How genetic testing works, which tests to ask for, and how results can unlock treatments and clinical trials.
About 72% of rare diseases are genetic, according to a 2020 analysis of more than 6,000 rare diseases in the Orphanet database, yet many patients go years without a definitive molecular diagnosis. Genetic testing can end a diagnostic odyssey by identifying the specific mutation causing your condition. Beyond closure, a genetic diagnosis unlocks access to targeted therapies, determines eligibility for gene therapy trials, informs family planning decisions, and connects you with the right specialist community.
For clinical trials specifically, genetic testing has become increasingly essential. Many current trials for rare diseases are mutation-specific, meaning they only enroll patients with particular genetic variants. Without testing, you may be eligible for a life-changing trial and never know it.
Single-gene testing analyzes one specific gene when your doctor strongly suspects a particular condition based on symptoms and family history. This is the fastest and least expensive approach when the clinical picture clearly points to a known genetic disorder.
Gene panels test a curated set of genes (typically 10 to 100+) associated with a group of related conditions. For example, a cardiomyopathy panel might test 50 genes known to cause inherited heart muscle disease. Panels are commonly used when symptoms could be caused by mutations in any of several genes.
Whole exome sequencing (WES) reads the protein-coding regions of all 20,000+ genes. This approach is used when gene panels have been inconclusive or when the condition doesn't fit a recognized pattern. WES identifies a diagnosis in approximately 25-40% of previously undiagnosed rare disease cases.
Whole genome sequencing (WGS) reads the entire DNA sequence, including non-coding regions that WES misses. WGS can detect structural variants, deep intronic mutations, and regulatory region changes. It is becoming more accessible as costs continue to decrease and is increasingly used in undiagnosed disease programs.
Chromosomal microarray detects deletions and duplications of chromosomal segments that are too small to see on a standard karyotype. This test is particularly useful for conditions like 22q11.2 deletion syndrome, Williams syndrome, and other microdeletion or microduplication syndromes.
Start with your treating physician or a clinical geneticist. Many academic medical centers have genetics clinics that specialize in rare diseases. A genetic counselor can help determine which test is most appropriate for your situation and guide you through the process, including interpreting results and understanding implications for family members.
In many cases, health insurance plans cover genetic testing when a doctor recommends it, but each plan, including Medicare, has its own rules about which tests it covers. Ask your insurer about coverage before testing, and ask the lab whether prior authorization is needed. Many testing laboratories offer financial assistance programs, and some rare disease foundations sponsor testing for patients who qualify.
The NIH Undiagnosed Diseases Program (UDP) and the Undiagnosed Diseases Network (UDN) review cases from patients who remain undiagnosed despite extensive medical evaluation. Both require a referral or recommendation letter from a health care provider, and only some applicants are accepted. The UDP does not charge for participation at the NIH Clinical Center, and the UDN works to keep out-of-pocket costs low and has patient assistance funds.
Genetic test results are classified into five categories by clinical laboratories: pathogenic (disease-causing), likely pathogenic, variant of uncertain significance (VUS), likely benign, and benign. A pathogenic or likely pathogenic variant in a gene associated with your symptoms typically confirms the diagnosis and opens the door to targeted treatments and clinical trials.
Variants of uncertain significance can be frustrating. These are genetic changes where there isn't enough evidence yet to determine whether they cause disease. VUS results may be reclassified over time as more research is published. Your genetic counselor can help you understand what a VUS means for your care and whether follow-up testing for family members might help clarify the result.
A negative genetic test does not rule out a genetic condition. Current testing technologies have limitations, and some mutations are in regions of the genome that aren't well covered by standard tests. If clinical suspicion remains high, discuss reanalysis or alternative testing strategies with your genetics team. Asking the lab to reanalyze your existing exome or genome data after a year or more can sometimes find an answer, because databases and interpretation tools keep improving.
The main types are single-gene tests (when one condition is strongly suspected), gene panels that test 10 to 100+ related genes, whole exome sequencing (WES) that reads the protein-coding regions of all 20,000+ genes, whole genome sequencing (WGS) that also covers non-coding regions and structural variants, and chromosomal microarray for detecting small deletions and duplications. A genetic counselor can help determine which test fits your situation.
About 72% of rare diseases are genetic, according to a 2020 analysis of the Orphanet database. That is why genetic testing has become central to rare disease diagnosis, and why many current clinical trials are mutation-specific and only enroll patients with particular genetic variants.
In many cases, health insurance plans cover genetic testing when a doctor recommends it, but each plan, including Medicare, has its own rules about which tests it covers. Many testing laboratories offer financial assistance programs, some rare disease foundations sponsor testing for patients who qualify, and the NIH Undiagnosed Diseases Network evaluates hard-to-diagnose cases and has patient assistance funds to help with out-of-pocket costs.
A variant of uncertain significance is a genetic change where there is not yet enough evidence to determine whether it causes disease. VUS results can be reclassified over time as more research is published, and a genetic counselor can advise whether follow-up testing for family members might help clarify the result.
A negative genetic test does not rule out a genetic condition. Current testing technologies have limitations, and some mutations lie in regions of the genome that standard tests do not cover well. If clinical suspicion remains high, ask your genetics team about reanalysis or alternative testing strategies; reanalysis of your existing exome or genome data after a year or more can sometimes find an answer as databases and interpretation methods improve.
Many rare disease trials enroll only patients with a confirmed molecular diagnosis, and gene therapy trials nearly always require one. Without testing, you may be eligible for a life-changing trial and never know it. A confirmed genetic diagnosis also connects you with the correct disease subtype community and informs family planning decisions.