I have heard from a credible source that legendary Downtown DJ Mark Kamins, who is credited with discovering Madonna and who produced her first single ("Everybody"), has died of a heart attack. I will post more info as I receive it.

He summed up his connection to Madonna simply in 2011:

In 2011, Kamins said:

"Well, you know, I'm just a DJ—I started as a DJ from New York City. There was a girl dancing at my club. And her name was Madonna. Went to a recording studio and made a record. And the rest is history."

In 2008, Kamins said of "Everybody":

"I produced Madonna’s first record, 'Everybody'. I discovered her and brought her to Seymour Stein. At that time, I was working for Chris Blackwell at Island Records, but I was the DJ for the Talking Heads so I knew Seymour. I brought Madonna to see him, and he gave me a singles deal, and then we did it. That was probably her best record, the only one she made with a live drummer."

Of Danceteria, where he met Madonna, Kamins said:

"First of all, I think Danceteria was a magical space like Andy Warhol’s Factory or Max’s Kansas City or CBGBs. Jim Fouratt and Rudolph had this amazing finesse to hire people that they believed in. Why were the Beastie Boys the sweepers at Danceteria? Why was Madonna one of the dancers? Why Sade was the bartender at Danceteria? That’s crazy shit man. So you’re talking about a magical moment, a magical space, and a magical time where it was the beginning of something. Even Karen Finley was the bartender, and LL Cool J was a busboy. Rick Rubin, who is now one of the greatest producers in the music business, his first gig was playing with the Beastie Boys on the second floor of Danceteria because I had to go to a gig in Europe."

UPDATE: Madonna had this to say about Kamins in a statement to The Hollywood Reporter:

"I'm very sorry to hear about Mark's death. I haven't seen him for years, but if it weren't for him I might not have had a singing career. He was the first DJ to play my demos before I had a record deal. He believed in me before anyone else did. I owe him a lot. May he rest in peace."

What is reportedly Madonna's first-ever performance of "Everybody", at Danceteria's No Entiendes Cabaret: