Atypical aging in Down syndrome

Abstract

At present, there may be over 210,000 people with Down syndrome (DS) over the age of 55 in the United States (US) who have significant needs for augmented services due to circumstances related to ordinary and/or pathological aging. From 1979 through 2003, the birth prevalence of DS rose from 9.0 to 11.8 (31.1%) per 10,000 live births in 10 representative US regions. This increase, largely due to women conceiving after age 35, portends an ever-growing population of people with DS who may be subject to pathogenic aging. Whereas Trisomy 21 is one of the most widespread genetic causes of intellectual disability (ID), it still is one of the least understood of all genetic ID syndromes. While longevity in people with DS has improved appreciably in as modest a period as 30 years, age-specific risk for mortality still is considerably increased compared both with other people with ID or with the typically developing population. The penetrance of the phenotype is widely distributed, even though a consistent genotype is assumed in 95% of the cases. Some, but not all body systems, exhibit signs of premature or accelerated aging. This may be due to both genetic and epigenetic inheritance. We now know that the long-term outcome for people with DS is not as ominous as once contemplated; a number of people with DS are living into their late 60s and 70s with few if any major signs of pathogenic aging. Alzheimer's disease (AD), a devastating disease that robs a person of their memory, abilities and personality, is particularly common in elder adults with DS, but is not a certainty as originally thought, some 20% to 30% of elder adults with DS might never show any, or at most mild signs of AD. DS has been called a mature well-understood syndrome, not in need of further research or science funding. We are only beginning to understand how epigenetics affects the phenotype and it may be feasible in the future to alter the phenotype through epigenetic interventions. This chapter is divided into two sections. The first section will review typical and atypical aging patterns in somatic issues in elder adults with DS; the second section will review the multifaceted relationship between AD and DS.

Keywords: Alzheimer's disease; Down syndrome; accelerated aging; aging; dementia; epigenetics; trisomy 21.