Early-onset Alzheimer’s disease, also called younger onset Alzheimer’s disease, is an uncommon form of dementia which affects individuals younger than the age of 65. Of all the people afflicted with Alzheimer’s disease, only an estimated five percent will develop symptoms at a younger age.
In limited cases, about a few hundred families worldwide, scientists have discovered several rare genes which directly cause this condition. Those who inherit these particular genes develop symptoms in their 30s, 40s and 50s. (1)
Autosomal Dominant Inheritance
In genetic research, familial Alzheimer’s is distinguished from sporadic Alzheimer’s. Currently, all cases of familial Alzheimer’s have an early onset. An estimated 50 percent of these cases are known to be caused by mutations in three genes located on three different chromosomes, which are the structures inside cells that house the genetic code.
Defects in the gene called amyloid precursor protein causes an abnormal form of the amyloid protein to be produced. Mutations in the gene called presenilin 1 cause an abnormal form of the presenilin 1 protein to be produced while mutations in the gene called presenilin 2 cause an abnormal form of the presenilin 2 protein to be produced.
The Fisher Center for Alzheimer’s Research Development states that “even if one of these
mutations is present in only one of the two copies of a gene inherited from a person’s parents, the person will inevitably develop that form of early-onset Alzheimer’s.”
This pattern of inheritance of a condition requiring only a single copy of a disease associated mutation is called autosomal dominant inheritance. (2)
Ten Warning Signs
Typically, the disease develops slowly and progressively worsens. Ten warning signs begin with memory loss, especially short term memory or forgetting recently learned information. Others become challenged by following a recipe, keeping track of monthly bills, concentrating or developing and following a plan.
Some find it hard to complete familiar tasks at home or at work, have trouble driving to a familiar location or remembering the rules of a favorite game.