-A curious adult from Michigan
July 13, 2004
You are right, both Alzheimer's and Down syndrome have been linked to chromosome 21. As you probably know, chromosomes have lots of genes, many of which can cause disease when mutated. Chromosome 21, which has around 225 genes, is involved in many diseases.
Alzheimer's and Down syndrome are caused by different changes in chromosome 21. Down syndrome is caused when some or all of chromosome 21 is duplicated. The Alzheimer's link is to a single gene, APP, found on chromosome 21.