Potential blindness in children of patients with hereditary bone disease

Osteoporosis, Fractures, and Blindness Due to a Missense Mutation in the LRP5 Receptor

Familial exudative vitreoretinopathy (FEVR) is a genetic disorder whose presentation can include osteoporosis, multiple fractures, and incomplete retinal angiogenesis leading to retinal detachment and blindness if left untreated. Discussed herein are the cases of two pediatric siblings who presented to the orthopedic service with multiple fractures and, through interdisciplinary management, were diagnosed with FEVR and treated appropriately before permanent visual impairment. The skeletal manifestations of FEVR, which have not been explored in depth in prior literature, are described. One sibling presented to orthopedic services for evaluation of a closed distal radius fracture sustained while playing sports. A comprehensive history revealed he had suffered at least four appendicular fractures in his lifetime, and dual-energy x-ray absorptiometry (DEXA) scan revealed his bone density to be in the first percentile for his age. Concurrent evaluation of his younger sibling revealed a similar history of multiple fractures and low bone density. Referral to genetic services and ensuing whole-exome sequencing revealed a likely pathogenic variant in both siblings' LRP5 gene, the only known causative mutation for FEVR that leads to skeletal manifestations. While FEVR is well known in genetic and ophthalmologic settings, greater awareness of FEVR and other genetic disorders that predispose to fractures in pediatric populations is warranted in orthopedic settings. This will lead to reduced sequelae in pediatric patients with genetic disorders and improved interdisciplinary expertise. The story of these siblings illustrates that a high index of suspicion for genetic diseases is essential when treating children with osteoporosis and growth delays.

Osteoporosis-pseudoglioma syndrome in four new patients: identification of two novel LRP5 variants and insights on patients' management using bisphosphonates therapy

This study describes the clinical, radiological, and molecular data of four new patients with osteoporosis-pseudoglioma syndrome and assesses their response to bisphosphonate therapy.

INTRODUCTION

Osteoporosis-pseudoglioma syndrome (OPPG) is a very rare disorder characterized mainly by severe juvenile osteoporosis and congenital blindness. OPPG is caused by biallelic mutations in the gene encoding low-density lipoprotein receptor-related protein 5 (LRP5).

METHODS

We present the clinical, radiological, and molecular findings of four new patients with OPPG from Egypt. We also assessed patients' response to oral and intravenous bisphosphonate therapy.

RESULTS

All patients had reduced bone mineral density (BMD) with variable number of fractures per year, in addition to bone abnormalities and the characteristic eye phenotype associated with OPPG. Mutation analyses of LRP5 gene revealed three different homozygous variants including two novel ones, c.7delG (p.A3Qfs*80) and c.3280G > A (p.E1094K). The c.3280G > A (p.E1094K) was recurrent in two unrelated patients who shared a unique haplotype suggesting a possible founder effect. The use of bisphosphonate therapy was beneficial; however, intravenous bisphosphonate administration led to a more favorable response.

CONCLUSION

Our study described the phenotypic and genetic features of four patients with OPPG and identified two new LRP5 variants, thus expanding the mutational spectrum of OPPG. In addition, our study reinforces the efficiency of using intravenous bisphosphonates in the management of patients with OPPG.

Neogenin-loss in neural crest cells results in persistent hyperplastic primary vitreous formation

Neogenin is a transmembrane receptor critical for multiple cellular processes, including neurogenesis, astrogliogenesis, endochondral bone formation, and iron homeostasis. Here we present evidence that loss of neogenin contributes to pathogenesis of persistent hyperplastic primary vitreous (PHPV) formation, a genetic disorder accounting for ~ 5% of blindness in the USA. Selective loss of neogenin in neural crest cells (as observed in Wnt1-Cre; Neof/f mice), but not neural stem cells (as observed in GFAP-Cre and Nestin-Cre; Neof/f mice), resulted in a dysregulation of neural crest cell migration or delamination, exhibiting features of PHPV-like pathology (e.g. elevated retrolental mass), unclosed retinal fissure, and microphthalmia. These results demonstrate an unrecognized function of neogenin in preventing PHPV pathogenesis, implicating neogenin regulation of neural crest cell delamination/migration and retinal fissure formation as potential underlying mechanisms of PHPV.

Novel Homozygous LRP5 Mutations in Mexican Patients with Osteoporosis-Pseudoglioma Syndrome

AIMS

Osteoporosis-pseudoglioma syndrome (OPPG) is an uncommon autosomal recessive disorder characterized by the rare association of early-onset osteoporosis and severe ocular abnormalities such as persistent fetal vasculature and microphthalmia. Biallelic mutations in the low-density lipoprotein receptor-related protein-5 gene (LRP5) have been associated with OPPG. We present clinical and genetic data from three Mexican OPPG patients, a pair of sibs, and a sporadic case.

MATERIALS AND METHODS

Three patients underwent clinical examination, including a complete ophthalmic evaluation. Based on the clinical diagnosis of OPPG, the entire coding sequence of LRP5 was polymerase chain reaction-amplified and directly Sanger-sequenced. Genetic testing was extended to the parents of the affected patients.

RESULTS

Phenotypic variability was observed in the familial case and molecular analysis identified a novel homozygous c.1145C>T, p.(Pro382Leu) variant in both sibs. As expected, their parents were heterozygous carriers. The sporadic patient exhibited a severe osseous phenotype, microphthalmia, and neurological symptoms. In this patient, homozygosity for the c.442C>T, p.(Gln148*) variant was demonstrated, whereas her parents were heterozygous carriers. The p.(Pro382Leu) pathogenic mutation has been previously reported only in a compound heterozygous state in OPPG patients.

CONCLUSIONS

Two novel homozygous missense and nonsense variants were demonstrated in three OPPG cases from Mexico. Our results expand the spectrum of disease-causing LRP5 mutations. This is the first report of OPPG in our population and our findings may potentially add to a genotype-phenotype correlation.