RESUMEN
The case histories of three patients with hematologic disorders are reviewed. The patients are members of the same family composed of three brothers and two sisters. Two have osteomyelofibrosis and one essential thrombocythemia. Hematologic, enzymatic, cytogenetic, immunocytologic and immunogenetic investigations allow the following conclusions: - all the 5 siblings have identical blood group and rhesus factor (0+); - there is an HLA identity in the 5 siblings characterized by the alleles: A2, A3, B5, B7 (w4, w6); - the white blood cell alkaline phosphatase is not increased; - no monoclonality can be shown; - the chromosome Ph 1 is absent. In the second (osteomyelofibrosis) and third (essential thrombocythemia) patient an additional chromosome has been found, while the caryotype of the other three siblings, including the first patient with osteomyelofibrosis, is normal.