint in two children with achondroplasia.

Two children with achondroplasia who developed an abnormal bony outgrowth at the distal radioulnar joint (DRUJ), indistinguishable from an osteochondroma on histology, but the radiographic appearance, location, and asymmetry suggested the rare diagnosis of dysplasia epiphysealis hemimelica (DEH or "Trevor's disease"). One child experienced symptomatic relief with surgical excision and one was observed clinically due to lack of significant symptoms. These are the first presented cases of DEH in achondroplasia, both affecting the DRUJ. Due to the infrequency of DEH, more research is needed to better understand the potential connection to achondroplasia. For management, we suggest shared surgical decision making based on symptoms.

Biallelic disruption of PKDCC is associated with a skeletal disorder characterised by rhizomelic shortening of extremities and dysmorphic features.

BACKGROUND: During mouse embryonic development the protein kinase domain containing, cytoplasmic (Pkdcc) gene, also known as Vlk, is expressed in several tissues including the ventral midbrain, with particularly strong expression in branchial arches and limb buds. Homozygous Pkdcc knockout mice have dysmorphic features and shortened long bones as the most obvious morphological abnormalities. The human PKDCC gene has currently not been associated with any disorders. OBJECTIVE: To use clinical diagnostic exome sequencing (DES) for providing genetic diagnoses to two apparently unrelated patients with similar skeletal abnormalities comprising rhizomelic shortening of limbs and dysmorphic features. METHODS: Patient-parents trio DES was carried out and the identified candidate variants were confirmed by Sanger sequencing. RESULTS: Each patient had a homozygous gene disrupting variant in PKDCC considered to explain the skeletal phenotypes shared by both. The first patient was homozygous for the nonsense variant p.(Tyr217*) (NM_1 38 370 c.651C>A) expected to result in nonsense-mediated decay of the mutant transcripts, whereas the second patient was homozygous for the splice donor variant c.639+1G>T predicted to abolish the donor splice site by three in silico splice prediction algorithms. CONCLUSIONS: Biallelic gene disrupting variants in PKDCC in humans, just like in mice, cause dysmorphic features and rhizomelic shortening of limbs.

Development, behaviour and sensory processing in Marshall-Smith syndrome and Malan syndrome: phenotype comparison in two related syndromes.

BACKGROUND: Ultrarare Marshall-Smith and Malan syndromes, caused by changes of the gene nuclear factor I X (NFIX), are characterised by intellectual disability (ID) and behavioural problems, although questions remain. Here, development and behaviour are studied and compared in a cross-sectional study, and results are presented with genetic findings. METHODS: Behavioural phenotypes are compared of eight individuals with Marshall-Smith syndrome (three male individuals) and seven with Malan syndrome (four male individuals). Long-term follow-up assessment of cognition and adaptive behaviour was possible in three individuals with Marshall-Smith syndrome. RESULTS: Marshall-Smith syndrome individuals have more severe ID, less adaptive behaviour, more impaired speech and less reciprocal interaction compared with individuals with Malan syndrome. Sensory processing difficulties occur in both syndromes. Follow-up measurement of cognition and adaptive behaviour in Marshall-Smith syndrome shows different individual learning curves over time. CONCLUSIONS: Results show significant between and within syndrome variability. Different NFIX variants underlie distinct clinical phenotypes leading to separate entities. Cognitive, adaptive and sensory impairments are common in both syndromes and increase the risk of challenging behaviour. This study highlights the value of considering behaviour within developmental and environmental context. To improve quality of life, adaptations to environment and treatment are suggested to create a better person-environment fit.

Novel ANKRD11 gene mutation in an individual with a mild phenotype of KBG syndrome associated to a GEFS+ phenotypic spectrum: a case report.

BACKGROUND: KBG syndrome is a very rare autosomal dominant disorder, characterized by macrodontia, distinctive craniofacial findings, skeletal findings, post-natal short stature, and developmental delays, sometimes associated with seizures and EEG abnormalities. So far, there have been over 100 cases of KBG syndrome reported. CASE PRESENTATION: Here, we describe two sisters of a non-consanguineous family, both presenting generalized epilepsy with febrile seizures (GEFS+), and one with a more complex phenotype associated with mild intellectual disability, skeletal and dental anomalies. Whole exome sequencing (WES) analysis in all the family members revealed a heterozygous SCN9A mutation, p.(Lys655Arg), shared among the father and the two probands, and a novel de novo loss of function mutation in the ANKRD11 gene, p.(Tyr1715*), in the proband with the more complex phenotype. The reassessment of the phenotypic features confirmed that the patient fulfilled the proposed diagnostic criteria for KBG syndrome, although complicated by early-onset isolated febrile seizures. EEG abnormalities with or without seizures have been reported previously in some KBG cases. The shared variant, occurring in SCN9A, has been previously found in several individuals with GEFS+ and Dravet syndrome. CONCLUSIONS: This report describe a novel de novo variant in ANKRD11 causing a mild phenotype of KGB syndrome and further supports the association of monogenic pattern of SCN9A mutations with GEFS+. Our data expand the allelic spectrum of ANKRD11 mutations, providing the first Brazilian case of KBG syndrome. Furthermore, this study offers an example of how WES has been instrumental allowing us to better dissect the clinical phenotype under study, which is a multilocus variation aggregating in one proband, rather than a phenotypic expansion associated with a single genomic locus, underscoring the role of multiple rare variants at different loci in the etiology of clinical phenotypes making problematic the diagnostic path. The successful identification of the causal variant in a gene may not be sufficient, making it necessary to identify other variants that fully explain the clinical picture. The prevalence of blended phenotypes from multiple monogenic disorders is currently unknown and will require a systematic re-analysis of large WES datasets for proper diagnosis in daily practice.

Terminal osseous dysplasia with pigmentary defects (TODPD) in a Turkish girl with new skin findings.

Terminal osseous dysplasia with pigmentary defects (TODPD; MIM #300244) is an extremely rare, X-linked dominant, in utero male-lethal disease, characterized by skeletal dysplasia of the limbs, pigmentary defects of the skin, and recurrent digital fibromatosis of childhood. Delayed/abnormal ossification of bones of the hands and feet, joint contractures, and dysmorphic facial features may accompany. A single recurrent mutation (c.5217 G>A) of the FLNA gene which causes cryptic splicing was identified as the cause of the disease. We here present the first TODPD case from Turkey with full-blown phenotype who exhibit unique additional findings, hypopigmented patch on the lower extremity following Blaschko's lines and smooth muscle hamartoma of the scalp in review of all the previously reported TODPD cases.

Diagnostic strategy in segmentation defect of the vertebrae: a retrospective study of 73 patients.

BACKGROUND: Segmentation defects of the vertebrae (SDV) are non-specific features found in various syndromes. The molecular bases of SDV are not fully elucidated due to the wide range of phenotypes and classification issues. The genes involved are in the Notch signalling pathway, which is a key system in somitogenesis. Here we report on mutations identified in a diagnosis cohort of SDV. We focused on spondylocostal dysostosis (SCD) and the phenotype of these patients in order to establish a diagnostic strategy when confronted with SDV. PATIENTS AND METHODS: We used DNA samples from a cohort of 73 patients and performed targeted sequencing of the five known SCD-causing genes (DLL3, MESP2, LFNG, HES7 and TBX6) in the first 48 patients and whole-exome sequencing (WES) in 28 relevant patients. RESULTS: Ten diagnoses, including four biallelic variants in TBX6, two biallelic variants in LFNG and DLL3, and one in MESP2 and HES7, were made with the gene panel, and two diagnoses, including biallelic variants in FLNB and one variant in MEOX1, were made by WES. The diagnostic yield of the gene panel was 10/73 (13.7%) in the global cohort but 8/10 (80%) in the subgroup meeting the SCD criteria; the diagnostic yield of WES was 2/28 (8%). CONCLUSION: After negative array CGH, targeted sequencing of the five known SCD genes should only be performed in patients who meet the diagnostic criteria of SCD. The low proportion of candidate genes identified by WES in our cohort suggests the need to consider more complex genetic architectures in cases of SDV.

Further delineation of Malan syndrome.

Malan syndrome is an overgrowth disorder described in a limited number of individuals. We aim to delineate the entity by studying a large group of affected individuals. We gathered data on 45 affected individuals with a molecularly confirmed diagnosis through an international collaboration and compared data to the 35 previously reported individuals. Results indicate that height is > 2 SDS in infancy and childhood but in only half of affected adults. Cardinal facial characteristics include long, triangular face, macrocephaly, prominent forehead, everted lower lip, and prominent chin. Intellectual disability is universally present, behaviorally anxiety is characteristic. Malan syndrome is caused by deletions or point mutations of NFIX clustered mostly in exon 2. There is no genotype-phenotype correlation except for an increased risk for epilepsy with 19p13.2 microdeletions. Variants arose de novo, except in one family in which mother was mosaic. Variants causing Malan and Marshall-Smith syndrome can be discerned by differences in the site of stop codon formation. We conclude that Malan syndrome has a well recognizable phenotype that usually can be discerned easily from Marshall-Smith syndrome but rarely there is some overlap. Differentiation from Sotos and Weaver syndrome can be made by clinical evaluation only.

Severe rhizomelic shortening in a child with a complex duplication/deletion rearrangement of chromosome X.

Mesomelic and rhizo-mesomelic dysplasias are a group of disorders characterized by abnormal shortening of the limbs. One of the most common causes of mesomelic shortening is the loss of the transcription factor SHOX. In this clinical report, we present a patient who in addition to mesomelic shortening has severe rhizomelic shortening and developmental delay. Karyotyping revealed a recombinant X chromosome in which the region distal to Xp22.33 (where SHOX is found) was replaced with material from Xq28. Included in the region distal to Xq28 is the gene MECP2 and this patient presents with features of MECP2 duplication syndrome. We find that this patient has skeletal features not typical with the loss of SHOX that are likely explained by the rearrangement of the X chromosome. Further delineation of this rearrangement may allow for the identification of additional genetic mechanisms critical for the development of the limbs.

Elsahy-Waters syndrome is caused by biallelic mutations in CDH11.

Elsahy-Waters syndrome (EWS), also known as branchial-skeletal-genital syndrome, is a distinct dysmorphology syndrome characterized by facial asymmetry, broad forehead, marked hypertelorism with proptosis, short and broad nose, midface hypoplasia, intellectual disability, and hypospadias. We have recently published a homozygous potential loss of function variant in CDH11 in a boy with a striking resemblance to EWS. More recently, another homozygous truncating variant in CDH11 was reported in two siblings with suspected EWS. Here, we describe in detail the clinical phenotype of the original CDH11-related patient with EWS as well as a previously unreported EWS-affected girl who was also found to have a novel homozygous truncating variant in CDH11, which confirms that EWS is caused by biallelic CDH11 loss of function mutations. Clinical features in the four CDH11 mutation-positive individuals confirm the established core phenotype of EWS. Additionally, we identify upper eyelid coloboma as a new, though infrequent clinical feature. The pathomechanism underlying EWS remains unclear, although the limited phenotypic data on the Cdh11-/- mouse suggest that this is a potentially helpful model to explore the craniofacial and brain development in EWS-affected individuals.

Update on treatment of adolescent Blount disease.

PURPOSE OF REVIEW: Treatments available to correct adolescent Blount disease deformities differ in terms of features, advantages, and disadvantages. Each is indicated, therefore, for different scenarios of severity, physeal condition, and maturity. The purpose of this review is to update basic concepts, surgical treatments, and controversies concerning this disorder. RECENT FINDINGS: The cause of Blount disease is unknown although etiologic factors as morbid obesity and hypovitaminosis D are thought to be associated with it. Recently, semiinvasive techniques (guided growth) have been proposed for mild deformities but remain controversial. Osteotomies with external fixation (hexapodes) are still the most recommended corrective treatment in this condition. SUMMARY: Little is known about the origin and natural history of Blount disease. Treatment is always surgical and, given their complexity, should be preceded by a thorough analysis and planning regarding all deformities. Treatment principles are to correct the three-dimensional deformity and avoid recurrence. The choice of technique mainly depends on patient maturity and severity. Guided growth is a good choice for more immature patients with moderate deformities. Progressive correction using osteotomy or physeal distraction is indicated for patients with severe deformities and low remaining growth. The Taylor spatial frame is currently the most popular progressive correction device.

Proximal Femoral Growth Modification: Effect of Screw, Plate, and Drill on Asymmetric Growth of the Hip.

BACKGROUND: Guided growth has long been used in the lower extremities but has not been applied to varus or valgus deformity in the hip, as may occur in children with cerebral palsy or developmental dysplasia of the hip. The purpose of this study was to determine if screw, plate, or drilling techniques decreased the femoral neck-shaft angle (NSA) and articular trochanteric disease (ATD), as well as describe growth plate structural changes with each method. METHODS: Twelve 8-week-old lambs underwent proximal femoral hemiepiphysiodesis (IACUC approved) using either a screw (n=4), plate (n=4), or drilling procedure (n=4). Postoperative time was 6 months. Radiographs taken after limb harvest were used to measure NSA and ATD. Differences between treated and control sides were determined by 1-tailed paired t tests and Bonferroni (α=0.05/3). Histology was obtained for 1 limb pair per group. Proximal femurs were cut in midcoronal plane and the longitudinal growth plates were examined for structural changes. RESULTS: The mean NSA measured 7 degrees less than controls in this model using the screw technique, and this difference was statistically significant. Differences between the control and the treated groups did not reach statistical significance for either the plate or the drill group. Differences in ATD were not statistically significant, although there was a trend for larger ATD measurements using the screw technique. Histologically, physeal changes were observed on the operative sides in screw and plate specimens, but not drill specimens, compared with contralateral sham control. The screw specimen exhibited the most severe changes, with growth plate closure over half the section. The plate specimen showed focal loss of the physis across the section, but with no evidence of closure. CONCLUSIONS: This study builds on previous work that indicates screw hemiepiphysiodesis can effectively alter the shape of the proximal femur, and result in a lower neck-shaft ankle (or lesser valgus). This study suggests that implantation of a screw is likely to be more effective than a plate or drilling procedure in decreasing the NSA in skeletally immature hips. CLINICAL SIGNIFICANCE: If further preclinical, and later clinical, studies demonstrate reproducible efficacy, guided growth of the proximal femur may eventually become a viable option for treatment or prevention of hip deformity in select patients.

Short stature, unusual face, delta phalanx, and abnormal vertebrae and ribs in a girl born to half-siblings.

Delta phalanx is a rare abnormality typically associated with additional features. We describe a patient with a phenotype resembling Catel-Manzke syndrome, but with delta phalanx and abnormal vertebrae and ribs. The patient was the only child of half siblings born with a marked prenatal growth deficiency. At 10 years of age, she had a short stature, long face, long and tubular nose with small alae nasi, high palate, short and broad thorax, and short index fingers with radial deviation. There were hyperpigmentations following Blaschko's lines. Radiology showed a proximal delta phalanx in the index finger of hands, abnormal vertebrae, and fused and small ribs. GTG-Banding karyotype and microarray analysis yielded normal results. Exome sequencing identified 25 genes that harbored homozygous variants, but none of these is assumed to be a good candidate to explain (part of) the phenotype. The here described patient may have a new condition, possibly following an autosomal recessive pattern of inheritance, although due to the high degree of consanguinity a compound etiology of the phenotype by variants in various genes may be present as well.

Guided Growth Implant Failure is a Result of Cyclic Fatigue: Explant Analysis With Scanning Electron Microscopy.

BACKGROUND: Guided growth is often used to correct limb deformity and yet implant screw failure in modular systems has been reported. There have been no reports of plate failure and we do not know the exact mode of failure when screws do break. METHODS: We report the first published case of a fractured plate in a modular plate and screw construct that was used to correct Blount disease in a child through guided growth. The implants were removed and analyzed for method of failure using scanning electron microscopy. RESULTS: Scanning electron microscopy of the explant confirms that the mode of failure was not a result of static tension from growth. Rather, analysis confirms cyclic fatigue that led to crack propagation across the anterior side of the plate until overload caused complete plate failure. CONCLUSIONS: This analysis confirms an in vivo cyclic compression-relaxation of the growth plate presumably to weight-bearing, and that when excessive may lead to implant failure as seen here in this case. LEVEL OF EVIDENCE: Level V.

A second family with CATSHL syndrome: Confirmatory report of another unique FGFR3 syndrome.

Here we describe the second reported family with the CATSHL syndrome, a condition resulting from a unique mutation in the fibroblast growth factor receptor 3 (FGFR3) gene. Our family confirms the consistent and unique phenotype of this condition, and the specificity of the mutation in FGFR3. The CATSHL syndrome appears to be an autosomal dominant disorder with full penetrance. © 2016 Wiley Periodicals, Inc.

Osteoblast dysfunctions in bone diseases: from cellular and molecular mechanisms to therapeutic strategies.

Several metabolic, genetic and oncogenic bone diseases are characterized by defective or excessive bone formation. These abnormalities are caused by dysfunctions in the commitment, differentiation or survival of cells of the osteoblast lineage. During the recent years, significant advances have been made in our understanding of the cellular and molecular mechanisms underlying the osteoblast dysfunctions in osteoporosis, skeletal dysplasias and primary bone tumors. This led to suggest novel therapeutic approaches to correct these abnormalities such as the modulation of WNT signaling, the pharmacological modulation of proteasome-mediated protein degradation, the induction of osteoprogenitor cell differentiation, the repression of cancer cell proliferation and the manipulation of epigenetic mechanisms. This article reviews our current understanding of the major cellular and molecular mechanisms inducing osteoblastic cell abnormalities in age-related bone loss, genetic skeletal dysplasias and primary bone tumors, and discusses emerging therapeutic strategies to counteract the osteoblast abnormalities in these disorders of bone formation.

Prevalence of Hypertension in Pediatric Tibia Vara and Slipped Capital Femoral Epiphysis.

BACKGROUND: Slipped capital femoral epiphysis (SCFE) and tibia vara (Blount disease) are associated with childhood obesity. However, the majority of obese children do not develop SCFE or tibia vara. Therefore, it is hypothesized that other obesity-related biological changes to the physis, in addition to increased biomechanical stress, potentiate the occurrence of SCFE and tibia vara. Considering that hypertension can impose pathologic changes in the physis similar to those observed in these obesity-related diseases we set out to determine the prevalence of hypertension in patients with SCFE and tibia vara. METHODS: Blood pressure measurements were obtained in 44 patients with tibia vara and 127 patients with SCFE. Body mass index and blood pressure were adjusted for age, sex, and height percentiles utilizing normative distribution data from the CDC. These cohorts were compared with age-matched and sex-matched cohorts derived from an obesity clinic who did not have either bone disease. A multivariable proportional odds model was used to determine association. RESULTS: The prevalence of prehypertension/hypertension was significantly higher in the tibia vara (64%) and SCFE cohort (64%) compared with respective controls (43%). Patients diagnosed with either SCFE or tibia vara had 2.5-fold higher odds of having high blood pressure compared with age-matched and sex-matched obese patients without bone disease. Sex, age, and race did not have a significant effect on a patient's blood pressure. CONCLUSIONS: This is the first study to establish that the obesity-related bone diseases, SCFE and tibia vara, are significantly associated with high blood pressure. These data have immediate clinical impact as they demonstrate that children with obesity-related developmental bone disease have increased prevalence of undiagnosed and untreated hypertension. Furthermore, this prevalence study supports the hypothesis that hypertension in conjunction with increased biomechanical forces together potentiate the occurrence of SCFE and tibia vara. If proven true, it is plausible that hypertension may represent a modifiable risk factor for obesity-related bone disease. LEVEL OF EVIDENCE: Level III-case-control study.

Ribosome biogenesis in skeletal development and the pathogenesis of skeletal disorders.

The skeleton affords a framework and structural support for vertebrates, while also facilitating movement, protecting vital organs, and providing a reservoir of minerals and cells for immune system and vascular homeostasis. The mechanical and biological functions of the skeleton are inextricably linked to the size and shape of individual bones, the diversity of which is dependent in part upon differential growth and proliferation. Perturbation of bone development, growth and proliferation, can result in congenital skeletal anomalies, which affect approximately 1 in 3000 live births [1]. Ribosome biogenesis is integral to all cell growth and proliferation through its roles in translating mRNAs and building proteins. Disruption of any steps in the process of ribosome biogenesis can lead to congenital disorders termed ribosomopathies. In this review, we discuss the role of ribosome biogenesis in skeletal development and in the pathogenesis of congenital skeletal anomalies. This article is part of a Special Issue entitled: Role of the Nucleolus in Human Disease.