It’s a situation many have faced before or will in the future: last month, I was up early waiting for a call and a medical update. Unfortunately, the news wasn’t great: a doctor said I had an elevated risk—around two to three times higher than the average person—of developing late-onset Alzheimer's disease.

On the bright side, this news was complicated.

My regular physician or local hospital didn’t deliver the diagnosis. Instead, a doctor from Turkey contacted me on Skype to go through a detailed analysis of my DNA. Because of some family history with early onset Alzheimer’s and an interest in what’s becoming an emerging field, I sought out some direct-to-consumer (DTC) genetic testing within the last six months. Turns out that these days, it takes nothing more than some money and a mailed spit sample to get a routine DNA exam; a brief glimpse at fate is then conveniently sent to your inbox.

The Skype session was actually included with the DTC genetic test I took. Belgium-based Gentle Labs is one of a handful of companies worldwide that offers DTC genetic testing, and its package (which costs you $1,990) wraps up with this 40-minute post-test consultation with a physician. Beyond the customer service, Ars Science Editor John Timmer suggested Gentle due to an unusual component of the company’s testing process.

Gentle's test was a highly involved endeavor compared to my second DTC genetic testing experience from the American-based 23andMe. For a fraction of the price ($100), 23AndMe offered no consultation—just the spit mail-to-e-mailed results. But sure enough, 23AndMe presented the same conclusion: my risk for late-onset Alzheimer’s was two-to-three times greater than the average person.

Both companies are involved in a small but growing DTC genetics market estimated to be worth more than $233 million globally by 2018, according to Global Industry Analysts. 23andMe is the older of the two firms, having been co-founded in 2006 by Anne Wojcicki, the (now-estranged) wife of Google co-founder Sergey Brin. Gentle, by contrast, is a newcomer that only launched in late 2013.

It was all so simple to do, but understanding what those tests meant was a bit more involved.

Who's down with A, C, G, and T?

Let's start with some basics on genetics.

The human genome, the totality of what makes an individual genetically unique, is composed of 23 pairs of chromosomes. Those chromosomes carry our genetic blueprint through the arrangement of chemical units called nucleotides, or bases. Our DNA is composed of long strings of these building blocks: adenine, cytosine, guanine, and thymine. The sequence of those A, C, G, and Ts dictates or influences much about us: blood type, ability to clear alcohol, allergies, and predisposition to diseases.

Some specific nucleotides differ within the human population—where you have a T, I might have a C. These differences are known formally as “single nucleotide polymorphisms” (known as SNPs, or “snips”), and they can be used as genetic markers. As science has progressed over the last few decades, it has rapidly expanded the catalog of what SNPs are associated with what disease. Some have very strong links now. For instance, there are SNPs associated with BRCA1 mutations that have been shown to lead to greater risk of breast cancer. However, it’s important to underscore that the presence of a particular SNP doesn’t always guarantee that the person will develop the disease. There are two reasons for this.

The first is that genetic changes often simply push people toward a condition rather than dictate that it develops. Some genetic changes are said to be “fully penetrant,” meaning that their presence or absence definitively denotes a certain physical characteristic (like color blindness or ABO blood type) and, in some cases, the presence of disease. But more often, such changes are only partially penetrant. Their presence, in conjunction with other genetic changes and other factors, leads to a particular risk factor.

The second reason has to do with the relationship between the SNPs and the genetic changes that we're interested in. In some cases, the SNP changes the DNA of a gene and is the genetic change we're interested in. In others, it's just very close by, typically associated with a disease or trait. But "typically" is not the same as always, which can introduce a certain level of uncertainty.

What most DTC genetic testers do is scan for particular SNPs known to have links to various disease. 23andMe, for example, says that it analyzes about half a million SNPs, roughly five percent of the 10 million SNPs in the entire human genome. Of those, the company then identifies those SNPs that have links to 240 known health conditions and traits.

In short, 23andMe is just looking for the presence or absence of individual SNPs, and that’s part of why the company's test is so cheap. In contrast to Gentle Labs, it's doing less work. Gentle instead does exome sequencing, examining and recording each A, C, T, and G from the 1.5 percent of the entire human genome that is translated into proteins. That small focal area drives the main functionality in everyone’s cells. So with exome sequencing, you can identify any significant changes in protein coding regions—even changes we've never seen previously. Exome sequencing is a decent alternative to a full genome sequencing, which would record every single base pair but cost multiple thousands of dollars.

Still, compared to what companies like 23AndMe do, exome sequencing remains a costly and time-consuming procedure. Gentle touts this fact in its own company literature: “We screen for over 1700 conditions, about 10 times as much as most other companies.”

In my case, both methods led to heightened risk uncovered. But each path had a few red flags on closer look.