Frequency and clinical outcomes of platelet membrane glycoprotein polymorphisms in antiphospholipid syndrome

The pathogenesis of thrombus formation in antiphospholipid syndrome (APS) is not clear. Therefore, it is difficult to estimate thrombus formation time in APS. Platelet membrane glycoprotein (GP) receptors play important roles in the development of thrombosis. Our study aimed to understand the relationship between thrombosis and polymorphisms in GPIb alpha variable number of tandem repeats (VNTR), Kozak, and GPIa C807T in patients with APS.

The study group consisted of 60 APS patients (50 females, 10 males) and 63 controls (44 females, 19 males). Thirty patients with APS had thrombosis (nine arterial and venous, 10 arterial, 11 venous), and the remaining 30 were positive for antiphospholipid antibodies without thrombosis. C807T polymorphism was determined with real-time polymerase chain reaction (PCR). Genotyping was performed with melting curve analysis. Melting temperature was 66°C for C allele and 59°C for T allele. Kozak and VNTR polymorphisms were determined by conventional PCR. PCR product of Kozak polymorphism was digested with AvaII restriction enzyme to produce three bands (125, 157, and 175 bp), two bands (125 and 332 bp), or four bands (125, 157, 175, and 332 bp) from T/T homozygotes, C/C homozygotes, and heterozygotes respectively. PCR product for VNTR was 239 bp for allele A, 200 bp for allele B, 161 bp for allele C, and 122 bp for allele D.

Frequency of thrombocytopenia and pregnancy morbidity in APS were not related to the studied polymorphisms. Genotype distribution and allele frequencies of the polymorphisms are shown in Tables 1 and 2. Frequency of mutant TT genotype of C807T polymorphism was significantly higher in APS with thrombosis than without thrombosis (p=0.023). Frequency of TT genotype for C807T polymorphism was significantly higher in APS with multiple thrombi than APS without thrombi (p=0.023). This is the first study investigating the relationship between thrombosis and Kozak polymorphism in APS. Neither comparison of APS versus controls nor APS with thrombosis versus APS without thrombosis exhibited any differences in the distribution of Kozak polymorphism genotype. TC genotype was more frequent in APS with arterial thrombosis than in APS with venous thrombosis, controls, and APS without thrombosis (p=0.03, p=0.0007, and p=0.0024, respectively). D allele frequency and D allele carrier state of VNTR polymorphism were significantly less in APS than in controls (p=0.0018 and p=0.0046, respectively).

Our findings demonstrated the relationship between TT genotype of C807T polymorphism and the risk of thrombosis as well as the increased tendency to development of multiple thrombi. Frequency of TC genotype of Kozak polymorphism was significantly higher in APS with arterial thrombosis. This may indicate that TC genotype predisposes to arterial thrombosis. Lower frequency of VNTR D allele and D allele carrier state in APS suggest a protective role for D allele. Detection of these polymorphisms may be useful for thrombotic risk assesment in APS. Specific inhibition of platelets GPIa and GPIb alpha may be an alternative for treating recurrent thrombosis despite appropriate anticoagulant or antiaggregant therapy.

No relevant conflicts of interest to declare.