In 2003, Warren was an inaugural inductee of the National Institute of Child Health and Human Development’s Hall of Honor for the "identification of triplet repeat expansion as the cause of fragile X syndrome and as an entirely new inherited mechanism of genetic disease".
During his summer breaks he worked with geneticists Lester Weiss and Gene Jackson at Henry Ford Hospital in Detroit.
He completed his post graduate training at the University of Illinois at Chicago at the Center for Genetics and at the European Molecular Biology Laboratory Heidelberg.
Using his somatic cells hybrids, Warren led an international group, including his longtime collaborator David L. Nelson at Baylor College of Medicine, that isolated the FMR1 gene responsible for fragile X syndrome in 1991.
The cloning of this locus also uncovered, for the first time, a trinucleotide repeat expansion mutation, a mechanism now known to be responsible for dozens of genetic diseases.
[6] Warren and collaborators subsequently demonstrated that the expanded FMR1 repeat in patients leads to transcriptional suppression and the absence of the encoded protein, FMRP.