Defining Aging

Experts propose new framework for classification of age-related diseases

close up photo of a senior man's hands on a cane
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The biomedical and public health advances of the past century have increased human longevity around the globe. These great strides notwithstanding, the increase in life expectancy has resulted in the growth of an aging population worldwide, posing a set of medical, public health and socioeconomic challenges.

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The aging population has urgent and unmet health care and economic needs related to chronic disease and multimorbidity, which require solutions at the national and international levels.

To address these needs and challenges, a group of international experts has put forward a position statement laying out a new health care framework for the classification of age-related diseases in an effort to help aging populations stay healthier longer.

The statement, published Oct. 31 in Science, was authored by researchers at 36 institutions in six countries, including Harvard Medical School, MIT, University of Liverpool, the Buck Institute for Research on Aging, University College London, Stanford University, University of Cambridge, Imperial College London, Medical Research Council, London Institute of Medical Sciences and the National Institute on Aging.

“A new framework for the classification of aging as a disease process will be critical in providing a unified way to think about age-related disease and achieve new preventive strategies and design new therapies,” said George Church, professor of genetics at HMS and co-author on the statement. “Scientists are rapidly gaining novel insights into the molecular origins of age-related diseases, and we are seeing these insights lead to small molecules, proteins and cell and gene therapies to stem the tide of age-related disease and enhance humankind’s general wellness and longevity.”

New research by Church and colleagues published in PNAS on Nov. 4 outlines the promise of gene therapy for treating age-related diseases in animals. In the study, scientists successfully improved four age-related conditions in animals by injecting two longevity-associated genes.

Today, for the first time in history, most people can expect to live into their 60s and beyond. By 2020, the number of people age 60 and older will outnumber children younger than 5. By 2050, the world’s population of people age 60 and older is expected to total 2 billion, up from 900 million in 2015, according to the World Health Organization.

Common conditions in older people include cardiovascular illness; cognitive and neurologic diseases such as dementia; back and neck pain; osteoarthritis; chronic obstructive pulmonary disease; diabetes; and sarcopenia, among others.

Additionally, as people age, they are more likely to experience multiple conditions at the same time, including advanced diseases developed over decades. The effective management, prevention and treatment of these conditions demands dedicated research, new disease terminology and new metrics and analytical methods, the authors of the report write.

The current approach to classifying and staging age-related diseases is suboptimal, experts say, because it is inconsistent, incomplete and nonsystematic. For example, certain diseases that affect multiple organs and organ systems, including intrinsic organ aging, or organ atrophy or wasting, are classified in one organ but not another.

"This system of balkanization is far from optimal, where we would be seeking processes key to common and rare diseases, nearly all of which are greatly accelerated by aging,” Church said.

The lack of adequate diagnostic criteria and severity staging for age-related diseases also limits prevention and treatment efforts and hampers the development of new drugs and interventions.

The new position statement proposes a framework for properly and comprehensively classifying and staging the severity of diseases of aging. Importantly, the statement calls for classification of ageing at the tissue and organ level, as well as organ atrophy, pathologic remodelling and calcification, and age-related systemic and metabolic diseases.

The statement is a “call to action” to governments, the WHO and the scientific and medical community to come together to develop classification and staging systems using this proposed framework as the basis for diagnosis and treatment of age-related diseases, including directly treating all aging tissue and organs.

“This framework will increase our ability to develop drugs and interventions that target the processes of aging and that can accumulate with age, which would have unprecedented benefits in relation to the treatment and prevention of serious diseases,” said Stuart Calimport, lead author of the report and University of Liverpool Honorary Fellow.

While aging is classified as a condition within the WHO International Classification of Diseases (ICD-11) in relation to intrinsic skin aging and photoaging, the framework proposes the classification of aging a condition in all organs, along with the comprehensive classification of all aging-related diseases and syndromes.

As part of this work, initial classification submissions related to diseases of aging in line with the framework have already been submitted to the latest version of WHO ICD-11.

“Aging is the greatest biomedical challenge of the 21st century. As such, this framework will increase our ability to develop longevity drugs and interventions that target diseases related to the aging process,” said report co-author Joao Pedro De Magalhaes, a senior lecturer at the University of Liverpool.

Adapted from a University of Liverpool news release.