Hepatic disease is mentioned in reviews of dyskeratosis congenita, estimated at about seven percent of patients, but not well characterized and often blamed on hemochromatosis from frequent blood transfusions 
. A few case reports describe cirrhosis and hepatic cell necrosis in affected individuals in autosomal dominant pedigrees 
. Liver complications are described as more frequent and severe in occasional case reports of bone marrow transplantation in dyskeratosis congenita 
. In a recent series of 150 patients with idiopathic interstitial pneumonias, four patients (3%) also had cryptogenic liver cirrhosis diagnosed in the sixth or seventh decades of life; none of these four patients, however, carried a telomerase mutation 
Our families did not present in childhood or display the characteristic physical anomalies typical of dyskeratosis congenita, except for the premature graying of hair in families A and C that did not track with the mutations. Similar to the spectrum of hematological findings associated with telomerase mutations, ranging from isolated macrocytosis to acute myeloid leukemia, liver disease was heterogeneous in severity and pathology among telomerase-mutation carriers. However, in our comprehensive histopathological analysis, some findings were recurrent: most patients had both inflammatory and fibrotic components; several patients developed cirrhosis; individuals from three different families (A, C, and E) had histological findings consistent with hepatic nodular regeneration (). In others, iron accumulation was observed, in the absence of a history of blood transfusion or HFE
gene mutation. In two instances from different families, CD34 stained positive in sinusoidal endothelial cells, consistent with portal hypertension. Alcohol consumption was observed in affected individuals in families B and D, suggesting a role for environmental factors triggering organ injury; however, serologies for viral hepatitis were negative for all individuals tested. Of interest, more than a decade ago, we identified two families with a “new familial syndrome” characterized by a combination of bone marrow failure and chronic liver disease 
. A recent study reports a family with pulmonary fibrosis, hepatic nodular regenerative hyperplasia, and aplastic anemia 
and another describes a case of regenerative hyperplasia and aplastic anemia 
. Unfortunately, telomerase complex genes were not sequenced in these two families. The wide range in clinical phenotypes associated with telomerase mutations is compatible with the variable genetic penetrance of these mutations and of their effects on telomere shortening. The variety in histopathological findings in liver specimens also suggests that other genetic, epigenetic, and environmental factors are essential for disease development and progression.
Hepatic profile of patients with telomerase mutations and liver disease.
Our current findings parallel the recently reported association of loss-of-function TERT
mutations with familial idiopathic pulmonary fibrosis 
. As was hypothesized for pulmonary fibrosis, shortened telomeres may result from dysfunctional telomere repair, increased cell turn-over, or a combination of factors and contribute to liver fibrosis.
In murine models, chronic chemical liver injury is associated with increased regeneration defects and liver cirrhosis in telomerase-deficient mice; restoration of telomerase activity by gene transduction abrogates liver cirrhosis and improves liver function 
. Short and dysfunctional telomeres in Tert
-deficient (and p53-mutated) mice also increase susceptibility to toxin-induced hepatocellular carcinoma 
. In murine livers lacking telomeric repeat binding factor 2, hepatocytes remained viable and regenerated despite telomeric deprotection and fusion through endoreduplication 
. Telomeres in liver cells might be maintained by recombination only as long as lengthy telomere repeat tracts are available on some chromosome ends, which is unlikely when telomerase is deficient. Alternatively, the presence of inflammatory cells in liver sections even at very early stages of liver disease (Subject B-III-7, ) suggests that these cells may be the key mediators of pathogenic fibrosis in the setting of telomere shortening. At damaged sites of chronically injured tissues or organs, such as the liver and lung, the release of inflammatory mediators recruits leukocytes to the extracellular matrix 
. T cells chronically secrete profibrotic cytokines that activate macrophages and fibroblasts, which subsequently stimulate myofibroblasts, which may be of bone marrow derivation. Telomere erosion in neutrophils and lymphocytes, cells critical to the inflammatory response, may elicit an abnormal, sustained profibrotic response.
The pathophysiology for hepatic nodular regenerative hyperplasia is unknown. It is associated with vasculitis and exposure to drugs, such as azathioprine; one case in our series (Subject A-III-11) developed fatal liver disease after azathioprine administration. More than five percent of autopsied individuals over eighty years old have nodular regenerative hyperplasia, and portal hypertension is a major complication 
. Taken together, the link of telomerase deficiency to pulmonary fibrosis and the present findings open a new perspective in the investigation of inflammation, regeneration, and fibrosis and lend support to a crucial role of telomerase in these processes. Up-regulation of telomerase expression and activity may be an attractive therapeutic target for the treatment of fibrotic and regenerative diseases.
In family A, both the patient and his father showed clonal evolution of a malignant cell population, a finding also observed in families C and D. Leukemic cells appear to require telomerase activity for proliferation. However, telomerase deficiency increases the presence of critically short telomeres, which are prone to chromosomal instability. Myelodysplasia and acute leukemia are observed in classic dyskeratosis congenita in 1% 
to 3% of cases 
, and the risk of developing acute myeloid leukemia in dyskeratosis congenita patients is increased almost 200 fold in comparison to the expected incidence in the population 
. We recently found an increased rate of constitutional TERT
hypomorphic mutations in patients with acute myeloid leukemia 
. Telomerase mutations were associated with cytogenetic abnormalities, especially trisomy 8 and inv(16). Short telomeres may limit normal stem cell division by inducing proliferation arrest and select for stem cells with dysfunctional telomeres and defective DNA damage responses that are prone to chromosomal instability. Additionally, genome-wide association studies implicated TERT
as a strong susceptibility locus (chr 5p15.33) for a large variety of cancers 
Notable characteristics of telomerase mutations in these families include incomplete penetrance and variable expressivity. Some family members have the mutation and short telomeres but appear healthy. Of clinical relevance, these findings indicate that the presence of a telomerase gene mutation and very short telomeres do not necessarily translate into disease. In addition, the phenotypes associated with the mutation are quite disparate in nature. Mutations in telomerase and short telomeres must work in concert with other genetic and environmental factors to result in the diverse phenotypes with which these mutations now have been associated.