use strict;
use warnings;
sub mean {...}
my @genes = (
#'GeneName E1  E2  E3  E4',
'ATA1      12  44  45  33',
'OSA2     100  79  85  83',
'DUA5      66  65  64  67',
'AXANT      4   4   6   2',
);
foreach  (@genes) {
    my ($name, @values) = split;
    print  $name, mean(@values);
}


##</code><code>##

use List::Util qw(sum);
...
sub mean { return sum(@_)/@_ }