On the Trail of Telomeres – American Association for Clinical Chemistry (AACC)

Rapid advances in telomere biology are paving the way to new clinical applications that promise better diagnosis and treatment options in select patients. Scientists understanding about the role of telomerescaps at the ends of chromosomes that prevent attrition of DNAhas progressed to the point that telomere measurements are being used in diagnostic workups at some medical centers. Broader dissemination of this type of analysis will go hand-in-hand not only with a deeper understanding of the link between telomere length and health and disease but also more standardized testing methods and parameters. Expanding the use of telomere testing also will depend on better coordinated care among clinical disciplines that have not traditionally worked together, according to Mary Armanios, MD, professor of oncology, genetic medicine, molecular biology and genetics, and pathology at Johns Hopkins University in Baltimore.

The causal role telomeres play in aging and age-related diseases has been known for decades. However, new studies now reveal that extreme short or long telomere lengths are associated with specific heritable diseases and cancers. This knowledge, a pivotal advance, has added urgency to the quest to accurately measure telomere length and define clinically relevant short and long thresholds. With the advent of precision genomics, we have the opportunity to identify and manage these disorders for the benefit of patients, said Mrinal Patnaik, MBBS, an associate professor of medicine and oncology and a consultant hematologist at the Mayo Clinic in Rochester, Minnesota.

Telomeres shorten every time a cell divides, naturally shortening with age and at a certain point signaling cells to stop dividing and become senescent. However, when genes responsible for telomere synthesis, trafficking, maintenance, and for telomerase function are perturbed, accelerated telomere shortening leads to a group of genetic disorders called short telomere syndromes (STS). Notably, although 13 causative genes have been identified, these account for only about 40% of STS cases. The fact that more than half of our patients with short telomeres do not have detectable gene mutations on sequencing panels indicates that we havent yet discovered all the mutations that affect telomere length, said Patnaik.

STS encompass disparate clinical manifestations across multiple organ systems including immunodeficiency, idiopathic pulmonary fibrosis and emphysema, esophageal stenosis and enterocolitis, hepatic fibrosis and cirrhosis, and bone marrow failure. Anytime you see a triad of symptoms that include premature greying of hair, fibrotic involvement of lung and liver, and bone marrow failure, it should raise flags as a potential STS, said Patnaik.

In contrast, mutations that lengthen telomeres cause long telomere syndromes. These are associated with a high cancer risk: glioma and familial melanoma, in particular. Insights from genome-wide association studies have identified genetic variants in telomere-related genes concurrent with these cancers, further strengthening the telomere-cancer link.

Diagnosing patients with telomere length disorders is challenging, especially STS, given their broad clinical spectrum. The Telomere Clinic at Johns Hopkins Sidney Kimmel Comprehensive Cancer Center, which Armanios leads, offers a telomere measurement service to clinicians and provides multidisciplinary care to patients with telomere-related disorders. Our goal was to establish a clinically reliable tool for telomere length measurement in a hospital setting and make it available to physicians and their patients for precise diagnosis and treatment recommendations, she said.

Patients with severe STS often need organ transplants as a result of end-organ failure. Telomere-related testing can offer these patients a more tailored approach to managing their disease, especially in pre-transplant settings. For example, most patients with STS cant tolerate standard doses of radiation and cytotoxic therapies; recognizing this enables physicians to choose a different conditioning regimen. Also, dysfunctional telomere-related gene(s) are passed through autosomal or X-linked transmission; physicians can therefore screen potential donorsoften patients close relativesto make sure they do not carry these same faulty gene(s).

Armanios and her team recently reported using telomere length as a diagnostic tool to identify patients with STS (Proc Natl Acad Sci U S A 2018;115:E235865). After establishing normal telomere ranges from a healthy control population and determining that telomere measurements have tight concordance and reproducible upper and lower boundaries across populations, they also found that most patients with variants in telomere-related genes had short telomere lengths. In addition, they observed a correlation between the severity of the disease phenotype and the age at diagnosis. We saw different clinical presentations depending on when telomeres reached a critical threshold, said lead author Jonathan Alder, PhD, now an assistant professor of medicine at the University of Pittsburgh. Crucially, the Johns Hopkins team reported that telomere measurements led to treatment changes in one-quarter of 38 pediatric and adult patients with idiopathic bone marrow failure as physicians changed to less harsh therapies like reduced doses of chemotherapy and less use of immunosuppressant drugs.

Patnaik and his colleagues also use telomere testing to assess patients with bone marrow failure, as part of Mayo Clinics Center for Individualized Medicine. We found very quickly that the most common referrals to the Center were people with short telomere syndromes that extended beyond bone marrow failure into conditions like lung and liver fibrosis, he said. In recent reports, he and his team have described their diagnostic workups for patients with suspected inherited STS and with unexplained cytopenias. In the case of inherited STS, they defined this population as having telomere lengths in either granulocytes or lymphocytes less than the first centile of normal controls (Mayo Clin Proc 2018;93:834-9). They perform this screening in concert with an in-house next-generation-sequencing (NGS) panel that consists of telomere-associated genes. Patients who test negative for the NGS panel proceed to research-based whole-exome sequencing to identify other potential mutations.

The options for measuring telomere length are broadand complicated. We are measuring a population of cells, and each cell has between 92 and 184 telomeres, so we are really measuring a population of telomere lengths in an individual, said Alder. Some methods measure individual telomere length, some measure the average, some measure the average of many cells together, and still others measure the average of individual cells.

These methodologies encompass quantitative polymerase chain reaction (qPCR), fluorescence in situ hybridization (FISH)-based techniquesincluding flow cytometry combined with FISH (flow-FISH) and quantitative FISHtelomere restriction fragment length analysis, optical techniques, and hybridization protection assays. In hospital settings, the preferred method is flow-FISH, which both Johns Hopkins and Mayo Clinic use. Both favor this approach because of its accuracy, reproducibility, ability to define normal telomere length range, and ability to test large numbers of samples. Flow-FISH is standardized, clinically validated, cost-effective, commercially available, and can be implemented anywhere to screen patients with suboptimal telomere length, said Patnaik. Flow-FISH reports also provide data on telomere lengths relative to age, which is important because telomere attrition is part of the normal aging process.

Although an estimated 5,000 to 10,000 individuals in the U.S. have STS, the place for telomere testing remains unclear in diagnosing and predicting long telomere-associated cancers. In cancers where telomere length is elongated, the role of telomere-related testing is still ongoing and not quite ready for clinical prime time, said Patnaik. He added that more research into understanding why shorter telomeres negatively impact outcomes in the management of bone marrow failure syndromes and blood cancers will be quite useful, potentially informing future clinical interventions.

Others remain skeptical about how broadly telomere testing might disseminate. Telomere length testing makes complete sense for rare diseases like STS where you have a specific genetic cause. But I dont think it has any clinical relevance as yet for identifying risk factors for more common diseases like cancer, cardiovascular disease, diabetes, chronic lung disease, Alzheimers disease, and infectious diseases, said Brge Nordestgaard, MD, professor of clinical medicine at the University of Copenhagen and chief physician in the department of clinical biochemistry at Herlev and Gentofte Hospital and Copenhagen University Hospital Denmark. Nordestgaard has conducted genetic epidemiology studies exploring long telomere length and cancer risk and short telomere length and ischemic heart disease risk.

Alder agreed that work remains in identifying the best diagnostic niches for this emerging field. Telomere testing is definitely not a standard part of every clinical work-up in the nation. In the future, it is important to define clinical scenarios where it makes sense for telomeres to be measured, he said. The next step would be to define what the critical thresholds are for making a diagnosis that can lead to an actionable intervention.

Even as the science and practice of telomere testing remains in flux, Armanios, speaking at a Pulmonary Fibrosis Foundation meeting, laid out a future in which genetic evaluation with telomere length might replace lung biopsies in affected patients. She also envisions a time when identifying patients with telomere-mediated lung disease could aid in managing lung transplants, both for anticipating and averting complications.

One catch in advancing the field is that there are no specific treatments for telomere biology disorders. Patnaik echoed Armanios call for specialty-crossing care to plot next steps for newly diagnosed patients. More centers of excellence are needed that can integrate different clinical fields and provide a unique multidisciplinary skill set to manage and counsel these patients, he stressed.

Pranali P. Pathare, PhD, is a medical writer and editor in St. Louis. +Email: ppranali@gmail.com

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On the Trail of Telomeres - American Association for Clinical Chemistry (AACC)