Acute promyelocytic leukaemia in patients originating in Latin America is associated with an increased frequency of the bcr1 subtype of the PML/RARalpha fusion gene

Abstract

The PML/RARalpha fusion gene in acute promyelocytic leukaemia (APL) has three subtypes based on the breakpoint site of the PML gene: long (bcr1), short (bcr3) and variable (bcr2) subtypes. The PML/RARalpha fusion protein is involved in the pathogenesis of APL and the breakpoint site of the PML gene might be associated with aetiological factor(s). Because APL is over-represented in patients that originate in Latin America (Latinos), we evaluated whether the distribution of the PML/RARalpha fusion mRNA in this population is different to that reported in non-Latinos. Among 52 APL patients (28 from Mexico and Central America diagnosed in Los Angeles and 24 from Peru, South America), bcr1, bcr2 and bcr3 expression was 75%, 10% and 15% respectively. However, bcr1 breakpoints were significantly higher compared with non-Latino patients (340/654, 52%) reported in four studies. Often bcr1 and bcr2 are reported together; 862 (60%) of 1429 non-Latino APL patients reported in nine studies were either bcr1 or bcr2, compared with 44 (85%) in our 52 Latino patients. This difference was also statistically significant when our patients were compared to each of the individual studies from USA and Europe, but not for a small series from China and Japan. These results suggest that the overrepresentation of APL among Latin American patients can be accounted for by an increase of a single subtype--bcr1, and the breakage sites in the PML gene may not be random but possibly influenced by genetic and/or environmental factor(s).