Patients asking about APOE gene test results? Here’s what to tell them

7 clinical scenarios and how to approach them

Six of the following vignettes describe common clinical scenarios in which patients seek medical advice regarding APOE test results. The seventh vignette describes a patient whose APOE genotype may play a role in possible disease-modifying treatments down the road. Each vignette is designed to guide your approach to patient discussions and follow-up. Recommendations and considerations are also summarized in TABLE 2^13-16.

Vignette 1

Janet W, age 65, comes to the clinic for a new patient visit. She has no concerns about her memory but recently purchased DTC genetic testing to learn about her genetic health risks. Her results showed an APOE ε4/ε4 genotype. She is now concerned about developing AD. Her mother was diagnosed with AD in her 70s.

Several important pieces of information can be conveyed by the primary care physician. First, patients such as Ms. W should be told that the APOE gene is not deterministic; many people, even those with 2 ε4 alleles, never develop dementia. Second, no specific preventive measures or treatments exist based on an individual’s APOE genotype (see Vignette 5 for additional discussion).

In this scenario, patients may ask for numeric quantification of their risk for dementia (see TABLE 1⁴ for estimates). When conveying probabilistic risk, consider using simple percentages or pictographs (eg, out of 100 individuals with an ε4/ε4 genotype, 30 to 55 develop MCI or AD). Additionally, because people tend to exhibit confirmatory bias in thinking about probabilistic risk, providing opposing interpretations of an estimate may help them to consider alternative possibilities.¹⁷ For example, ε4/ε4 individuals have a 30% to 55% risk for MCI or AD. Alternatively, they have a 45% to 70% risk of not developing MCI or AD.

There are important caveats to the interpretation of APOE risk estimates. Because APOE risk estimates are probabilistic and averaged across a broader spectrum of people in large population cohorts,⁴ estimates may not accurately reflect a given individual’s risk. The ranges reflect the uncertainty in the estimates. The uncertainty arises from relatively small samples, the rareness of some genotypes (notably ε4/ε4) even in large samples, and variations in methods and sampling that can lead to differences in estimates beyond statistical variation.

Vignette 2

Eric J, age 85, presents for a new patient visit accompanied by his daughter. He lives independently, volunteers at a senior center several times a week, and exercises regularly, and neither he nor his daughter has any concerns about his memory. As a gift, he recently underwent DTC genetic testing and unexpectedly learned his APOE result, which is ε4/ε4. He wants to know about his chances of developing AD.

Risk conveyed by APOE genotype can be modified by a patient’s age. At age 85, Mr. J is healthy, highly functional, and cognitively unimpaired. Given his age, Mr. J has likely “outlived” much of the risk for dementia attributable to the ε4/ε4 genotype. His risk for dementia remains high, but this risk is likely driven more by age than by his APOE genotype. Data for individuals older than age 80 are limited, and thus risk estimates lack precision. Given Mr. J’s good health and functional status, his physician may want to perform a brief cognitive screening test to serve as a baseline for future evaluations.

Continue to: Vignette 3