Background

Telomeres are structural elements that seal the ends of chromosomes protecting them from recombination and end to end fusion. Maintenance of the integrity of telomeres requires the telomerase ribonucleoprotein complex. Abnormal telomere maintenance is a feature of a variety of human diseases including constitutional aplastic anemia. Predisposition to the development of marrow failure has been conferred by genetic alternations results in low telomerase activity. Short telomeres in leukocytes and reduced hematopoietic function.

Aim

To evaluate the telomerase functional activity in Egyptian children with inherited and acquired bone marrow failure and its relation to the phenotypic features of the acquired disease and its response to immunosuppressive therapy.

Patients and Methods

This was a case-control study conducted on unrelated children (n=40) with bone marrow failure syndromes and forty healthy subjects age and sex-matched as controls.

The diagnosis of bone marrow failure was based on the bone marrow biopsy and blood-count results. Patients with acquired aplastic anemia (AAA) were considered severe if at least 2 of the following were noted: neutrophil count < 0.5×109/L; platelet count < 20×109/L with hypocellular marrow. Response to immunosuppressive therapy (IST) was evaluated after 6 months of initiation of therapy.

Assessment of Telomerase Activity

Telomerase activity was measured in mononuclear cells utilizing the Telomeric Repeat Amplification Protocol (TRAP )using the TeloTAGGG Telomerase PCR ELISA.

Results

Forty patients were included in the study (30 AAA , 6 Fanconi Anemia (FA), 2 Pure Red Cell Aplasia (PRCA), one case with Dyskeratosis Congenita (DCK) and one case with constitutional aplastic anemia. The Mean age was 11.1±4.9 years (range 3.5 to 18 years, median 11 years ) and the duration of follow-up mean; 5.14 (±3.84) years (range 1-13 years). Patients with AAA (n=30) received treatment with cyclosporine A( n =27) and ATG( n=3).

Telomerase level

The median telomerase level was significantly lower in inherited BMF syndromes when compared to controls [5.05 (4.60 – 8.70 IQR) Vs 11.15 (5.90-16.60 IQR), p=0.04]. In AAA the median telomerase level was insignificantly lower than controls [5.4 (2.3 – 21.0 IQR) Vs 11.15 (5.90-16.60 IQR), p=0.228]. A good inverse correlation was detected between the telomerase level and age of the patients (r=-0.39, p=0.026).

No correlation was found between the telomerase level and disease duration in hereditary or AAA (r= -0.303, p=0.111 and r=0.305, p=0.156 respectively).

Telomerase activity and clinical variables

We classified our cases into two groups according to the median value of the control group (11.5): Low telomerase level group: (n=27): included 18 AAA (66.7%) and 9 hereditary aplastic Anemia (33.3%).

Cases with AAA 14/18 (77.8%) with low telomerase activity were severe cases with bone marrow cellularity less than 10 % Vs 6/12 (50%) with normal telomerase. Fifty per cent of cases (9/18) with low telomerase responded partially or completely to IST Vs. 83.4% of the normal telomerase (10/12) group.

Patients of AAA who received cyclosporine therapy (n=27), 19 cases (70.4%) were responders versus zero % of patients who received ATG (n=3). The median telomerase of responders was 16.5 + 4.7 Vs 11.6 + 3.8 of none responders.

Conclusion

• Telomerase activity was affected in hereditary and acquired bone marrow failure.

• Evaluation of telomerase activity is essential for therapeutic and prognostic aspects of these diseases.

Cyclosporin A can be used as a monotherapy in the treatment of acquired aplastic anemia even in the presence of decreased telomerase activity

Disclosures:

No relevant conflicts of interest to declare.

Table 1

Telomerase level in AAA and response to IST

Responders
(n=19)
Non responders
(n=11)
Telomerase level:
mean±SEa
median (IQRb
16.5±4.7
5.8 (2.6-25.4) 
11.6±3.8
5.0 (1.7-16.5) 
 Cyclosporine
(n=27) 
ATG
(n=3) 
Telomerase level:
mean±SEa
median (IQRb)
Response to IST:
responders
non responders 
15.5±3.6
5.8 (1.9-25.4)
19 (70.4%)
8 (29.6%) 
7.2±3.7
3.5 (3.5-11.8)
0
3 (100%) 
Responders
(n=19)
Non responders
(n=11)
Telomerase level:
mean±SEa
median (IQRb
16.5±4.7
5.8 (2.6-25.4) 
11.6±3.8
5.0 (1.7-16.5) 
 Cyclosporine
(n=27) 
ATG
(n=3) 
Telomerase level:
mean±SEa
median (IQRb)
Response to IST:
responders
non responders 
15.5±3.6
5.8 (1.9-25.4)
19 (70.4%)
8 (29.6%) 
7.2±3.7
3.5 (3.5-11.8)
0
3 (100%)