In the latest sign that the luster of many of Silicon Valley's tech superstars continues to fade, the mutual fund firm T. Rowe Price recently marked down the value of many of its priciest tech investments.

Weakness in the global economy and concern about the uneasiness of markets, as well as uncertainty about many lushly-priced private companies known as unicorns, drove the markdown, investment experts said.

T. Rowe Price cut valuations for 12 of its 17 investments in private tech companies, including the accommodations share site Airbnb, ride share company Uber, cloud storage company Dropbox as well as open-source development company Cloudera, and Evernote, the organization app company, the Wall Street Journal reported on Friday.

Mutual fund companies have been reevaluating their tech investments since the fall. In September, Fidelity Investments slashed the value of its holdings in Snapchat, the mobile messaging app, to $12 billion from $16 billion. In March both Fidelity and Blackrock knocked down Dropbox, Cloudera, and Zenefits by 38 percent.

T. Rowe Price released its revisions in a quarterly report that prices its shares in these companies through March 31, the Journal reports. A spokesman for T. Rowe Price noted in a statement that the first quarter had been an extremely volatile period for global equity markets.

"In determining fair values for our private investments, we continued to follow our long-established process of considering a variety of company-specific and market-based factors," the statement said.

While T. Rowe did not specify what those factors are, other sources from prominent investment companies, commenting on background, provided some insight. Private company valuations are typically determined by independent research groups within the investment companies themselves, they said. These groups operate separately from the portfolio managers.

Some of the factors they might consider in reevaluating  a company include its financials, the performance of comparable companies that are publicly traded, as well as the overall performance of equities markets. Additionally, they may use data provided by third party companies, such as Dun & Bradstreet, which specializes in financial information about private companies.

T. Rowe dropped Dropbox shares by 16 percent, meaning the current value of its holdings in that company is reportedly under water--13 percent below the firm's original purchase price in 2012.

But the biggest surprise was T. Rowe's slashing its Uber valuation by 6 percent, bringing the ubercorn closer to earth, if only slightly. Earlier this year, Uber received $2.2 billion in additional investment, which then marked the company at more than $62 billion. T. Rowe similarly cut the value of its Airbnb holdings by six percent. Airbnb last received $100 million in a November, 2015 round; it had been valued at about $24 billion before T. Rowe decided otherwise. By comparison, Marriott Corp. has a market cap of about $17.25 billion.