TERT and Down syndrome: Our studies showed that telomere lengths in individuals with 5p– syndrome, who are haploinsufficient for the TERT gene, are only slightly shorter than telomere lengths in normal controls, who have two copies of TERT. Shorter telomeres were previously demonstrated by Zhang and colleagues in eight individuals with 5p– syndrome compared to eight normal controls, with the conclusion that significant telomere shortening was evident in 5p– and might contribute to the 5p– phenotype (2003).