David L. Nelson (born 1956) is an American human geneticist, currently an associate director at the Intellectual and Developmental Disabilities Research Center (1995), and professor at the Department of Molecular and Human Genetics at Baylor College of Medicine BCM since 1999. Since 2018, he is the director at the Cancer and Cell Biology Ph.D program, and the director of Integrative Molecular and Biomedical Sciences Ph.D since 2015 at BCM. Education and career Nelson received a bachelor's degree from the University of Virginia in 1978 and received his PhD in molecular genetics from the Massachusetts Institute of Technology in 1984. He carried out his postdoctoral training at Massachusetts Institute of Technology (1984–1985) and National Institutes of Health before moving to Baylor College of Medicine. Nelson joined the MIT Center for Cancer Research (CCR) group of David Housman at the Massachusetts Institute of Technology as a postdoctoral trainee (1986–1989). Nelson's work using introduced selectable genes expanded approaches to whole human genome mapping. From 1984 to 1985, in an intramural National Institutes of Health program at the laboratory of Robert Lazzarini, Nelson studied neuroscience and defined genes encoding neurofilament proteins. In 1986 he joined the C. Thomas Caskey laboratory at the Institute of Molecular Genetics, Baylor College of Medicine. Applying PCR, a technique that allows rapid gene mapping and isolation of specific chromosomal regions, Nelson et al. identified chromosomal locations of large fragments of the human X chromosome; Nelson contributed to the human, mouse and fly reference sequences and was a co-discoverer of the mutation that causes Fragile X syndrome as an expansion of a trinucleotide repeat in the FMR1 gene. Nelson's contributions have led to the description of Lowe syndrome, and the identification of FMR2 for FRAXE syndrome. Contributions to science Human Genome Project Nelson's molecular techniques led to the development of genome mapping and sequencing and discovery of disease genes, contributing efforts to map and sequence of the human X chromosome. He was a leader in genetic and genomic analyses across all species. Incontinentia Pigmenti (IP) With a group of international collaborators, Nelson's research group was able to identify a recurrent, homology-driven deletion in the NEMO gene in Incontinentia pigmenti (IP), an X-linked genetic disease. Fragile X syndrome Unstable repeats as mutations in human genetic disease Nelson and other collaborators at BMC, Emory University, and Erasmus University Rotterdam identified a massive expansion of CGG repeat (Trinucleotide repeat disorder) in FMR1. This