%0 Journal Article
%T ¦Â-Secretases, Alzheimer¡¯s Disease, and Down Syndrome
%A Robin L. Webb
%A M. Paul Murphy
%J Current Gerontology and Geriatrics Research
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/362839
%X Individuals with Down Syndrome (DS), or trisomy 21, develop Alzheimer¡¯s disease (AD) pathology by approximately 40 years of age. Chromosome 21 harbors several genes implicated in AD, including the amyloid precursor protein and one homologue of the ¦Â-site APP cleaving enzyme, BACE2. Processing of the amyloid precursor protein by ¦Â-secretase (BACE) is the rate-limiting step in the production of the pathogenic A¦Â peptide. Increased amounts of APP in the DS brain result in increased amounts of A¦Â and extracellular plaque formation beginning early in life. BACE dysregulation potentially represents an overlapping biological mechanism with sporadic AD and a common therapeutic target. As the lifespan for those with DS continues to increase, age-related concerns such as obesity, depression, and AD are of growing concern. The ability to prevent or delay the progression of neurodegenerative diseases will promote healthy aging and improve quality of life for those with DS. 1. Introduction According to the CDC, 1 in 700 infants born have Down syndrome (DS), approximately 400,000 people in the US and 6 million people world-wide. DS is caused by an extra copy of chromosome 21 that arises during gametogenesis. In 95% of cases, this occurs as the result of chromosomal nondisjunction [1]. This is usually due to improper segregation of chromosomes into daughter cells during meiosis I (Figure 1), although nondisjunction in meiosis II also occurs. This results in gametes that have two copies of chromosome 21 (HSA 21), and upon fusion with another gamete, results in trisomy 21. Although HSA 21 is the smallest human autosome, the chromosome encodes more than 400 known genes [2], a number that may increase with further study. Less frequently, DS occurs due to somatic mosaicism or translocations [1]. DS presents with an easily recognizable phenotype, including a characteristic set of facial features, delayed development, and varying levels of intellectual disability, shortened stature, muscle hypotonia, joint laxity, AD-like neuropathology, and a heterogeneous range of other traits. Figure 1: Chromosomal nondisjunction. (a) Most often Down syndrome (DS) occurs as an error in meiosis I (usually in the oocyte). Chromosomal nondisjunction, or improper segregation of chromosome 21 (the smallest autosome; orange), results in one precursor cell having 2 copies (b), upper half) while the other has zero (b), lower half). (c) Meiosis II then proceeds, with the outcome being two gametes that possess an extra copy of chromosome 21 which, after fusion with another gamete, bears 3 copies of
%U http://www.hindawi.com/journals/cggr/2012/362839/