He is the Bullard Professor of Neurogenetics in the Department of Genetics at Harvard Medical School and an investigator at the Center for Genomic Medicine at the Mass General Research Institute.
[2] As a doctoral student of David Housman, Gusella developed linkage analysis techniques using restriction fragment length polymorphisms (RFLPs) to identify human disease genes.
[3] Gusella joined the faculty of Harvard Medical School in 1980, where he began collaborating with Nancy Wexler to study the genetic basis of Huntington's disease.
[5] Building on this success, the team cloned the huntingtin gene in 1993 and established the CAG trinucleotide repeat expansion as the underlying genetic etiology of Huntington's disease.
[8] In 1999, along with Cynthia Morton, he co-founded the Developmental Genome Anatomy Project (DGAP),[9] harnessing de novo balanced chromosomal rearrangements to identify genes associated with autism and other neurodevelopmental disorders.