Directto Consumer Testing

Since the completion of the Human Genome Project in 2003, more companies now offer direct-to-consumer (DTC) genetic testing. The public profile of DTC testing increased dramatically over the last several years with the advent of inexpensive, genome-wide scans for SNPs. Tests that measure millions of genetic variations simultaneously can be obtained with a saliva sample and a few hundred dollars. The majority of these markers are probably of little significance to the tested individual's health, and patients may both overestimate and underestimate their personal risk of disease based on the results of such testing. The other types of tests offered can be grouped into "medical" and "nonmedical" categories. Medical tests include highly validated DNA testing for specific mutations in classic single-gene mendelian disorders, pharmacogenetic testing, and paternity testing. Nonmedical testing ranges from determining one's ethnic and geographic origins or athletic prowess to ear wax type. DTC testing can offer advantages of anonymity for testing as well as easy access to genetic tests that might be difficult to obtain through routine health care channels. The consumer pays for most DTC genetic testing.

Clinicians should recognize that "buyer beware" applies to DTC genetic testing. National regulatory oversight ensuring the analytic and clinical validity of these tests is inadequate, although some states (California, New York) have enacted laws to increase scrutiny of consumer-oriented tests. Even

Table 44-4 Pharmacogenetic Testing

Drug

Gene

Notes

Abacavir

HLA-B*5701

HIV-1 patients

Aminoglycosides

A1555G

Not routinely

Antifolate chemotherapy

MTHFR

Not routinely

Azathioprine

TPMT

Not routinely

Beta blockers

CYP2D6

Not routinely

Irinotecan

UGT1A1

Not routinely

Opioids

CYP2D6

Not routinely

Oral contraceptives

FVL, prothrombin G20210A, others

Family and personal history of VT can be used

SSRIs

CYP450

EGAPP recommended against, 2007.

Carbamazepine

HLA-B*1502

For Asian-Americans

Warfarin

CYP2C9 and VKORC1

Algorithms may work as well/better.

HIV-1, Human immunodeficiency virus type 1; EGAPP, Evaluation of Genomic Applications in Practice and Prevention; SSRIs, selective serotonin reuptake inhibitors; ]VT, venous thrombosis.

with accurate testing, there is no assurance that the result will be clinically useful to the individual. This is particularly problematic when a trained health professional is not available to help individuals appropriately select and interpret genetic testing. Companies now offer phone-based genetic counseling services independent of any testing services. Phone counseling has been shown to be effective for a variety of genetic conditions, and it remains to be seen how this type of counseling service might affect the movement to increasing DTC access to genetic tests. Ideally, a trained health professional should be involved in ordering and interpreting any genetic or genomic testing with health implications.

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