SURVIVAL OF STEROID 21-HYDROXYLASE-DEFICIENT MICE WITHOUT ENDOGENOUS CORTICOSTEROIDS AFTER NEONATAL TREATMENT AND GENETIC RESCUE BY TRANSGENESIS AS A MODEL SYSTEM FOR TREATMENT OF CONGENITAL ADRENAL-HYPERPLASIA IN HUMANS

The genome of mice with the H-2(aw18) haplotype has a deletion of appr oximately 80 kilobases in the H-2 class III region of chromosome 17. M ice that are homozygous for the mutation die soon after birth. A funct ional form of steroid 21-hydroxylase (21-OHase) is encoded by the dele ted DNA fragment, and H-2(aw18) homozygotes are deficient in this enzy me. 21-OHase catalyzes the conversion of progesterone to deoxycorticos terone during adrenal steroidogenesis in mice; therefore, H-2(aw18) ho mozygous mice are unable to synthesize corticosteroids. The deleted re gion also includes the gene for complement component C4, which has a r ole in the classical pathway of the complement activation cascade. To clarify the cause of the lethality of the mutation, we first administe red either an adrenal homogenate or synthetic steroids to newborn mice ; as a result, several H-2(aw18) homozygotes were rescued. The results demonstrated that the mutant mice die as the result of a defect in ad renal steroidogenesis. The low efficiency of the rescue by treatment o f newborns (16.0% by the adrenal homogenate and 14.8% by the synthetic steroids) suggested that mutant mice should be treated prenatally. Mo reover, because the 21-OHase gene is expressed before birth, introduct ion of a gene for 21-OHase should improve the efficiency of rescue. Th e results of the murine mutation are similar to those of the inherited human disease known as congenital adrenal hyperplasia, which is cause d by steroid 21-hydroxylase deficiency. As a model system for treatmen t of the human disease by genetic therapy, we used transgenic approach es to introduce a recombinant DNA fragment containing the murine genom ic gene for 21-OHase into the mutant mice. We produced four lines of t ransgenic mice, and in all four transgenic lines, the transgene rescue d the lethal mutation. The apparent efficiencies of rescue were 80.2%, 80.0%, 68.7%, and 16.7% for the respective lines of transgenic mice. During the course of our experiments, we also found an unexpected prop erty associated with the role of corticosteroids. The H-2(aw18) homozy gous mice rescued by neonatal treatment survived for a long period wit hout further treatment. This observation indicates that corticosteroid s down-stream of 21-OHase in the pathway for adrenal steroidogenesis a re not essential for the survival of mice, except during the period im mediately after birth.