Men whose blood cells had lost the Y chromosome were at higher risk of developing Alzheimer's disease in three independent case-control and prospective studies. Most genetic risk studies focus on specific mutations or structural variations in the genome, but men can develop a far more wholesale genomic change – loss of the Y chromosome in specific cells. Recent studies have shown that roughly 15 percent of men over the age of 70 have lost the Y chromosome in at least 10 percent of their blood cells.