The array-of-arrays returned by the module Text::CSV_XS is a more appropriate data structure. It works well with other modules to compute and print your sums.

use strict;
use warnings;
# node_id=11115481
use Text::CSV_XS qw( csv );
use List::MoreUtils qw(first_index true);

my $aoa = csv(in=>'data.csv', sep_char=>"\t");

my $header = shift @$aoa;
use constant REGULATION => first_index {/^Regulation$/} @$header;

printf   "Number of up is:   %d\n"
        ."Number of down is: %d\n"
        ."Number of NA is:   %d\n",
        map {count($_)} qw(up down NA);

exit(0);

sub count{
    my $Regulation = $_[0];
    local $_;
    return true {$_->[REGULATION] eq $Regulation } @$aoa;
}
[download]

OUTPUT:

Number of up is:   9
Number of down is: 5
Number of NA is:   3
[download]