There's no questioning that some of the more exciting investments are high-growth stocks. However, those investments aren't for the faint of heart. Holding high-growth stocks for the long haul can be a wild, volatile, and stressful experience, but investors who find them early in their growth stories and are willing to wait out the ups and downs could find themselves well rewarded. Here are three Motley Fool contributors who believe CRISPR Therapeutics (CRSP -2.99%), Carvana (CVNA -0.48%), and Appian Corporation (APPN -2.00%) are high-growth stocks that are just getting started.

Emulating evolution with designer genes

Chuck Saletta (CRISPR Therapeutics): Traditionally, evolution has been something that has taken generations to work, with much of the impact coming from chance adjustments that happened to provide a benefit for the species. For fast-reproducing species like bacteria, that often leads to superbugs that are resistant to ordinary medical treatments. For us slower-reproducing humans, that often means that our evolution is too slow to allow affected individuals to survive modern diseases.

Enter CRISPR Therapeutics, a company based on genetic engineering using the Cas9 enzyme that can cut out and insert new genes inside existing cells. That technology, once fully mastered, can potentially give us the ability to fight diseases by directly changing DNA. The potential to address and possibly even cure modern scourges like diabetes, cancer, and blood-related diseases like sickle cell disorder is astounding.

Yet despite the incredible potential behind its technology, CRISPR Therapeutics today sports a mere $35 million in trailing four-quarter revenues. Indeed, CRISPR Therapeutics isn't expected to launch its first major commercial therapeutic product based on its gene-editing technology until 2022, putting its major potential growth still a few years out.

A lot can go wrong between now and then, making CRISPR Therapeutics a high-risk potential investment. Still, if you're looking to get in on a company with tremendous potential growth as it's starting out, CRISPR Therapeutics is certainly one to consider.

Carvana's Indianapolis car vending machine that holds 26 vehicles.

Carvana's new Indianapolis vending machine. Image source: Carvana.

Triple-digit growth

Daniel Miller (Carvana): Investors scouring the market for growth stocks that are in their infancy have likely overlooked Carvana for a couple of reasons: it's in a cyclical automotive industry surrounded by pessimism, and it's a young company that only went public in April 2017. But before you brush Carvana off for those two reasons, take a look at some of its growth figures.

Carvana posted 116% year-over-year growth in retail units sold during the third quarter, a 137% increase in revenue, and a 181% increase in total gross profit. You might be thinking those figures are a flash in the pan, but that's not the case. In fact, Carvana's impressive third-quarter growth was its 19th consecutive quarter of triple-digit year-over-year unit and revenue growth. Let those numbers sink in for a moment. Looking at them another way, as CEO Ernie Garcia pointed out, Carvana sold more cars to consumers in the third quarter than it did in 2015 and 2016 combined.

The good news for investors is that Carvana is just getting started. Management was focused on entering 40 new markets throughout 2018 and plans to end the year with a footprint in 84 markets. That expansion into 40 new markets was a leap from entering 23 during 2017. In recent years, management has fine-tuned its entrance strategy and can enter a market with next-day delivery, not including a more expensive vending machine, for roughly $500,000. Currently, the company is focused on expanding into low-hanging fruit, or the roughly 200 markets in the U.S. with populations of more than 200,000.

Investors considering Carvana will have to accept the speed bumps that come with owning shares of a young and rapidly expanding company, especially one in a cyclical retail industry. But there's no question that the company has proven it can produce explosive growth and that there are plenty of juicy markets remaining for Carvana to enter. The company has made progress improving its gross profit per unit (GPU), and if it continues improving its GPU while expanding its footprint nationally, this growth story is likely barely begun.

A cure for software development headaches

Nicholas Rossolillo (Appian): As the business world embraces all things digital, software development has been in increasingly high demand. Building new digital tools is easier said than done, though. According to a survey conducted by research group IDG and Appian, half of all business requests for new software applications end in failure, and the leading cause for new software projects never starting or not meeting the organization's needs is high cost.

Appian has a solution: low-code software development, a visual drag-and-drop toolkit for building applications faster and more cheaply. Low code is still a very small part of the tech industry, but as organizational change picks up the pace in the years ahead, it has plenty of room to grow. Appian itself is a case in point. Though it's a leader in the movement, its trailing 12-month revenue is only $217 million.

The small tech firm is just getting started, though. It's quickly growing its subscription-based revenues, which were up 42% year over year in the third quarter of 2018. Management says they should increase at least another 34% during the fourth quarter, making recurring service subscriptions its largest sales generator. That's great news, as the low-code subscription business model carried a gross profit margin of 89.4% as of the last quarter. That compares to just 30% for the rest of the business, which is made up of other software-development professional services.

Appian has just begun spreading the word on its time- and money-saving development tools, but the story so far has been eager adoption by organizations looking to get an edge in the digital world. That makes this stock a worthy candidate for investor portfolios that want high growth and don't mind the accompanying volatility.