Abnormality of platelet size and T-lymphocyte proliferation in an autosomal recessive form of dyskeratosis congenita.

Dyskeratosis congenita (DC) is a rare familial hematologic disorder that has various modes of inheritance. We have studied 2 siblings with DC. 1 sibling had thrombocytopenia, which responded to therapy with nandrolone decanoate and oxymetholone. Platelets were abnormally small, which indicates that a qualitatively abnormal megakaryocytopoiesis is a feature of DC. Myeloid and erythroid progenitors in specimens of the blood and bone marrow from both siblings were either absent or greatly reduced in numbers. The qualitatively abnormal megakaryocytopoiesis, and the quantitative abnormality of hematopoietic progenitor cells committed to myelopoiesis and erythropoiesis, indicates involvement of the pluripotent stem cell in DC. Cytogenetic studies of the bone marrow and peripheral blood lymphocytes from these patients showed normal karyotypes, a normal sister chromatid exchange frequency, and a rapid proliferation of peripheral T lymphocytes, a feature of the disorder that has not been reported previously.