A Large Sample Of Osteogenesis Imperfecta Genotype-phenotype Relationship And The Effect Of Zoledronic Acid On Vertebral Body Morphology In Children With Osteogenesis Imperfecta

Part 1.Genotype-phenotype relationship in a large cohort of osteogenesis imperfecta patientsObjective:Osteogenesis imperfecta(OI)is a common heritable bone disease with serious harm,which is characterized by decreased bone mineral density(BMD),impaired bone strength,recurrent bone fractures and resulting in progressive bone deformity.At present,research on pathogenic gene spectrum and genotype-phenotype relationship of OI in China is still insufficient.We seek to investigate the gene mutation spectrum and quantitatively assess the genotype-phenotype relationship in a large cohort of Chinese OI patients.Methods:A total of 380 patients who were diagnosed as OI in the department of endocrinology in Peking Union Medical College Hospital up to December 2018 were included in this study.Pathogenic genes were identified by next generation sequencing and confirmed by Sanger sequencing.We collected a detailed medical history of these patients,performed a physical examination on them,measured the bone turnover biomarks(alkaline phosphatase,ALP and beta cross-linked carboxy-terminal telopeptide of type ? collagen,?-CTX)and BMD and assess the bone X-ray film.Then patients were classified as OI type ?,?,or IV according to the Sillence classification.Besides,a new clinical scoring system was developed to exactly assess the clinical severity of OI patients and quantitatively analyze the genotype-phenotype relationship.Results:In the present study,we identified 239 kinds of mutations in 13 kinds of OI genes,including 44 novel mutations.The type ? collagen-encoding genes(COL1A1 and COL1A2)were the major causative genes in our cohort,accounting for 77.9%,which were followed by IFITM5(4.5%).SERPINF1(2.1%)was the most common autosomal recessive(AR)causative gene,and successively followed by WNT1(1.6%)and FKBP10(1.6%),TMEM38B(1.1%)and PLOD2(1.1%),SERPINH1(0.3%),BMP1(0.3%)and SEC24D(0.3%).We also identified the extremely rare autosomal dominant causative gene P4HB and X-linked dominant causative gene PLS3 in our cohort.There were differences in gene mutation spectrum among different Sillence classifications.In addition,we also found some correlations between genotype and phenotype in OI patients.The clinical score of AR group was the highest(14.8�5.6),followed by IFITM5 group(12.8�5.0)and COL1A2 group(11.6�4.9),and the clinical score of COL1A1 group was the lowest(9.6�4.8).Compared to patients with quantitative mutations of ?1 chains,patients with qualitative mutations of ?1chains and ?2 chain had higher clinical score(12.9�5.7 and 11.8�4.8 vs 7.8�3.4),and higher proportion of dentinogenesis imperfecta(DI)(33.3%and 42.0%vs 3.9%)but lower proportion of blue sclera(BS)(91.5%and 88.5%vs 100.0%).Patients would present with BS but without DI if the Gly substitutions happened before the 79th amino acid in the triple helix of ?1 chains.The position of Gly substitutions in triple helix of ?2 chain was positive with fracture times(r=0.317,P=0.006)and fracture frequency(r=0.255,P=0.027)and negative with LS-BMD Z score(r=-0.290,P=0.011),FN-BMD Z score(r=-0.446,P<0.001),height Z score(r=-0.249,P=0.030)and weight Z score(r=-0.301,P=0.008).Patients with Gly instead of Ser(13.6�5.7 and 12.8�5.1)had higher clinical score than those with Gly instead of Arg(8.0�4.0 and 9.6�3.2)in ?1 chains and a2 chain.Conclusions:The present study enriched and updated the OI pathogenic gene spectrum in a large cohort of Chinese OI patients,which may contribut to accurate diagnosis and classification of OI,understanding the pathogenesis and promote genetic counseling and molecular targeted therapy in the future.In addition,we also found mutiple correlations of clinical phenotype with pathogenic gene types,mutation types of type I collagen-encoding genes and the kind and position of Gly substitutions in OI patients,which had positive implications for predicting the prognosis of OI and guiding clinical treatment.Part 2.Effects of zoledronic acid on vertebral shape of children and adolescents with osteogenesis imperfectaObjective:Vertebral compression fracture(VCF)is a common and severe complication of osteogenesis imperfecta(OI).We aim to prospectively observe the changes of vertebral shape during zoledronic acid(ZOL)treatment and assess influence factors of VCF in OI children.Methods:A total of 42 children were diagnosed with OI in the department of endocrinology of Peking Union Medical College Hospital from October 2014 to March 2018,who were classified into VCF and non-VCF(NVCF)groups matched for age and gender and received ZOL(infusion,5mg/year)with calcium and vitamin D for 2-year.Another 17 historical untreated OI patients with VCF were also included who were matched for age,gender and clinical severity to 17 patients in VCF group after ZOL treatment for 1 year.We measured patients' height,weight and calcium,phosphate,alkaline phosphatase,beta cross-linked carboxy-terminal telopeptide of type I collagen,25-hydroxyvitamin D and intact parathyroid hormone,alanine aminotransferase and creatinine.Bone mineral density(BMD)at lumbar spine(LS)and femoral neck(FN)were measured by dual energy X-ray.And we performed quantitative vertebral morphometry on lateral spine radiographs and calculated concavity index(mh/ph),height-length ratio(ah/LL,mh/LL,ph/LL)and projection area(PA)of vertebrae from T4 to L4 before and after treatment.Results:There were 32 OI patients with VCFs,who had significantly lower PA,mh/ph,ah/LL,mh/LL and ph/LL than patients without VCF(n=10)at baseline.After 1-year treatment,PA,mh/ph,ah/LL,mh/LL,and ph/LL of patients with VCF elevated by(35.2�19.5)%,(22.9�15.1)%,(19.6�13.9)%,(33.6�25.5)%,and(8.1�8.8)%(P<0.01).After 2-year treatment,the above parameters increased by(71.8�28.2)%,(42.8�21.8)%,(35.1�20.6)%,(65.4�43.2)%,and(12.5�11.4)%in VCF group(P<0.01).Compared to the untreated group,the average of mh/ph,ah/LL and mh/LL were significantly higher(P<0.01)in ZOL treatment group.Multiple linear regressions analysis revealed that LS-BMD was positively correlated to PA(?=337.0,P=0.001),mh/ph(?=0.866,P=0.015),ah/LL(?=0.499,P=0.001),mh/LL(?=0.492,P=0.005)and ph/LL(?=0.334,P<0.001)at baseline.After ZOL treatment for 1 year,the increase rate of LS-BMD was positively correlated to the increase degree of PA(?=0.131,P=0.011),mh/ph(?=0.127,P=0.002),ah/LL(?=0.141,P=0.013),mh/LL(?=0.209,P=0.002)and ph/LL(?=0.106,P=0.005).Conclusions:In conclusion,the compressed vertebrae of OI children could be effectively reshaped during ZOL treatment.Low LS-BMD was an independent risk factor for VCF and the increase in LS-BMD was positively correlated to the improvement in vertebral shape after ZOL treatment.