Accelerated Aging: Human Progeroid Syndromes

Detractors argue that segmental progeroid syndromes do not reflect normal aging, usually pointing out symptoms unrelated to aging or the lack of specific normal aging characteristics. Moreover, some accelerated aging symptoms described in progeroid syndromes may have subtle physiological differences that distinguish them from similar features of normal aging. This would suggest that the defect that underlies such an accelerated aging characteristic is distinct from defects that occur during normal aging. Clearly, normal aging is a genetically complex process that cannot be fully explained by comparison to several diseases involving a very small set of genes.

However, these weaknesses of progeroid syndromes as models of normal aging also highlight their strengths. The specific genetic defects that cause progeroid syndromes facilitate examination of biochemical deficiencies associated with certain accelerated aging characteristics. By contrast, the contributions of the many genes that impinge on normal aging are almost impossible to evaluate. It is likely that there are multiple underlying causes for all of the features of normal aging. Thus, the acceleration of specific aging characteristics that occur in progeroid syndromes may provide insight into specific pathways that fail and underlying mechanisms that operate, albeit at a slower pace, during the later development of similar characteristics during normal aging. Moreover, identification of defective genes that result in accelerated aging allows discovery of beneficial disadvantageous alleles of those genes (and other functionally related genes) that might delay or modestly hasten, respectively, the onset of normal aging characteristics. Below are brief descriptions of five genetic diseases that are regarded as the best models of accelerated aging.