Human Platelet Alloantigens (HPA)1, HPA2 and HPA3 SNPs in Tunisian Sickle Cell Disease Patients

Abstract 4852

Sickle Cell Disease (SCD) is a complex disease with various complications such as stroke, vaso-occlusive crisis (VOC), acute chest syndrome and leg ulcers. Sickle cell anemia (SCA; homozygous hemoglobin SS) is the most common form of SCD. Genetic variations and/or environmental modifiers may modulate clinical presentation of SCD. Few studies have examined hemoglobinopathies in Tunisia, North Africa. However, recently, frequencies of beta-thalassemia and sickle cell trait were estimated at 2.21% and 1.89%, respectively (Fattoum, 2006). In order to identify genetic factors that may predispose patients to SCD complications in this population, a pilot case control study was designed to assess polymorphisms in Human Platelet Antigen (HPA) Genes. HPA polymorphisms were recently associated with severe coronary artery disease in the general population in Tunisia (Abboud et al, 2010) and VOC presentation in SCA patients from Bahrain (Al-Subaie et al, 2009). We present here a study conducted in collaboration with the Department of Clinical Hematology at the Aziza Othmana Hospital in Tunis (Tunisia). The National Medical Ethics committee of Tunisia as well as the Institutional Review Board (IRB) of Morehouse School of Medicine (MSM) approved the study. Blood samples, clinical history and DNA samples were collected from SCD adult patients and healthy controls after informed consent. Previously validated questionnaires for genetic risks in patients with SCD (courtesy of Dr Telen, Duke University) were adapted to French. The Helena test kit was used to generate hemoglobin variant data in conjunction with cellulose acetate electrophoresis. Blood samples were collected in EDTA vacutainer tubes and genomic DNA was isolated,stored at −80°C and then shipped to MSM. Single nucleotide polymorphisms, SNPs (Table 1) were genotyped using PCR-RFLPs and compared with different clinical sub-phenotypes such as, onset age, strokes, cardiac problems, splenectomies, etc. as defined in the questionnaire. Pearson Chi-Square was used for comparison and a P<0.05 value was considered significant. A total of 98 DNA samples were collected and 54 questionnaires were filled (Table 2). Age of patients at time of sample collection ranged from 19 to 61 (n = 49) with a mean ± sd (standard deviation) of 29 ± 7. The reported age at onset ranged from 1 to 30 (n = 44) with a mean ± sd of 12 ± 9. No significant differences were found in the HPA alleles and genotype frequencies in SCD versus healthy controls. There was significant association between HPA1 polymorphism with patient defined cardiac problems in all SCD patients (P = 0.002) as well as in the SS sub-group separately (P = 0.01). There was significant association between HPA1 and reported age of onset in SCD patients (P = 0.05) as well as in the non-SS sub-group alone (P = 0.04). The HPA1 variant was linked to self-reported age of disease onset and heart complications in adult SCD patients in Tunisia. This present study is one of the first genetic studies in a seldom-studied group of Tunisian adult SCD patients. These results show that identification of biomarkers of SCD disease severity may be possible using a validated self-reporting instrument. This kind of approach could help to improve early diagnosis of at risk patients and enable development of early interventions.