The gene encoding the RNA component of human telomerase (hTERC) is mutated in families with the autosomal dominant form of dyskeratosis congenita (DC). The phenomenon of genetic anticipation has recently been reported to accompany this form of DC, with disease severity increasing in offspring of affected individuals. It has been postulated that anticipation in these families relates to the adverse impact of hTERC mutations on inherited telomere length, with progressive telomere shortening seen in succeeding generations (

Nat Gen 2004; 36:447
). We describe here a novel hTERC mutation, with affected individuals presenting in adulthood with mild mucocutaneous abnormalities, bone marrow failure and a pattern of penetrance supporting the presence of disease anticipation. The proband in the family studied presented at age 49 with squamous cell carcinoma of the tongue and a history of oral leukoplakia which he had developed at age 30. Peripheral blood on presentation was remarkable only for a mild macrocytic anemia. During treatment of his malignancy, severe and irreversible bone marrow hypoplasia was precipitated by a single cycle of cisplatinum chemotherapy. The patient’s brother at age 25 had been previously diagnosed with severe aplastic anemia; this was refractory to standard immunosuppression with cyclosporine and antithymocyte globulin. No somatic abnormailites were identified in this patient. Testing for Fanconi anemia in both siblings was negative. Direct sequencing analysis of hTERC in these patients revealed both to be heterozygous for a novel hTERC mutation (79 deletion C). Further studies among family members documented heterozygosity for the mutation in the mother of these two siblings. At age 77, she displayed none of the mucocutaneous signs associated with DC, while the only abnormality seen in her peripheral blood was an elevated mean corpuscular volume. The hTERC mutation seen in this family most likely exerts its effects through disruption of the pseudoknot domain. The findings of an individual with normal longevity, minimal phenotypic expression and affected offspring are further evidence of genetic anticipation being an important feature of autosomal dominant DC. Correlation with determination of telomere length has been initiated.

Topics:
anticipation, genetic, dyskeratosis congenita, anemia, macrocytic, antithymoglobulin, aplastic anemia, bone marrow, hypocellular, cancer, chemotherapy regimen, cisplatin, cyclosporine

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2005, The American Society of Hematology
2004
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