Genetic Testing and Disease Inheritability

Genetic Testing and Disease Inheritability

Anil Kumar, PhD
Oct 08 2019 20:12

Direct-to-consumer health testing is putting patients at the center of healthcare. As the decision making power moves to the consumer, it allows better engagement to reduce cost while effectively using the limited healthcare resources.

In that regard, genetic tests provide insights into pre-disposition to certain diseases, e.g., cardiovascular disease or Alzheimer’s disease. This can be a great motivator for living a healthier life style and helping inform consumers to work towards disease prevention and effective treatment plans.

But how much of our health is determined by the way we live and how much is predetermined in our genes?

Two recent studies tried to answer this crucial question by looking at very large number of people. They conclude genetics plays a key role but it depends on what disease we are looking at. Some of them, e.g., diseases of eyes, ears, nose and throat can be attributed as much as 60-70% to the genetic inheritance. In contrast, infections (e.g., flu) and life style diseases such as diabetes have a strong dependence on the environment.


Genetic Test

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On average, about 40 to 50% of diseases studied have a genetic contribution. Approximately 15 to 25% have environmental and social contribution. Together, two-third of the all the diseases around us have genetic and environmental variables.

The non-genetic factors include environment and life-style. Those are determined by geographic location and neighborhood (e.g., zip code), time of the year (manifested as temperature variation), income levels, air pollution, access to food, transport, loneliness, and other socioeconomic factors. Impact of some may be difficult to quantify.

The CaTCH Study – for young and insured

First study looked at 45 millions Americans with the insurance company Aetna. It analyzed 560 common diseases and conditions and specifically studied twins and siblings under the age of 24 years. By looking at the billing codes, lab tests, and other insurance data they concluded:

  • That 60% of the average monthly healthcare cost is explainable by our genetics and the environment we live in.
  • Socio-economic variations and zip-code have little effect in general but contribute most to morbid obesity and skin tissue growth (e.g., moles etc.).
  • Air-quality shows highest impact on Lyme disease and contributes the most to variation in monthly expenses.
  • Diseases with largest temperature variation contribution are flu and lead poisoning.

The MaTCH Study – with 50 years of global research

The second study reviewed the published research in past 50 years across 39 different countries. From the several thousand common diseases and conditions analyzed across all ages, they concluded:

  • All diseases have some genetic contribution but almost 50% are significant enough to impact the cost of healthcare.
  • The probability of highest genetic inheritance is for eye disorders (71%), conditions of ear, nose and throat (64%), skin diseases (60%), bones and skeleton (59%), and related to breathing (54%).
  • Environmental factors seem to impact highest for cell structure, e.g., inflammation (67%), infection (35%), conditions related to blood, e.g., low red-blood-cell count (32%), hormone related diseases, e.g., diabetes, thyroid, cortisol (stress hormone), testosterone (32%), and diseases related to fertility and sex (32%).

The boom in genetic testing

The field of genetic testing has the best days ahead of it. Because of high genetic disease inheritability for so many conditions, lot of effort is going into looking at genes linked to various diseases. This growth is driving the consumer focus on direct-to-consumer genetic testing.

EXAMPLES OF POPULAR TESTS

Genetic tests related to ancestry and criminal investigations have gotten lots of attention recently. However, tests related to inheritability of certain diseases, e.g., BRCA test for breast cancer are at early stage of popularity. Two other popular genetic risk of Alzheimer’s and early stage of dementia as well as cardiovascular disease are:

  • APOE: Although the cause of Alzheimer’s remains unknown, research suggests APOE (apo-lipo-protein E) E4 alleles are major genetic risk factor for early stage neuro-de-generative disease as well as cardiovascular disease. Studies show that people carrying the E4 allele pair have a higher prevalence of Alzheimer’s disease (at 91%) and much lower mean age of onset (at 68 years of age). In comparison, for those carrying E2 pair, the rate is approximately 20% and mean age at onset about 84 years. Studies show chronic inflammation, low vitamin D, and other hormonal deficiencies can accelerate early onset of cognitive decline. An APOE genetic test with a simple swab can help assess your genetic risk of Alzheimer’s and cardiovascular disease risk risk.
  • MTHFR: The MTHFR (methyele-tetra-hydro-folate reductase) is a gene responsible for helping our bodies make proteins. It is specifically important to digest folate or vitamin B9, and helps regulate homocysteine levels. Also, it is important in the metabolism of metho-trex-ate, a drug for rheumatoid arthritis and chemotherapy. An MTHFR genetic test can help assess your genetic risk.

The FDA says “no test is 100% accurate” and recommends that “the results from direct-to-consumer tests should not be the sole basis of any type of medical decision making”. It further clarifies that “these tests are not a substitute for visits to a health care provider for recommended screenings or appropriate follow-up and should not be used to determine any treatments”.

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