Analysis of p16 gene mutations and deletions in childhood acute lymphoblastic leukemias

Abstract

Context: The p 16 tumor suppressor gene encodes a cyclin-dependent kinase 4 inhibitor that blocks cell division during the G1 phase of the cell cycle. Alterations in this gene have been reported for various neoplasia types, including acute lymphoblastic leukemias (ALL), especially T-cell acute lymphoblastic leukemias (ALL). Objective: To determine probable alterations in the p 16 gene in children with acute lymphoblastic leukemias using the polymerase chain reaction (PCR) and direct DNA sequencing and also to analyze event-free survival (EFS). Design: Restrospective study. Setting: Department of Child Care and Pediatrics, Faculty of Medicine of Ribeirá Preto, Universidade Federal de Sá Paulo. Participants: Fifty-six children with ALL (mean age 4 years). Forty (71.43%) had B-cell and 12 (21.43%) had T-cell ALL; 4 (7.1%) were biophenotypic. Sample: DNA samples were extracted from bone marrow upon diagnosis and/or relapse. In 2 T-cell cases, DNA from cerebrospinal fluid (CSF) was analyzed. Main Measurements: Deletians or nucleotide substitutions in exons 1, 2 and 3 of the p16 gene were determined by PCR and nucleotide sequencing. Event-free survival was determined by the Kaplan-Meyer and long-rank test for patients carrying normal and altered p 16. Results: Deletions in exon 3 were observed in five cases. Abnormal migration in PCR was observed in seven cases for exon 1, six for exon 2, and five for exon 3. Mutations in exon 1 were confirmed by direct DNA sequencing in four cases and in exon 2 in two cases. The Kaplan-meyer survival curves and the log-rank test showed no significant differences in 5-year. EFS between children with normal or altered p 16, or between patients with B- ALL carrying normal or altered p 16 gene. Patients with T-ALL could not be evaluated via Kaplan-Meier due to the small number of cases. Conclusions: Our results, particularly regarding deletion frequency, agree with others suggesting that deletions in the p 16 are initial events in leukemia genesis. The small number of samples did not allow stablishment of correlation between childhood ALL and the p 16 point mutations found in our study Kaplan-Meier analysis revealed not significant correlation between EFS and alterations in ALL. The p 16 alterations frequency observed for B and T-ALL agreed with reports from other centers.