A novel type 2A von Willebrand factor mutation located at the last nucleotide of exon 26 (3538G>A) causes skipping of 2 nonadjacent exons.
In this manuscript, we describe a case of type 2A von Willebrand disease (VWD) caused by the novel heterozygous G>A transition at nucleotide 3538, which should result in the putative, nonconservative substitution of G1180R. This mutation was reproduced by site-directed mutagenesis; however, the recombinant mutant protein was efficiently secreted from cells and assembled correctly into multimers. Because the substitution is located at the last nucleotide of exon 26, the patient's platelet von Willebrand factor (VWF) mRNA was analyzed and 3 transcripts were observed: the normal transcript without the 3538G>A transition, a transcript with the in-frame deletion of exon 26, and a transcript with the in-frame deletions of exons 23 and 26. These deletion VWF cDNA constructs were created and the resulting recombinant proteins were analyzed following transfection into COS-7 cells. Cotransfection results demonstrate that the exon-skipped transcripts led to intracellular retention, and the levels of VWF antigen (VWF:Ag) produced by these constructs were as follows: del23/26<del26< G1180R<or=wild type. The homozygous exon-skipped transcripts show the presence of only the lowest molecular weight multimers. The G>A transition at nucleotide (nt) 3538 does not result in the expression of the G1180R missense mutation, but rather leads to exon skipping, which is the pathogenic basis of the patient's phenotype. This is the first report of a coding region mutation resulting in the skipping of 2 nonadjacent exons.
James
Paula D
PD
Department of Pathology and Molecular Medicine, Queen's University, Kingston, ON, Canada K7L 3N6.
O'Brien
Lee A
LA
Hegadorn
Carol A
CA
Notley
Colleen R P
CR
Sinclair
Gary D
GD
Hough
Christine
C
Poon
Man-Chiu
MC
Lillicrap
David
D
D000293:Adolescent; D000595:Amino Acid Sequence; D005091:Exons; D005192:Family Health; D005260:Female; D006801:Humans; D017354:Point Mutation / Q000502:physiology*; D012313:RNA / Q000235:genetics; D017384:Sequence Deletion; D014842:von Willebrand Diseases / Q000209:etiology / Q000235:genetics; D014841:von Willebrand Factor / Q000235:genetics* / Q000378:metabolism
D014841:von Willebrand Factor; D012313:RNA