1. A case of Down's syndrome (G 21 trisomy) in a boy, age 4, associated with twinning and AGL is described. Multiple chromosomal aberrations were found prior to and during antileukemic chemotherapy.

2. The initial modal number ranged from 47 to 53 and subsequently 49 to 53, and 42 to 52 chromosomes respectively. The overwhelming leukemic cell population was represented by 51 chromosomes on three occasions (74.2, 80 and 79.5 per cent respectively).

3. The autosomal aberrations—trisomies and polysomies—were constant, involving predominantly the chromosomes of the G, F and D series.

4. Heterokaryotic twinning with one normal and one affected was encountered twice in this family (G 21 trisomy and normal) and (normal and mentally affected) sets of twins.

5. A possible tendency to nondisjunction has been demonstrated in three healthy members of the family.

6. Multiple mitotic nondisjunction anomalies might be of etiologic importance in the leukemic process.

7. The implication of different injurious agents and factors, such as ionizing radiation, x-ray exposure, chemicals and parental age in the development of trisomic syndromes and/or neoplasia are briefly discussed.

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© 1964 by American Society of Hematology, Inc.
1964
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