IN 1959 Tuffy et al1 described 11 infants with a syndrome which they called infantile pyknocytosis. Seven of these infants had a clinical picture consistent with erythroblastosis fetalis; two of these seven infants required exchange transfusions, because of a bilirubin level over 20 mg/100 ml. Four other infants had no significant neonatal hyperbilirubinemia, but presented at 3 weeks of age with anemia or jaundice. Evidence of a hemolytic process persisted until 4 months, after which all abnormalities disappeared.
The common denominator in these infants was the presence of abnormal erythrocytes in the peripheral blood called pyknocytes, or burr cells. All known forms of maternal isoimmunization were excluded. In one infant, the burr cells persisted following two exchange transfusions. One patient had diminished red blood cell glucose-6-phosphate dehydrogenase (RBC G-6-PD) activity, but this was felt to be an incidental finding. It was concluded that these patients had an extracorpuscular