Osteoporosis-Pseudoglioma in a Mauritanian Child due to a Novel Mutation in LRP5

Clinical Response to Treatment with Teriparatide in an Adolescent with Osteoporosis-Pseudoglioma Syndrome (OPPG): A Case Report

INTRODUCTION

Osteoporosis-pseudoglioma syndrome (OPPG) is a rare autosomal recessive disorder characterized by severe osteoporosis and eye abnormalities that leads to vision loss. In this study, we report the outcome of a short period of treatment with teriparatide in one patient with OPPG.

CASE PRESENTATION

The patient was a 17-year-old girl who suffered a bone fracture at the age of two and was diagnosed with OPPG at the age of three. Genetic testing was performed for the patient, and a novel homozygous nonsense mutation (c.351G>A) in exon 2 of the LRP5 gene was reported. She was treated with pamidronate, but the bone fracture increased, and the disability progressed. Therefore, at the age of 11 years and nine months, teriparatide was administered subcutaneously at a dose of 20 micrograms per day for four consecutive months. After the treatment with teriparatide, physical activity was achieved, and no further fractures were observed besides the gradual rise in bone mineral density (BMD) (from 0.532 to 0.711 gr/cm² in lumbar spine and 0.372 to 0.635 gr/cm² in femur neck).

CONCLUSIONS

In children and adolescents diagnosed with OPPG who do not respond to other conventional therapies, short courses of teriparatide therapy may be helpful.

Emerging insights into the comparative effectiveness of anabolic therapies for osteoporosis

Over the past three decades, the mainstay of treatment for osteoporosis has been antiresorptive agents (such as bisphosphonates), which have been effective with continued administration in lowering fracture risk. However, the clinical landscape has changed as adherence to these medications has declined due to perceived adverse effects. As a result, decreases in hip fracture rates that followed the introduction of bisphosphonates have now levelled off, which is coincident with a decline in the use of the antiresorptive agents. In the past two decades, two types of anabolic agents (including three new drugs), which represent a novel approach to improving bone quality by increasing bone formation, have been approved. These therapies are expected to lead to a new clinical paradigm in which anabolic agents will be used either alone or in combination with antiresorptive agents to build new bone and reduce fracture risk. This Review examines the mechanisms of action for these anabolic agents by detailing their receptor-activating properties for key cell types in the bone and marrow niches. Using these advances in bone biology as context, the comparative effectiveness of these anabolic agents is discussed in relation to other therapeutic options for osteoporosis to better guide their clinical application in the future.

Pathway Mutations in Breast Cancer Using Whole-Exome Sequencing

The genomic landscape of breast cancer (BC) is complex. The purpose of this study was to decipher the mutational profiles of Taiwanese patients with BC using next-generation sequencing. We performed whole-exome sequencing on DNA from 24 tumor tissue specimens from BC patients. Sanger sequencing was used to validate the identified variants. Sanger sequencing was also performed on paired adjacent nontumor tissues. After genotype calling and algorithmic annotations, we identified 49 deleterious variants in canonical cancer-related genes in our BC cohort. The most frequently mutated genes were PIK3CA (16.67%), FKBP9 (12.5%), TP53 (12.5%), ATM (8.33%), CHEK2 (8.33%), FOXO3 (8.33%), NTRK1 (8.33%), and NUTM2B (8.33%). Seven mutated variants (ATR p.V1581fs, CSF1R p.R579Q, GATA3 p.T356delinsTMKS, LRP5 p.W389*, MAP3K1 p.T918fs, MET p.K1161fs, and MTR p.P1178S) were novel variants that are not present in any gene mutation database. After grouping the samples according to molecular subtype, we found that the cell cycle, MAPK, and chemokine signaling pathways in the luminal A subtype of BC; the focal adhesion, axon guidance, and endocytosis pathways in the luminal B subtype; and amyotrophic lateral sclerosis in the basal-like subtype were exclusively altered. Survival curve analysis showed that the presence of the MAPK signaling pathway and endocytosis mutations were correlated with a poor prognosis. These survival data were consistent with cBioPortal analyses of 2,051 BC cases. We discovered novel mutations in patients with BC. These results have implications for developing strategic, adjuvant, and gene-targeted therapies.

BMP4 mutations in tooth agenesis and low bone mass

OBJECTIVE

To identify an uncommon genetic cause of tooth agenesis (TA) by utilizing whole exome sequencing (WES) and targeted Sanger sequencing in a cohort of 120 patients with isolated TA.

DESIGN

One deleterious mutation in the gene encoding bone morphogenetic protein 4 (BMP4) was identified in 6 unrelated patients with TA by WES. After that, the coding exons of BMP4 were examined in 114 TA patients using Sanger sequencing. Dual-energy X-ray absorptiometry (DEXA) was used to measure the bone mineral density of patients who carried a BMP4 mutation. Finally, preliminary functional studies of two BMP4 mutants were performed.

RESULTS

We detected 3 novel missense mutations (c.58 G > A: p.Gly20Ser, c.326 G > T: p.Arg109Leu and c.614 T > C: p.Val205Ala) and 1 reported mutation in the BMP4 gene among 120 TA probands. The previously reported BMP4 mutation (c.751C > T: p.His251Tyr) was associated with urethra and eye anomalies. By extending the pedigrees, we determined that the tooth phenotypes had an autosomal dominant inheritance pattern, as individuals carrying a BMP4 mutation exhibit different types of dental anomalies. Interestingly, we observed that patients harboring a BMP4 mutation manifested early onset osteopenia or osteoporosis. Further in vitro functional assays demonstrated that two BMP4 mutants resulted in a decreased activation of Smad signaling. Therefore, a loss-of-function in BMP4 may contribute to the clinical phenotypes seen in this study.

CONCLUSIONS

We identified 4 mutations in the BMP4 gene in 120 TA patients. To our knowledge, this is the first study to describe human skeletal diseases associated with BMP4 mutations.

Sclerostin neutralization unleashes the osteoanabolic effects of Dkk1 inhibition

The WNT pathway has become an attractive target for skeletal therapies. High-bone-mass phenotypes in patients with loss-of-function mutations in the LRP5/6 inhibitor Sost (sclerosteosis), or in its downstream enhancer region (van Buchem disease), highlight the utility of targeting Sost/sclerostin to improve bone properties. Sclerostin-neutralizing antibody is highly osteoanabolic in animal models and in human clinical trials, but antibody-based inhibition of another potent LRP5/6 antagonist, Dkk1, is largely inefficacious for building bone in the unperturbed adult skeleton. Here, we show that conditional deletion of Dkk1 from bone also has negligible effects on bone mass. Dkk1 inhibition increases Sost expression, suggesting a potential compensatory mechanism that might explain why Dkk1 suppression lacks anabolic action. To test this concept, we deleted Sost from osteocytes in, or administered sclerostin neutralizing antibody to, mice with a Dkk1-deficient skeleton. A robust anabolic response to Dkk1 deletion was manifest only when Sost/sclerostin was impaired. Whole-body DXA scans, μCT measurements of the femur and spine, histomorphometric measures of femoral bone formation rates, and biomechanical properties of whole bones confirmed the anabolic potential of Dkk1 inhibition in the absence of sclerostin. Further, combined administration of sclerostin and Dkk1 antibody in WT mice produced a synergistic effect on bone gain that greatly exceeded individual or additive effects of the therapies, confirming the therapeutic potential of inhibiting multiple WNT antagonists for skeletal health. In conclusion, the osteoanabolic effects of Dkk1 inhibition can be realized if sclerostin upregulation is prevented. Anabolic therapies for patients with low bone mass might benefit from a strategy that accounts for the compensatory milieu of WNT inhibitors in bone tissue.

Novel PLS3 variants in X-linked osteoporosis: Exploring bone material properties

BACKGROUND

Idiopathic Juvenile Osteoporosis (IJO) refers to significantly lower than expected bone mass manifesting in childhood with no identifiable aetiology. IJO classically presents in early pubertal period with multiple fractures including metaphyseal and vertebral crush fractures, and low bone-mass.

METHODS

Here we describe two patients and provide information on their clinical phenotype, genotype and bone material analysis in one of the patients.

RESULTS

Patient 1: 40-year old adult male diagnosed with IJO in childhood who re-presented with a hip fracture as an adult. Genetic analysis identified a pathogenic PLS3 hemizygous variant, c.1765del in exon 16. Patient 2: 15-year old boy with multiple vertebral fractures and bone biopsy findings suggestive of IJO who also has a diagnosis of autism spectrum disorder. Genetic analysis identified a maternally inherited PLS3 pathogenic c.1295T>A variant in exon 12. Analyses of the transiliac bone sample revealed severe reduction of trabecular volume and bone turnover indices and elevated bone matrix mineralisation.

DISCUSSION

We propose that genetic testing for PLS3 should be undertaken in patients presenting with a current or previous history of IJO as this has implications for genetic counselling and cascade screening. The extensive evaluation of the transiliac biopsy sample of Patient 2 revealed a novel bone phenotype.

CONCLUSION

This report includes a review of IJO and genetic causes of osteoporosis, and suggests that existing cases of IJO should be screened for PLS3. Through analysis of bone material properties in Patient 2, we can conclude that PLS3 does have a role in bone mineralisation.