A novel homozygous splice site variant in the CLCN7 causes osteopetrosis

Abstract

Objectives: Osteopetrosis is a monogenic disorder represented by disturbed osteoclast resorption or osteoclastogenesis differentiation. Clinical symptoms are intensive and brittle bones, recurrent fractures, thrombocytopenia, impaired immune function, optic nerve compression, and anemia. Several osteopetrosis-causing genes have been identified and reported. Methods: The present study describes two consanguineous Saudi families segregating a severe autosomal recessive osteopetrosis disease. A single proband (II-2) in family A and two probands (II-2; II-4) in family B exhibited increased bone density, multiple fractures, teeth abnormalities, bilateral optic atrophy with nystagmus, and progressive blindness. DNA of the affected individuals was exposed to whole-exome sequencing (WES) and Sanger sequencing. Further, reverse transcriptase-polymerase chain reaction (RT-PCR) and western blotting analysis were done to investigate the impact of the identified mutation. Results: WES revealed a novel homozygous splice site variant (c.739-18G > A) in the CLCN7 gene on chromosome 16p13.3, segregating perfectly with the disorder phenotype. RT-PCR resulted in the retention of a 50 bp sequence of intron 8 in the mutated sequence. As a result, this variant resulted in a large size exon 9 compared to the wild type. In addition, the western blot revealed the heteromeric form of ClC-7 disappeared in the patient’s fibroblasts versus the control, indicating identified variant pathogenicity. Conclusion: The present research provides certain proof that homozygous variants in the CLCN7 gene are responsible for intense osteopetrosis disorders with diverse phenotypes. These findings have significant implications for decisions regarding the clinical therapeutic regimen, prognosis assessment, and antenatal diagnosis.

Keywords

• CLCN7
• Osteopetrosis
• Osteoclast
• Splice site variant
• Autosomal recessive