[show abstract][hide abstract] ABSTRACT: The primary pathology in many cases of myelodysplasia (MDS) and acute myeloid leukemia (AML) remains unknown. In some cases, two or more affected members have been identified in the same family. To date, mutations in two genes have been directly implicated: the hematopoietic transcription factors RUNX1 (runt-related transcription factor 1) and CEBPA (CCATT-box enhancer binding protein alpha). However, there are also other familial cases of MDS/AML where the genetic basis remains unknown. Both MDS, and to a lesser extent AML, have been observed in cases of the bone marrow failure syndrome dyskeratosis congenita, in which telomerase mutations have been identified. Recently, an increased incidence of telomerase reverse transcriptase mutations has been reported in a series of de novo AML. We have now identified novel mutations in the telomerase RNA (TERC) or telomerase reverse transcriptase component (TERT) within 4 of 20 families presenting with familial MDS/AML. Functional analysis has demonstrated that all mutations adversely impact on telomerase activity in vitro, and affected individuals have short telomeres. These families, in conjunction with a review of previously published cases, help to further define the pathological role of telomerase mutations in MDS/AML and have implications for the biology, treatment and screening regimen of de novo cases.
[show abstract][hide abstract] ABSTRACT: Dyskeratosis congenita (DC) is a multisystem bone marrow failure syndrome characterized by a triad of mucocutaneous abnormalities and an increased predisposition to malignancy. X-linked DC is due to mutations in DKC1, while heterozygous mutations in TERC (telomerase RNA component) and TERT (telomerase reverse transcriptase) have been found in autosomal dominant DC. Many patients with DC remain uncharacterized, particularly families displaying autosomal recessive (AR) inheritance. We have now identified novel homozygous TERT mutations in 2 unrelated consanguineous families, where the index cases presented with classical DC or the more severe variant, Hoyeraal-Hreidarsson (HH) syndrome. These TERT mutations resulted in reduced telomerase activity and extremely short telomeres. As these mutations are homozygous, these patients are predicted to have significantly reduced telomerase activity in vivo. Interestingly, in contrast to patients with heterozygous TERT mutations or hemizygous DKC1 mutations, these 2 homozygous TERT patients were observed to have higher-than-expected TERC levels compared with controls. Collectively, the findings from this study demonstrate that homozygous TERT mutations, resulting in a pure but severe telomerase deficiency, produce a phenotype of classical AR-DC and its severe variant, the HH syndrome.
Blood 01/2008; 110(13):4198-205.
Amanda Walne added a full-text to this article and 5 others.
[show abstract][hide abstract] ABSTRACT: Dyskeratosis congenita (DC) is a heterogeneous bone marrow failure syndrome with seven disease-causing genes identified to date, six of which are linked to telomere maintenance. Mutations in one of these genes (TINF2), which encodes a component of the shelterin complex, are associated with particularly short telomeres. Among the 224 consecutive patients with different forms of bone marrow failure (46 with DC, 122 with aplastic anaemia and 57 with some features of DC), we have identified 16 new families with variants in exon 6 of the TINF2 gene, eight of which are novel. We observe that the phenotype associated with these mutations extends to a severe early presentation, not always classified as DC. In addition, we see that some of the variants identified are not associated with short telomeres and are also found in asymptomatic individuals. In the absence of any direct functional assay, the data indicates that the telomere length measurement can inform us as to which variants in TINF2 are pathogenic and which may be non-pathogenic.