Analyses of 6 families with PV. (A) Pedigrees of 6 families with polycythemia vera (PV). Filled symbols indicate affected individuals. In families A and B, black dots indicate hematologically normal family members with Epo-independent erythroid cells detectable in their peripheral blood cultures. (B) Clonality analysis of individuals A01 and A06 using the IDS gene exonic polymorphism. RNA isolated from T lymphocytes (T), granulocytes (GRA), platelets (PLT), and Epo-independent erythroid cells (EEC) were used for the analysis. The presence of only one expressed allele of the IDS gene in platelets, granulocytes, and Epo-independent erythroid cells is consistent with clonal origin of cells. (C) Exclusion of linkage between chromosome 9p microsatellite markers and PV. LOD scores less than -2.0 satisfy the criteria of exclusion of linkage. The dotted line depicts the customary evidence for genetic exclusion of linkage. cM indicates centimorgan.