title: A Comparative Study of SMN Protein and mRNA in Blood and Fibroblasts in Patients with Spinal Muscular Atrophy and Healthy Controls.
abstract: BACKGROUND
  Clinical trials to test safety and efficacy of drugs for patients with spinal muscular atrophy (SMA) are currently underway. Biomarkers that document treatment-induced effects are needed because disease progression in childhood forms of SMA is slow and clinical outcome measures may lack sensitivity to detect meaningful changes in motor function in the period of 1-2 years of follow-up during randomized clinical trials.
  
  
  OBJECTIVE
  To determine and compare SMN protein and mRNA levels in two cell types (i.e. PBMCs and skin-derived fibroblasts) from patients with SMA types 1-4 and healthy controls in relation to clinical characteristics and SMN2 copy numbers.
  
  
  METHODS
  We determined SMN1, SMN2-full length (SMN2-FL), SMN2-delta7 (SMN2-Δ7), GAPDH and 18S mRNA levels and SMN protein levels in blood and fibroblasts from a total of 150 patients with SMA and 293 healthy controls using qPCR and ELISA. We analyzed the association with clinical characteristics including disease severity and duration, and SMN2 copy number.
  
  
  RESULTS
  SMN protein levels in PBMCs and fibroblasts were higher in controls than in patients with SMA (p<0.01). Stratification for SMA type did not show differences in SMN protein (p>0.1) or mRNA levels (p>0.05) in either cell type. SMN2 copy number was associated with SMN protein levels in fibroblasts (p = 0.01), but not in PBMCs (p = 0.06). Protein levels in PBMCs declined with age in patients (p<0.01) and controls (p<0.01)(power 1-beta = 0.7). Ratios of SMN2-Δ7/SMN2-FL showed a broad range, primarily explained by the variation in SMN2-Δ7 levels, even in patients with a comparable SMN2 copy number. Levels of SMN2 mRNA did not correlate with SMN2 copy number, SMA type or age in blood (p = 0.7) or fibroblasts (p = 0.09). Paired analysis between blood and fibroblasts did not show a correlation between the two different tissues with respect to the SMN protein or mRNA levels.
  
  
  CONCLUSIONS
  SMN protein levels differ considerably between tissues and activity is age dependent in patients and controls. SMN protein levels in fibroblasts correlate with SMN2 copy number and have potential as a biomarker for disease severity.
authors.affiliation: Brain Centre Rudolf Magnus, Department of Neurology and Neurosurgery, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors.forename: Renske I
authors.initials: RI
authors.lastname: Wadman
authors.affiliation: Brain Centre Rudolf Magnus, Department of Neurology and Neurosurgery, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors.forename: Marloes
authors.initials: M
authors.lastname: Stam
authors.affiliation: Brain Centre Rudolf Magnus, Department of Neurology and Neurosurgery, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors.forename: Marc D
authors.initials: MD
authors.lastname: Jansen
authors.affiliation: Brain Centre Rudolf Magnus, Department of Neurology and Neurosurgery, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors.forename: Yana
authors.initials: Y
authors.lastname: van der Weegen
authors.affiliation: Brain Centre Rudolf Magnus, Department of Neurology and Neurosurgery, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors.forename: Camiel A
authors.initials: CA
authors.lastname: Wijngaarde
authors.affiliation: Brain Centre Rudolf Magnus, Department of Neurology and Neurosurgery, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors.forename: Oliver
authors.initials: O
authors.lastname: Harschnitz
authors.affiliation: Brain Centre Rudolf Magnus, Department of Neurology and Neurosurgery, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors.forename: Peter
authors.initials: P
authors.lastname: Sodaar
authors.affiliation: Brain Centre Rudolf Magnus, Department of Neurology and Child Neurology, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors.forename: Kees P J
authors.initials: KP
authors.lastname: Braun
authors.affiliation: Department of Genetics, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors.forename: Dennis
authors.initials: D
authors.lastname: Dooijes
authors.affiliation: Department of Genetics, University Medical Centre Groningen, Groningen, The Netherlands.
authors.forename: Henny H
authors.initials: HH
authors.lastname: Lemmink
authors.affiliation: Brain Centre Rudolf Magnus, Department of Neurology and Neurosurgery, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors.forename: Leonard H
authors.initials: LH
authors.lastname: van den Berg
authors.affiliation: Brain Centre Rudolf Magnus, Department of Neurology and Neurosurgery, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors.forename: W Ludo
authors.initials: WL
authors.lastname: van der Pol
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000032:analysis*; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D056915:DNA Copy Number Variations / Q000235:genetics; D005260:Female; D005347:Fibroblasts / Q000378:metabolism* / Q000473:pathology; D005500:Follow-Up Studies; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D009134:Muscular Atrophy, Spinal / Q000097:blood / Q000175:diagnosis* / Q000235:genetics; D011379:Prognosis; D012333:RNA, Messenger / Q000235:genetics*; D060888:Real-Time Polymerase Chain Reaction; D055540:Survival of Motor Neuron 2 Protein / Q000097:blood / Q000235:genetics; D055815:Young Adult
chemical_list: D015415:Biomarkers; D012333:RNA, Messenger; C526477:SMN2 protein, human; D055540:Survival of Motor Neuron 2 Protein