my @prettybase;

my $seen = 0;
while (<PRETTYBASE>)
{
    chomp;
    my @info = split /\t/;

    unless ($info[1] == $patient_number)
    {
        # Use this to short-cut out of the file once we've found our patient info.
        last if $seen;
        next;
    }

    $seen = 1;

    push @prettybase, $_;
}

# At this point, everything in @prettybase corresponds to the patient specified.
# Modify your algorithms accordingly.