TERC levels in peripheral blood samples. The TERC/ABL transcript ratio is shown for a group of healthy individuals (○), P721R and R901W TERT heterozygotes (⧫ and , respectively), TERT homozygotes (▴ for R811C and ■ for R901W), and patients with DKC1 mutations (•). The family with the heterozygous P721R TERT mutation and those with DKC1 mutations³³  are shown for comparison. The numbers of samples in each group is given below along with their corresponding t test value, if appropriate.