Before her son’s first birthday, Xi began to worry that something was wrong. “Bosyn was only around a year old, but I could tell he was very distracted — he wouldn’t look up when a phone rang or when a character in a movie yelled,” recalls Xi. “He would respond more to bright lights or colors than to sounds.”

The nine months following his second birthday were filled with appointments, inconclusive hearing tests and pediatricians dismissing Xi’s worries because she was a first-time parent.

But Xi couldn’t shake the feeling that something was wrong. …