Mayor Anthony Williams on Tuesday fired the director of the District’s mental retardation office and replaced her with a consultant from Alabama.

Marsha Thompson, who had served as interim director of the Mental Retardation and Developmental Disabilities Administration for only a year, was given her notice Tuesday morning, effective immediately. Her brief tenure, city leaders say, produced little progress for the long-challenged agency, which is tasked with providing care and housing for the city’s most vulnerable residents.