I bet there's a better way, using something in perlvar, but this works:

perl -ne 'next unless $after_first_line++;@A=split(","); print join(",", @A[0 .. 3]),"\n"'

Update: Yeah, $. contains the line number, so:

perl -ne 'next if ($.==1);@A=split(","); print join(",", @A[0 .. 3]),"\n"'