Telomere Length in Inherited Bone Marrow Failure Syndromes

Background: Telomeres are short DNA repeats and a protein complex at chromosome ends that are essential for genome integrity. Telomeres are very short in patients with dyskeratosis congenita (DC) due to germline mutations in telomere biology genes. Telomere lengths (TL) were reported to be “short” in a few small studies of patients with other inherited bone marrow failure syndromes (IBMFS), specifically Fanconi anemia (FA), Diamond-Blackfan anemia (DBA), and Shwachman-Diamond syndrome (SDS), although their relation to the very short TL seen in DC was not clear, and various analytic methods were used.

Objectives: 1) To compare TL in a cohort of patients with FA, DBA, and SDS, with TL in DC. 2) To determine whether any individuals with non-DC IBMFS had TL as short as in DC.

Methods: Blood was obtained from 100 patients with DC, 30 FA, 34 DBA, and 14 SDS enrolled in the NCI IBMFS Cohort Study. TL was measured by flow cytometry with fluorescence in situ hybridization (flow-FISH) in 6 leukocyte subsets: granulocytes, total lymphocytes, CD45RA-positive/CD20-negative naïve T cells, CD45RA-negative memory T cells, CD20-positive B cells, and CD57-positive NK/NKT cells. “Very short” TL was below the 1^st percentile for age (defined by 400 normal controls). The diagnosis of DC required very short TL in 3 of 4 lymphocyte lineages including total lymphocytes. Z-scores were used to adjust for age; a Z-score of -2.3 equals the 1^st percentile. Canonical Variate Analysis (CVA) including all 6 Z-score measurements was used for group comparisons and outlier identification.

Results: Two patients with FA and 1 each with DBA and SDS had TL slightly below the 1^st percentile in 3 or more lymphocyte lineages. In univariate analysis, the mean of the DC TL Z-scores was approximately -4, versus approximately -0.5 in FA, DBA, and SDS. Most individual DC Z-score measurements were well below -2.3, and all were below zero (the mean for the control data). Seventy percent of the FA, DBA and SDS lymphocyte TL Z-scores clustered in the bottom half of the normal range (i.e. -2.3 to 0, p <0.001), compared with the expected 50% if the non-DC patients had essentially normal TLs. In addition, short lymphocyte TL correlated with severity of marrow failure in DC; there was a non-significant trend in FA and no trend in DBA or SDS. Further refinement of interpretation utilized the CVA analysis. The first canonical variate captured 89.7% of the total variance, and separated DC widely from the other three IBMFS. The second canonical variate captured 10% of the variance, and separated DBA, FA, and SDS. In the CVA analysis, only 2 patients with FA and 1 each with DBA and SDS had results closer to the mean for DC patients than to the mean for their own disorder.

Conclusions: Only 5% of individuals with FA, DBA, or SDS had TL in the DC range, and thus non-DC IBMFS in general do not have “very short” TL. However, 70% of non-DC IBMFS patients did have average TLs below the average for normal individuals. Thus disorders of DNA repair or ribosome biogenesis may result in TL changes, but the deficit in TL is not nearly as extreme as in DC itself.