title: Heritability of spinal curvature and its relationship to disc degeneration and bone mineral density in female adult twins.
abstract: OBJECTIVE
  To determine the heritability of spine curve using plain radiographs and to identify risk factors for spine curvature including age, body mass index, smoking, bone mineral density (BMD), and lumbar disc degeneration (LDD).
  
  
  METHODS
  A classical twin study of 110 MZ and 136 DZ adult female twins. Demographic and clinical information obtained from long spine radiographs, lumbar spine degeneration on spine MR scan, and BMD assessed by DEXA at hip and lumbar spine were included in multiple logistic regression models to determine risk factors for spine curvature.
  
  
  RESULTS
  Heritability estimates ranged between 41 (19-59) % for pelvic incidence to 61 (46-72) % for thoracic kyphosis; with lumbar lordosis and cervical lordosis having 59 (42-71) % and 43 (23-59) % heritability, respectively. For each spine curve, the model showing the best fit contained additive genetic and shared environmental components with no contribution from the unique environment. Significant risk factors for increased thoracic kyphosis were lumbar spine BMD, age, and cervical lordosis; for pelvic incidence were lumbar spine BMD and lumbar lordosis; for lumbar lordosis were cervical lordosis, pelvic incidence and LDD; and age alone predicted cervical lordosis (p = 0.001).
  
  
  CONCLUSIONS
  In this sample of middle-aged and elderly women, there were significant genetic influences on all spine curves but particularly thoracic kyphosis and lumbar lordosis. The strongest predictor for lumbar lordosis was LDD (p < 0.0001) which is itself genetically determined in part. For thoracic kyphosis, BMD was strongly associated and remained so (for lumbar BMD) with the inclusion of age, showing BMD to be an independent risk factor. This work highlights the genetic factors influencing normal spine curvature in women.
authors: Department of Twin Research and Genetic Epidemiology, St Thomas' Hospital, King's College London, London, SE1 7EH, UK.|University of Bath, Bath, UK.
authors: Millicent A
authors: MA
authors: Stone
authors: Department of Twin Research and Genetic Epidemiology, St Thomas' Hospital, King's College London, London, SE1 7EH, UK.
authors: Daniel-Clement
authors: DC
authors: Osei-Bordom
authors: Toronto Western Research Institute, Toronto, Canada.
authors: Robert D
authors: RD
authors: Inman
authors: University of Bath, Bath, UK.
authors: Cormac
authors: C
authors: Sammon
authors: Department of Twin Research and Genetic Epidemiology, St Thomas' Hospital, King's College London, London, SE1 7EH, UK.
authors: Lisa E
authors: LE
authors: Wolber
authors: Department of Twin Research and Genetic Epidemiology, St Thomas' Hospital, King's College London, London, SE1 7EH, UK. frances.williams@kcl.ac.uk.
authors: Frances M K
authors: FM
authors: Williams
mesh_terms: D000328:Adult; D015519:Bone Density / Q000235:genetics*; D004200:Diseases in Twins / Q000453:epidemiology / Q000235:genetics; D005260:Female; D006801:Humans; D055959:Intervertebral Disc Degeneration / Q000453:epidemiology / Q000235:genetics; D012307:Risk Factors; D013121:Spinal Curvatures / Q000453:epidemiology / Q000235:genetics
keywords: Bone mineral density; Heritability; Lumbar disc degeneration; Spine curvature; Twin study