HEMOGLOBIN DISORDERS ARE POTENTIAL CANDIDATES FOR GENE THERAPY, BUT PROSPECTS FOR CLINICALS ARE BEYOND "FORESEEABLE FUTURE," ACCORDING TO OTA BACKGROUNDER
Hemoglobin disorders such as sickle cell anemia and thalassemias are potential candidates for treatment by gene therapy, but are not likely to be among its initial clinical uses, a recent background paper prepared by the Congressional Office of Technology Assessment (OTA) asserts. Because hemoglobin disorders are among the best defined, and most common single-gene diseases and because of the accessibility of hemoglobin-producing bone-marrow cells, "hemoglobinopathies were presumed, until several years ago, to be the first candidates for human gene therapy," the report notes. However, "although innovative rDNA technology has pinpointed the genetic defects responsible for different hemoglobin disorders, recent experiments revealing that the regulatory complexities in the manufacture of hemoglobin, and in gene regulation in general indicate that hemoglobinopathies will not be effectively treated until these processes are better understood and can be controlled," the report asserts. The OTA report, prepared at the request of Rep. Gore (D-Tenn.), is the fourth in a series on genetics. The other publications in the series include "Commercial Biotechnology: An International Analysis," issued in January 1984 ("The Pink Sheet" Jan. 30, p. 6) and "The Role of Genetic Testing in the Prevention of Occupational Disease," issued in April 1983. Gore, who is moving to the Senate in January, held a press briefing on the report Dec. 17. He also stressed that he intends to continue to focus on the issue in the Senate (see related T&G this issue). The OTA report included a list of disorders for which gene therapy might be considered, along with relative rankings as to when clinical studies might be conceivable. Hemoglobin disorders were listed as potential gene therapy treatments, but "further off" than the foreseeable future. The first clinical tests of the technology will likely be somatic cell therapy for the treatment of rare enzyme deficiency disorders, according to the report. Robert Cook-Degan, the OTA study director, added that research groups in Texas, San Diego, and Boston will probably submit the first protocols. "None have been sent through NIH yet, so we don't know who is going to come in with it first," he said. "A couple have gone through local review" by institutional review boards. The background paper provided four examples of diseases for which "protocols for human gene cell therapy in somatic cells [are] expected in [the] next several" years: "immunodeficiency caused by adenosine deaminase or purine nucleoside phosphorylase deficiencies"; Lesch-Nyhan syndrome; "urea cycle defects caused by deficiencies of arginosuccinate synthetase (citrulinemia) or ornithine carbamoyl transferase" (OCT). Tabular information in the background paper indicates that all of the near-term treatment candidates, except Lesch-Nyhan syndrome are rare. Lesch-Nynan syndrome occurs in about one in 10,000 males each year worldwide; about 200 new cases are reported in the U.S. each year. Among the disorders which might be candidates in the "foreseeable future" are: phenyl-ketonuria (as an improvement over dietary therapy); familial hypercholesterolemia; "defects of the urea cycle other than citrullinemia and OCT deficiency"; some forms of Gaucher disease; Hunter syndrome and severe grades of branched chain ketoaciduria. The paper also cites several disorders, including chromosomal disorders such as Down syndrome, and environmental and multi-genic disorders such as hypertension and diabetes; for which gene therapy "may not be applicable." The OTA group points out that if gene therapy proves viable, it may eventually spawn patentable products and technologies. However, the paper asserts, the "criteria for granting each patents . . . will be the same ones used for other rDNA products . . ." Copies of the OTA report, "Human Gene Therapy" are available from the U.S. Govt. Printing Office, Superintendent of Documents, Washington, D.C. 20402. The GPO stock number for the publication is 052-003-00983-8.
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