In the 11 weeks since Frates was formally diagnosed, he has seen evidence of the disease's swift progression.
"My calf muscles and ankles seem to be slowing first, making me a little clumsier than usual," he said. "I'm definitely not running or throwing the ball around as much."
And Frates' left hand below the wrist smacked with a speeding ball last summer has lost 90 percent of its function. Some experts think such injuries may act as triggers for a disease that lies dormant in the nervous system.
"It may seem like an everyday encounter, so to speak, but in the right setting it may trigger motor neuron degeneration," said Brown. Or, he added, injuries might signal the earliest symptoms of the disease.
"If an ankle gets weak, people might catch their toe when stepping up on a curb and fall," said Brown. "It's still an open question, which came first: the fall or the weakness."
Either way, however, Frates was destined to be afflicted with ALS.
Researchers have started to uncover the biological roots of the disease, opening doors for new treatments.
"I'm cautiously upbeat about where things are going," said Brown, who has long been studying the genetic causes of ALS. "When we understand the cause, we can see how the molecular dominos fall. It turns out there are a number of ways a cell can fall apart, so at least we have the targets."
But Frates is short on time and eager for a breakthrough. He hopes more funding will accelerate the drug-discovery process, and he's ready to do his part. Less than two months after his diagnosis, "Team Frate Train," a group of Frates' family and friends, raised $27,000 for New York City's Walk to Defeat ALS.
"I hope it's a microcosm of what will happen in the greater population," he said. "The support I've seen has been overwhelming, and I can't thank everyone enough."
Determined to get the word out on ALS across the country, Frates threw the first pitch for the Boston Red Sox at Fenway Park Wednesday as part of Major League Baseball's ALS Awareness Day.
"Hopefully, people will see the juxtaposition of me hitting home runs and making diving catches just last year, to limping out there and throwing a pitch from 40 feet instead of the mound," he said. "If they see a 27-year-old guy in the prime of his life dealing with this, maybe it'll get them thinking about what they can do to help."