|
|
 Previous Article | Table of Contents | Next Article 
Bernard-Soulier Syndrome Caused by a Dinucleotide Deletion and Reading Frameshift in the Region Encoding the Glycoprotein Ib Transmembrane Domain
Vahid Afshar-Kharghan and
José A. López
From the Division of Hematology/Oncology, Department of Internal Medicine, and the Department of Molecular and Human Genetics, Baylor College of Medicine and Veterans Affairs Medical Center, Houston, TX.
We investigated the molecular genetic and biosynthetic basis of Bernard-Soulier syndrome in a severely affected white woman. Flow cytometric analysis showed a severe deficiency of glycoprotein (GP) Ib, GP IX, and GP V on the surface of her platelets. Similarly, GP Ib was undetectable by immunoblot analysis of platelet lysates. Surprisingly, a large quantity of a 70-kD protein (which probably represents a GP Ib degradation product) was found in the patient's plasma in much greater quantities than in the plasma of an unaffected individual. To analyze the molecular lesion responsible for the disorder, we amplified and sequenced gene segments corresponding to the entire coding regions of the GP Ib, GP Ib , and GP IX genes. The patient was homozygous for a specific GP Ib allele that contained two tandem VNTR repeats in the region encoding the macroglycopeptide (C variant) and three differences from the published GP Ib gene sequence. Two mutations were unlikely to be involved in the disorder: the substitution of a single base (T  C) in the second nucleotide of exon 2, which is in the 5' untranslated region of the GP Ib transcript, and a silent mutation in the third base of the codon for Arg342 (A G) that does not change the amino acid sequence. The third mutation was a deletion of the last two bases of the codon for Tyr492 (T ). This mutation causes a frameshift that alters the GP Ib amino acid sequence, beginning within its transmembrane region. The mutant polypeptide contains 81 novel amino acids and is 38 amino acids shorter than its wild-type counterpart. The new sequence changes the hydrophobic nature of the transmembrane domain and greatly decreases the net positive charge of what had been the cytoplasmic domain. The deletion mutation was introduced into the GP Ib cDNA, alone and in combination with the 5' mutation, and expressed in Chinese hamster ovary (CHO) cells. The deletion alone severely reduced GP Ib expression on the cell surface. Expression was not decreased further by addition of the 5' mutation, confirming that the deletion was the cause of the Bernard-Soulier phenotype. Stable cell lines expressing the mutant polypeptide secreted large amounts of the polypeptide into the medium, suggesting that the mutant anchors poorly in the plasma membrane. Nevertheless, a fraction of the mutant was able to associate with GP Ib, as demonstrated by their coimmunoprecipitation with a GP Ib antibody.
Blood, Vol. 90 No. 7 (October 1), 1997:
pp. 2634-2643
© 1997 by The American Society of Hematology.
 CiteULike  Connotea  Del.icio.us  Digg  Reddit  Technorati What's this?
This article has been cited by other articles:
|
|
|
|
 
S. Feng, X. Lu, and M. H. Kroll
Filamin A Binding Stabilizes Nascent Glycoprotein Ib{alpha} Trafficking and Thereby Enhances Its Surface Expression
J. Biol. Chem.,
February 25, 2005;
280(8):
6709 - 6715.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
V. Afshar-Kharghan, N. Matijevic-Aleksic, C. Ahn, E. Boerwinkle, K. K. Wu, and J. A. Lopez
The variable number of tandem repeat polymorphism of platelet glycoprotein Ib{alpha} and risk of coronary heart disease
Blood,
February 1, 2004;
103(3):
963 - 965.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. Savoia, C. L. Balduini, M. Savino, P. Noris, M. Del Vecchio, S. Perrotta, S. Belletti, V. Poggi, and A. Iolascon
Autosomal dominant macrothrombocytopenia in Italy is most frequently a type of heterozygous Bernard-Soulier syndrome
Blood,
March 1, 2001;
97(5):
1330 - 1335.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
V. Afshar-Kharghan, C. Q. Li, M. Khoshnevis-Asl, and J. A. Lopez
Kozak Sequence Polymorphism of the Glycoprotein (GP) Ibalpha Gene Is a Major Determinant of the Plasma Membrane Levels of the Platelet GP Ib-IX-V Complex
Blood,
July 1, 1999;
94(1):
186 - 191.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
D. Kenny, P. A. Morateck, J. C. Gill, and R. R. Montgomery
The Critical Interaction of Glycoprotein (GP) Ibbeta With GPIX---A Genetic Cause of Bernard-Soulier Syndrome
Blood,
May 1, 1999;
93(9):
2968 - 2975.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
D. Kenny, O. G. Jonsson, P. A. Morateck, and R. R. Montgomery
Naturally Occurring Mutations in Glycoprotein Ibalpha That Result in Defective Ligand Binding and Synthesis of a Truncated Protein
Blood,
July 1, 1998;
92(1):
175 - 183.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. A. Lopez, R. K. Andrews, V. Afshar-Kharghan, and M. C. Berndt
Bernard-Soulier Syndrome
Blood,
June 15, 1998;
91(12):
4397 - 4418.
[Full Text]
[PDF]
|
|
|
|
|
