The Alzheimer amyloid precursor protein maps to human chromosome 21 bands q21.105-q21.05.

The Alzheimer amyloid protein precursor (APP) has previously been localized to human chromosome 21q11.2-q21. We have refined the regional localization to a small region including chromosome bands 21q21.105-q21.05 by using quantitative Southern blot analysis of cell lines aneuploid for parts of chromosome 21. Our findings exclude the APP gene from the minimal region producing the classical phenotypic features of Down syndrome. This further narrowing of the APP location will help in identifying the physical location of the gene causing familial Alzheimer disease.