A novel homozygous splice junction mutation in GPIIb associated with alternative splicing, nonsense-mediated decay of GPIIb-mRNA, and type II Glanzmann's thrombasthenia.
This work reports the study of a patient suffering a bleeding disorder clinically diagnosed as Glanzmann's thrombasthenia (GT). Immunoblotting and flow cytometric analysis showed a low (</= 10% of control) platelet content of GPIIb-IIIa, confirming it was indeed a type II GT. The molecular genetic analysis of the proband revealed the presence of a homozygous G188A transition in GPIIb. This mutation alters the consensus sequence of the splice donor site of intron 1 changing arginine 63 for lysine (R63K). No other mutation than [G188A]GPIIb was found in the proband and her parents after complete analysis of GPIIb and GPIIIa coding sequences, and the promoter, 3'-UTR, and intronic flanking regions of GPIIb. The GT phenotype of the proband is the result of a limited availability of GPIIb-mRNA. The etiopathogenic role of the [G188A]GPIIb mutation is supported by the following observations: (i) both parents, who are heterozygous for the [G188A]GPIIb mutation, show a marked decrease in the platelet content of GPIIb-mRNA; (ii) exontrap analysis demonstrated that the G188A mutation leads to a marked reduction in the steady-state level of GPIIb-mRNA. The reduced availability of platelet GPIIb-mRNA associated with the G188A mutation seems to be caused by either inefficient RNA splicing or a preferred utilization of alternative intronic donor sites that generate an in-frame STOP codon with the result of activation of nonsense-mediated mRNA decay, or both.
González-Manchón
C
C
Department of Pathophysiology and Human Molecular Genetics, Centro de Investigaciones Biológicas (CSIC), Madrid, Spain. cgmanchon@cib.csic.es
Arias-Salgado
E G
EG
Butta
N
N
Martín
G
G
Rodríguez
R B
RB
Elalamy
I
I
Parrilla
R
R
Favier
R
R
D017398:Alternative Splicing / Q000235:genetics; D018389:Codon, Nonsense; D017124:Conserved Sequence / Q000235:genetics; D005192:Family Health; D005260:Female; D006720:Homozygote; D006801:Humans; D007223:Infant; D020125:Mutation, Missense; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000235:genetics*; D010980:Platelet Membrane Glycoproteins; D017354:Point Mutation; D022821:RNA Splice Sites / Q000235:genetics*; D020871:RNA Stability / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D013915:Thrombasthenia / Q000235:genetics*
D018389:Codon, Nonsense; D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins; D022821:RNA Splice Sites; D012333:RNA, Messenger; C032193:glycoprotein receptor GPIb-IX