enetic testing for the diagnosis or risk assessment of Alzheimer’s disease experimental, investigational and unproven, including but not limited to testing for:
- The apolipoprotein E (APOE) epsilon 4 allele,
- Presenilin genes, or
- Amyloid precursor gene.
Federal mandate prohibits denial of any drug, device or biological product fully approved by the FDA as investigational for the Federal Employee Program (FEP). In these instances coverage of these FDA-approved technologies are reviewed on the basis of medical necessity alone.
This medical policy was developed through consideration of peer reviewed medical literature, FDA approval status, accepted standards of medical practice in Montana, Technology Evaluation Center evaluations, and the concept of medical necessity. BCBSMT reserves the right to make exceptions to policy that benefit the member when advances in technology or new medical information become available.
The purpose of medical policy is to guide coverage decisions and is not intended to influence treatment decisions. Providers are expected to make treatment decisions based on their medical judgment. BCBSMT recognizes the rapidly changing nature of technological development and welcomes provider feedback on all medical policies.
When using this policy to determine whether a service, supply or device will be covered, please note that member contract language will take precedence over medical policy when there is a conflict.
Susceptibility Testing at the Apolipoprotein E (APOE) Gene
The policy regarding apolipoprotein epsilon (APOE) genotyping derives from a 1999 TEC Assessment (7) that offered the following conclusions and observations:
- Several consensus statements regarding APOE genotyping have been published, which conclude that APOE genotyping in asymptomatic patients, as a technique of risk assessment, is not recommended. Statements regarding its use as a diagnostic test in symptomatic patients are mixed. In 1998, the American College of Medical Genetics/American Society of Human Genetic Working Group on APOE and Alzheimer’s Disease stated, “Studies to date indicate that the APOE genotype alone does not provide sufficient sensitivity or specificity to allow genotyping to be used as a diagnostic test. In 1997, a national study group supported by the National Institutes of Health (NIH) and composed of Alzheimer’s disease (AD) geneticists, policy experts, and ethicists, stated “The use of APOE genetic testing as a diagnostic adjunct in patients already presenting with dementia may prove useful but it remains under investigation.” In contrast, a report by the Working Group on Molecular and Biochemical Markers of Alzheimer’s Disease stated that APOE genotyping can add “confidence to the clinical diagnosis of AD…” but “...the sensitivity and specificity of the epsilon 4 allele alone are low, indicating that this measure cannot be used as the sole diagnostic test for AD.”
- Considering the published data regarding the sensitivity and specificity of APOE genotyping, the TEC Assessment concluded that the addition of APOE genetic testing does not improve the sensitivity of clinical criteria and only marginally improves the specificity of clinical criteria for the diagnosis of AD. In addition, APOE genetic testing would not alter recommended diagnostic testing for other treatable causes of dementia.
Subsequent to the TEC Assessment advances in genetic understanding of AD have been considerable (8) with associations between late-onset AD and more than 20 non-APOE genes suggested. However, relevant literature through August 2012 does not provide evidence supporting clinical utility or benefit from genetic testing for AD.
Tsuang et al (9) prospectively evaluated APOE testing for AD diagnosis in a community-based case series of older patients presenting with memory complaints but no previous diagnosis of dementia. Of 1,028 potential cases, 970 were evaluated; of these, 425 died and 132 were autopsied; of the 132, 71% were confirmed to have AD. The sensitivity and specificity of APOE epsilon 4 alone were poor, yielding positive and negative predictive values of 83% and 41% compared to 81% and 56%, all respectively, for clinical diagnosis alone. Using a criterion of positive clinical diagnosis or APOE epsilon 4 resulted in positive and negative predictive values of 79% and 70%. A criterion of positive clinical diagnosis and APOE epsilon 4 improved positive predictive value to 88% but at the expense of negative predictive value (40%). Eleven individuals had an epsilon 4 allele without neuropathologically confirmed AD. While APOE epsilon 4 increases disease susceptibility, it is associated with only approximately 50% of Alzheimer’s cases.
The effect of APOE genotype on response to AD therapy has also been examined. The USA-1 Study group found APOE genotype did not predict therapeutic response. (10) Rigaud et al followed 117 individuals with AD over 36 weeks in an open-label trial of donepezil; 80 (68%) completed the trial. (11) They found no statistically significant effect of APOE genotype on change in cognition (assessed by ADAS-Cog). However, the study was not designed to examine predictive therapeutic response, and there were baseline cognitive differences according to APOE genotype. There is currently insufficient information to make treatment decisions based on APOE subtype.
The REVEAL study was designed to examine consequences of AD risk assessment by APOE genotyping. (12) Of 289 eligible participants 162 were randomized (mean age, 52.8 years; 73% female; average education, 16.7 years) to either risk assessment based on APOE testing and family history (n=111) or family history alone (n=51). During a 1-year follow-up, those undergoing APOE testing with a high-risk genotype were more likely than low-risk or ungenotyped individuals to take more vitamins (40% vs. 24% and 30%, respectively), change diet (20% vs. 11% and 7%, respectively), or change exercise behaviors (8% vs. 4% and 5%, respectively). While in this well-educated sample of women there were some behavior changes, none can be considered a meaningful surrogate endpoint.
Genetic Testing for Early Onset Familial AD
Genetic testing for PSEN1 detects 30–60% of familial early onset AD. A number of mutations have been reported scattered throughout the presenilin 1 (PSEN1) gene, requiring sequencing of the entire gene when the first affected member of a family with an autosomal dominant pattern of AD inheritance is tested. Mutations in APP and PSEN2 genes account for only a small fraction of cases; it is likely that other causative genes will be discovered.
In 1998, the Alzheimer Disease Working Group of the Stanford Program in Genomics, Ethics, and Society (13) suggested that “predictive or diagnostic genetic testing for highly penetrant mutations (e.g., APP [amyloid-beta precursor protein], PSEN1, PSEN2 [presenilin 2]) may be appropriate for individuals from families with a clear autosomal dominant pattern of inheritance, particularly those with a family history of early onset of symptoms.” Such families generally have 3 affected members in 2 generations. In the case of diagnostic testing of clearly symptomatic individuals, testing would do little to change diagnostic confidence; however, it might assist excluding other causes of early onset dementia, as potentially treatable contributory causes would still require exploring. In cases of early detection of questionably symptomatic individuals (i.e., those with mild cognitive impairment, mutation identification might secure a diagnosis and lead to early treatment. The possibility that earlier diagnosis might lead to improved outcomes, while plausible, is not based on current evidence. Pharmacologic interventions for mild cognitive impairment have not demonstrated benefit in reducing progression to AD. (14)
The nearly complete penetrance of a PSEN1 disease-associated mutation would change the probability of developing AD in an unaffected family member from 50% to either 0% or 100%. Testing for PSEN1 mutations is not useful in predicting age of onset (although it is usually similar to age of onset in affected family members), severity, type of symptoms, or rate of progression in asymptomatic individuals. However, identification of asymptomatic, young adult carriers could allow for reproductive planning. Identification of both symptomatic and asymptomatic carriers could also allow for other types of life planning in advance of incapacitating disease.
It is not uncommon to discover previously unreported PSEN1 mutations in an individual, and without additional family information, these may reflect mutations not associated with disease, or new causative mutations restricted to a single family (private mutation). Thus, interpretation of test results of asymptomatic individuals without identification of a mutation in affected family members may be inconclusive in a significant proportion of patients. Should testing be undertaken, affected family members should be tested first or in conjunction with unaffected family members. When no mutation can be identified in affected family members with a clear autosomal dominant pattern of disease inheritance, the family can be referred to a research program for additional study. Any testing should be performed only in the context of adequate pre- and post-test genetic counseling. Finally, it should be noted that pharmacologic therapy for Alzheimer’s disease should be based on the patient’s symptomatology rather than testing results.
GeneTests.org (available online at: www.genetests.org ) notes availability of testing for PSEN1, PSEN2, and APP through a number of laboratories.
A systematic review on the psychological and behavioral impact of genetic testing for AD found few studies on the impact of testing for early onset familial AD. The existing studies generally have small sample sizes and retrospective designs, and the research was conducted in different countries, which may limit the generalizability of the findings. (15)
Mihaescu et al. (16) cite a proposed framework by Khoury and colleagues (17) for the continuum of translational research that is required to move genomics research findings in Alzheimer’s disease to clinical and public health applications that benefit population health…The 4 phases of translation research include: 1) translation of basic genomics research into a potential health care application; 2) evaluation of the application for the development of evidence-based guidelines; 3) evaluation of the implementation and use of the application in health care practice; and 4) evaluation of the achieved population health impact.
Mihaescu and colleagues conclude that genetic testing for Alzheimer’s disease is still in the first phase. At this point, the sensitivity and specificity of APOE for detecting individuals at risk of developing AD is too low. For those from families with early onset, familial AD, there are currently no known preventive measures or treatments that can mitigate the effect of the disease.
Many genes, including APOE, have been associated with late-onset AD. However, the sensitivity and specificity of these genes is low for diagnosing AD, and genetic testing has not been shown to add value to the diagnosis of AD made clinically. For individuals with early-onset AD, mutations in the PSEN1 and APP genes are found in a substantial number of patients. However, there is no direct or indirect evidence to establish that clinical outcomes are improved as a result of genetic testing for these mutations.
Therefore, the current evidence does not support genetic testing for AD. The lack of effective methods to prevent the onset of AD or to target AD treatments based on genetic characteristics limits the clinical benefit for such genetic testing. The low sensitivity and specificity of APOE testing for indicating which individuals will progress to AD or as a diagnostic tool, as well as the high likelihood that other genetic findings may affect progression, lend further support to this conclusion. Therefore, genetic testing for AD is considered investigational.
American Academy of Neurology (18)
- Routine use of APOE genotyping in patients with suspected AD is not recommended at this time (Guideline).
- There are no other genetic markers recommended for routine use in the diagnosis of AD (Guideline).
This guideline is currently being updated (available online at: http://www.aan.com/practice/guideline/index.cfm?fuseaction=home.welcome&Topics=15&keywords=&Submit=Search+Guidelines ).
European Federation of Neurological Sciences (EFNS) (19)
Recommendations: genetic testing (level of evidence not reported)
Screening for known pathogenic mutations can be undertaken in patients with appropriate phenotype or a family history of an autosomal dominant dementia. Testing of patients with familial dementia and of unaffected at-risk-relatives should be accompanied by neurogenetic counseling and undertaken only after full consent and by specialist centers. Presymptomatic testing may be performed in at-risk members of family-carrying mutation. It is recommended that the Huntington’s disease protocol is followed for pre-symptomatic testing.
Routine Apo E genotyping is not recommended.
Third Canadian Consensus Conference on Diagnosis and Treatment of Dementia (CCCDTD) (20)
Predictive genetic testing for asymptomatic “at risk” individuals with an apparent autosomal dominant inheritance, and a family-specific mutation has been identified:
- With appropriate pre- and post-testing counseling, predictive genetic testing (PGT) can be offered to “at-risk” individuals (Grade B, Level 2**). Examples:
- First-degree relatives of an affected individual with the mutation (e.g., children and siblings);
- First cousins of an affected individual if the common ancestors (parents who were siblings) died before the average age of onset of dementia in the family;
- Nieces and nephews of affected individuals whose parent (sibling of the affected individual) died well before the average age of onset of dementia in the family;
- PGT in minors is not generally offered in Canada, but occasionally may be considered on a case-by-case basis by the relevant medical ethics committee(s);
- Individuals who are not “at risk” for the inherited disease do not require testing.
- In young persons (60 years or younger) presenting with an early onset dementia, it is sometimes worthwhile to test for the most common mutations based on the “best estimate” diagnosis (e.g., in early onset AD, one might test for the most common mutations in PS1, APP). (Grade B, Level 2**) If a mutation is identified, it would have direct implications for offspring of the individual (if a de novo mutation is assumed). Conversely, it would also be important to test other family members such as parents and siblings for possible non-penetrance of a mutation.
Genetic screening with APOE genotype in asymptomatic individuals in the general population is not recommended because of the low specificity and sensitivity. (Grade E, Level 2**)
Genetic testing with APOE genotype is not recommended for the purpose of diagnosing AD because the positive and negative predictive values are low. (Grade E, Level 2**)
The 2012 Canadian Consensus Conference on Dementia was held in May 2012. The results have not been released to date (available online at: http://www.healthplexus.net/article/2012-canadian-consensus-conference-dementia ).
**CCCDTD Evidence Ratings
Grade (B) There is fair evidence to support this maneuver.
Grade (E) There is good evidence to recommend against this procedure.
Level 2: (1) Evidence obtained from well-designed controlled trial without randomization, or (2) Evidence obtained from well-designed cohort or case control analytic studies, preferably from more than one center, or (3) Evidence obtained from comparisons between times or places with or without intervention. Dramatic results in uncontrolled experiments are included in this category.
Joint Practice Guidelines of the American College of Genetics and the National Society of Genetic Counselors (2)
- Pediatric testing for AD should not occur. Prenatal testing for AD is not advised if the patient intends to continue a pregnancy with a mutation.
- Genetic testing for AD should only occur in the context of genetic counseling (in person or through videoconference) and support by someone with expertise in this area.
- Symptomatic patients: Genetic counseling for symptomatic patients should be performed in the presence of the individual’s legal guardian or family member.
- Asymptomatic patients: A protocol based on the International Huntington Association and World Federation of Neurology Research Group on Huntington’s Chorea Guidelines is recommended.
- DTC APOE testing is not advised.
- A ≥3-generation family history should be obtained, with specific attention to the age of onset of any neurologic and/or psychiatric symptoms, type of dementia and method of diagnosis, current ages, or ages at death (especially unaffected relatives), and causes of death. Medical records should be used to confirm AD diagnosis when feasible. The history of additional relatives may prove useful, especially in small families or those with a preponderance of early death that may mask a history of dementia.
- A risk assessment should be performed by pedigree analysis to determine whether the family history is consistent with EOAD [early-onset AD] or LOAD [late-onset AD] and with autosomal dominant (with or without complete penetrance), familial, or sporadic inheritance.
- Patients should be informed that currently there are no proven pharmacologic or lifestyle choices that reduce the risk of developing AD or stop its progression.
- The following potential genetic contributions to AD should be reviewed:
- The lifetime risk of AD in the general population is approximately 10–12% in a 75–80 year lifespan.
- The effect(s) of ethnicity on risk is still unclear.
- Although some genes are known, there are very likely others (susceptibility, deterministic, and protective) whose presence and effects are currently unknown.
For families in which an autosomal dominant AD gene mutation is a possibility:
- Discuss the risk of inheriting a mutation from a parent affected with autosomal dominant AD is 50%. In the absence of identifying a mutation in apparent autosomal dominant families, risk to offspring could be as high as 50% but may be less.
- Testing for genes associated with early-onset autosomal dominant AD should be offered in the following situations:
- A symptomatic individual with EOAD in the setting of a family history of dementia or in the setting of an unknown family history (e.g., adoption).
- Autosomal dominant family history of dementia with one or more cases of EOAD.
- A relative with a mutation consistent with EOAD (currently PSEN1/2 or APP).
- The Alzheimer Disease & Frontotemporal Dementia Mutation Database should be consulted (available online at: www.molgen.ua.ac.be/ADMutations/ ) before disclosure of genetic test results, and specific genotypes should not be used to predict the phenotype in diagnostic or predictive testing.
- Discuss the likelihood of identifying a mutation in PSEN1, PSEN2, or APP, noting that current experience indicates that this likelihood decreases with lower proportions of affected family members and/or older ages of onset.
- Ideally, an affected family member should be tested first. If no affected family member is available for testing and an asymptomatic individual remains interested in testing despite counseling about the low likelihood of an informative result (a positive result for a pathogenic mutation), he/she should be counseled according to the recommended protocol. If the affected relative, or their next of kin, is uninterested in pursuing testing, the option of DNA banking should be discussed.
Ongoing Clinical Trials
There are a number of clinical trials on APOE testing and the clinical manifestations of AD among patients with APOE epsilon 4 (at online site: www.clinicaltrials.gov).