ACMG Secondary Findings: The Genetic Results You Did Not Know to Look For
When you sequence your genome, you might find more than you were looking for. ACMG secondary findings are clinically actionable hereditary variants discovered incidentally, and they affect roughly 1 in 38 people.
Category: Diagnostics · By GenomeNarrator Team · · 8 min read
You sequence your genome to understand your ancestry or check for a specific condition. Then your clinician mentions something unexpected: a variant in a gene you have never heard of, associated with a condition you had no reason to suspect. This is the world of secondary findings, and the American College of Medical Genetics and Genomics has built a framework for when and how to report them.
What are ACMG secondary findings?
Secondary findings are variants in well-established, medically actionable genes that are discovered during genome or exome analysis, even when those genes were not the reason for testing. The ACMG publishes a curated list (currently version 3.3, covering 84 genes) where returning findings is recommended because the clinical benefit clearly outweighs the potential harms of knowing.
The philosophy is direct: if a pathogenic variant in a gene has an effective intervention (surveillance, medication, surgery, or lifestyle change that meaningfully reduces harm), patients should know about it regardless of why they had their genome analyzed.
What is on the ACMG SF v3.3 list?
The list spans several disease categories.
Cardiovascular conditions form the largest group. This includes hereditary cardiomyopathy genes covering hypertrophic cardiomyopathy (MYH7, MYBPC3, TNNT2), dilated cardiomyopathy (LMNA, TTN), and arrhythmogenic right ventricular cardiomyopathy (PKP2, DSG2). Long QT syndrome genes (KCNQ1, KCNH2, SCN5A) are included because identifying carriers enables lifesaving interventions: beta-blockers, ICD implantation, and avoidance of QT-prolonging drugs. Aortic disease genes such as FBN1 (Marfan syndrome) and TGFBR1 (Loeys-Dietz) are also on the list.
Hereditary cancer syndromes include BRCA1 and BRCA2, Lynch syndrome genes (MLH1, MSH2, MSH6, PMS2), and several rarer hereditary cancer conditions including VHL (von Hippel-Lindau), RET (multiple endocrine neoplasia), APC (familial adenomatous polyposis), and PTEN (Cowden syndrome).
Metabolic and other conditions: familial hypercholesterolemia (LDLR, APOB), Wilson disease (ATP7B), hereditary hemochromatosis (HFE), and others where early diagnosis prevents irreversible organ damage.
Why secondary findings are medically important
The actionability requirement is the critical filter. Unlike variants of uncertain significance, which may take years to interpret, ACMG secondary findings are restricted to situations where a confirmed pathogenic variant has well-established clinical implications and proven intervention options.
Finding a Lynch syndrome variant in someone who came in for an unrelated reason, for example, allows their gastroenterologist to implement colonoscopy surveillance that can prevent colorectal cancer. Studies suggest approximately 1 in 38 people who undergo whole exome or whole genome sequencing will have a reportable ACMG secondary finding. That is not a frightening statistic; it is an argument for the value of looking.
Secondary findings from consumer genetic data
SNP arrays like those used in 23andMe and AncestryDNA test for many of the common pathogenic variants in ACMG genes. GenomeNarrator applies the ACMG SF v3.3 gene list when analyzing consumer genotype files, flagging variants that meet ClinVar clinical significance criteria in ACMG genes.
The important caveat: consumer arrays do not sequence full gene coding regions. They test specific known pathogenic variants. A negative result on consumer data does not rule out a pathogenic variant in an ACMG gene; it only confirms that the specific tested positions were not flagged.
What to do with a secondary finding
If GenomeNarrator flags an ACMG secondary finding, the appropriate next step is referral to a genetics clinic for confirmatory clinical-grade testing. Consumer genetic data is a screening layer. Positive signals should always be confirmed with diagnostic-quality sequencing before any clinical action is taken.
The finding will appear in your report with the gene name, associated condition, and a plain-language explanation of what the variant means and what follow-up is recommended. The goal is not to alarm; it is to ensure you have information that could genuinely affect your health.
The right to not know
In formal clinical settings, secondary findings are opt-in: ACMG guidelines allow patients to decline them if they prefer not to know. Consumer genetic data does not provide that same formal opt-out, but you can always choose how much weight to give results and how aggressively to pursue follow-up, ideally in consultation with a healthcare provider who understands both genetics and your broader medical history.
More from GenomeNarrator: all genomics articles, how the analysis works, or GenomeNarrator home.