Homozygosity of TERT p.T567M results in dramatic telomere shortening. Telomere lengths determined by telomere flow FISH analysis (courtesy of University Hospital, Bern and Repeat Diagnostics, Vancouver). Reference percentiles indicated in the top left graph obtained from the determination of telomere length in 400 normal controls.¹⁴  The proband’s telomere length is indicated by the diamond, the mother’s by the square, and the father’s by the circle.