Brain astrocytomas: human leukocyte antigen (HLA) genotyping and, tumor suppressor gene(p53) genetic alterations detected by polymerase chain reaction (PCR/SSP-SSCP)

The current study investigated the association between HLA-A, - B, -DR alleles, and astrocytoma in Iraqi patients. In.addition, the genetic alterations of p53 tumor suppressor gene were also investigated. A total of 30 patients with grade I, II, and IV astrocytoma were studied (24 males and 6 females). The mean age was 52.3 ± 4.55 years (ranged between 6 and 85 years). Blood samples and tumor biopsies were taken from each patient. In addition, blood samples were obtained from 17 age and sex matched apparently healthy controls. Blood samples were used for HLA- A, -B, -DR genotyping by PCR-SSP. The allelic frequencies were calculated and compared with controls. Tumor biopsies were used to investigate p53 tumor suppressor gene mutations by PCR-SSCP. There are certain HLA alleles that showed significant association with brain astrocytoma. The incidence of HLA-A risk group of alleles (A*03011, A*0302, A*0303, A*0304, A*0305, A*0306, A*0307, A*0308 and A*0309) was significantly decreased in patients group by a (6) folds risk (frequency in patients 60% and in controls 93%, OR= 5.07, p<0.01).Thereby assigning a protective role. The patients-had a trend towards a consistent association between HLA-B, B*4415 and B*4420 and brain astrocytoma (frequency in patients 93% and in controls 70%, OR= 4.24, PO.01). Thereby conferring disease susceptibility. Regarding HLA-DRB locus, there was a significant decrease in the frequencies of risk group alleles in patients than in controls. These include DRB1*10011 and DRB1*10012 (Frequency in patients 53% and in controls 93%,OR=8.76, p<0.01). The importance of HLA-A,-B,-DRB1 risk group of alleles was more striking in certain HLA combinations. Individuals HLA-A*03012, which were in linkage disequilibrium with HLA-B*3804, had an increased risk for brain astrocytoma (Corrected Cumulative Risk Value, CCRV= 15.34). As did individuals with the following HLA-A,-B,-DERB1 haplotypes combinations (CCRV=20.02) such as: (03011 & 3804 & 10011) (03011 & 3804 & 10012) (0302 & 3804 & 10011) p53 mutations were detected in 76.7% of astrocytomas. In addition, p53 mutation occurred most frequently at exon 5 (16/23, 69.6%), followed by exon 7 (15/23, 65.2%), exon 6 (14/23, 60.9%), exon 8 (9/23, 39.1%) and exon 9 (4/23, 17.4%). Multiple mutations amongp53 exons 5-9 in the same examined samples were found in 73.9% of astrocytoma patients. Our results further showed tliat there were strong age, sex differences and the number ofp53 mutations (p<0.001). Moreover, the old age group of patients 50-85yrs have increased rate of p53 exon mutations in comparison With other age groups. Male sex show-ed significant differences with the ,mean number of p53 mutations than the female sex (3.2 folds). , Regarding the grade of strocytoma, it was found there was no association between p53 mutations and tumor grade. However, GIV shows the higher p53 mutation rates (15/15, 100%). In the case of tumor location, 80% of astrocytoma were supratentorial in location classified as Grade IV and 20% were Grade II and infratentorial in location. The correlation (r) was negative between the total number of HLA-A,B,DRB1 lost alleles (risk group) (- 0.053, - 0.211, - 0.107, - 0.190, -0.156) and the total number of p53-mulaied exons (exon 5, 6, 7, 8, and 9), respectively . However, the correlation relation was positive and significant (p<0.0l) in case of exon 5 (0.743), exon 6 (0.714) and exon 7 (0.276), and the total number of HLA lost alleles. In conclusion, these data suggested that some single HLA alleles and combinations were associated with a significant increased risk for astrocytoma. Thus, they may predispose to developing this malignant disease. These associations may be indicative of the involvement of the immune system of the host anti tumor surveillance, recognition, and destruction of human tumor cells. In addition, p53 mutations are frequent event in the pathogenesis of grade I, II, and grade IV astrocytomas.