Acute lymphoblastic leukemia and Klinefelter's syndrome.

We report two children with acute lymphoblastic leukemia (ALL) who in initial cytogenetic investigation were coincidently found to have a 47, XXY karyotype. In one patient 100% of peripheral blood lymphocytes showed a 47,XXY complement, but in the other only 30% of cells had such a complement, the remainder having a normal male karyotype (46, XY). In neither case was the diagnosis of Klinefelter's syndrome clinically obvious. Antileukemic therapy may exacerbate both the hypogonadism and the learning difficulties seen in this condition. Routine cytogenetic investigations on peripheral blood and bone marrow should be performed in all new cases of leukemia. Cytogenetic analysis of cultured fibroblasts is essential in all cases in which the abnormal X line did not disappear after initial therapy. Evidence of an increased risk of leukemia in association with Klinefelter's is beginning to accumulate.