Acute lymphoblastic leukemia in two children with a congenital chromosome anomaly: familial inv(11)(p15q13) in one and ring chromosome No. 21 in the other.

A congenital chromosome abnormality was found in two unrelated children with acute lymphoblastic leukemia (ALL). In the first case, a pericentric inversion of chromosome No. 11, inv(11)(p15q13), was observed and discovered to be familial, being present in five other members of the family over two generations. In the second case, the presence of a congenital ring chromosome No. 21, 46,XX,r(21), was considered to be the result of a de novo mutation. The possible relation between these congenital chromosome anomalies and a predisposition to neoplasia is discussed and could be explained by different mechanisms: (1) amplification of oncogenic determinants by gene duplication, and/or (2) alteration of the effects of wildtype alleles through deletion or changes in position.