Cerebro, named after Professor X's mutant-finding gizmotron, was published by THE OFFICIAL X-MEN FAN CLUB, presumably with Marvel's blessing. I recall the club recieved a mention in one mid-eighties British Bullpen Bulletins.
These issues hail from the period 1979-81. I believe that it was published (roughly) bimonthly which - I guess - means the club was inaugurated late in '78 or earlier in '79.
Each issue is A4 and stapled along the left hand side. The cover is printed on colour paper using coloured ink (the result is quite satisfying, in a low-fi way) whilst the interiors are mostly black print on white paper with the occasional colour sheet tucked in.
The page count - and thus cover price - varies considerably from issue-to-issue.
Contents included the latest X-news (its worth remembering that Marvel's mutant ambitions at the time were limited to the core monthly title, the occasional outing of a character in MARVEL TALES and assorted crossovers, guest slots and cameos), extensive letters of comments from club members, fan-penned articles and extensive fan art. The fourth issue also premiered a new section which profiled a single character (beginning with the Angel although I don't know if subsequent issues followed an alphabetical pattern).
The club's launch would have - roughly - coincided with US editions of the comic book going (to use collectors parlance) "non-distributed" (ND in the price guides) at the request of Dez Skinn to avoid competing with the New X-Men reprints running in Marvel UK's RAMPAGE monthly. One of the club's services was the ability to subscribe to the US editions through the club.
The 100th member signed-up just in time to get their name into the 4th issue.
Cerebro was obviously sent out to club members (members names, when published, would always be followed by their membership number) but - I think - it was also sold in selected comic book shops. I remember finding a stack (or box) in Bristol's FOREVER PEOPLE store (the one that had a mezzanine floor which made it seem like the geek equivalent of a department store) in the mid-eighties and picking-up several copies (none of which I managed to keep... doh!). Whether this was a one-off or not, I don't know.
I'm not sure when the club folded but it must have kept a (very) low profile by the end of the eighties as I don't recall ever seeing it mentioned in other fanzines. A successor, MUTANT MEDIA, appeared during the boom years of the early nineties by which time there were oodles of X-titles and copious crossovers. I'll get around to posting those here sometime.
I briefly posted about the 'zine once before. See here for another cover.