A U.S. judge has ruled against investors who accused Paris-based AXA SA of charging excessive fees on variable annuity products, in one of the rare such cases to go to trial.

U.S. District Judge Peter Sheridan in Trenton, New Jersey, said late Thursday that the investors did not show that AXA breached its fiduciary duties by keeping most fees charged for mutual fund investments and back-office duties, while remitting only a small amount to subadvisers that did most of the work.

In a 148-page decision, Sheridan said the plaintiffs did not prove that the fees were too high, the underlying funds performed poorly, or that AXA failed to act conscientiously. He also said AXA retained "significant" duties.

Investors' contributions to the annuities had been allocated to 12 mutual funds, including from Allianz's Pimco unit and T. Rowe Price, the judge wrote.

The case is one of a growing number focusing on investing costs, as fewer workers are covered by pension plans and more are expected to direct and monitor their own investments.

Sheridan ruled in favor of AXA Equitable Life Insurance Co and AXA Equitable Funds Management Group LLC after a five-week, non-jury trial last winter.

In a statement, AXA said the trial was the first of its kind since 2009, and vindicated its "manager-of-managers" structure where AXA Equitable Funds Management Group provides essential services to the funds and hires third parties to provide "limited" services.

AXA is pleased that Sheridan found the fees "fair and reasonable," AXA Equitable Life General Counsel Dave Hattem said in the statement.

Robert Lakind, a lawyer for the investors, declined to comment.

In lawsuits filed this month, several major U.S. universities, including Columbia, Duke, the Massachusetts Institute of Technology and Yale, were accused of charging excessive fees on employees' retirement savings.