Identification and Characterization of a Novel CLCN7 Variant Associated with Osteopetrosis

Abstract

Osteopetrosis is a group of rare inheritable disorders of the skeleton characterized by increased bone density. The disease is remarkably heterogeneous in clinical presentation and often misdiagnosed. Therefore, genetic testing and molecular pathogenicity analysis are essential for precise diagnosis and new targets for preventive pharmacotherapy. Mutations in the CLCN7 gene give rise to the complete spectrum of osteopetrosis phenotypes and are responsible for about 75% of cases of autosomal dominant osteopetrosis. In this study, we report the identification of a novel variant in the CLCN7 gene in a patient diagnosed with osteopetrosis and provide evidence for its significance (likely deleterious) based on extensive comparative genomics, protein sequence and structure analysis. A set of automated bioinformatics tools used to predict consequences of this variant identified it as deleterious or pathogenic. Structure analysis revealed that the variant is located at the same “hot spot” as the most common CLCN7 mutations causing osteopetrosis. Deep phylogenetic reconstruction showed that not only Leu614Arg, but any non-aliphatic substitutions in this position are evolutionarily intolerant, further supporting the deleterious nature of the variant. The present study provides further evidence that reconstructing a precise evolutionary history of a gene helps in predicting phenotypical consequences of variants of uncertain significance.

CRISPR/Cas9-Mediated Gene Correction in Osteopetrosis Patient-Derived iPSCs

“…Biallelic CLCN7 mutations and single allele CLCN7 mutations account for severe forms of osteopetrosis and ADO2, respectively. Despite that the mutations in CLCN7 gene, such as R286W [20], L614R [30], A511P [31], R784W [32], G793R [33], etc., have been intensively studied by virtue of the development of genomic sequenc- ing, the precise mechanism of CLCN7-related osteopetrosis remains twilight. Therefore, more efforts are necessary to unveil the disease.…”

<p>Subtrochanteric Femoral Fracture in a Patient with Osteopetrosis: Treated with Internal Fixation and Complicated by Intraoperative Femoral Neck Fracture</p>

“…15 Mutations in T cell immune regulator 1 (TCIRG1), chloride channel 7 (CLCN7), osteopetrosis-associated transmembrane protein 1, sorting nexin 10, and pleckstrin homology and RUN domain containing M1 lead to osteoclast-rich ARO, in which the osteoclasts are abundant but have severely impaired resorptive function. 16 More than 50% of ARO cases are caused by mutations in the TCIRG1 gene. 11 TCIRG1-mutated osteoclasts have a defective ruffled border and significantly reduced resorptive activity.…”

“…18 CLCN7 is essential for bone remodeling, and mutations of the CLCN7 gene make the bone brittle. 16 Mutations in TNFSF11 (also known as RANKL) and its receptor TNFRSF11A (also known as RANK) lead to osteoclast-poor ARO. 19 IAO is attributed to hypomorphic mutations in the NF-κB essential regulator gene.…”