A number of people have been sharing the hashtag #The27Percent on Twitter to highlight the importance of the pre-existing health condition mandate of the Affordable Care Act (ACA).

As noted by The Mighty writer Jordan Davidson, surgeon Atul Gawande started the hash tag on Wednesday in a tweet revealing that his son is among the 27 percent of Americans under the age of 65 with a pre-existing health issue. Prior to Obamacare, this group — comprising of about 52 million Americans — would have been uninsurable, according to a recent Kaiser Family Foundation analysis.

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Without the pre-existing healthcare mandate in the ACA, people like Gawande's son could lose coverage:

A pre-existing health condition is something that a person has prior to the start of their health care plan. If you had a pre-existing condition prior to the enactment of Obamacare, "private insurers in the individual health insurance market could use applicants’ health status, health history and other risk factors to determine whether and under what terms to issue coverage," the Kaiser Family Foundation analysis states.

But that thankfully changed when Obamacare was rolled out. "Under the Affordable Care Act, health insurance companies can’t refuse to cover you or charge you more just because you have a 'pre-existing condition' — that is, a health problem you had before the date that new health coverage starts," the U.S. Department of Health & Human Services states on its site. "They also can’t charge women more than men."

Many others chimed in to share their pre-existing health conditions, and how their health would be affected should the ACA mandate should repealed.

The tweets come at a time when the future of Obamacare is uncertain.

At one point during his campaign, president-Elect Donald Trump said that he would ask Congress for a "full repeal of Obamacare" in office, so there is currently a lot of uncertainty among Americans, about what could happen to their health coverage under his presidency. However, Trump has most recently said that he would make sure Americans with pre-existing conditions can have access to healthcare even if and when he gets rid of Obamacare.

"We will protect Americans with pre-existing conditions so that they are not charged more or denied coverage, just because they have been sick, so long as they have paid their premiums consistently," Trump's running mate Mike Pence said in a November speech.

Whether or not he can overhaul it and how quickly is still debatable. Some experts say that might be easier said than done. Sara Rosenbaum, a health law and policy professor at George Washington University, told NPR in November that it is a "complex process to alter a law as complicated as the ACA." Healthcare industry consultant Robert Laszewski told NPR that it could take at least two years for Obamacare to be repealed if Trump does decide to do so.

[H/T The Mighty]