Mutation Analysis Of â…¥ - Type Osteogenesis Imperfecta And Analysis Of Serum PEDF Level In Osteogenesis Imperfecta

Objectives:Osteogenesis imperfecta （OI） is a group of inherited disorders characterized by recurrent fragile fractures. Mutations in gene encoding Serpin peptidase inhibitor, clade F, member 1 （SERPINFl） are known to cause a distinct, extremely rare autosomal recessive type VI OI characterized by moderate to severe bone fragility and undetectable serum pigment epithelium-derived factor （PEDF） level. PEDF belongs to the serpin superfamily and involves in processes such as angiogenesis, tumorigenesis, neuroprotection and fat metabolism. PEDF contains binding sites for collagen type I, which can also regulate osteoblastogenesis and osteoclast activities and influence osteoblast development through interaction with vascular epithelial growth factor （VEGF）.Methods:Clinical manifestations and demographic features were collected. Serum calcium and phosphate levels and bone turnover markers were assessed by the clinical laboratory of the hospital. Bone mineral density （BMD） was measured by DXA. We designed a novel targeted next generation sequencing panel （NGS） including OI-related genes to identify pathogenic mutations and confirmed with Sanger sequencing. We also used enzyme linked immunosorbent assay （ELISA） to detect the serum PEDF levels in 134 OI patients with different genotypes or Sillence types,6 SERPINF1 gene mutation carriers and 24 age-and sex-matched normal controls. The association between serum PEDF levels and age, sex, height, weight, body mass index, bone turnover markers,25 hydroxy vitamin D, parathyroidsm hormone, bone mineral density, OI severity and the bisphosphonates （BPs） usage condition were analysed in all OI patients.Results:Six patients with moderate to severe bone fragility, significantly low BMD and severe deformities of extremities were recruited from five unrelated families and included in this study. Seven pathogenic mutations in SERPINF1 gene were identified and six of which were novel:a homozygous in-frame insertion in exon 3 （c.271₂79dup, p.Ala91_Ser93dup）; compound heterozygous mutations in intron 3 （c.283+1G>T, splicing site） and exon 5 （c.498₄99delCA, p.Arg167SerfsX35, frameshift）; a homozygous frameshift mutation in exon 8 （c.1202₁203delCA, p.Thr401ArgfsX）; compound heterozygous missense mutation （c.184G>A, p.Gly62Ser） and in-frame insertion （c.271₂79dup, p.A191_Ser93dup） in exon 3; and heterozygous nonsense mutation in exon 4 （c.397C>T, p.Gln133X）. The serum PEDF levels were extremely low or barely detectable in all patients with mutations in SERPINF1 gene as compared with sex-and age-matched OI patients grouped according to genotypes, OI patients grouped according to Sillence types, normal controls and SERPINF1 gene mutation carriers. Based on mutilple regression analysis, weight was predicted to be positively correlated with serum PEDF levels as compared with OI severity, BMD and bone turnover markers.Conclusion:We reported the clinical features of the extremely rare OI type VI for the first time in Chinese patients. We also identified five novel mutations in SERPINF1 gene which expanded the mutation spectrum of OI. The undetectable serum PEDF levels were unique in 01 type VI. The Z score of body weight was one of the risk factors of serum PEDF levels, which was expected since PEDF could be secreted by adipocytes and serum PEDF levels were siginificantly increased among obesity populations. BPs were proved poor effects on 01 type VI, thus new pharmaceutical treatment needed to be explored.