A Large Mennonite Family with a Novel K570N TERT Gene Mutation: Association with a Clinical Spectrum of Bone Marrow Failure, Acute Myeloid Leukemia, and Acute Liver Failure.
Authors: Regal Joshua A. , Calado Rodrigo T. , Shenoy Aarthi , Lansdorp Peter M. , Young Neal S. 
Published: April 2020

Abstract
Mutations in telomere repair complex genes TERT (encoding telomerase reverse transcriptase) and TERC (telomerase RNA component) are associated with bone marrow failure, especially acquired aplastic anemia and dyskeratosis congenita. Low telomerase activity leads to short telomeres of leukocytes, predisposing highly proliferative tissues such as the bone marrow to early senescence and exhaustion of the stem cell compartment. Telomere repair gene mutations have been suggested to result in disease anticipation, defined as earlier and/or worsening clinical manifestations in successive generations. We have identified a six-generation pedigree in a large Mennonite family carrying a novel TERT mutation (K570N), which localizes in the catalytic domain with reverse transcriptase activity (RT domain). The index patient is a 26 year old male dairy farmer with a ten-year history of severe aplastic anemia (5% bone marrow cellularity) unresponsive to immunosuppression. A long history of hematologic diseases was well known and named in the family--the patient’s paternal great-great-grandmother had died of a severe blood disorder at age 65 years. However, the great-grandmother and the grandfather had never presented any hematological disease. The patient’s father had myelodysplastic syndrome at age 33 years, evolving to acute myeloid leukemia and death due to failure to recover blood counts after chemotherapy. One of the proband’s paternal aunts had aplastic anemia develop when she was a young woman and has been transfusion-independent for decades in response to chronic androgen therapy. A second proband’s paternal aunt underwent a liver transplant at age 20 for submassive hepatic necrosis with fibrosis. A third proband’s paternal aunt has macrocytosis only at age 47. Two sisters (ages 21 and 23) also have macrocytosis in the absence of other hematological abnormality, and two other sisters are healthy. Genetic analysis showed that TERT K570N mutation is present in the patient’s paternal (including grandfather, three aunts and two affected sisters) but not maternal relatives (making his father an obligatory carrier). The patient’s oldest of three sons, now age four years, has the mutation but is asymptomatic. There was no nail dystrophy, leukoplakia or skin hyperpigmentation in any of the TERT K570N carriers; although the index patient and some of his relatives showed early graying of hair, this characteristic did not track with the mutation. Telomere shortening of leukocytes, as measured by Flow-FISH, tracked to the mutation in three generations analyzed, being shortest in the proband and in his aunt with marrow failure. Mutagenized TERT vectors transfected into telomerase-deficient VA13 cell lines yielded no telomerase activity using the telomeric repeat amplification protocol (TRAP) assay, whereas when wild-type TERT vectors were co-transfected, telomerase activity was approximately half of wild-type transfected only, indicating haploinsufficiency as a mechanism of telomere shortening. Our results confirm the association between aplastic anemia and TERT mutations. The pattern of hematologic disease in this kindred does not support disease anticipation in TERT mutations. Most remarkably, there is a likely relationship between a telomerase gene mutation and hematological malignancy and severe liver disease.