The following common disorders come with varying degrees of genetic risk. That risk, if it is known, can sometimes be lessened through preventive measures. Other times, it cannot. In these cases, the results of a genetic test can, like a boomerang, lead nowhere and so their value is questionable.


HYPERTENSION
About one in four people in industrialized countries are affected by hypertension, which increases the risk of heart attack and stroke by as much as 40 percent.

Genetic risk
At least 10 genetic variants are known to predispose individuals to hypertension. The most studied are the angiotensinogen (AGT), adducin and angiotensinogen-converting enzyme (ACE) genes.

Prevention
Low sodium intake, drug therapy, smoking cessation.


ASTHMA
Affects five to 10 percent of the population; figures are increasing.

Genetic risk
Scientists have associated about 10 regions on the genome with this disorder, but have not identified any specific genes.

Prevention
Exterminate household mites, the most common environmental factor causing syptoms to appear.


NON INSULIN-DEPENDENT (TYPE 2) DIABETES
Affects one in 10 people older than age 65.

Genetic risk
Researchers have recently identified variants of a susceptibility gene in chromosome 2 (CAPN10). Another 10 regions of the genome are associated with the disorder.

Prevention
Sports, diet, smoking cessation


INSULIN DEPENDENT (TYPE 1 OR JUVENILE) DIABETES
Autoimmune disease. Affects one to three in 1,000 people under the age of 20.

Genetic risk
HLA variants DR3 and DR4 increase the risk 15-fold. Another 15 regions in the genome probably contain predisposing genes.

Prevention No prevention is currently available.


ALZHEIMERs DISEASE
One in five people older than age 80 and 6 to 10 in 100 people older than age 75 are affected.

Genetic risk
People carrying two copies of the E4 version of the apolipoprotein (Apo) gene have ten times the risk of developing Alzheimers as do those with other Apo variants. Rare familial forms are due to mutations in the presenilin (PS1) or amyloid protein (APP) genes.

Prevention
No prevention is currently available. An immunotherapy is under study.


BREAST CANCER
Affects one in eight women in the U.S. About 10 percent of all cases are genetic in origin.

Genetic risk
Hundreds of predisposing mutations have been found in the genes BRCA1 and BRCA2. Women with these mutations have an increased probability (up to 85 percent) of developing breast cancer.

Prevention
Three options are currently available: surveillance using mammograms and clinical breast exams; chemoprevention using drugs such as tamoxifen and ramoxifen; or the surgical removal of healthy breasts and/or ovaries.


AUTISM
From two to 10 in 10,000 children are affected.

Genetic risk
Researchers beleive that a region on chromosome 7, and perhaps another on chromosome 15, are associated with the disease.

Prevention
No prevention is currently available.


COLORECTAL TUMOURS
Five to 10 percent of all cases are hereditary in origin.

Genetic risk
People carring mutations in genes MLH1 or MSH2 are at very high risk.

Prevention
Regular colonoscopies can reduce the risk by more than 60 percent.


MULTIPLE ENDOCRINE NEOPLASIA
Rare tumor of the thyroid gland

Genetic risk
People carrying mutations in the oncogene RET face virtually a 100 percent chance of developing the condition.

Prevention
Surgical removal of thyroid gland.


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