House Administration Chairwoman Juanita Millender-McDonald (D-Calif.) was granted a leave of absence from her Congressional duties on Monday to undergo medical treatment for an undisclosed illness.

Millender-McDonald’s official leave of absence, granted by Majority Leader Steny Hoyer (D-Md.), extends through May 25 and her office would not say Tuesday night what ailment afflicts the Congresswoman.

“I am very much saddened by the recent news of Juanita’s illness,” House Administration ranking member Vernon Ehlers (R-Mich.) said in a statement Tuesday afternoon.

“She has been a dear friend and a well-respected colleague for a number of years, especially during the time we have spent working closely together on this committee,” he said. “My thoughts and prayers are with her and her family during these difficult times. I know that I speak for all of our colleagues in wishing her a speedy recovery.”

As of last week, Millender-McDonald had missed more than 40 votes in the 110th Congress, giving her one of the largest absentee rates among all House Members.

The Los Angeles-area Congresswoman has made a habit of guarding information regarding her health.

In May 2005 Millender-McDonald underwent what her office would only describe as a “major surgery,” but the Congresswoman has never disclosed the ailment that necessitated the procedure. She was away from Capitol Hill for almost a month at that time.

Later that year, Millender-McDonald’s son, R. Keith McDonald, received an unusual “temporary emergency release” from prison by a federal judge to be with his ailing mother and his family.

McDonald had been serving a 41-month prison term after being convicted on federal corruption charges in 2004.

According to California newspapers, when McDonald was due back in prison in early 2006, his lawyers filed papers requesting an extension, citing “the continuing illness of his wife and mother.”

During those incidents, Millender-McDonald either shrugged off or strenuously denied any suggestion that she might be in ill health.

Millender-McDonald was tapped to head the House Administration Committee in the 110th Congress by Speaker Nancy Pelosi (D-Calif.). She had become the ranking member at the beginning of the 109th Congress, her second term on panel.

Under House rules, Rep. Robert Brady (D-Pa.), who currently serves as vice chairman of the committee, will take over the chairmanship during Millender-McDonald’s leave of absence.

“Chairwoman Millender-McDonald is my leader and my dear friend. [Brady’s wife] Debbie and I are keeping her and her family in our hearts and in our prayers,” Brady said Tuesday. “I am eagerly awaiting her return to Congress and to her work on behalf of the people of California’s 37th district and of the entire United States.”

Brady, who currently is running for mayor of Philadelphia, temporarily takes over a committee that operates quite differently from how it did a year ago.

The most obvious change that has taken place since Millender-McDonald took over House Administration is the return of a subcommittee structure that hasn’t existed on the panel since before Republicans won control of the House in 1994.

The subcommittee on election issues, headed by House Administration veteran Zoe Lofgren (D-Calif.), has held several hearings since it was formed in mid-February. The second subcommittee, created to oversee issues of Capitol security, is led by Brady.

Meanwhile, the committee recently established a task force to look into possible voting-rights violations in Florida. That task force may decide in the next few weeks whether a full House investigation of the disputed 13th district election is warranted.

But as House Administration has focused on voting-rights issues in recent months, some Capitol Hill insiders note that other Congressional committees have taken the lead on some issues that share jurisdiction with the panel.

Under Florida Rep. Debbie Wasserman Schultz (D), the newly reformed Appropriations subcommittee on the legislative branch has been asserting its oversight role on the behind-schedule and over-budget Capitol Visitor Center since February. In that time span, the subcommittee has held three hearings with acting Architect of the Capitol Stephen Ayers.

And the Senate Rules and Administration Committee, under Sen. Dianne Feinstein (D-Calif.), has taken the lead in Congressional oversight of the Smithsonian Institution, which also falls under House Administration’s jurisdiction. Feinstein is getting ready to hold her second hearing to review questionable spending by the former president of the Smithsonian Institution next week.

Also on the Senate side, the Health, Education, Labor and Pensions subcommittee on employment and workplace safety under the direction of Sen. Patty Murray (D-Wash.) has taken the lead in another high-profile issue on Capitol Hill — this one involving the existence of dangerous amounts of asbestos in the underground utility tunnels that supply steam and chilled water to Capitol Hill.

Wasserman Schultz’s subcommittee already has discussed the problems in the utility tunnels during appropriations hearings with the AOC, and she said she plans to convene a hearing specifically on that issue.