Clinical Relevance of Clonal Hematopoiesis in the Oldest-Old Population: Analysis of the "Health and Anemia" Study

Background. Age-dependent clonal expansion of somatic mutations in the hematopoietic system is associated with an increased risk of hematological cancers (including myelodysplastic syndromes, MDS) and other illnesses (coronary heart disease and stroke). However, the presence of clonal hematopoiesis per se in a given individual has only limited predictive power. We hypothesized that the study of oldest-old population can define more specifically the relationship between mutations in the hematopoietic system and risk for MDS, inflammation and vascular diseases.

Methods. We analyzed 1004 oldest-old subjects (median age 84.2y, range 80-105) included in the "Health and Anemia" population-based study [Haematologica 2010;95:1849]. Using peripheral blood DNA, we looked for somatic mutations in 47 genes recurrently mutated in hematologic cancers.

Results. Clonal mutations were observed in 32.8% of individuals (range 1-5). The majority of variants occurred in 3 genes: DNMT3A (36.4%), TET2 (24.3%) and ASXL1 (6.5%). Mutations in splicing genes, PPM1D and TP53 were found in 7.4%, 5% and 2% of cases, respectively. The mutation frequencies increased with age, up to 50% in individuals aged over 90 years (P=.011). Clonal hematopoiesis was associated with a lower 5-y probability of survival (P=.03), and prognosis was even poorer in patients carrying ≥2 mutations (P=.002)

We first focused on the relationship between clonal hematopoiesis and MDS phenotype. Carrying a somatic mutation with a variant allele frequency (VAF) ≥.10, carrying ≥2 mutations, spliceosome gene mutations and co-mutation patterns involving TET2, DNMT3A had a positive predictive value for MDS (from .85 to 1.0). The most frequent early phenotypic changes in patients who developed MDS included an increasing red blood cell distribution width (RDW) and mean corpuscular volume (MCV). Preliminary analyses suggested that the combination of mutations and non-mutational factors (RDW, MCV, after excluding iron/vitamin depletion and thalassemia) may improve the capability to capture individual risk of developing MDS with respect to molecular data alone (P=.01)

We studied clonal evolution in 72 patients with multiple samples available over a period of 5y. Clonal hematopoiesis was found at baseline in 22 cases: 2 individuals acquired additional mutations during follow-up, and 5 displayed significant increase in VAF. In 9 subjects without clonal hematopoiesis, mutations were acquired during follow-up. RDW and MCV changes, induction of unexplained cytopenia and overt MDS phenotype were significantly restricted to subjects displaying clonal evolution.

We hypothesized that in oldest-old populations MDS could be underdiagnosed (many patients are not considered for bone marrow aspiration because of age). Cytopenia was a common finding in our cohort (20%) the underlying cause remaining unexplained in 27% of cases. In patients with unexplained anemia, carrying a somatic mutation had a positive predictive value for persistent, progressive, multilineage cytopenia (findings consistent with a MDS phenotype) and shorter survival (from .8 to .94). On this basis, 8% of all cytopenias might be undiagnosed MDS.

Finally, we investigated the association between clonal hematopoiesis with inflammatory and vascular diseases. Mutations in DNMT3A, TET2, and ASXL1 were each individually associated with risk of coronary heart disease and death, and preliminary analyses suggest that clonal hematopoiesis is also associated with increased risk of rheumatological diseases (P from .03 to.009). We identified mutations in macrophages isolated from synovial fluid of 4/17 patients with rheumatoid arthritis and from atherosclerotic plaques of 3/25 patients with carotid stenosis. Functional studies of macrophages (expression of specific chemokine and cytokine gene patterns) are ongoing.

All these findings are under validation in an independent cohort of 800 subjects enrolled in the "Monzino 80-plus" study [Alzheimers Dement 2015;11:258]].

Conclusion. Clonal hematopoiesis was associated with reduced survival in an oldest-old population. Specific mutational profiles define different risks of developing MDS and inflammatory/vascular diseases. Non mutational factors, such as early changes in red blood cell indices, may improve the capability to identify patients at increased risk of developing myeloid cancers.