Anticipation of disease onset in familial myeloproliferative neoplasms. Age-adjusted telomere length in 10 families with 2-generation pairs. Lines connect 2 members of each family. The average length of telomere in granulocytes was measured by flow cytometry combined with fluorescence in situ hybridization. Telomere length was adjusted for age to avoid the age-effect on telomere shortening. Telomere length was expressed as the difference between the observed length and the age-adjusted normal telomere length predicted from the linear regression line (ΔTEL). Wilcoxon matched pairs test demonstrated that second-generation patients had significantly shorter telomeres than first-generation patients.