Results of study of family affected with FET. (A) Pedigree of FET. Members of the family, designated as `a' through `h' and `1' through `8', were examined clinically; solid symbols (a-h) indicate ET-affected members, and numbers 1-8 indicate unaffected members. Square symbols denote men; circles, women; and symbols with a slash, deceased members. This pedigree shows the autosomal-dominant inheritance of disease penetration. (B) Sequence of the Asn505 mutation of the c-MPL gene detected in ET-affected members of the family. Upper sequence indicates the wild type, and the lower sequence indicates the point mutation detected in the affected members. The nucleotide change from guanine to adenine caused an amino acid substitution from Ser505 to Asn505. (C) Platelet counts for the family members and the association with the status of the Asn505 mutation of the c-MPL gene. ▪ indicates platelet counts of the members carrying the Asn505 mutation of the c-MPL gene; □, platelet counts of the members with wild-type alleles of the homozygous Ser505, showing that the Asn505 mutation is unique in affected members; 1-8 and a-h correspond to the designations in panel A.