Head Injury Raises Risk of Alzheimer's - Brief Article - Statistical Data Included

Family Practice News, Jan 15, 2000 by Barbara Baker

SAN FRANCISCO -- Head injury is an independent risk factor for the development of Alzheimer's disease.

The risk is independent of whether patients carry apolipoprotein E4 (apo E-4), the genotype known to predispose to the disease, Dr. Lindsay A. Farrer, Ph.D., said in a poster presentation at the annual meeting of the American Society of Human Genetics.

The apo E-4 allele on chromosome 19, found in 5%-25% of the population depending on ethnicity, was identified in 1991 as a risk factor for developing Alzheimer's disease after age 60. The allele is present in at least half of Alzheimer's disease patients.

The relationship between head injury apo E-4, and Alzheimer's disease was evaluated in a multicenter epidemiologic study of 2,233 probands with probable or definite Alzheimer's disease, 4,465 parents, 7,694 siblings, and 2,509 spouses.

A history of head injury was found in 18% of probands, but only 5% of spouses without the disease. A history of head injury with loss of consciousness was found in 9% of prohands and 1% of spouses. A history of head injury without loss of consciousness was found in 10% of probands and 4% of spouses, reported Dr. Farrer of Boston University.

Survival analysis showed that at 93 years of age, parents and siblings had a 77% cumulative risk of developing Alzheimer's disease if they had a head injury and a 34% risk without a head injury.

The combined effects of head injury and the apo E-4 genotype was evaluated in a subgroup of 942 probands with Alzheimer's disease and 327 spouses and siblings. Individuals with two apo E-4 alleles and a history of head injury had a 10-fold increased risk of developing Alzheimer s disease compared with those lacking both these factors. Those who were homozygous for the apo E-4 allele and had no history of head injury had an eightfold increased risk.

Individuals heterozygous for the apo E-4 allele had a sixfold increased risk of developing Alzheimer's disease if they had a head injury and threefold increased risk if they hadn't had a head injury compared with those with neither of these risk factors.

A head injury in the absence of an apo E-4 allele was associated with a threefold increased risk of Alzheimer's disease.