Outline for an Experimental Attack on the Treatment of Certain Varieties of Genetic Disease

OUTLINE FOR AN EXPERIMENTAL ATTACK ON THE TREATMENT OF CERTAIN VARIETIES OF GENETIC DISEASE MAURICE OGUR, Ph.D.* The treatment ofhuman disease, although deeply rooted in empiricism, has experienced several "breakthroughs" when understanding based on a verifiable dieoretical model has guided die design of experimental dierapy. The emergence of a sound dieory of infectious disease contributed to die development of immunology, chemodierapy, and antibiotics. The concept ofnutritional deficiency disease was a stimulus to the search for and discovery ofthe vitamins, the essential amino acids, and methods oftreatment. On die odier hand, metabolic diseases, considered in die broadest sense to include the molecular-genetic as well as the developmental-degenerative, have responded only partly to empirical study and treatment largely because the former were until recently, and the latter are to diis date, still lacking in adequate dieoretical models. At present, however, the recognition ofgenetic disease as a molecular lesion [i], the development of a helical dieory of macromolecular structure [2], die recognition of a double helical structure for the genetic material [3], the breaking ofthe genetic code [4], the completion ofdie sixty-fourcodonassignments inEscherichiacoli [5], and the generally assumed code universality have all laid the basis for considering theoretically sound and experimentally feasible attacks on molecular disease. Although some predictions concerning the future treatment or cure of genetic disease at die molecular level have appeared [6, 7], diese have tended to assume either (a) deliberate modification ofdie genotype by manipulating die DNA or (b) supplying a functional messenger RNA or a functional enzyme protein from an outside source. No detailed models or strategies have been proposed which might serve as the basis for serious immediate experimental attack. The possibility diat human DNA might be deliberately modified in vivo by processes akin to bacterial transformation or viral transduction seems still fairly remote. The intent of this paper is to outline an experimental attack on certain varieties of genetic disease, diose which may be due to mutation forming a nonsense (or perhaps a missense) codon. Its principal virtue may lie in stimulating work on testing its main strategies, which he within die scope ofpresent-day molecular genetics. Taking only slight liberties beyond the evidence rapidly emerging from studies ofthe * Biological Research Laboratory, Southern Illinois University, Carbondale, Illinois. Results in my laboratory were obtained under the Mamie B. Histle Memorial Grant ofthe American Cancer Society. 47I bacteria, dieir viruses, and the yeasts, I may summarize die basic tenets of die model as follows: 1.Several ofthe sixty-four possible triplet codons are nonsense, not normally read for any amino acid and probably involved, in part, in normal chain termination during polypeptide synthesis [8, 9, 10, 11]. 2.Mutations involving codon alteration from sense to nonsense produce premature chain termination generally resulting in an inactive protein [12]. 3.Nonsense mutants are probably an appreciable fraction of the mutants in nature (25 per cent ofall mutants in yeast may be nonsense mutants) [13]. 4.Certain classes ofsuppressor genes are probably nonsense suppressors (in yeasts the allele-specific, locus nonspecific suppressors are probably nonsense suppressors) [13]. 5.The nonsense suppressed mutant may exhibit restored capacity to syndiesize die protein in question but often with a detectable alteration in physical properties [14, 15]. 6.The mechanism by which a nonsense suppressor gene functions may involve die production ofan altered tRNA capable ofinserting an amino acid at a nonsense codon. This would enable the suppressed mutant to complete die syndiesis ofa protein altered by the substitution ofasingleamino acid coded bya triplet onlyone base change removed from the nonsense codon [16, 17]. Ifthese generalizations are valid, we may assume die following as reasonable extensions of the model: a) Nonsense suppressors in yeast can now be induced, characterized, and classified by genetic [18] and biochemical [19] mediods with respect to identity, die codons affected, and die amino acid inserted. ' b) Yeast strains can be constructed widi specified nonsense suppressor genes and serve for the isolation oftRNA preparations with die capacity to read one or more nonsense codons. c)Code universality should enable yeast tRNA to function in an animal protein synthesizing system. d)Some animal genetic disease can be shown to involve a nonsense mutation. e)A mutatedgene in a...