Endocrinol Metab.  2018 Sep;33(3):380-386. 10.3803/EnM.2018.33.3.380.

Genetic Analysis of CLCN7 in an Old Female Patient with Type II Autosomal Dominant Osteopetrosis

• Kim SY
• Lee Y
• Kang YE
• Kim JM
• Joung KH
• Lee JH
• Kim KS
• Kim HJ
• Ku BJ
• Shong M
• Yi HS

• KMID: 2447028
• DOI: http://doi.org/10.3803/EnM.2018.33.3.380

Abstract

BACKGROUND
Type II autosomal dominant osteopetrosis (ADO II) is a rare genetically heterogeneous disorder characterized by osteosclerosis and increased bone mass, predominantly involving spine, pelvis, and skull. It is closely related to functional defect of osteoclasts caused by chloride voltage-gated channel 7 (CLCN7) gene mutations. In this study, we aimed to identify the pathogenic mutation in a Korean patient with ADO II using whole exome sequencing.
METHODS
We evaluated the clinical, biochemical, and radiographic analysis of a 68-year-old woman with ADO II. We also performed whole exome sequencing to identify pathogenic mutation of a rare genetic disorder of the skeleton. Moreover, a polymorphism phenotyping program, Polymorphism Phenotyping v2 (PolyPhen-2), was used to assess the effect of the identified mutation on protein function.
RESULTS
Whole exome sequencing using peripheral leukocytes revealed a heterozygous c.296A>G missense mutation in the CLCN7 gene. The mutation was also confirmed using Sanger sequencing. The mutation c.296A>G was regarded to have a pathogenic effect by PolyPhen-2 software.
CONCLUSION
We detect a heterozygous mutation in CLCN7 gene of a patient with ADO II, which is the first report in Korea. Our present findings suggest that symptoms and signs of ADO II patient having a c.296A>G mutation in CLCN7 may appear at a very late age. The present study would also enrich the database of CLCN7 mutations and improve our understanding of ADO II.

Keyword

Type 2 autosomal dominant osteopetrosis; CLCN7 gene; Osteosclerosis; Whole exome sequencing

MeSH Terms

Aged
Exome
Female*
Humans
Korea
Leukocytes
Mutation, Missense
Osteoclasts
Osteopetrosis*
Osteosclerosis
Pelvis
Skeleton
Skull
Spine

Figure

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  Fig. 1 Radiographic signatures of the patient with type II autosomal dominant osteopetrosis. (A) Mile sclerosis of skull base and cortical thickening (arrowhead). (B) Cortical thickening (arrowheads) in femurs. LAT-LT, lateral-left.

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  Fig. 2 Bone mineral density (BMD), T and Z score in the patient with type II autosomal dominant osteopetrosis. (A) BMD at lumbar spine. (B) BMD at left femur. The reference data for the Z score was calculated from healthy Asian people of the same age and sex. BMC, bone mineral content.

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  Fig. 3 Whole-body bone scintigraphy with technetium 99m-methyl diphosphonate. Tracer uptake in proximal epiphysis of both the humeri, tibias and fibulas, head and acetabulum of the femurs was increased. Faint visualization of both kidneys and bladder. RT, right; IV, intravenous; ANT, anterior; POST, posterior.

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  Fig. 4 Genetic analysis of chloride voltage-gated channel 7 (CLCN7) gene in the patient with type II autosomal dominant osteopetrosis (ADO II). Direct DNA sequencing of the patients with ADO II; arrow indicates a heterozygous A-to-G transition at c.296 in exon 4, leading to p.Tyr99Cys.

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  Fig. 5 Alignment of the product of chloride voltage-gated channel 7 (CLCN7) indicating the conservation of mutated residues (Y99C) among different species.

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  Fig. 6 Polymorphism Phenotyping v2 (PolyPhen-2) can predict the possible impact of amino acid substitutions on the stability and function of human proteins using structural and comparative evolutionary considerations. The missense mutations Y99C in chloride voltage-gated channel 7 (CLCN7) were predicted to have a pathogenic effect.

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