How Nick Reiner Will Spend First Birthday Behind Bars

Nick Reiner won't be blowing out any birthday candles behind bars ... as authorities say he'll be treated just like every other inmate ... meaning no perks -- and no presents.

Nick -- who is accused of brutally murdering filmmaker father Rob Reiner and producer mother, Michele Singer Reiner -- will have no extra privileges Monday, which is when the accused killer turns 33.

"Birthdays are treated like every other day, no special treatment from LASD," a Los Angeles County Sheriff’s Department representative told Page Six.

The official added ... "Inmates have access to telephones in accordance to Module schedules and visits (both in person or video) ... There are no additional privileges for birthdays."

However, it's possible that Nick might have visitors ... "Sept. 14 will be a normal visiting day," the rep said. But based on what we know, we doubt those visitors will include his siblings.

We reported earlier ... Jake and Romy Reiner testified before the Los Angeles grand jury that would later indict him on two counts of first-degree murder in connection with their parents' deaths.