Identification And Mutation Analysis Of Pathogenic Genes In Chinese Families With Osteopetrosis

Aims: We conducted a genetic study of a rare disease(osteopetrosis)and a common disease(osteoporosis)in bone metabolism from the perspective of individual and group.The objectives of the study were: 1)to identify and analyze the pathogenic genes of patients with osteopetrosis,and also investigate the clinical manifestations and biochemical characteristics for better understanding of osteopetrosis phenotypes;2)to evaluate the association of serum osteocalcin with bone mineral density(BMD)in postmenopausal women of Shanghai and to observe the relationships between single-nucleotide polymorphisms(SNPs)and haplotypes in and around the osteocalcin gene with osteocalcin and BMD.Methods: In the study of osteopetrosis,we recruited 16 families that have been diagnosed or suspected osteopetrosis clinically but had not been reported.We analyzed the inheritance patterns,clinical manifestations,biochemical changes and radiographic features of the probands,extracted their DNA and amplified common genes(CLCN7?TCIRG1).For those whose mutation was not found,Next Generation Sequencing(NGS)was adopted for further screening of other known or suspected virulence genes.A cross-sectional study was conducted with 725 postmenopausal Chinese women.Routine biomarkers and bone turnover markers(BTMs)were measured.The BMD of lumbar spine ? femoral neck and total hip was measured by dual-energy X-ray absorptiometry(DXA).Nine SNPs of the osteocalcin gene(rs1543294,rs1800247,rs759330,rs2842880,rs933489,rs2241106,rs2758605,rs2277872,rs12563631)were genotyped.Results: We identified four TCIRG1-dependent ARO families,of which three displayed life-threatening symptoms,one who received HSCT(hematopoietic stem cell transplantation)survived,the other family manifested benign symptoms,we found a total of 7 mutations of TCIRG1 mutations,5 of which were novel;we also identified 8 CLCN7-dependent families including 7 ADO families and 1 ARO,found a total of 9 mutations,4 of which were novel,virulence genes of the other 4 families remained unknown.Osteocalcin was negatively correlated with BMD at femoral neck(P=0.027)and total hip(P=0.043).The significance existed after adjustment of age and BMI.The haplotype CTAGCCTC showed correlation with BMD at femoral neck(P=0.027),but this significance disappeared after FDR correction,none association was obtained between the SNPs,haplotypes of the osteocalcin gene and BMD or osteocalcin.Conclusion: Our study showed that CLCN7-depentdent ADO? was the most common type of osteopetrosis in China,patients with TCIRG1-dependent ARO displayed symptoms from mild to fatal,the fatal form urgently need HSCT(hematopoietic stem cell transplantation)treatment;we also reported for the first time that mutations of TCIRG1 were responsible for benign ARO in Chinese population;in addition,there are new pathogenic genes of osteopetrosis to be found.In the study of osteoporosis,our results suggested that osteocalcin was correlated with BMD at femoral neck and total hip.Common genetic variants of osteocalcin gene may not be a major contributor to variations in serum osteocalcin or BMD in postmenopausal Chinese women.