Direct-to-Consumer Genetic Testing
Developed by Dr. June Carroll, Ms. Shawna Morrison and Dr. Judith Allanson
Last updated April 2014
Disclaimer
• This presentation is for educational purposes only and should
not be used as a substitute for clinical judgement. GEC-KO
aims to aid the practicing clinician by providing informed
opinions regarding genetic services that have been developed
in a rigorous and evidence-based manner. Physicians must use
their own clinical judgement in addition to published articles
and the information presented herein. GEC-KO assumes no
responsibility or liability resulting from the use of information
contained herein.
Objectives
• Following this session the learner will be able to:
– Discuss and address patient concerns regarding direct-toconsumer genetic testing
– Find high quality genomics educational resources
appropriate for primary care
Case
•
•
•
•
Jim, 53yo male
Healthy, active, non-smoker
Has been your patient for 15 years
Recently promoted as a corporate executive
and is being asked to undergo a thorough
medical evaluation including personal genome
testing and would like to know your thoughts
Family history
d.79
82
Prostate
cancer
53
54
Hypertension
Arthritis
Mid-50s
3
A&W
Jim
A&W
Judy
A&W
26
N
A&W
4
A&W
A&W
2
A&W
54
A&W
What is direct-to-consumer genetic
testing?
• Direct-to-consumer (DTC) genetic testing also
referred to as personal genome testing
– offered with the promise of providing:
• predictive genetic risk assessment for a variety of
health conditions (i.e. diabetes, cancer, obesity)
• information about carrier status
• information regarding response to and/or side-effect
risk of certain pharmaceuticals (i.e. clopidogrel, statins,
antidepressants)
What is direct-to-consumer genetic
testing?
• Uses odds ratios and relative risks to categorize an
individual as at increased risk (higher than average),
average, or at decreased risk (lower than average)
• Can also screen for single gene disorders (e.g. cystic
fibrosis, HFE-associated hemochromatosis, BRCA)
• Can uncover medically irrelevant information such as
bitter taste perception or curly hair
What do I need to know about the genetics
of direct-to-consumer genetic testing?
SNPs (pronounced ‘snips’) are the most common type
• Uses
data generated
from
genome-wide
association
of genetic
variation. Each
SNP
represents a difference
studies
(GWAS)
in a single
DNA building block, a nucleotide. SNPs
normally
in an individual’s
genome
once in
– occur
case-control
studies
which examine
manyabout
common
every
300 nucleotides,
and
so there
about 10
variations
in our genetic
code
(singleare
nucleotide
million
SNPs in the
human genome
polymorphisms
[SNPs])*
– compare large groups of individuals (unaffected controls
versus individuals with symptoms of a specific disease) in an
attempt to distinguish between non-harmful changes in the
DNA code and pathogenic, disease-causing/predisposing
changes
Who can obtain direct-to-consumer
genetic testing?
• Generally, direct-to-consumer (DTC) genetic
testing is available online to anyone for a cost
• Genetic testing for DTC genetic testing is
usually performed on a saliva sample
How will genetic testing help you and your
patient?
• While there are limited data to support the clinical validity
(ability to predict clinical outcome) and utility (the likelihood
of improving patient outcome), some consumers might
benefit from direct-to-consumer genetic testing as results
may:
– Encourage positive behaviour modifications (e.g. increase
exercise, smoking cessation)
– Provide useful information for medication choice and/or dose,
or management
– Provide information to individuals who have no or limited
information about their family history (e.g. an individual who
was adopted)
– Reveal carrier status of a genetic condition that could have
implications for family planning or medical management
Are there harms/limitations of direct-toconsumer genetic testing?
• Caution when interpreting direct-to-consumer (DTC)
genetic testing should be exercised as:
– DTC genetic testing does not take into account numerous
factors important when interpreting genetic test results
such as age, family history, lifestyle (e.g. smoking, obesity)
and other environmental factors that are a significant
contribution to common complex disease development
– Questionable clinical utility of some of reported results
– Family health history-based risk assessment is still the
gold standard in the initial assessment for heritable
conditions
Are there harms/limitations of direct-toconsumer genetic testing?
• No testing regulation
• Concerns re downstream testing and costs as result
of direct-to-consumer (DTC) results
• “misattributed equivalence”
– if a DTC test indicates a lower than average lifetime risk for
a certain condition, when FH indicated a much higher risk,
a consumer could be falsely reassured and not be as
vigilant about medical interventions indicated by FH
– This phenomenon speaks to the need for knowledgeable
healthcare provider involvement in pre- and post-test
counselling
• Pearls
– Direct-to-consumer (DTC) genetic testing is over-thecounter genetic testing available online to consumers
through private companies
– Generally, results report an individual’s probabilistic risk to
develop a medical condition based on genome wide
association studies (GWAS)
– Results may provide medically useful information for
consumers in addition to medically irrelevant information
(e.g. curly hair)
– Interpret DTC results with caution
– Family health history-based risk assessment is still the
gold standard in initial assessment for heritable
conditions
References
• Aiyar et al. Risk estimates for complex disorders: comparing personal
genome testing and family history. Genet Med 2013;. [Epub ahead of
print]
• Goldsmith L et al. Direct-to-consumer genomic testing: systematic review
of the literature on user perspectives. Eur J Hum Genet 2012; 20:811-816
• Heald B et al. Prospective comparison of family medical history with
personal genome screening for risk assessment of common cancers. Eur J
Hum Genet 2012; 20(5):547-51
• Special thanks to genetic counsellor Jill Davies at The Medcan
Clinic