Ajmal Muhammad, Mir Asif, Wahid Sughra, Khor Chiea Chuen, Foo Jia Nee, Siddiqi Saima, Kauser Mehran, Malik Salman Akbar, Nasir Muhammad
Institute of Biomedical and Genetic Engineering, 24-Mauve area, G-9/1, Islamabad, 44000, Pakistan.
Department of Biotechnology, International Islamic university, Islamabad, Pakistan.
BMC Med Genet. 2017 Dec 13;18(1):148. doi: 10.1186/s12881-017-0506-4.
Osteopetrosis is a rare inherited bone disorder mainly described as an increased bone density caused by defective osteoclastic bone resorption. To date, genetic variants of eleven genes have been reported so far to be associated with different types of osteopetrosis. However, malignant infantile osteopetrosis, a lethal form of the disease, is mostly (50%) caused by mutation(s) in TCIRG1 gene. In this study, we investigated a consanguineous Pakistani family clinically and genetically to elucidate underlying molecular basis of the infantile osteopetrosis.
DNA samples from five family members were subjected to SNP-array based whole genome homozygosity mapping. Data was analyzed and potentially pathogenic mutation was identified by Sanger sequencing of two affected as well as three phenotypically healthy individuals in the family. The significance of identified pathogenic variation and its impact on protein structure and function was studied using various bioinformatics tools.
DNA samples from five family members were subjected to genome-wide SNP array genotyping and homozygosity mapping which identified ~4 Mb region on chr11 harboring the TCIRG1 gene. Sanger sequencing unveiled a novel homozygous deletion c. 624delC in exon 6 of the TCIRG1 gene encodes a3 subunit of V-ATPase complex. The identified deletion resulted in a frame shift producing a truncated protein of 208 aa. In silico analysis of premature termination of the a3 subunit of V-ATPase complex revealed deleterious effects on the protein structure, predicting impaired or complete loss of V-ATPase function causing infantile osteopetrosis.
Since a3 subunit of V-ATPase complex plays a crucial role in bone resorption process, structurally abnormal a3 subunit might have adversely affected bone resorption process, leading to infantile osteopetrosis in Pakistani family. Therefore, the present study not only expands the genotypic spectrum of osteopetrosis but also improve understandings of the role of V-ATPase a3 subunit in bone resorption process. Moreover, our findings should help in genetic counseling and provide further insight into the disease pathogenesis and potential targeted therapy.
骨质石化症是一种罕见的遗传性骨病，主要表现为破骨细胞骨吸收缺陷导致骨密度增加。迄今为止，已有11个基因的遗传变异被报道与不同类型的骨质石化症相关。然而，恶性婴儿型骨质石化症是该疾病的一种致命形式，主要（50%）由TCIRG1基因突变引起。在本研究中，我们对一个巴基斯坦近亲家庭进行了临床和遗传学调查，以阐明婴儿型骨质石化症的潜在分子基础。
对五名家庭成员的DNA样本进行基于单核苷酸多态性（SNP）芯片的全基因组纯合性图谱分析。对数据进行分析，并通过对该家庭中两名患病个体以及三名表型健康个体进行桑格测序，鉴定出潜在的致病突变。使用各种生物信息学工具研究已鉴定的致病变异的意义及其对蛋白质结构和功能的影响。
对五名家庭成员的DNA样本进行全基因组SNP芯片基因分型和纯合性图谱分析，确定了11号染色体上约4 Mb的区域，该区域包含TCIRG1基因。桑格测序揭示了一个新的纯合缺失c.624delC，位于TCIRG1基因外显子6中，该基因编码V-ATP酶复合物的a3亚基。所鉴定的缺失导致移码，产生一个208个氨基酸的截短蛋白。对V-ATP酶复合物a3亚基过早终止的计算机分析显示对蛋白质结构有有害影响，预测V-ATP酶功能受损或完全丧失，从而导致婴儿型骨质石化症。
由于V-ATP酶复合物的a3亚基在骨吸收过程中起关键作用，结构异常的a3亚基可能对骨吸收过程产生不利影响，导致该巴基斯坦家庭出现婴儿型骨质石化症。因此，本研究不仅扩展了骨质石化症的基因型谱，还增进了对V-ATP酶a3亚基在骨吸收过程中作用的理解。此外，我们的发现应有助于遗传咨询，并为疾病发病机制和潜在的靶向治疗提供进一步的见解。
