David L. Nelson, Ph.D.
Cullen Foundation Professor, Department of Molecular and Human Genetics
Co-Director, Cell and Molecular Biology Graduate Program; Director, BCM - Emory Fragile X Research Center
Associate Director, Intellectual and Developmental Disabilities Research Center
President, American Society of Human Genetics (2019)
The Nelson lab has been involved in research into the causes of and therapies for Fragile X syndrome since the late 1980s, participating in the discovery of the mutation that results in the disorder and the gene that is affected by that mutation. For more than 20 years, the Nelson lab has worked to define both the characteristics of the unusual repeat expansion in the disease and the function(s) of the FMR1 gene that is down regulated in the disease. More recently, the Nelson lab has worked to understand the neurodegenerative disorder (Fragile X-associated tremor/ataxia syndrome) that can impact carriers of the Fragile X premutation (the repeat expansion that predisposes to Fragile X syndrome, but does not cause intellectual disability). The Nelson lab principally employs model systems for its studies; working with mice, flies, yeast and bacteria, but it also has participated in human studies where appropriate.
In collaboration with Drs. Richard Paylor, Baylor College of Medicine, and Ben Oostra, Erasmus University Rotterdam, the Nelson lab created additional mutant mice that lack genes related to FMR1 (FXR1 and FXR2). With additional collaborators, the lab demonstrated that these gene products are capable of compensating for some of the functions missing when FMR1 is absent. This is observed through the enhancement of abnormalities in mutant mice. These anomalies include behavioral, electrophysiological and biochemical differences. The lab continues to characterize animals lacking FXR1 and FXR2 in combination with FMR1 KO to understand this gene family’s range of functions and compensation by the FXRs for absence of FMR1 in Fragile X syndrome. This has uncovered a role for these genes in circadian activity. Current studies point to metabolic alterations as well. These changes relate to human patients’ phenotypes and provide an avenue to understanding additional aspects of Fragile X symptoms.
With these same collaborators, the Nelson lab has developed mice that allow FMR1 to be turned on or off in specific tissues or at specific developmental time points. There are a number of important studies that now can be done with these mice. The lab has completed work to determine whether the restoration of FMR1 in a late adolescent mouse can reverse abnormalities. This is especially relevant to the potential therapies for Fragile X syndrome, since it is currently unknown whether these can be expected to be effective in older patients.
The lab has shown that restoration of FMR1 expression in mice at four weeks of age can restore nearly all functions such that they cannot be distinguished from non-mutant mice. Eliminating FMR1 expression at the same time point also causes these abnormalities to develop. The lab has investigated behavior and learning, biochemical, and anatomical differences. These exciting findings suggest considerable potential for treatment in Fragile X syndrome.