Genetic testing can detect a wide range of conditions, from inherited diseases and cancer risk to how your body processes specific medications. The term covers dozens of different test types, each designed to answer a different question. Some confirm a diagnosis when symptoms are already present. Others reveal risks you’d never know about without looking at your DNA. Here’s what each type of testing can actually find.
Diagnosing Conditions You Already Have Symptoms Of
Diagnostic genetic testing is used when someone already has symptoms and a doctor suspects a genetic cause. The goal is to confirm or rule out a specific disorder. This might happen when a child shows developmental delays, when an adult develops unexplained muscle weakness, or when a pattern of symptoms doesn’t match a straightforward diagnosis.
For patients with rare diseases that have gone undiagnosed through standard workups, a technique called whole exome sequencing can scan nearly all of the protein-coding regions of your DNA at once. In a study of 825 patients who underwent this type of testing, 33.7% received a definitive genetic diagnosis. That means roughly one in three people with a previously unexplained condition got an answer. The success rate varies depending on the type of symptoms and whether other family members can also be tested, but for many families, it ends a years-long diagnostic journey.
Carrier Screening Before or During Pregnancy
Carrier screening identifies people who carry a single copy of a gene mutation for a recessive disorder. Carriers typically have no symptoms themselves, but if both parents carry mutations in the same gene, each pregnancy has a 25% chance of producing a child with the condition.
The conditions most commonly screened for include cystic fibrosis, sickle cell disease, and spinal muscular atrophy. Cystic fibrosis is the most common life-threatening recessive condition in the non-Hispanic white population, affecting about 1 in 2,500 individuals in that group. Spinal muscular atrophy, which causes progressive muscle weakness due to degeneration of motor neurons in the spinal cord, has gained increasing screening attention because of its severity and relatively high carrier frequency across ethnic groups.
Carrier screening is typically offered to people planning a pregnancy or already pregnant, those with a family history of a genetic condition, and individuals from ethnic or racial groups with higher carrier rates for specific disorders. The results help couples understand their reproductive options, not predict whether they personally will get sick.
Hereditary Cancer Risk
Predictive genetic testing can identify inherited mutations that significantly raise your lifetime risk of developing certain cancers, even when you’re completely healthy at the time of testing. This is one of the most well-known applications of genetic testing, largely because of the BRCA1 and BRCA2 genes.
Mutations in BRCA1 or BRCA2 cause hereditary breast and ovarian cancer syndrome. Women with these mutations face substantially elevated risks of breast and ovarian cancer compared to the general population. But hereditary cancer syndromes go well beyond breast cancer. Lynch syndrome, caused by mutations in any of five different genes, increases the risk of colorectal, endometrial, ovarian, and several other cancers. Familial adenomatous polyposis, caused by a mutation in the APC gene, leads to hundreds or thousands of polyps in the colon that will almost certainly become cancerous without intervention.
Knowing about these mutations before cancer develops changes the game. It can lead to earlier and more frequent screening, preventive surgeries, or targeted surveillance that catches cancer at its most treatable stage. Testing is generally recommended for people with a strong family pattern of cancer, such as multiple relatives diagnosed at young ages or clusters of related cancer types.
Prenatal Chromosomal Conditions
Non-invasive prenatal testing, commonly called NIPT, analyzes fragments of fetal DNA circulating in a pregnant person’s blood. It screens for extra or missing chromosomes in the developing baby, and it’s remarkably accurate for certain conditions.
NIPT detects 98 to 99% of pregnancies affected by Down syndrome (trisomy 21), trisomy 18, and trisomy 13. The false-positive rate for Down syndrome and trisomy 18 is very low, roughly 1 in 500 tests. Detection rates for sex chromosome differences, such as Turner syndrome or Klinefelter syndrome, are somewhat lower at 79 to 92%.
It’s important to understand that NIPT is a screening test, not a diagnostic one. A positive result indicates elevated risk and is typically followed by a confirmatory procedure like amniocentesis. But the high detection rate and low false-positive rate make it a powerful first step, available as early as 10 weeks of pregnancy.
How Your Body Processes Medications
Pharmacogenomic testing reveals how your genetic makeup affects the way you metabolize certain drugs. Two key genes, CYP2D6 and CYP2C19, influence how your liver breaks down a wide range of medications. The FDA maintains a table of pharmacogenetic associations that now includes dozens of drugs where genetic variation meaningfully changes effectiveness or safety.
The practical impact can be significant. If you’re a “poor metabolizer” for CYP2D6, drugs like certain antipsychotics, ADHD medications, and heart rhythm drugs build up to higher levels in your blood, increasing the risk of side effects. For the blood thinner clopidogrel, poor metabolizers of CYP2C19 actually get less benefit from the drug because their bodies can’t convert it into its active form, potentially leaving them underprotected against blood clots.
On the other end of the spectrum, “ultrarapid metabolizers” convert some drugs too quickly. With codeine and tramadol, ultrarapid CYP2D6 metabolizers produce dangerously high levels of the active compound, which can cause life-threatening respiratory depression. Both drugs are contraindicated in children under 12 for this reason. Pharmacogenomic testing is increasingly used before prescribing psychiatric medications, pain management drugs, and certain cardiac therapies to get the dose right the first time.
Direct-to-Consumer Health Risk Reports
Home DNA kits offer a different, more limited window into genetic health. The FDA has authorized direct-to-consumer genetic health risk reports for a specific list of conditions. These include late-onset Alzheimer’s disease (testing for the APOE ε4 variant), Parkinson’s disease, hereditary hemochromatosis (iron overload), celiac disease, alpha-1 antitrypsin deficiency (a lung and liver condition), and several blood clotting disorders.
The FDA has also authorized a consumer test for three specific BRCA1/BRCA2 variants most common in people of Ashkenazi Jewish descent. This is a critical distinction: those three variants represent a tiny fraction of the thousands of known BRCA mutations. A negative result on a consumer test does not mean you’re free of BRCA risk, especially if you have a family history of breast or ovarian cancer. Clinical BRCA testing ordered through a healthcare provider sequences the entire gene and catches far more mutations.
Consumer tests tend to return results faster and cost less than clinical tests. But they check only for selected variants rather than performing comprehensive analysis, so they work better as a starting point for awareness than as a definitive medical assessment.
Presymptomatic Testing for Known Family Conditions
Predictive testing falls into two categories, and the distinction matters. Presymptomatic testing applies when a known gene mutation guarantees that symptoms will eventually develop. The classic example is Huntington disease: if you inherit the mutation, you will develop the condition. Testing tells you whether that future is ahead of you.
Predispositional testing is different. It identifies mutations that raise your likelihood of a condition but don’t make it certain. The BRCA mutations fall into this category. Carrying the mutation increases risk dramatically, but not every carrier develops cancer. This distinction shapes how results are used: presymptomatic results often trigger planning for inevitable disease management, while predispositional results guide screening intensity and prevention strategies.
What Results Can and Can’t Tell You
Genetic test results aren’t always a clean yes or no. Between 20% and 40% of variants identified on multi-gene panels are classified as “variants of uncertain significance,” meaning the lab found a DNA change but current science can’t determine whether it’s harmful or harmless. These results are not actionable, which can create real frustration and anxiety. Larger gene panels tend to produce more of these ambiguous findings. Over time, as more data accumulates, some of these variants get reclassified as either benign or disease-causing, but that process can take years.
A negative result also has limits. Most genetic tests look for known mutations in specific genes. A negative result means those particular mutations weren’t found, not that your risk is zero. Your family history, personal health, and other risk factors still matter even when genetic testing comes back clear.