PRDM9 and acute lymphoblastic leukemia: However, as discussed by Hussin et al., [35], the relatively high frequency among Africans [26], [36] of the rare PRDM9 alleles associated with childhood ALL in Caucasian populations, along with a proportionally low incidence of childhood leukemias among African-Americans [37] indicates that variant alleles of PRDM9 are insufficient to predispose to leukemia and suggestive of further contributory parental genetic background factors.