Mosaic loss of chromosome Y

Mosaic loss of chromosome Y (mLOY) also known as loss of chromosome Y (LOY) occurs to many men in some cells due to aging. Instead of the expected 46,XY karyotype, the affected cells have a 45,X karyotype due to the loss of the Y chromosome.

Discovery
The occurrence of LOY was discovered in 1963.

Risk factors
"Age, genetic variants, ChrY structural aberrations and environmental stressors" such as smoking tobacco are all risk factors for developing LOY. The prevalence increases exponentially with age and more than 40 percent of men over 70 are affected. Unlike loss of autosomal chromosomes, loss of sex chromosomes except the one active X chromosome does not typically cause cell death. Elderly women also experience mosaic loss of chromsome X, but it is less common than LOY.

Health implications
LOY in a small proportion of leukocytes (white blood cells) has been associated with a number of diseases such as cancer, Alzheimer's disease, and cardiovascular disease. Why this is the case is not understood. LOY can also occur in cells of the buccal mucosa and dorsolateral prefrontal cortex.