Absence of Factor V Leiden, thrombomodulin and prothrombin gene variants in Black South African women with pre-eclampsia and eclampsia
* J. Moodley, Department of Obstetrics and Gynaecology, Nelson R. Mandela School of Medicine, University of Natal, Private Bag 7, Congella, Durban, 4013, South Africa.
It has been suggested that gene aberrations may contribute to vascular endothelial dysfunction of pre-eclampsia in Caucasian and Japanese women. This study was undertaken to examine the association between pre-eclampsia in Black Zulu speaking South African women and the Factor 5 Leiden mutation. 100 patients with pre-eclampsia comprised the study group. The control group comprised 110 normotensive pregnant women of the same population group. Genotyping was performed to detect the G or A allele at residue 506 of the Factor V gene, and the C or T allele at residue 455 of the thrombomodulin gene. Our findings demonstrate that these particularly genetic loci are of little use in disease association studies for pre-eclampsia in homogenous Zulu speaking Africans.
The aetiology of pre-eclampsia remains elusive although there is almost certainly a multifunctional genetic component. The vascular endothelial dysfunction of pre-eclampsia suggests that aberrations in genes involved in the clotting cascade may be contributory. To this end there have been several recent conflicting reports focussing on the potential roles of Factor V Leiden, prothrombin (Factor II), thrombomodulin and 5,10-methylenetetrahydrofolate reductase (MTHFR) in the development of pre-eclampsia in both Caucasian and Japanese women1–3. Very little data are available on African populations but a recent study reported by this group demonstrated the absence of an association between the 677C→T MTHFR polymorphism in pre-eclampsia in Black Zulu-speaking South African women4, a population with a high incidence of pre-eclampsia. The current study was undertaken to examine the association between pre-eclampsia in this population and the Factor V Leiden mutation (R506Q) believed to cause activated protein C resistance, the thrombomodulin (A455V) polymorphism which may impair activation of the protein C coagulation pathway and the prothrombin/Factor II (20210 G→A) polymorphism, which confers a moderate risk for venous thrombosis.
Methods and results
The cohort in this study comprised 50 patients with documented severe pre-eclampsia (defined by a BP >160/110 mmHg, +++ proteinuria on dipstix and a platelet count ≤150 × 109/L) and 50 patients with eclampsia (defined as pre-eclampsia associated with seizures). The control group comprised 110 pregnant women of the same population group who remained normotensive throughout pregnancy. Genotyping was performed on lymphocytic DNA using primers specifically designed to detect the G or A allele at residue 506 of the Factor V gene, and the C or T allele at residue 455 of the thrombomodulin gene. A published5 PCR-based HindIII restriction enzyme analysis was used for detection of the 20210 G→A substitution in the prothrombin gene. In the case of the allele-specific analyses, all homozygous samples were repeated once to exclude possible non-amplification. For each of the polymorphisms examined, a sample of DNA shown previously to be heterozygote by nucleic acid sequencing was included as a control in every run.
The subjects in the control group were recruited from the post-delivery wards after review of their records to ensure that there were no antenatal, intrapartum or postpartum complications, specifically looking for hypertension. Informed consent was obtained and blood was taken post-delivery for DNA analysis.
The subjects in the pre-eclampsia and eclampsia groups were recruited from our labour ward high care complex where all high risk patients are monitored. Antenatal and delivery details were obtained from patient records. Clinical data of subjects are shown in Table 1.
Table 1. Clinical data. Values are expressed as mean (range) or n (%).
|Mean age (years)||25 (13–42)||26 (18–43)||24 (15–34)||0.054|
|Mean parity||1 (0–7)||1 (0–7)||1 (0–4)||NS|
|Abdominal||2 (1.8)||20 (40)||40 (80)|| |
|Vaginal||108 (98.2)||30 (60)||10 (20)||<0.001|
|Alive||100 (100)||30 (60)||20 (40)|| |
|Stillborn||0 (0)||20 (40)||30 (60)||<0.001|
|Gestation (weeks at delivery)||37 (30–42)||32 (20–41)||32 (26–35)||<0.001|
|Weight (kg)||3.1 (2–4.9)||2.1 (0.6–4.2)||2.0 (0.8–3.1)||<0.001|
|Systolic/diastolic||110/80 (100/70–120/80)||160/110 (140/90–200/140)||160/110 (150/100–190/120)|| |
|Proteinuria (dipstix)||Nil||3+ (2+–4+)||3+ (2+–4+)|| |
Results showed that for both the Factor V Leiden and prothrombin polymorphisms, the variant gene allele was not detected in either the patient or control groups. Similarly, the thrombomodulin polymorphic variant was not detected in either of the two patient groups but three heterozygotes (3%) were found in the control group yielding a variant allele frequency rate of 1.5%. Clearly, these results indicate that the variants of the Factor V Leiden (R506Q), thrombomodulin (A455V) and prothrombin/Factor II (20210 G→A) genes seen in other population groups are either non-existent or extremely rare within African populations, ethnic variations in genetic polymorphisms being widely reported.
The findings demonstrate that these particular three genetic loci are of little use in disease association studies for pre-eclampsia in homogenous Zulu-speaking Africans. This does not, however, rule out the possibility that these genes may be influential in the aetiology of pre-eclampsia. Informative polymorphisms in these and other thrombolytic genes need to be sought to assist in the elucidation of pre-eclampsia and related pregnancy disorders.