title: Novel missense MTTP gene mutations causing abetalipoproteinemia.
abstract: OBJECTIVE
  The microsomal triglyceride transfer protein (MTTP) plays a critical role in the formation of hepatic very low density lipoprotein. Abetalipoproteinemia (ABL) is a rare, naturally occurring extreme form of MTTP inhibition, which is characterized by the virtual absence of apolipoprotein (apo) B-containing lipoproteins in blood. The goal of this study was to examine the effect that four novel MTTP missense mutations had on protein interactions, expression and lipid-transfer activity, and to determine which mutations were responsible for the ABL phenotype observed in two patients.
  
  
  RESULTS
  In two patients with ABL, we identified in MTTP a novel frameshift mutation (K35Ffs*37), and four novel missense mutations, namely, G264R, Y528H, R540C, and N649S. When transiently expressed in COS-7 cells, all missense MTTP mutations interacted with apoB17, apoB48, and protein disulfide isomerase. Mutations Y528H and R540C, however, displayed negligible levels of MTTP activity and N649S displayed a partial reduction relative to the wild-type MTTP. In contrast, G264R retained full lipid-transfer activity.
  
  
  CONCLUSIONS
  These studies indicate that missense mutations Y528H, R540C, and N649S appear to cause ABL by reducing MTTP activity rather than by reducing binding of MTTP with protein disulfide isomerase or apoB. The region of MTTP containing amino acids 528 and 540 constitutes a critical domain for its lipid-transfer activity.
authors.affiliation: School of Pathology and Laboratory Medicine, University of Western Australia, Perth, Australia. Electronic address: sharon.miller@health.wa.gov.au.
authors.forename: Sharon A
authors.initials: SA
authors.lastname: Miller
authors.affiliation: School of Medicine and Pharmacology, University of Western Australia, Perth, Australia; Department of Clinical Biochemistry, PathWest Laboratory Medicine WA, Royal Perth Hospital, Perth, Australia. Electronic address: john.burnett@health.wa.gov.au.
authors.forename: John R
authors.initials: JR
authors.lastname: Burnett
authors.affiliation: Division of Gastroenterology, Hepatology and Nutrition, Cincinnati Children's Hospital Medical Center and Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, USA. Electronic address: mike.leonis@cchmc.org.
authors.forename: Mike A
authors.initials: MA
authors.lastname: Leonis
authors.affiliation: Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA, USA. Electronic address: cjmck@bu.edu.
authors.forename: C James
authors.initials: CJ
authors.lastname: McKnight
authors.affiliation: Department of Clinical Biochemistry, PathWest Laboratory Medicine WA, Royal Perth Hospital, Perth, Australia; School of Surgery, University of Western Australia, Perth, Australia. Electronic address: frank.vanbockxmeer@health.wa.gov.au.
authors.forename: Frank M
authors.initials: FM
authors.lastname: van Bockxmeer
authors.affiliation: School of Pathology and Laboratory Medicine, University of Western Australia, Perth, Australia; School of Medicine and Pharmacology, University of Western Australia, Perth, Australia; Department of Clinical Biochemistry, PathWest Laboratory Medicine WA, Royal Perth Hospital, Perth, Australia. Electronic address: amanda.hooper@health.wa.gov.au.
authors.forename: Amanda J
authors.initials: AJ
authors.lastname: Hooper
keywords: Abetalipoproteinemia; Lipid-transfer activity; Microsomal triglyceride transfer protein; Missense mutations